Neurotransmitter effects on in vitro prolactin and growth hormone release from fowl pituitary glands: dopamine and noradrenaline.

Pituitary glands and hypothalami from broiler fowl heads were incubated alone or together with dopamine, noradrenaline or monoaminergic drugs (apomorphine, pimozide, phentolamine, isoproterenol and propranolol). The basal release of both prolactin and growth hormone was not affected by any of these amines or aminergic drugs. The co-incubation of pituitary glands with whole hypothalami consistently stimulated prolactin and growth hormone secretion. Apomorphine inhibited hypothalamus-induced prolactin and growth hormone release and the response was blocked by pimozide. Noradrenaline markedly stimulated hypothalamus-induced prolactin release, an effect antagonised by phentolamine. Thyrotrophin-releasing hormone (TRH) stimulated the release of prolactin and this stimulation was reversed, in a dose-related manner, by dopamine. TRH also increased the release of growth hormone, in the presence or absence of dopamine. These results demonstrate inhibitory dopaminergic effects on prolactin and growth hormone secretion and stimulatory noradrenergic effects on prolactin release. These aminergic effects may be mediated at pituitary and/or hypothalamic sites.