Evidence that inhibition of myometrial activity by oestradiol in the rat is mediated by an RNA synthetic pathway.

Within some 14 h of treatment with oestradiol benzoate (5 microgram), the intra-uterine pressure cycles in ovariectomized puerperal rats were almost abolished. However, treatment with 600 microgram actinomycin D 30 min before the administration of oestradiol benzoate interfered significantly with the inhibition of uterine mechanical activity during the following 14h. Treatment of rats with actinomycin D alone produced no significant fall in the frequency of pressure cycles. These results suggest that oestrogen inhibits myometrial activity in the rat through a mechanism which involves the synthesis of protein.