FSH and LH Response to Gonadotropin-Releasing Hormone During the Ovine Estrous Cycle and Following Progesterone Administration12

Abstract

Synthetic gonadotropin releasing hormone (Gn–RH) which is identical to ovine LHreleasing hormone was given by intracarotid infusion (1.5 ng'hr for 4–5 hr) to ewesat various stages of their estrous cycle. It was found that LH and FSH responses to Gn–RH were significantly lower (p< 0.02) in the sheep infused on days 2–12 compared to sheep treated on days 15–17 after estrus. Continuous infusion of exogenous progesterone (500 'Mg'hr for 76 hr) significantly suppressed LH (p < 0.05) and FSH (p < 0.01) response to Gn–RH in ewes at the proestrous stage of their cycle. It is concluded that progesterone has a modulating influence upon LH and FSH secretion and could be responsible for thelower gonadotropin response to Gn-RH during the luteal stage of the cycle. (Endocrinology 95: 937,1974)