Front. Vet. Sci. Frontiers in Veterinary Science Front. Vet. Sci. 2297-1769 Frontiers Media S.A. 10.3389/fvets.2022.903195 Veterinary Science Original Research Exogenous Melatonin Directly and Indirectly Influences Sheep Oocytes Chen Yang 1 † Shan Xuesong 1 † Jiang Huaizhi 1 * Guo Zhenhua 2 * † 1Key Laboratory of Livestock and Poultry Resources (Sheep & Goat) Evaluation and Utilization, Ministry of Agriculture and Rural Affairs, College of Animal Science and Technology, Jilin Agricultural University, Changchun, China 2Heilongjiang Academy of Agricultural Sciences, Animal Husbandry Research Institute, Harbin, China

Edited by: Valeria Pasciu, University of Sassari, Italy

Reviewed by: Jaime Palomino, Universidad Bernardo O'Higgins, Chile; Ignacio Contreras Solís, University of Sassari, Italy

 *Correspondence: Huaizhi Jiang 13756293858@126.com Zhenhua Guo gzhh00@163.com

This article was submitted to Animal Reproduction - Theriogenology, a section of the journal Frontiers in Veterinary Science

†These authors have contributed equally to this work

 26 05 2022 2022 9 903195 24 03 2022 05 05 2022 Copyright © 2022 Chen, Shan, Jiang and Guo. 2022 Chen, Shan, Jiang and Guo

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Understanding whether and how melatonin (MT) may impact sheep oocyte development competence is central to our ability to predict how sheep oocytes will respond to artificially regulated estrus. Implanting MT can make sheep enter estrus during the non-breeding season. One study found that the blastocyst rate increased under MT treatment, while another found that the blastocyst rate decreased. Therefore, we conducted a meta-analysis of MT directly and indirectly influencing sheep oocytes. A total of 433 articles were collected from which 20 articles and 34 treatments were finally selected. A method for estimating the default value was established for the litter size analysis. We found that exogenous MT add into in vitro maturation medium was positively related to the blastocyst rate in the lab. However, subcutaneous implanting MT did not affect the in vivo ovulation rate, fertilization rate, blastocyst rate, or pregnancy rate at farm. MT did not affect the in vitro cleavage rate. However, MT improved the in vivo cleavage rate. We hypothesized that implanted MT could increase the concentration of MT in oviduct fluid in vivo, and also that in vitro MT could increase the early cleavage rate of sheep zygotes without affecting the total cleavage rate. In the analysis of oocyte apoptosis caused by injury, the results suggested that pyroptosis would be more suitable for further research. MT produces responses in all body organs, and thus implanting of MT during non-breeding seasons should consider the effect on animal welfare.

 animal welfare ewe follicle meta-analysis development Natural Science Foundation of Jilin Province10.13039/100007847 Introduction

Sheep oocyte development competence can be directly affected by adding exogenous melatonin (MT) during in vivo culture as well as indirectly by implanting MT in ewes. The concentration of MT in various tissues differs widely. The concentration of MT in the gastrointestinal tract is 10–100 times higher than that in blood (1). The concentration of MT is different in different size sheep follicles (2). This indicates that MT is positively correlated with the developmental ability of sheep oocytes. MT can maintain the reproductive process (3). MT has anti-inflammatory (4) and wound healing functions (5) and is associated with many signaling pathways (6). This article focuses on the impact of MT on sheep oocytes. Different drug delivery routes can have different effects; for example, magnesium sulfate is taken orally for catharsis (7), and intramuscular or intravenous injection can relieve muscle spasms (8). Therefore, we were curious to know how MT directly and indirectly affects sheep oocytes.

Sheep are seasonal estrous animals. The estrous period and intensity are significantly different depending on the region, breed, and other factors (9). Implanting MT can make sheep enter estrus in non-breeding seasons. However, this phenomenon is not uniform in all aspects. One study found that blastocyst cell number decreased (10), whereas another study found that blastocyst cell number increased (11). Some studies have suggested that the blastocyst rate is decreased (12), whereas others have found that the blastocyst rate is increased (13). In particular, litter size changes with the season (9, 14). According in vitro study, the blastocyst rate of cultured sheep oocytes can be improved by adding MT to in vitro maturation (IVM) (10, 11, 15). However, there is no report on the simultaneous control study of in vivo and in vitro studies. Therefore, we performed a meta-analysis and reviewed the results concerning the direct and indirect effects of MT on sheep oocytes.

 Methods Database Search Strategy

We collected articles concerning the effects of MT on sheep oocytes both in vitro and in vivo. A search of PubMed, Ovid, Science Direct, and ProQuest from 2006.01.01 to 2021.09.01 used the key search terms melatonin AND (Ovine OR sheep OR ewe) AND (oocyte OR follicle), producing a total of 238 articles. The effects of melatonin on litter size used the key search terms melatonin AND (ram OR ewe) AND implant, and 195 articles were found.

 Data Extraction

We selected the relevant articles according to the criteria listed in Table 1. Specifically, oocytes cultured in vitro should have follicle growth data or embryonic development data. In the experiment of subcutaneous implantation in ewes, ovulation data or oocyte development data should be available. The data of litter size should be available in the experiment of ram subcutaneous implantation. The studies of melatonin's effect on sheep oocyte development tended to explore the mechanism, and many experimental groups had observed positive results. When extracting the data, only the groups with the largest positive value were retained. Each experimental group was studied in different seasons or in different sheep varieties about litter size study. Therefore, when extracting data, each experimental group was used as a treatment. When the experimental data were incomplete, we contacted the authors to obtain the data. We were unable to contact all the authors to obtain the raw data. When analyzing the effect on litter size, we supplemented the missing data using the default value; refer Supplementary Data 1 for the method.

