In vitro study of bovine uterine contractility at various stages of pregnancy

Introduction - Throughout pregnancy, the uterus does not remain quiescent, but displays contractile activity in several species. This is made possible by the presence of interstitial Cajal cells in the myometrium and by the ability of myometrium to contract/relax even under the action of hormonal or neuronal stimuli. Aim - This in vitro study investigates spontaneous uterine contractility in cows during different months of pregnancy (from the first at 30 days to the last at 270 days). Materials and methods - Basal contractility was evaluated in an isolated organ bath and the functionality of strips throughout the experiment was evaluated by a dose of carbachol (10-5 M), which always had to be repeatable (≤ difference of 20%) with the previous administration of the same substance. Amplitude, frequency and area under the curve (AUC) of contractions for each strip were determined by analysing the sequence corresponding to the last 30 min of contraction, from the recording section. Results and discussion - This in vitro study demonstrates a variations in contractile capacity, that was highly dependent on the month of bovine pregnancy. Contractility proved extremely limited in early pregnancy (from 0-30 to 90-120 days) and even more so between 120-150 and 180-210 days, reaching maximum force (amplitude) of contraction between 150-180 days.After this period, it decreases from days 180- to 210 and then rises again from days 240- to 270.The contractility detected in the latter two periods is very unusual: between 210-240 days, it is made up of alternating waves with low and high strength, while the period from 240-270 daysis characterized by contractures (high-amplitude, low-frequency and long-lasting). The data suggest that the bovine pregnant uterus does not remain quiescent, but displays contractile activity, and raise the hypothesis that steroid hormones may play a role in the modulation of uterine contractions during pregnancy. Conclusions - Our results provide a new vision of embryonic and fetal mortality, probably attributable to alterations in uterine contractility and cytokine production.