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Possible mechanisms of diverse spaceflight effects on endothelial function in different vascular beds

Olga L. Vinogradova1, 2*, Oxana O. Kiryukhina1, 2, 3, Dina K. Gaynullina1, 2 and Olga S. Tarasova1, 2, 3
  • 1 Institute of Biomedical Problems (RAS), Russia
  • 2 Lomonosov Moscow State University, Russia
  • 3 Institute for Information Transmission Problems (RAS), Russia

OBJECTIVES. The release of vasoactive substances from the endothelium is an important mechanism influencing arterial structure and function, whereas endothelium disfunction is typical for various cardiovascular disturbances (Triggle et al., 2012; Vanhoutte et al., 2016). Importantly, recent studies have demonstrated increasing risk for cardiovascular disease resulting from long-lasting space travel (Delp et al., 2016). This fact can be associated with the weightlessness-induced hemodynamic shifts and vascular remodeling (Prisby et al., 2006; Zhang, 2013; Zhang and Hargens, 2018). Another established endothelium-damaging factor of the space flight is space radiation which induces a sustained vascular endothelial cell dysfunction (Delp et al., 2016; Ghosh et al., 2016). According to our recent observations, basilar artery (cerebral) and saphenous artery (hindlimb, mainly cutaneous) of C57BL/6 mice demonstrated qualitatively different alterations after 30-day-long spaceflight on the Bion-M №1 biosatellite. The endothelium-dependent relaxation to acetylcholine was suppressed in basilar artery but somewhat augmented in saphenous artery (Sofronova et al., 2015; Tarasova et al., 2016). Beside different location in the mouse body (rostral vs. caudal), such diverse post-flight alterations can be associated with the inherent differences in the contribution of endothelium-derived mechanisms in these arteries. Of note, the contributions of key mediators of endothelium-derived relaxation (NO, prostacyclin and endothelium-derived hyperpolarizing factor, EDHF) can differ significantly in vessels of different branching order, as well as in vasculature of different organs (Hill et al., 2000; Kostyunina et al., 2016). Therefore, this study tested the hypothesis that murine basilar and saphenous arteries differ in the contribution of endothelium-derived mechanisms to the regulation of their smooth muscle tone. METHODS. All experimental procedures were approved by the by the Biomedical Ethics Committee of the Institute for Information Transmission Problems, Russian Academy of Sciences (protocol 12-051), conforming to the U.S. National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals (Eighth edition, 2011). С57Bl/6 male mice aged 2 to 3 month were housed in the animal vivarium under controlled environmental conditions (12:12 hour light-dark cycle, 22-25°C) and provided food and water ad libitum. For isolated vessel studies mice were euthanized by cervical dislocation. Basilar and saphenous arteries were isolated and arterial segments (1 to 2 mm long) were mounted in wire myograph (620М, DMT, Denmark) to study their responses under isometric conditions. The preparations were kept at 37°C in the solution containing (mM): 120 NaCl, 26 NaHCO3, 4.5 KCl, 1.2 NaH2PO4, 1.0 MgSO4, 1.6 CaCl2, 5.5 D-glucose, 0.025 EDTA, 5 HEPES. The solution was continuously bubbled with gas mixture 5% CO2 + 95% O2 to maintain pH 7.4. Transducer readings were sampled at 10 Hz using E14-140 ADC (L-CARD, Russia) and PowerGraph 3.3 software (DISoft, Russia). All preparations were stretched to an internal circumference at which they developed maximal active tension (Mulvany and Halpern, 1977) and activated with two contraction/relaxation cycles (5 min/10 min). Saphenous arteries were contracted by the maximum concentration of α1-adrenoceptor agonist phenylephrine (10-5 M, Sigma). Basilar arteries were contracted by the maximum concentration of U46619 (10-6 M, Cayman Chemicals), the agonist of thromboxane A2 receptors, which are important regulators of cerebrovascular tone (Toth et al., 2011). Relaxation responses to acetylcholine (in the concentration range from 10-8 M to 10-5 M) were studied cumulatively after precontraction with the respective agonist to 70 to 80% of the maximum active force (Figure 1). After washout, the segments were incubated with blockers of one or several endothelium-derived pathways and the concentration-response to acetylcholine was repeated. We used L-NNA (10-4 M, Alexis Biochemicals) to block NO-synthase, indomethacin (10-5 M, Sigma) to block cyclooxygenases and the combination of SKCa and IKCa channel blockers (TRAM-34, 10-6 M, and UCL-1684, 10-7 M, both from Sigma) to eliminate the contribution of EDHF. Relaxation responses to NO-donor DEA/NO (in the concentration range from 10-9 M to 10-6 