Inclusion and exclusion criteria.

Inclusion Exclusion
Species evaluated included but was not limited to sheep Sheep were not used
English literature Non-English
Melatonin treatment alone or with other treatments in sheep No melatonin treatment of sheep
Oocyte or reproduction data included No oocyte or reproduction data
Data Analysis

Review Manager (Copenhagen: Nordic Cochrane Center, Cochrane Collaboration, Version 5.4) was used for the meta-analysis. A standard mean difference (SMD) meta-analysis using a continuous model was used to calculate in vitro culture follicle diameter and blastocyst cell number. The effects of implanting MT on ovulation rate, fertilization rate, and litter size were also analyzed with a continuous model. Relative risk (RR) was analyzed with a dichotomous model. This included in vitro culture follicle normal rate, IVM rate, cleavage rate, and blastocyst rate. The effects of implanting MT on cleavage rate, blastocyst rate, and pregnancy rate were also analyzed with a dichotomous model.

Heterogeneity was analyzed by the Higgins I2 statistic (I2 >50% means a high level of heterogeneity) (16). When heterogeneity was found in the analysis, the source of the heterogeneity was identified according to the differences in follicle diameter and culture methods as well as the experimental details such as different research seasons (Table 2). The heterogeneous groups were analyzed by a random effects model. The groups without heterogeneity were analyzed by a fixed effects model. Litter size was analyzed without considering subgroups, as the location in the northern and southern hemispheres and different time periods of the studies were the sources of heterogeneity. Potential bias was identified using Begg's funnel plots and rechecked by Egger's linear regression (28) and Begg's rank correlation tests. Statistical analyses were performed using Stata 12.0 (Stata Corp, College Station, TX, USA). Furthermore, trial sequential analysis (TSA) was used to evaluate the reliability of our results. For the TSA we set the IVM rate control to 70% according to experimental experience.

Characteristics of studies included.

Study IVC
Year Breed Location and latitude Treated Oocytes recovered Culture method Culture Time (h) Mature oocytes treated Embryo IVC medium Cleavage observed time
1 Barros et al. (17) Mixed-breed Petrolina, Brazil S 16.1 Secondary follicles, >295 and <330 μm IVC follicles 100 μl droplet Follicle, 18 days IVM,32–48 h NM NM NM
2 Barros et al. (18) Mixed-breed Petrolina, Brazil S 16.1 Early antral follicles, >400 and <500 μm IVC follicles 100 μl droplet Follicle, 12 days IVM, 36 h NM NM NM
3 Deng et al. (19)* NM Beijing, China N 39.5 COCs Abattoir 6-well plate IVM, 19 h Sperm injection mSOF 120 h
4 Goodarzi et al. (11) Lory Bakhtiary Karaj, Iran N 35.8 COCs Abattoir 50 μl droplet IVM, 24 h IVF SOF 48 h
5 Tian et al. (15) NM Beijing, China N 39.5 COCs Abattoir 60 μl droplet IVM, 24 h PA mSOF 48 h
6 Tian et al. (10) Merino Beijing, China N 39.5 COCs OPU 4-well plate IVM, 24 h IVF SOF 48 h
Implant ewe
Breed Location and latitude Seasons Oocytes recovered Time, month Live weight/age Melatonin treatment Embryo IVC medium Cleavage observed time
7 Buffoni et al. (20) Merino Trelew, Argentina S 43.0 Breeding and anestrous OPU Feb to Apr Sep to Nov Adult, 63 kg 61 kg 58 days NM NM
8 Fang et al. (13) Hu-sheep Tianjin, China N 39.1 12 light:12 dark, in temperature control room OPU NM 4 week old 17 days SOF 48 h
9 Vazquez, 2009 Rasa Aragonesa Zaragoza, Spain N 41.4 breeding and anestrous OPU Jan Mar 64 kg 57 kg 42 days SOF NM
10 Vazquez et al. (21) Rasa Aragonesa Zaragoza, Spain N 41.4 breeding and anestrous OPU Jan Mar 64 kg 59 kg 42 days SOF 24 and 36 h
11 Vazquez et al. (22) Rasa Aragonesa Zaragoza, Spain N 41.4 lactation OPU Feb Apr 61 kg 45 days SOF 24 and 36 h
12 Vazquez et al. (12) Rasa Aragonesa Zaragoza, Spain N 41.4 parturition OPU Nov 61 kg 45 days SOF 24 and 36 h
13 Abecia et al. (23) Rasa Aragonesa Spain N 41.4 Breeding Ewe Mar 56.3 kg NM 41 days 40 days
Implant Ram/ewe For litter size
Breed Location and latitude Seasons Treat Time, month Ewe Weight/age Ram age Melatonin treatment Ram introduction
14 Abecia et al. (9) Rasa Aragonesa Assaf, Merino Zaragoza Zamora Badajoz NM Ram Ewe Jan, Feb, Apr, May NM NM Ram 49 days Ewe 42 days 45 days
15 Cosso et al. (24) Sarda Sardinia, Italy N 40.5 breeding Ram Jun Jul 32 kg 240 days 2.5–6.5 years 35 days 45 days
16 Cosso et al. (24) Romney composite New Zealand N 40 Not breeding Ewe Oct NM NM 35 days 22 days
17 Luridiana et al. (25) Sarda Sardinia, Italy N 39.5 breeding Ewe Mar 3–6 years NM 35 days 40 days
18 Mura et al. (26) Sarda Sardinia, Italy N 40.5 breeding Ewe Jun 26 kg 195 days NM 35 days 40 days
19 Mura et al. (14) Sarda Sardinia, Italy N 40.0 NM Ram Ewe Feb, Mar Apr, May 3–6 years NM 35 days 45 days
20 Mura et al. (27) Sarda Sardinia, Italy N 40.0 NM Ram Ewe Mar 3–5 years At least 3 years 34 days 40 days

*Contacted the author to obtain experimental data.

