Involvement of Growth Hormone (GH)-Releasing Factor in GH Secretion Induced by Serotoninergic Mechanisms in Conscious Rats*

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Abstract
A possible role of hypothalamic GH-releasing factor (GRF) in GH secretion induced by serotoninergic stimuli was investigated in conscious freely moving rats with a passive immunization technique. Either iv injection of 5-hydroxy-L-tryptophan (1 mg/100 g BW) or intracerebroventricular injection of serotonin (10 .mu.g/rat) caused an increase in plasma GH in rats treated with normal rabbit serum (0.5 ml/rat, iv) 30 min previously. Injection of rabbit antiserum specific for rat GRF (0.5 ml/rat, iv, 30 min previously) blunted the plasma GH increase induced by 5-hydroxy-L-tryptophan or serotonin in these animals. These results suggest that GH secretion induced by serotoninergic mechanisms is mediated, at least in part, by hypothalamic GRF in the rat.