Oestrogen-induced myometrial quiescence in the post-partum rat is not mediated by adrenaline or by alpha- or beta-adrenoceptor activation.

Ovariectomized post-partum rats exhibit in vivo continuous stable myometrial activity with a frequency of 45--50 pressure cycles per h, and a mean maximum amplitude of 45--50 mmHg for many days. Oestradiol benzoate (5 micrograms) reduced the frequency of intra-uterine pressure cycles to 5 cycles per h by 20 h after treatment. The decrease in frequency was due to increased periods of uterine quiescence. Pretreatment with reserpine caused significant reductions in the concentration of uterine adrenaline and noradrenaline as measured by a fluorometric assay but had no effect on the extent or time-course of oestrogen-induced myometrial quiescence. Neither intravenous infusion of the adrenergic beta-blocker, propranolol, altered the extent or the time-course of the reduction of intra-uterine pressure cycles after oestrogen treatment. These results suggest that the mechanism by which oestrogen induces myometrial quiescence does not involve adrenaline mediation or alpha- or beta-adrenoceptor activation.