NM, Not mentioned; OPU, ovum pick-up; IVC, in vitro culture; IVM, in vitro maturation; IVF, in vitro fertilization; PA, parthenogenetic activation; SOF, synthetic oviduct fluid medium.

 Results

The process and results of screening 433 articles are shown in Figure 1. A final group of 20 studies is shown in Table 2 (9–15, 17–27, 29, 30). The studies comprised 34 treatments.

Summary of the study selection process. Pub, PubMed; Ovi, Ovid; Pro, ProQuest; Sci, ScienceDirect.

Under in vitro conditions, exogenous MT was positively related to follicle diameter (SMD = 4.03, 95% CI = 0.42–7.63; p = 0.03; Figure 2A), in vitro maturation (IVM), and blastocyst rate (Figure 2B). MT had no effect on follicle normal rate (RR = 1.76, 95% CI = 0.89–3.47; p = 0.11; Figure 2B), cleavage rate (RR = 1.22, 95% CI = 1.01–1.47; p = 0.04; Figure 2B), or blastocyst cell number (SMD = 4.07, 95% CI = −2.08 to 10.22; p = 0.19; Figure 2A). There was significant heterogeneity in follicle diameter and follicle normal rate. Subgroup analysis according to follicle diameter was performed using a random model. The heterogeneity was produced by different follicle diameters. Cleavage rate and blastocyst cell number were heterogeneous owing to different culture methods according to the subgroup analysis using a random model. The sources of heterogeneity were culture wells and culture droplet size.

Forest plot of melatonin (MT) treatment effects on sheep oocytes. The subgroup analysis was based on different follicle diameters, different culture treatments, and different months. (A) SMD for the effects of in vitro culture of exogenous MT on follicle diameter and blastocyst cell number. Blastocyst cell number analysis culture droplet subgroup I2 = 36%. (B) RR for the effects of in vitro culture exogenous MT on follicle normal rate, IVM rate, cleavage rate, and blastocyst rate. Cleavage rate analysis of the culture droplet subgroup and the culture well subgroup yielded I2 = 0%. (C) SMD for implanted exogenous MT effects on ovulation rate and fertilization rate. (D) RR implanted exogenous MT effects on cleavage rate, blastocyst rate, and pregnancy rate. (E) Implanted exogenous MT effects on litter size.

For in vivo studies using treated ewes, implanting MT had no effect on ovulation rate, fertilization rate (SMD = 1.08, 95% CI = −1.00 to 3.16; p = 0.31; Figure 2C), blastocyst rate, or pregnancy rate (RR = 1.29, 95% CI = 1.1–1.5; p = 0.56; Figure 2D). Implanting MT was positively related to cleavage rate (Figure 2D). The results for fertilization rate were heterogeneous due to differences in experimental starting month as decided by a subgroup analysis using a random model. When implanted MT treatment was used for rams or ewes, implanting MT was positively related to litter size (Figure 2E). The implanted MT litter size was 1.3395, and the control litter size was 1.2795.

The funnel plot (Figures 3A,B) shows that there was no potential bias, and this result was corroborated by Egger's test (IVM rate, p = 0.972; implant ovulation rate p = 0.529) and Begg's test (IVM rate Pr > |z| = 1; implant ovulation rate, Pr > |z| = 0.602). The TSA results showed that the in vitro exogenous MT effect on sheep oocyte IVM was real (Figure 3C). It should be noted that the actual IVM rate was 80%−90%. We set the IVM rate control to 70%. Setting the control rate to 50% according to the statistical method would not allow the significance threshold to be reached. The influence of implanted MT on ewe oocytes needs further research (Figure 3D). Although the number of studies is large, the actual number of samples is small.

Bias analysis and TSA of MT of sheep oocytes. Funnel plots of IVM rate (A) and implant ovulation rate (B). TSA of IVM rate (C) and implant ovulation rate (D).

 Discussion

Understanding how MT directly and indirectly influences sheep oocyte development competence is an important goal. MT also significantly promoted the development of embryos in vitro, for example, in mice (31), bovines (32), swine (33), and goats (34).

Direct Exogenous MT Employed in <italic>in vitro</italic> Culture

The beneficial effects of MT on early embryos depend on two key factors. An important function of it used in vitro is antioxidation. As an effective antioxidant, MT can significantly reduce the level of intracellular ROS and improve the in vitro maturation (IVM) of oocytes and the in vitro developmental potential of embryos (32). MT can significantly reduce the apoptosis of cultured cells and improve the quality of embryos. Previous studies have confirmed that MT can inhibit apoptosis and decreases in cell proliferation of sheep granulosa cells under heat stress (35). MT can inhibit the expression of the apoptosis genes p53 and Bax and promote the expression of antioxidant genes SOD1 and GPX4 in embryos (36). In addition to its antioxidant properties, MT activates the SIRT1/PGC-1α pathway to compensate for mitochondrial depletion and energy deficiency caused by environmental toxin exposure and thereby promotes mitochondrial biosynthesis (33). MT can activate two G protein coupled receptors, MT1 and MT2, which regulate the growth of oocytes (37, 38). In addition, the effect of MT on oocytes may also be related to apoptosis, mitochondrial function (39), antioxidant enzymes (40), DNA methylation (41), cumulus cell expansion (42), and histone acetylation (43).

