Effects of estrogen and progesterone on LHRH release from a hypothalamic synaptosomal fraction of ovariectomized rats

Mitochondrial-synaptosomal fractions (P₂) from the basomedial hypothalamus of adult ovariectomized rats were employed to study the effects of estradiol benzoate (EB) and progesterone (P) on the release of luteinizing hormone-releasing hormone (LHRH). Treatment of ovariectomized rats with 5 or 50 g of EB significantly reduced the total LHRH released from P₂ under both control and K⁺-stimulated conditions. Furthermore, rats given 50 g EB demonstrated cyclic variations in the magnitude of inhibition of LHRH release. Comparison of LHRH release from P₂ of rats sacrificed at 0900 hr with that from those sacrificed at 1500 hr revealed a small persistent facilitation of LHRH release each afternoon. This facilitation, associated with an increase in the soluble component of LHRH release, was absent when rats also received 5 mg of P. No effects on LHRH release were observed when 17-estradiol alone or when P was applied to P₂ in vitro. The data show that the regulatory effects of estrogen and progesterone given in vivo on LHRH secretion can be observed in a subcellular fraction of the hypothalamus containing neurosecretory cell terminals.Supported by grants from the NIH, HD08389 and NS11753.U.S.P.H.S. Career Development Awardee, K04-HD00022