Evidence that opiatergic and alpha-adrenergic mechanisms stimulate rat growth hormone release via growth hormone-releasing factor (GRF).

An antiserum raised against human pancreatic growth hormone-releasing factor-(1-40) (hpGRF-40) was found to recognize the rat hypothalamic growth hormone-releasing factor (rhGRF): This antiserum, when given iv to adult male rats, completely abolished GH release induced by a synthetic rhGRF (0.2, 1 microgram/kg BW), and inhibited the physiological GH secretion over 2 days. After passive immunization with anti-hpGRF-40 serum, iv injection of either FK 33-824 (100 micrograms/kg BW), an enkephalin analogue, or clonidine (125 micrograms/kg BW), an alpha-adrenergic agent, failed to stimulate GH release in the unanesthetized rat. These results indicate that the GH-releasing actions of opiatergic and alpha-adrenergic mechanisms are mediated through stimulation of endogenous rhGRF release in the rat.