Original Research ARTICLE
Spatiotemporal mapping of the contracting gravid uterus of the rabbit shows contrary changes with increasing gestation and dosage with oxytocin
- 1College of Sciences, Massey University, New Zealand
- 2College of Health, Massey University, New Zealand
- 3Palmerston North Hospital, New Zealand
- 4School of Veterinary Sciences, College of Sciences, Massey University, New Zealand
Spontaneous and oxytocin induced contractile activity was quantified in the bicornuate uteri of pregnant rabbits maintained in situ, using data from two- and uni- dimensional video spatiotemporal maps (VSTM) of linear and area strain rate and compared statistically. Spontaneous contractions occurred over a range of frequencies between 0.1 and 10 cpm, in gravid animals at 18-21 and at 28 days of gestation, and propagated both radially and longitudinally over the uterine wall overlying each foetus. Patches of contractions were randomly distributed over the entire surface of the cornua and were pleomorphic in shape. No spatial coordination was evident between longitudinal and circular muscle layers nor temporal coordination that could indicate the activity of a localised pacemaker. The density and duration of contractions decreased, and their frequency increased with the length of gestation in the non-labouring uterus. Increasing intravenous doses of with oxytocin had no effect on the mean frequencies, or the mean durations of contractions in rabbits of 18-21 days gestation, but caused frequencies to decrease and durations to increase in rabbits of 28 days gestation, from greater spatial and temporal clustering of individual contractions. This was accompanied by an increase in the distance of propagation, the mean size of the patches of contraction, the area of the largest patch of contraction and the overall density of patches. Together these results suggest that progressive smooth muscle hypertrophy and displacement with increasing gestation is accompanied by a decrease in smooth muscle connectivity causing an increase in wall compliance and that oxytocin restores connectivity and decreases compliance, promoting volumetric expulsion rather than direct propulsion of the foetus by peristalsis. The latter effects were reversed by the β2 adrenergic receptor agonist salbutamol thus reducing area of contraction, duration and distance of propagation
Keywords: motility, Spatiotemporal mapping, Uterus - physiology, rabbit, Oxytocin, Salbutamol, Fetus, Contraction, paturition, Pregnancy, gestation, Birth
Received: 29 Jul 2019;
Accepted: 04 Nov 2019.
Copyright: © 2019 Hulls, Lentle, Chua, Suisted, King, Chagas, Chambers and Stewart. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Mx. Corrin M. Hulls, College of Sciences, Massey University, Palmerston North, 4442, Manawatu-Wanganui, New Zealand, firstname.lastname@example.org