STIMULATION BY ALPHA-ADRENERGIC MECHANISMS OF THE SECRETION OF GROWTH HORMONE-RELEASING FACTOR (GRF) FROM PERIFUSED RAT HYPOTHALAMUS

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Abstract
The possible involvement of adrenergic mechanisms in regulating the secretion of growth hormone (GH)-releasing factor (GRF) from the rat hypothalamus was examined in vitro with a perifusion system. A high potassium concentration (56 mM) stimulated GRF release from the hypothalamus. The infusion of clonidine (10-4 M), an .alpha.2-adrenergic stimulant, resulted in an increase in the spontaneous release of GRF. In the presence of propranolol (10-5 M), a .beta.-adrenergic blocking agent, clonidine (10-5 and 10-4 M) stimulated GRF release more prominently in a dose-related manner, whereas propranolol (10-5 and 10-4 M) stimulated GRF release more prominently in a dose-related manner, whereas propranolol (10-5 and 10-4 M) by itself did not affect the spontaneous GRF release. The stimulatory effect of clondine (10-4 M) on GRF release in the presence of propranolol was inhibited by yohimbine (10-4 M), an .alpha.2-adrenergic blocking agent. These findings suggest that .alpha.2-adrenergic mechanisms play a role in stimulating GRF release from the hypothalamus in rats.