Spontaneous contractility of bovine myometrium in vitro depending on topography and cycle phase

The bovine myometrium exerts different contractility patterns in dependency of the reproductive state. However, little is known about the contractile behaviour of the uterus in the cow regarding topography. Differences in the in vitro contractile activity of two regions of the bovine uterus were assessed using an organ bath model. Myometrial specimens from the larger horn: near corpus (nc) and near tip (nt) from healthy cows in oestrus (n = 11) or dioestrus (n = 6) were collected after slaughter. Two strips were prepared from each region corresponding to the circular and the longitudinal muscle layers, respectively. Spontaneous contractility of these strips was recorded in an organ bath. For analysis, the 2.5 h recordings were divided into five periods of 30 min each. The variables area under curve (AUC) and maximal (Amax) and minimal amplitude (Amin) were calculated separately for periods, and the results analysed with a non-parametric model regarding the influence of cycle phase (estrus vs. diestrus), region (nc vs. nt) and muscle layer (circular vs. longitudinal). The region had a influence on AUC (p < 0.05) with higher values for nt samples, while Amin was influenced by region (nt > nc) and muscle layer (longitudinal > circular) (p < 0.05). By using the same model in subgroups of region, differences among periods for AUC and Amax caused by increasing values over time, and an interaction of layer × time for Amin were evident for nt samples (p < 0.05). For nc samples, however, interactions of cycle × layer × time (AUC) and layer × time (Amax, Amin) revealed to be significant (p < 0.05). The relevance of the results for further research regarding uterine physiology is discussed.