Blockade of Episodic Secretion of Luteinizing Hormone in the Ram by the Administration of Antibodies to Luteinizing Hormone Releasing Hormone

Abstract

Administration of ovine serum containing LHRH antibodies to adult Soay rams during the autumn period of sexual activity resulted in an immediate blockade of episodic secretion of LH. The concentration of LH in the peripheral blood remained low for at least a day, but was increased 24 days later when episodic peaks of high frequency were again apparent. The plasma concentration of testosterone changed in close parallel with the changes in LU while the levels of FSH were unaffected and there were no clear effects on the size of the testes. The release of LH and testosterone following the i.v. injection of 200 ng synthetic LHRH was blocked on the day following the administration of the antiserum but the response returned to normal within 46 days by which time the antibodies to LHRH were virtually undetectable in the blood plasma. These results show that the episodic secretion of LU in the ram is dependent on LHRH from the hypothalamus and that neutralization of the neurohormonc results in a rapid decline in the circulating levels of LH. FSH on the other hand is largely unresponsive to changes in LHRH and secretion of FSH may occur for several days even after the complete neutralization of LHRH.