Inhibition by antiserum to rat growth hormone-releasing factor of growth hormone secretion induced by a met5-enkephalin analog, FK33-824, in rats.

A Met5-enkephalin analog, FK33-824 (5, 10 and 20 micrograms/100 g body wt, iv) caused a dose-related increase in plasma growth hormone (GH) in urethane-anesthetized male rats. Pretreatment with cysteamine (30 mg/100 g body wt, sc), a depletor of hypothalamic somatostatin, increased the plasma GH response to FK33-824 (10 micrograms/100 g body wt, iv). Antiserum specific for rat GH-releasing factor (GRF) (0.5 ml/rat, iv) blunted GH release induced by FK33-824 (10 micrograms/100 g body wt, iv) in rats with or without cysteamine pretreatment. These results suggest that GH secretion induced by the opioid peptide is mediated, at least in part, by hypothalamic GRF in the rat.