Our results show that MT is positively related to follicle growth in vitro. When cumulus oocyte complexes (COCs) were cultured alone, MT was positively related to IVM and blastocyst rate. That does not affect the quality of blastocysts, because blastocyst cell number is generally used as the standard to measure the quality of zygotes.

 Implanting MT in Ewes/Rams: Indirect Effects

Sheep are seasonal estrous animals, and the Assaf sheep are more seasonal than Merino sheep (9). MT is the key endogenic hormone regulating the estrus of sheep and that secretion is affected by light and by the season (44, 45). It can be secreted by cells of all tissues (1). MT is lipophilic and can penetrate all cell membranes and enter all tissues (38) and is particularly concentrated in follicles (46). The concentration of MT in follicles varies according to follicle size (2). The accumulation of ROS in the ovary will reduce the quality of oocytes and lead to the apoptosis of granulosa cells (47). MT can significantly reduce the level of intracellular ROS (32). It can penetrate the blood-testis barrier (48). When it was implanted in rams, the concentration of MT in seminal vesicles increased (49), and implanted MT affected semen quality. Oral administration of MT can also improve the human fertilization rate (50) and increase the number of high-quality embryos (51). Differences of implanted MT can cause differences in the release rate. One study found that the concentration of MT in seminal plasma peaked after 7 days and then decreased (52). Another study showed that the concentration of MT in seminal plasma gradually increased, reached the highest level after 90 days, and then decreased (53). In addition, the peak time of MT concentration differed according to different implant seasons (54). About 90% of MT is degraded through the liver (55).

Our results show that sheep from different regions and varieties can be made to enter estrus by implanting MT. It is positively related to litter size. Interestingly, MT has clear effects in vitro culture sheep oocytes and improves the blastocyst rate, although the embryo quality is unaffected in lab experimentation. Embryo quality is determined by the number of blastocyst cells number. MT has no effect on the cleavage rate in vivo but improves the rate in vitro. That declare the direct and indirect effects of MT on sheep oocytes are completely different.

Other studies have shown that there are MT receptors MT1 and MT2 in the sheep oviduct, and MT1 and MT2 are regulated by E2 (56). Cleavage occurs in the oviduct, and thus, the hypothesis is that implanted MT could increase the concentration of MT in oviduct fluid. During the present study, we noted that in vitro studies observed that the effect on the cleavage rate occurred 48 h after fertilization. The in vivo studies observed that most of the cleavage rate effect occurred 24–36 h after fertilization. In this way, different key time points can distinguish early cleavage rate and total cleavage rate (57). Hence the hypothesis that MT can improve the early cleavage rate, while the total cleavage rate will not be affected.

 Proposed Relation of MT to Sheep Oocyte Developmental Competence

MT is produced by the pineal gland. The normal secretion is a necessary condition for regulating physiological functions. However, excessive MT carries potential risks (58, 59). MT inhibits rat testosterone secretion by downregulating the hypothalamus-pituitary-gonadal axis (60). No studies have determined whether exogenic MT inhibits normal pituitary function (Figure 4A). MT is known to be involved in many oocyte-related signaling pathways. It is involved in the Hedgehog signaling pathway to promote swing oocyte IVM (61). MT reduces glyphosate herbicide toxicity during mouse oocyte maturation by regulating the GPER signaling pathway (62). MT-adjusted Nrf2 signaling decreased ROS in COCs and promoted swine (63) and mouse (64) oocyte IVM (Figure 4B). MT inhibited nicotinamide methylation signaling, promoting bovine oocyte IVM (65). In addition, MT is also involved in the Notch signaling pathway (66), the H4K16 deacetylation pathway (43), and the mTOR pathway (67).

Proposed mode of action of MT in relation to sheep oocyte developmental competence. (A) MT treatment of sheep oocytes cultured in vitro has antioxidant effects and can increase oocyte development potential. MT can improve early cleavage. Implantation of MT in ewes and rams can promote estrus. There is no evidence to indicate whether implanting MT in ewes inhibits the hypothalamus-gonadal axis. Implanted MT can be enriched in follicles through the blood ovum barrier. Our statistical results show that implanting MT can increase the number of fetuses. (B) MT is involved in many oocyte-related signaling pathways.

Melatonin promotes the excretion of exosomes (68), and it promotes exosome secretion from mesenchymal stem cells also (69). Early embryonic blastomeres are totipotent stem cells (70). The concentration of MT differs in follicles according to follicle diameter (2). One aspect that needs to be considered in this area is how MT is enriched from the blood and how it can pass through the blood ovum barrier. It is involved in the cell crosstalk of oocytes and cumulus cells (71). If MT is secreted by granulosa cells or cumulus cells, this suggests that we should study the effect of it on oocytes from the aspects of endogenous MT autocrine and paracrine functions. MT can inhibit oocyte apoptosis (71). Regarding studies on oocyte apoptosis caused by injury (72, 73), we suggest that this should be confirmed by pyroptosis.

 Implication of This Research

Melatonin's effect on sheep oocyte development in vitro is conducive to the study of the underlying molecular mechanism, because itself is a hormone secreted by the body. The MT extracted from sheep is best used in the research process. Future research will focus on the mechanism of the interaction between MT and other hormones, the signaling pathways in which MT participates, and how it is transported across membranes against a concentration gradient.

Implanting MT to promote estrus is no longer the most suitable method of estrus regulation. The sheep and goats of our farms all use the method of vaginal sponges impregnated with progesterone for estrus synchronization, and then use laparoscope minimally invasive surgery to inject semen into the oviduct; this method has achieved good results.

