PITUITARY RESPONSIVENESS TO A SINGLE INJECTION OF SYNTHETIC LUTEINIZING HORMONE RELEASING HORMONE BEFORE AND AFTER THE NATURAL PREOVULATORY PLASMA LUTEINIZING HORMONE PEAK IN THE SHEEP

Abstract

In the group injected 20 h after onset of estrus, the preovulatory LH [luteinizing hormone] peak occurred before the injection, which resulted in a small LH response in each case. In 2 ewes, the LH concentrations were still in the declining phase at the time of injection. In the other ewes the injection was administered after the LH concentration had reached baseline. In both cases the responsiveness of the pituitary gland was greatly reduced compared with the onset of estrus group. The responsiveness of the pituitary gland to LH-RH is decreased after a natural LH peak.