Influence of estrogens on in vivo and in vitro rat uterine motility. Relationships with histamine, cimetidine and tissue levels of 3',5' cyclic adenosine monophosphate.

In vivo intrauterine pressure (IUP) and in vitro isometric developed tension (IDT) of rat uterine strips were explored. Moreover, levels of 3',5' cyclic adenosine monophosphate (cAMP) were determined. The influence of 17-beta-estradiol (17-beta-E2), histamine and cimetidine on the above mentioned parameters were analyzed. IUP changes determined at proestrus, estrus and diestrus evidenced phasic waves of smaller magnitude at the first mentioned stage of the sex cycle. The injection of 17-beta-E2 (iv. bolus of 1.0 micrograms) in diestrous rats evoked at around 30 min a complete abolition of uterine motility, an action prevented by the previous injection of cimetidine (0.5 mg, iv.). The i.v. injection of histamine (0.25 mg) resulted in a distinct inhibition of IUP, also prevented by administering cimetidine. cAMP concentrations in uterine homogenates from ovariectomized rats were explored at 1 and at 30 min following injection of 17-beta-E2. At the 1 min period, but not at 30 min, cAMP increased significantly and cimetidine (delivered 30 min prior to the estrogen) completely blocked the enhancing effect of 17-beta-E2 on cAMP concentration. The IDT of uterine strips isolated from ovariectomized rats declined spontaneously less than 20% after 40 min of activity in the suspending solution, and 17-beta-E2, but not cimetidine (injected prior to sacrifice) produced an inotropic decrement of around 80% at 40 min. In preparations from animals receiving both cimetidine and 17-beta-E2, the contractile decrement was significantly smaller than with 17-beta-E2 alone.(ABSTRACT TRUNCATED AT 250 WORDS)