Future studies need to determine whether MT can improve the early cleavage rate of sheep embryos without affecting the total cleavage rate. It is also necessary to determine whether implanting MT can increase the MT level in sheep oviduct fluid. Implanting MT affects all body organs and produces side effects such as promoting the growth of goat hair (74). It also affects the cardiovascular system (75), the neurological system (76), the endocrine system (77), and metabolism (78). Thus, implanting MT in non-breeding seasons should consider the effects on animal welfare.

 Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

 Author Contributions

YC and ZG collected the data and conducted the analysis. YC, XS, and ZG checked the data. HJ and ZG designed the experiment. All authors contributed to the article and approved the submitted version.

 Funding

This work was supported by the Jilin Scientific and Technological Developing Program (20200402039NC). National Key Research and Development Project of China (2021YFF1000702). The funders had no role in study design or preparation of the manuscript.

 Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

 Publisher's Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

We would like to thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.

 Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fvets.2022.903195/full#supplementary-material

 References Tordjman S Chokron S Delorme R Charrier A Bellissant E Jaafari N . Melatonin: pharmacology, functions and therapeutic benefits. Curr Neuropharmacol. (2017) 15:434–43. 10.2174/1570159X1466616122812211528503116 Xiao L Hu J Song L Zhang Y Dong W Jiang Y . Profile of melatonin and its receptors and synthesizing enzymes in cumulus-oocyte complexes of the developing sheep antral follicle-a potential estradiol-mediated mechanism. Reprod Biol Endocrinol. (2019) 17:1. 10.1186/s12958-018-0446-730606208 Russo M Forte G Montanino Oliva M Lagana AS Unfer V. Melatonin and Myo-inositol: supporting reproduction from the oocyte to birth. Int J Mol Sci. (2021) 22:8433. 10.3390/ijms2216843334445135 Martin Gimenez VM Chuffa LGA Simao VA Reiter RJ Manucha W. Protective actions of vitamin D, anandamide and melatonin during vascular inflammation: epigenetic mechanisms involved. Life Sci. (2022) 288:120191. 10.1016/j.lfs.2021.12019134856208 Al-Otaibi AM Al-Gebaly AS Almeer R Albasher G Al-Qahtani WS Abdel Moneim AE. Melatonin pre-treated bone marrow derived-mesenchymal stem cells prompt wound healing in rat models. Biomed Pharmacother. (2022) 145:112473. 10.1016/j.biopha.2021.11247334861635 Yu LM Dong X Zhao JK Xu YL Xu DY Xue XD . Activation of PKG-CREB-KLF15 by melatonin attenuates angiotensin II-induced vulnerability to atrial fibrillation via enhancing branched-chain amino acids catabolism. Free Radic Biol Med. (2022) 178:202–14. 10.1016/j.freeradbiomed.2021.11.04334864165 Wang W Li J Ma G Li N Wang P Xiao Q . [Effect of rhubarb as the main composition of sequential treatment in patients with acute paraquat poisoning: a prospective clinical research]. Zhonghua Wei Zhong Bing Ji Jiu Yi Xue. (2015) 27:254–8. 10.3760/cma.j.issn.2095-4352.2015.04.00625891453 Lu JF Nightingale CH. Magnesium sulfate in eclampsia and pre-eclampsia: pharmacokinetic principles. Clin Pharmacokinet. (2000) 38:305–14. 10.2165/00003088-200038040-0000210803454 Abecia JA Valares JA Forcada F Palacín I Martín S Martino A. The effect of melatonin on the reproductive performance of three sheep breeds in Spain. Small Rumin Res. (2007) 69:10–16. 10.1016/j.smallrumres.2005.12.018 Tian H Qi Q Yan F Wang C Hou F Ren W . Enhancing the developmental competence of prepubertal lamb oocytes by supplementing the in vitro maturation medium with sericin and the fibroblast growth factor 2 - leukemia inhibitory factor - insulin-like growth factor 1 combination. Theriogenology. (2021) 159:13–19. 10.1016/j.theriogenology.2020.10.01933113439 Goodarzi A Zare Shahneh A Kohram H Sadeghi M Moazenizadeh MH Fouladi-Nashta A . Effect of melatonin supplementation in the long-term preservation of the sheep ovaries at different temperatures and subsequent in vitro embryo production. Theriogenology. (2018) 106:265–70. 10.1016/j.theriogenology.2017.10.00929096275 Vazquez MI Forcada F Sosa C Casao A Sartore I Fernandez-Foren A . Effect of exogenous melatonin on embryo viability and uterine environment in undernourished ewes. Anim Reprod Sci. (2013) 141:52–61. 10.1016/j.anireprosci.2013.07.00723948208 Fang Y Deng S Zhang J Liu H Li Y Zhang X . Melatonin-mediated development of ovine cumulus cells, perhaps by regulation of DNA methylation. Molecules. (2018) 23:494. 10.3390/molecules2302049429473888 Mura MC Luridiana S Farci F Di Stefano MV Daga C Pulinas L . Melatonin treatment in winter and spring and reproductive recovery in Sarda breed sheep. Anim Reprod Sci. (2017) 185:104–8. 