Comparison of changes in uterine reactivity to endogenous substances in rabbits and the effect of in vivo and in vitro administration of estradiol and testosterone

: Changes in uterus reactivity were studied in the rabbit after single and repeated administration of estradiol in the dose of 5 mg.kg-1 and of testosterone in the dose of 10 mg.kg-1. On applying the hormones in vitro, 1.8 x 10(-5) mol of estradiol and 5.8 x 10(-5) mol of testosterone was used. The method of isometric contraction served to study the cumulative curves of the uterus to histamine (HIST), serotonin (SEROT), and angiotension (ANGIO). Both after single and repeated administration of the hormones, the contractile response of the uterus to the substances studied was mostly increased. After hormonal pretreatment in vitro, the contractile responses of the uterus were predominantly reduced, and this diminished response was more pronounced after testosterone. Repeated hormonal pretreatment resulted in hypertrophy of the longitudinal and circular musculature, which was more marked after testosterone application. The results indicate that testosterone, similarly as estradiol, can affect the contractility of the uterus both at receptor and nonreceptor levels, as well as by its effect on the morphology of the uterus.