M) were studied using similar protocol. Before DEA/NO application the preparations were incubated with L-NNA for 15 min, to eliminate the interference of exogenous NO and endogenous NO effects. The responses to each acetylcholine or DEA/NO concentration were calculated as percentage of the precontraction level. Statistical analysis was performed in GraphPad Prism 7.0 using Repeated Measures ANOVA. Statistical significance was reached at P < 0.05. All data are given as mean ± S.E.M.; n represents the number of animals. RESULTS. Application of acetylcholine induced relaxation of basilar and saphenous arteries which reached the maximum at the concentration of 3*10-6 M (Figures 1 and 2). In the absence of pharmacological interventions, the response to acetylcholine was much larger in saphenous artery than in basilar artery. Combined blockade of NO, prostacyclin and EDHF pathways almost eliminated the response to acetylcholine in both arteries (Figure 2). L-NNA given alone halved the response to acetylcholine in basilar and saphenous arteries (Figure 2 A,B). The additional inhibition of cyclooxygenase by indomethacin was not accompanied by a further decrease in arterial relaxation response compared with the response in the presence of L-NNA alone (Figure 2 C,D). On the contrary, the response to acetylcholine was somewhat increased by indomethacin, which suggests rather constrictor than dilator influence of cyclooxygenase products in both studied arteries. Thus, in both arteries NO demonstrates a significant contribution to the relaxation in response to acetylcholine, this component of endothelium-dependent relaxation is comparable in basilar and saphenous arteries. Of note, relaxation responses to DEA/NO did not differ in basilar and saphenous arteries (data not shown). The blockade of EHDF pathway halved the response to acetylcholine in basilar artery (Figure 1E). However, EDHF pathway blockade did not decreased the response of saphenous artery (Figure 1F), even though a pronounced EDHF contribution was observed in this artery after combined blockade of NO synthase and cyclooxygenase (Figure 1D). This observation suggests NO to inhibit the activity of EDHF pathway in saphenous artery. Such effect of NO may be attributed by the decrease of Ca2+ concentration in the cytoplasm of endothelial cells and thereby a weaker activation of SKCa/IKCa channels, which are essential the realization of EDHF-mechanism (Bauersachs et al., 1996). CONCLUSIONS. The basilar and saphenous arteries of the mouse differ in the mechanisms of endothelium-dependent regulation of their smooth muscle tone. Endothelium-dependent relaxation response of basilar artery is caused by the additive effects of NO and EDHF pathways, each of which provides about half of the total relaxation response. However, saphenous artery demonstrates the redistribution of endothelium-derived pathways: reduced EDHF activity can be compensated by the increased contribution of NO and vice versa. Such redistribution of endothelium-dependent relaxation components in saphenous artery may underlie the unchanged or even elevated relaxation response after spaceflight in cutaneous vascular bed. On the other hand, cerebral arteries which lack the possibility of such redistribution can be more vulnerable to the influence of space flight factors than peripheral arteries. Violation of the endothelium-dependent regulation of cerebrovascular tone can be the reason for narrowing the range of cerebral blood flow control, the development of intracranial hypertension and visual impairment after long-lasting space flights (Delp et al., 2016; Zhang and Hargens, 2018).

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Acknowledgements

The work was performed according to the Plan for Fundamental research of SRC RF -Institute for Biomedical Problems RAS and was partially supported by the Russian Science Foundation (grant 17-15-01433).

References

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Keywords: Mouse (Black Swiss, C57BL/6), Brain, Skin, small arteries endothelium dysfunction, Space Flight

Conference: 39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018.

Presentation Type:

Topic: Cardiovascular, Fluid Shift and Respiration

Citation: Vinogradova OL, Kiryukhina OO, Gaynullina DK and Tarasova OS (2019). Possible mechanisms of diverse spaceflight effects on endothelial function in different vascular beds. Front. Physiol. Conference Abstract: 39th ISGP Meeting & ESA Life Sciences Meeting. doi: 10.3389/conf.fphys.2018.26.00029

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Received: 30 Aug 2018; Published Online: 16 Jan 2019.

* Correspondence: Prof. Olga L Vinogradova, Institute of Biomedical Problems (RAS), Moscow, Moscow Oblast, Russia, ovin@imbp.ru