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In order to establish whether thyrotropin-releasing hormone (TRH) inhibits lysine-vasopressin (LVP)-induced growth hormone (GH) release, six normal men were tested with LVP alone or in combination with TRH. LVP strikingly increased serum GH levels; this response was not altered by TRH. These results indicate that in man TRH is not involved in the control of GH secretion in response to LVP.

In order to determine whether nicotine exerts its stimulant effect on serum concentrations of growth hormone (GH) by interacting with an adrenergic pathway, we evaluated the effect of cigarette smoking on the response of GH to the administration of clonidine, a specific alpha-adrenoceptor agonist. In six normal volunteers, clonidine significantly increased serum levels of GH. When subjects smoked two non-filter cigarettes, GH response to the alpha-adrenoceptor agonist was greatly enhanced. These findings suggest that in man nicotinic cholinergic and adrenergic mechanisms might interact in the stimulation of GH secretion.