The effect of GnRH on in vitro bovine myometrial activity

The aim of this study was to evaluate, in vitro, the effects of increasing concentrations of GnRH on spontaneous mechanical activity patterns of uterine smooth muscle preparations of cows during the follicular and the luteal phases of the oestrus cycle. Uterine smooth muscle strips from 14 cows in follicular and 9 in luteal phase were collected immediately after slaughter and processed within 60 min from collection. Two strips of the same uterus were mounted in an isolated organ bath with two chambers to evaluate the role of decapeptide GnRH on spontaneous myometrial contractility. After equilibration period at 20 mN resting tension, the mechanical activity of the uterus was recorded for 10 min and the mean contractile force (MCF) was calculated. Then GnRH antagonist (antide) was added to one chamber at fixed concentration (10(-4)mol) and allowed to diffuse in solution and make contact with the strips. Subsequently, GnRH was added to the two baths at the same time at increasing concentration and MCF was recorded for 10 min. The effect of GnRH on spontaneous myometrial activity was evident only in the strips from subjects in follicular phase. Our results are suggestive of the presence of GnRH receptors in bovine myometrial tissue. The involvement of GnRH on uterine contractions at mating can be postulated.