The Contractile Response to Oxytocin in Non-pregnant Rat Uteri Is Modified After the First Pregnancy

During pregnancy, the uterus undergoes several modifications under the influence of hormonal and mechanical stimuli. We hypothesize that while most of these modifications are reverted during involution, some of the physiological properties of the uterus are permanently altered. To investigate this hypothesis, we conducted motility experiments to evaluate the contractility response of uterine tissue samples from non-pregnant virgin and proven breeder female rats to oxytocin (10^-10 to 10^-5 M). We found that the virgin tissue contracts more robustly than proven breeder tissue in the absence of oxytocin, yet with oxytocin, proven breeder samples displayed a significantly higher increase in activity. These results could depend on a more elevated expression of oxytocin receptor and/or on an alteration in the intracellular pathways affected by the activation of the oxytocin receptors. Here, we explored the impact of some structures involved in the management of intracellular calcium on the dose response to oxytocin recorded from virgin and proven breeder uterine strips. Specifically, we replicated the dose response experiments in low extracellular calcium (10 μM), in the presence of the intracellular calcium channel blocker ruthenium red (10 μM), and in the presence of the sarcoplasmic-endoplasmic reticulum calcium ATP-ase pump inhibitor, cyclopiazonic acid (10 μM). The results of these experiments suggest that also the expression of proteins that control intracellular calcium availability is affected by the experience of pregnancy. Molecular biology experiments will give us more detail on the magnitude of these expression changes.