Adrenergic and Dopaminergic Control of Growth Hormone Secretion in Urethane Anesthetized Adult Male Rats

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Abstract
The effects of drugs which interfere with .alpha.-adrenergic and dopaminergic mechanisms, involved in GH [growth hormone] and PRL [prolactin] secretion, were analyzed in urethane anesthetized rats. Clonidine induced a dose-dependent release of GH (0.0032-0.1 mg/kg i.v.) as well as of PRL (0.032-1.0 mg/kg i.v.). The lowest clonidine dose, when given into the 3rd ventricle, provoked a very pronounced GH release. Phentolamine, given i.v., inhibited clonidine-induced GH release in a dose-dependent manner. L-Dopa administered i.v. and apomorphine administered i.v. or intraventricularly did not affect basal GH secretion but produced a dose-dependent inhibition of clonidine-induced GH release. Pimozide did not change basal GH secretion. Pimozide did not attenuate the inhibition of clonidine-induced GH secretion seen after apomorphine administration; it completely reversed apomorphine-induced PRL inhibition. Apparently an .alpha.-adrenoceptor-mediated stimulatory mechanism is involved in GH and PRL secretion. An inhibitory dopaminergic mechanism is confirmed for PRL secretion and suggested for GH secretion.