INVOLVEMENT OF GROWTH HORMONE-RELEASING FACTOR IN GROWTH HORMONE SECRETION INDUCED BY GAMMA-AMINOBUTYRIC ACID IN CONSCIOUS RATS

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Abstract
Intracerebroventricular (icv) injection of GABA (10 .mu.mol/rat) resulted in an increase in plasma GH [growth hormone] in conscious freely moving rats pretreated with normal rabbit serum (0.5 ml/rat, i.v.). Rabbit antiserum specific for rat GH-releasing factor (GRF) (0.5 ml/rat, i.v.) abolished GH release induced by GABA in these animals. Rabbit anti-rat GRF serum also blunted GH release induced by a Met5-enkephalin analog, FK33-824 [D-Ala2, MePhe4, Met(O)5-ol enkephalin] (10 .mu.g/100 g body wt, i.v.) in conscious rats. Considering the previous findings that rat GH release induced by FK33-824 was blunted by GABA antagonists, these results suggest that GH secretion induced by opioid peptides via GABAerigc mechanisms is mediated, at least in part, by hypothalamic GRF in the rat.