ATTENUATION OF THE ESTRADIOL-INDUCED SURGE RELEASE OF LUTEINIZING-HORMONE BY ANTIHISTAMINE IN OVARIECTOMIZED EWES

Ovariectomized ewes received intramuscular (i.m.) injections of an H-1 -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, concen trations of histamine and GnRH in hypothalamic regions and histamine a nd LH in the pituitary gland were determined during the estradiol-indu ced surge of LH. Pretreatment mean, basal, and estradiol-induced secre tion of LH did not differ (P > 0.05) among seasons. However, the quant ity of LH (ng) measured during the estradiol-induced surge of LH was l ess (P < 0.05) in ewes treated with diphenhydramine (411 +/- 104) than saline (747 +/- 133). Treatment with diphenhydramine did not (P > 0.0 5) influence steady-state concentrations of histamine in hypothalamic or pituitary gland tissues, hypothalamic concentrations of GnRH, or an terior pituitary concentrations of LH during the estradiol-induced sur ge of LH. It is concluded that histamine may modulate the estradiol-in duced surge release of LH in ewes by affecting the secretion of GnRH.