HYPERSECRETION OF FOLLICLE-STIMULATING-HORMONE (FSH) ON ESTROUS AFTERNOON IN RATS TREATED WITH RU486 IN PROESTRUS

1. Intact or ovariectomized (OVX) cyclic rats injected or not with RU4 86 (4mg/0.2 ml oil) from proestrus onwards were bled at 0800 and 1800h on proestrus, estrus and metestrus. Additional RU486-treated rats wer e injected with: LHRH antagonist (LHRHa), estradiol benzoate (EB) or b ovine follicular fluid (bFF) and sacrified at 1800 h in estrous aftern oon. LH and FSH serum levels were determined by RIA. 2. RU486-treated intact or OVX rats had decreased preovulatory surges of LH and FSH, ab olished secondary secretion of FSH and hypersecretion of FSH in estrou s afternoon. The latter was decreased by LHRHa and abolished by EB or bFF. In contrast, EB induced an hypersecretion of LH in RU486-treated rats at 1800 h in estrus. 3. It can be concluded that in the absence o f the proestrous progesterone actions, the absence of the inhibitory e ffect of the ovary in estrus evoked a LHRH independent secretion of FS H.