10.1016/j.anireprosci.2017.08.00928823418 Tian X Wang F Zhang L He C Ji P Wang J . Beneficial effects of melatonin on the in vitro maturation of sheep oocytes and its relation to melatonin receptors. Int J Mol Sci. (2017) 18:834. 10.3390/ijms1804083428420163 de la Cruz ML Conrado I Nault A Perez A Dominguez L Alvarez J. Vaccination as a control strategy against Salmonella infection in pigs: a systematic review and meta-analysis of the literature. Res Vet Sci. (2017) 114:86–94. 10.1016/j.rvsc.2017.03.00528340428 Barros VRP Monte APO Santos JMS Lins T Cavalcante AYP Gouveia BB . Melatonin improves development, mitochondrial function and promotes the meiotic resumption of sheep oocytes from in vitro grown secondary follicles. Theriogenology. (2020) 144:67–73. 10.1016/j.theriogenology.2019.12.00631918071 Barros VRP Monte APO Santos JMS Lins T Cavalcante AYP Gouveia BB . Effects of melatonin on the in vitro growth of early antral follicles and maturation of ovine oocytes. Domest Anim Endocrinol. (2020) 71:106386. 10.1016/j.domaniend.2019.10638631809950 Deng SL Chen SR Wang ZP Zhang Y Tang JX Li J . Melatonin promotes development of haploid germ cells from early developing spermatogenic cells of Suffolk sheep under in vitro condition. J Pineal Res. (2016) 60:435–47. 10.1111/jpi.1232726993286 Buffoni A Vozzi PA Gonzalez DM Rios G Viegas-Bordeira H Abecia JA. The effect of melatonin and season on in vivo embryo production of Dohne Merino ewes. Small Rumin Res. (2014) 120:121–4. 10.1016/j.smallrumres.2014.05.003 Vazquez MI Forcada F Casao A Abecia JA Sosa C Palacin I. Undernutrition and exogenous melatonin can affect the in vitro developmental competence of ovine oocytes on a seasonal basis. Reprod Domest Anim. (2010) 45:677–84. 10.1111/j.1439-0531.2008.01329.x19281597 Vazquez MI Abecia JA Forcada F Casao A. Effects of exogenous melatonin on in vivo embryo viability and oocyte competence of undernourished ewes after weaning during the seasonal anestrus. Theriogenology. (2010) 74:618–26. 10.1016/j.theriogenology.2010.03.00720570337 Abecia JA Palacin I Forcada F Valares JA. The effect of melatonin treatment on the ovarian response of ewes to the ram effect. Domest Anim Endocrinol. (2006) 31:52–62. 10.1016/j.domaniend.2005.09.00316221539 Cosso G Luridiana S Pulinas L Curone G Pich G Carcangiu V . Melatonin treatment in rams and their replacement with novel treated rams advance first lambing and increase fertility in Sarda ewe lambs. Animals. (2021) 11:1227. 10.3390/ani1105122733922809 Luridiana S Mura MC Daga C Farci F Di Stefano MV Zidda F . Melatonin treatment in spring and reproductive recovery in sheep with different body condition score and age. Anim Reprod Sci. (2015) 160:68–73. 10.1016/j.anireprosci.2015.07.00426220680 Mura MC Luridiana S Vacca GM Bini PP Carcangiu V. Effect of genotype at the MTNR1A locus and melatonin treatment on first conception in Sarda ewe lambs. Theriogenology. (2010) 74:1579–86. 10.1016/j.theriogenology.2010.06.02820708235 Mura MC Luridiana S Pulinas L Bizzarri D Cosso G Carcangiu V. Melatonin treatment and male replacement every week on the reproductive performance in Sarda sheep breed. Theriogenology. (2019) 135:80–4. 10.1016/j.theriogenology.2019.06.00831203091 Egger M Davey Smith G Schneider M Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ. (1997) 315:629–34. 10.1136/bmj.315.7109.6299310563 Vázquez MI Forcada F Casao A Sosa C Palacín I Abecia JA. Effects of melatonin and undernutrition on the viability of ovine embryos during anestrus and the breeding season. Anim Reprod Sci. (2009) 112:83–94. 10.1016/j.anireprosci.2008.04.00418479848 DeNicolo G Morris ST Kenyon PR Morel PC Parkinson TJ. Melatonin-improved reproductive performance in sheep bred out of season. Anim Reprod Sci. (2008) 109:124–33. 10.1016/j.anireprosci.2007.10.01218082341 Caglar K Kocabay A Taskin AC Arat S. Treatment with melatonin enhances the embryo quality and the development of vitrified/warmed eight cell mouse embryos by solid surface vitrification (SSV). Cryo Lett. (2020) 41:62–7.33988655 Hao T Xu X Hao H Du W Pang Y Zhao S . Melatonin improves the maturation and developmental ability of bovine oocytes by up-regulating GJA4 to enhance gap junction intercellular communication. Reprod Fertil Dev. (2021) 33:760–71. 10.1071/RD2114534585659 Niu YJ Zhou W Nie ZW Shin KT Cui XS. Melatonin enhances mitochondrial biogenesis and protects against rotenone-induced mitochondrial deficiency in early porcine embryos. J Pineal Res. (2020) 68:e12627. 10.1111/jpi.1262731773776 Soto-Heras S Catala MG Roura M Menendez-Blanco I Piras AR Izquierdo D . Effects of melatonin on oocyte developmental competence and the role of melatonin receptor 1 in juvenile goats. Reprod Domest Anim. (2019) 54:381–90. 10.1111/rda.1337830444551 Fu Y He CJ Ji PY Zhuo ZY Tian XZ Wang F . Effects of melatonin on the proliferation and apoptosis of sheep granulosa cells under thermal stress. Int J Mol Sci. (2014) 15:21090–104. 