Inhibition by Oestradiol of the Pituitary Response to Luteinizing Hormone Releasing Hormone in the Dog

Abstract

Intravenous injections of synthetic LH-RH stimulated LH secretion in male dogs. Pretreatment with 50 mug oestradiol-17beta, 60 or 165 min but not 15 min before LH-RH, inhibited LH secretion. Injection of 0.1-10 mug oestradiol 165 min before administration of LH-RH, Blocked LH secretion. Basal plasma LH levels before LH-RH administration were lower in dogs given oestradiol than in controls.

Effect of Luteinizing Hormone Releasing Hormone on Plasma Levels of Luteinizing Hormone, Oestradiol and Testosterone in the Male Dog

“…Since a latent period, of about 60 min, is needed for oestradiol-17/? to inhibit the LH response to LH-RH (Jones & Boyns, 1976), the data suggest that this increasing plasma oestradiol concentration may be regulating LH secretion in the male dog. However, although androgens did not modify the pituitary response to LH-RH injection (Jones & Boyns, 1974), it still seems reasonable to assume that they can influence the mechanism at the hypothalamic level and inhibit LH-RH release.…”

“…Oestradiol-17/? also significantly reduced the basal plasma LH concentration before the LH-RH in¬ jection (Jones & Boyns, 1976); androgens were without effect (Jones & Boyns, 1974). It would seem reasonable to assume therefore that if a regulating feedback control system exists it should be expected that the administration of LH-RH would promote secretion of testosterone and oestradiol-17/?.…”