Evidence for α-Adrenergic Regulation of Episodic Growth Hormone and Prolactin Secretion in the Undisturbed Male Rat*

Publisher Website
Google Scholar
Abstract
The present experiments were designed to study the effect of the centrally active α-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-β-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 μg/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 μg/kg) restored the pulsatile pattern of GH secretion in FLA-63-treated rats, and 3) clonidine (15 and 150 μg/kg) stimulated PRL release in a dose-dependent manner. These findings suggest a major stimulatory role of α-adrenergic receptors in episodic GH and PRL secretion. (Endocrinology108: 1869, 1981)