10.3390/ijms15112109025405739 Su J Wang Y Xing X Zhang L Sun H Zhang Y. Melatonin significantly improves the developmental competence of bovine somatic cell nuclear transfer embryos. J Pineal Res. (2015) 59:455–68. 10.1111/jpi.1227526331949 Zhao XM Hao HS Du WH Zhao SJ Wang HY Wang N . Melatonin inhibits apoptosis and improves the developmental potential of vitrified bovine oocytes. J Pineal Res. (2016) 60:132–41. 10.1111/jpi.1229026485053 Yong W Ma H Na M Gao T Zhang Y Hao L . Roles of melatonin in the field of reproductive medicine. Biomed Pharmacother. (2021) 144:112001. 10.1016/j.biopha.2021.11200134624677 Mou Q Yang YW Chen L Fang T Yao YC Du ZQ . Melatonin mitigates chloroquine-induced defects in porcine immature Sertoli cells. Theriogenology. (2022) 177:1–10. 10.1016/j.theriogenology.2021.10.00534653791 Pal Chowdhury J Haldar C. Stress associated ovarian dysfunctions in a seasonal breeder Funambulus pennanti: role of glucocorticoids and possible amelioration by melatonin. Gen Comp Endocrinol. (2022) 316:113962. 10.1016/j.ygcen.2021.11396234890689 Shi F Qiu J Zhang S Zhao X Feng D Feng X. Exogenous melatonin protects preimplantation embryo development from decabromodiphenyl ethane-induced circadian rhythm disorder and endogenous melatonin reduction. Environ Pollut. (2022) 292:118445. 10.1016/j.envpol.2021.11844534737029 Zhu T Guan S Lv D Zhao M Yan L Shi L . Corrigendum: Melatonin modulates lipid metabolism in porcine cumulus-oocyte complex via its receptors. Front Cell Dev Biol. (2021) 9:727612. 10.3389/fcell.2021.72761234322493 Li C He X Huang Z Han L Wu X Li L . Melatonin ameliorates the advanced maternal age-associated meiotic defects in oocytes through the SIRT2-dependent H4K16 deacetylation pathway. Aging. (2020) 12:1610–23. 10.18632/aging.10270331980591 Chesneau D Guillaume D Chemineau P Malpaux B. Continuous light after 2 months of long days stimulates ram testis volume and increases fertility in spring. Animal. (2017) 11:1189–95. 10.1017/S175173111600229927890022 Abecia JA Chemineau P Keller M Delgadillo JA. Extended day length in late winter/early spring, with a return to natural day length of shorter duration, increased plasma testosterone and sexual performance in rams with or without melatonin implants. Reprod Domest Anim. (2017) 52:851–6. 10.1111/rda.1298828455947 Tamura H Takasaki A Taketani T Tanabe M Kizuka F Lee L . The role of melatonin as an antioxidant in the follicle. J Ovarian Res. (2012) 5:5. 10.1186/1757-2215-5-522277103 Yang L Chen Y Liu Y Xing Y Miao C Zhao Y . The role of oxidative stress and natural antioxidants in ovarian aging. Front Pharmacol. (2020) 11:617843. 10.3389/fphar.2020.61784333569007 Deng SL Zhang BL Reiter RJ Liu YX. Melatonin ameliorates inflammation and oxidative stress by suppressing the p38MAPK signaling pathway in LPS-induced sheep orchitis. Antioxidants. (2020) 9:1277. 10.3390/antiox912127733327643 Abd-Elhafeez HH Hassan AHS Hussein MT. Melatonin administration provokes the activity of dendritic reticular cells in the seminal vesicle of Soay ram during the non-breeding season. Sci Rep. (2021) 11 872. 10.1038/s41598-020-79529-y33441634 Tamura H Takasaki A Miwa I Taniguchi K Maekawa R Asada H . Oxidative stress impairs oocyte quality and melatonin protects oocytes from free radical damage and improves fertilization rate. J Pineal Res. (2008) 44:280–7. 10.1111/j.1600-079X.2007.00524.x18339123 Hu K .L Ye X Wang S Zhang D. Melatonin application in assisted reproductive technology: a systematic review and meta-analysis of randomized trials. Front Endocrinol. (2020) 11:160. 10.3389/fendo.2020.0016032508754 Pool KR Rickard JP Pini T de Graaf SP. Exogenous melatonin advances the ram breeding season and increases testicular function. Sci Rep. (2020) 10:9711. 10.1038/s41598-020-66594-632546776 Satta V Manca ME Torres-Rovira L Succu S Mereu P Nehme M . Effects of melatonin administration on seminal plasma metabolites and sperm fertilization competence during the non-reproductive season in ram. Theriogenology. (2018) 115:16–22. 10.1016/j.theriogenology.2018.04.01829702366 Abecia JA Chemineau P Gomez A Keller M Forcada F Delgadillo JA. Presence of photoperiod-melatonin-induced, sexually-activated rams in spring advances puberty in autumn-born ewe lambs. Anim Reprod Sci. (2016) 170:114–20. 10.1016/j.anireprosci.2016.04.01127133179 Pardridge WM Mietus LJ. Transport of albumin-bound melatonin through the blood-brain barrier. J Neurochem. (1980) 34:1761–3. 10.1111/j.1471-4159.1980.tb11272.x7381501 Hu JJ Xiao LF Song LL Ge WB Duan HW Jiang Y. The expression of melatonin receptors MT1 and MT2 is regulated by E2 in sheep oviduct. Gen Comp Endocrinol. (2020) 286:113135. 10.1016/j.ygcen.2019.03.00430849411 Guo Z Islam MS Liu D Liu G Lv L Yang Y . Differential effects of follistatin on porcine oocyte competence and cumulus cell gene expression in vitro. Reprod Domest Anim. (2018) 53:3–10. 