Effect of adrenergic blocking drugs on secretion of luteinizing hormone in the ovariectomized ewe.

The effects of the adrenergic blocking drugs phenoxybenzamine, phentolamine, and pimozide on basal luteinizing hormone (LH) levels and on estrogen-induced LH release were tested in ovariectomized ewes. Phentolamine was given at a dose of 10 mg/kg; phenoxybenzamine was given at a dose of 8 mg/kg; and pimozide was given at a dose of 800 mcg/kg. Estradiol benzoate (EB) was given at a dose of 50 mcg/animal. Sera were assayed for LH levels by double-antibody radioimmunoassay. Phenoxybenzamine given as a single dose significantly reduced basal LH levels. Given at extremenly high doses, phenoxybenzamine was unable to consistently block estrogen-induced LH release. Pimozide significantly reduced basal LH levels in the ewes and blocked or greatly reduced estrogen-induced LH release in 9 of 10 treated animals. Reduced basal LH levels were seen with phentolamine injection but were of short duration of action. It is concluded that normal function of noradrenergic neurons is required for maintenance of normal basal LH release but unnecessary for estrogen-induced LH release. Dopaminergic neurons appear to facilitate basal and estrogen-induced LH release.