DIFFERENTIAL CONTROL OF LUTEINIZING HORMONE AND FOLLICLE-STIMULATING HORMONE BY LUTEINIZING HORMONE RELEASING HORMONE IN THE RAM

Adult Soay rams with low concentrations of gonadotrophins in the circulation as a result of 12 weeks of exposure to long daylengths (16 h light: 8 h darkness) were given small doses (100 ng) of synthetic luteinizing hormone releasing hormone (LH-RH) into thejugular vein two, four or seven times/day for 10 days. Each injection of LH-RH induced a transitory increase in the concentration of LH and testosterone in the plasma, whereas the concentration ofFSH showed little immediate change, After repeated treatment with pulses of LH-RH, the responses of LH and testosterone became slightly enhanced and the plasma concentration of FSH became permanently raised; these changes were most conspicuous in the animals receiving the most frequent injections. At the end of the study when the injections of LH-RH were stopped, the concentrations of LH and testosterone remained low but the concentrations of FSH continued to be maintained at a high level for at least 24 h