10.1111/rda.1303529134682 Johnson HE Dotson JM Ellis CS Hill KK. Severe hypotension in an adolescent after a melatonin overdose. J Child Adolesc Psychopharmacol. (2019) 29:726–7. 10.1089/cap.2019.010831553200 Holliman BJ Chyka PA. Problems in assessment of acute melatonin overdose. South Med J. (1997) 90:451–3. 10.1097/00007611-199704000-000209114843 Yilmaz B Kutlu S Mogulkoc R Canpolat S Sandal S Tarakci B . Melatonin inhibits testosterone secretion by acting at hypothalamo-pituitary-gonadal axis in the rat. Neuro Endocrinol Lett. (2000) 21:301–6.11455362 Lee S Jin JX Taweechaipaisankul A Kim GA Ahn C Lee BC. Melatonin influences the sonic hedgehog signaling pathway in porcine cumulus oocyte complexes. J Pineal Res. (2017) 63. 10.1111/jpi.1242428512846 Cao M Wang Y Yang F Li J Qin X. Melatonin rescues the reproductive toxicity of low-dose glyphosate-based herbicide during mouse oocyte maturation via the GPER signaling pathway. J Pineal Res. (2021) 70:e12718. 10.1111/jpi.1271833503294 Kim EH Ridlo MR Lee BC Kim GA. Melatonin-Nrf2 signaling activates peroxisomal activities in porcine cumulus cell-oocyte complexes. Antioxidants. (2020) 9:1080. 10.3390/antiox911108033153240 Guo S Yang J Qin J Qazi IH Pan B Zang S . Melatonin promotes in vitro maturation of vitrified-warmed mouse germinal vesicle oocytes, potentially by reducing oxidative stress through the Nrf2 pathway. Animals. (2021) 11:2324. 10.3390/ani1108232434438783 El-Sheikh M Mesalam AA Song SH Ko J Kong IK. Melatonin alleviates the toxicity of high nicotinamide concentrations in oocytes: potential interaction with nicotinamide methylation signaling. Oxid Med Cell Longev. (2021) 2021:5573357. 10.1155/2021/557335733927796 Li Z Li X Bi J Chan MTV Wu WKK Shen J. Melatonin protected against the detrimental effects of microRNA-363 in a rat model of vitamin A-associated congenital spinal deformities: involvement of Notch signaling. J Pineal Res. (2019) 66:e12558. 10.1111/jpi.1255830653707 Kechiche S Venditti M Knani L Jablonska K Dziegiel P Messaoudi I . First evidence of the protective role of melatonin in counteracting cadmium toxicity in the rat ovary via the mTOR pathway. Environ Pollut. (2021) 270:116056. 10.1016/j.envpol.2020.11605633199064 Amini H Rezabakhsh A Heidarzadeh M Hassanpour M Hashemzadeh S Ghaderi S . An examination of the putative role of melatonin in exosome biogenesis. Front Cell Dev Biol. (2021) 9:686551. 10.3389/fcell.2021.68655134169078 Yea JH Yoon YM Lee JH Yun CW Lee SH. Exosomes isolated from melatonin-stimulated mesenchymal stem cells improve kidney function by regulating inflammation and fibrosis in a chronic kidney disease mouse model. J Tissue Eng. (2021) 12:20417314211059624. 10.1177/2041731421105962434868540 Lin PY Yang D Chuang CH Lin H Chen WJ Chen CY . Comparative analyses of single-cell transcriptomic profiles between in vitro totipotent blastomere-like cells and in vivo early mouse embryonic cells. Cells. (2021) 10:3111. 10.3390/cells1011311134831338 Zhang H Li C Wen D Li R Lu S Xu R . Melatonin improves the quality of maternally aged oocytes by maintaining intercellular communication and antioxidant metabolite supply. Redox Biol. (2021) 49:102215. 10.1016/j.redox.2021.10221534929573 Wang Y Xing CH Zhang HL Pan ZN Sun SC. Exposure to nivalenol declines mouse oocyte quality via inducing oxidative stress-related apoptosis and DNA damagedagger. Biol Reprod. (2021) 105:1474–83. 10.1093/biolre/ioab17134505141 Xing CH Wang Y Liu JC Pan ZN Zhang HL Sun SC . Melatonin reverses mitochondria dysfunction and oxidative stress-induced apoptosis of Sudan I-exposed mouse oocytes. Ecotoxicol Environ Saf . (2021) 225:112783. 10.1016/j.ecoenv.2021.11278334544023 Yang CH Xu JH Ren QC Duan T Mo F Zhang W. Melatonin promotes secondary hair follicle development of early postnatal cashmere goat and improves cashmere quantity and quality by enhancing antioxidant capacity and suppressing apoptosis. J Pineal Res. (2019) 67:e12569. 10.1111/jpi.1256930861591 Hansell JA Richter HG Camm EJ Herrera EA Blanco CE Villamor E . Maternal melatonin: effective intervention against developmental programming of cardiovascular dysfunction in adult offspring of complicated pregnancy. J Pineal Res. (2022) 72:e12766. 10.1111/jpi.1276634634151 Gunata M Parlakpinar H Acet HA. Melatonin: a review of its potential functions and effects on neurological diseases. Rev Neurol. (2020) 176:148–65. 10.1016/j.neurol.2019.07.02531718830 Ivanov DO Evsyukova II Mironova ES Polyakova VO Kvetnoy IM Nasyrov RA. Maternal melatonin deficiency leads to endocrine pathologies in children in early ontogenesis. Int J Mol Sci. (2021) 22:2058. 10.3390/ijms2204205833669686 Faria VS Pejon TMM Gobatto CA de Araujo GG Cornachione AS Beck WR. Acute melatonin administration improves exercise tolerance and the metabolic recovery after exhaustive effort. Sci Rep. (2021) 11:19228. 10.1038/s41598-021-97364-734584111