Effect of immunoneutralization of luteinizing hormone releasing hormone on the estrogen-induced luteinizing hormone and follicle-stimulating hormone surges in the ewe.

Abstract

The importance of luteinizing hormone releasing hormone (LHRH) in inducing the preovulatory luteinizing hormone (LH) surge in the ewe was investigated by administration of LHRH antiserum approximately 10 h before the expected onset of the rise in LH in the blood. Ten ewes with synchronized estrous cycles were studied. Luteolysis was induced by prostaglandin and 26 h later the ewes were injected with 50 �ig estradiol benzoate in arachis oil, and after a further 10 h, 5 control ewes received 100 ml ovine antiserum to bovine serum albumin (BSA) i.v., and 5 remaining animals 100 ml ovine antiserum to LHRH (LHRH antiserum). All 5 control ewes demonstrated the expected sharp rise in plasma LH concentrations, peak values occurring 26 ± 2 h (mean ± SEM) after estradiol benzoate administration. This rise was absent in the LHRH antiserum treated animals, who also failed to ovulate as judged from the absence of a rise in plasma progesterone concentrations during the following 16 days. Plasma LH concentrations remained low during the 16-day period in the treated animals. In the control ewes there was a clear surge of follicle-stimulating hormone (FSH) coincidently with the LH surge. This did not occur in the ewes treated with antibodies to LHRH. However, plasma FSH concentrations rose despite the presence of antibodies to LHRH and although a clear second FSH peak which occurred in the controls was not evident in the LHRH antibody treated animals, there was no significant difference in the amount of FSI-I released during this time period between the two groups. Also, plasma FSH concentrations during the remaining 16 days were unaltered by the LHRH antibodies. Thus in the ewe, the estrogen-primed hypothalamo-pituitary system cannot produce an LH surge if LHRH is neutralized by giving antiserum before the onset of the surge and basal LH output is also reduced. The major preovulatory FSH surge is also inhibited when LHRH is neutralized but basal secretion of the hormone remains unaltered.