Attenuation of the estradiol-induced surge release of luteinizing hormone by antihistamine in ovariectomized ewes

Ovariectomized ewes received intramuscular (i.m.) injections of an H₁-histamine receptor antagonist, diphenhydramine, or saline during the anestrous and breeding seasons to determine if histamine may regulate the estradiol-induced surge release of LH in ewes. In addition, concentrations of histamine and GnRH in hypothalamic regions and histamine and LH in the pituitary gland were determined during the estradiol-induced surge of LH. Pretreatment mean, basal, and estradiol-induced secretion of LH did not differ (P > 0.05) among seasons. However, the quantity of LH (ng) measured during the estradiol-induced surge of LH was less (P < 0.05) in ewes treated with diphenhydramine (411 ± 104) than saline (747 ± 133). Treatment with diphenhydramine did not (P > 0.05) influence steady-state concentrations of histamine in hypothalamic or pituitary gland tissues, hypothalamic concentrations of GnRH, or anterior pituitary concentrations of LH during the estradiol-induced surge of LH. It is concluded that histamine may modulate the estradiol-induced surge release of LH in ewes by affecting the secretion of GnRH.