Endocrinology, Vol 108, 1869-1873, Copyright © 1981 by Endocrine Society

ARTICLES

Evidence for alpha-adrenergic regulation of episodic growth hormone and prolactin secretion in the undisturbed male rat

LC Terry and JB Martin

The present experiments were designed to study the effect of the centrally active alpha-adrenergic receptor agonist, clonidine, on episodic GH and PRL secretion in male rats after selective blockade of norepinephrine (NE) and epinephrine (EP) synthesis with the dopamine- beta-hydroxylase inhibitor, FLA-63. Freely behaving, chronically cannulated rats were maintained on a constant light-dark cycle in isolation test chambers. Beginning at 1000 h, blood samples were removed every 20 min for 5-h periods without disturbing the animal. FLA- 63 was administered (10 or 20 mg/kg ip) at 0845 h. Clonidine (15 or 150 microgram/kg iv) was given at times that coincided with the spontaneous occurrence of episodic GH peaks or troughs observed in control animals. Results of the present study are summarized as follows: 1) selective blockade of NE and EP synthesis with FLA-63 (20 mg/kg) caused complete suppression of episodic GH but had no significant effect on PRL release; 2) clonidine (150 microgram/kg) restored the pulsatile pattern of GH secretion in FLA-63-treated rats, and 3) clonidine (15 and 150 microgram/kg) stimulated PRL release in a dose-dependent manner. These findings suggest a major stimulatory role of alpha-adrenergic receptors in episodic GH and PRL secretion.

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