Age related changes in pituitary responsiveness to luteinizing hormone-releasing hormone in the male rat

Changes in pituitary and serum concentrations of LH and FSH, determined by radioimmunoassay, were studied after administration of LH-RH to intact male rats of various ages. Although injection of LH-RH resulted in a depletion of pituitary LH and FSH in almost all age groups, thereby increasing the serum levels of these hormones, the magnitude and time course of the effects varied. Serum LH in the prepubertal and pubertal rats was maximal at 10 min after LH-RH injection, whereas the mature animals showed maximal increase only after 30 min. Peak serum concentrations of FSH found at 10 min in the prepubertal animals, but between 30 and 60 min in the pubertal and adult animals. At 35 days of age, significant pituitary depletion of LH and FSH occurred.