Differential release of LH and FSH in cyclic mares in response to synthetic Gn-RH

Abstract

Mares at different stages of the estrous cycle were given a single i.v. injection of 0.5 mg synthetic Gn-RH [gonadotropin releasing hromone]. The mean area of the induced LH [luteinizing hormone] peak was significantly less at mid-cycle (Day 10-11) than at any other time. The mean height of the LH peak above preinjection concentration was greater at late estrus and early cycle (Day 5-6) than at mid-cycle and early estrus. There were no significant differences in mean FSH [follicle stimulating hormone] responses. The LH:FSH ratio for both height and area of induced peaks was significantly less at mid-cycle than at other times of injection. One releasing hormone could cause the release of both FSH and LH in the normal cyclic mare.