Negative feedback on luteinizing hormone secretion requires infrequent exposure to testicular androgens

Abstract

Abstract The present study tested the hypothesis that a minimum frequency of testosterone pulses is required to exert negative feedback control of luteinizing hormone (LH). Effect of gonadal steroids on endogenous LH release in rams was investigated after injecting ovine LH (NIADDK-oLH-26, i.v.; 5 μg 100kg−1 BW) to induce testosterone pulses while rams were undergoing windows of LH suppression during the influence of a LH releasing hormone (LHRH) antagonist (SB-75; Bajusz et al., 1988, Int. J. Peptide Protein Res., 32: 425–435). Patterns of LH release were characterized as rams recovered from LH inhibition. Rams were exposed to artificial photoperiods of 12 weeks of long days (16L:8D) followed by short days (8L:16D) to initiate reproductive activity. The study began during Week 5 of short days. Serial plasma samples were collected from six postpubertal rams (five Suffolks and one Hampshire) at 15-min intervals for 69.5 h. All rams were given LHRH antagonist (10 μg kg−1 BW, s.c.) at Hour 24 during each of three collection periods which took place on alternating weeks in a Latin square design. Rams were given a different exogenous oLH treatment (no oLH, one dose at 12 h after antagonist or three doses at 6-h intervals with initial dose 6 h after antagonist) during each collection period. Exogenous oLH decreased the number of LH pulses during the recovery period (Hours 48 to 72 of experiment; 24 to 48 h after antagonist; P