Sensitivity of the Bothrops jararaca snake uterus to oxytocin and acetylcholine

Abstract

The influence of hormones on the uterine smooth muscle sensitivity has been demonstrated in mammals; however in nonmammalian species much remains to be clarified. This study investigated the sensitivity of the snake (Bothrops jararaca) uterus to oxytocin and acetylcholine. the snakes were divided into three experimental groups: snakes with uterine segments weighing less than or equal to 20.00 mg (A), snakes with uterine segments weighing between 20.01 and 35.00 mg (B) and snakes with uterine segments weighing greater than or equal to 35.01 mg (C). the histomorphometric analysis of the uterus showed an increase in the smooth muscle layer thickness in groups B and C, when compared with group A, suggesting different hormonal conditions of the animals. Cumulative concentration-effect curves to oxytocin and acetylcholine were obtained in uteri of the three experimental groups and the pD(2) values determined. the sensitivity of the snake uterus to oxytocin increased in groups B and C (concentration-effect curves shifted to the left and pD(2) values increased) when compared with group A. the concentration effect curves to acetylcholine were biphasic and shifted to the left, suggesting two binding sites (low and high affinity binding sites) in snake uteri of groups B and C. These results suggest that sex steroids may modulate the sensitivity of the snake uterus to oxytocin and acetylcholine.