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Pituitary responsiveness to LH-RH and TRH and the effects of progesterone or progesterone and oestradiol treatment in anoestrous sheep

Summary. Pituitary responsiveness to 200 µg synthetic LH-RH and to 10 µg TRH was determined in anoestrous sheep before and after treatment for 3 weeks with progesterone (100 mg/day), or oestradiol (250 µg/day) plus progesterone (100 mg/day). There was a marked decrease in pituitary responsiveness to LH-RH after progesterone (P < 0·01 ), or oestradiol + progesterone (P < 0·01) treatments, and an increase in response to TRH after oestradiol + progesterone (P < 0·01) treatment. The results demonstrate selective and simultaneous feedback effects of oestradiol and progesterone on pituitary responsiveness to two hypothalamic releasing hormones.