The effect of functional activation of the serotoninergic system on base line plasma growth hormone (GH) levels and the participation of serotonin (5 HT) in the GH response evoked by insulin induced hypoglycaemia were studied in the unanaesthetized dog with the aid of a specific and sensitive homologous radioimmunoassay method. In 4 dogs, intravenous injection of insulin (0.4 IU/kg iv) or infusion of L tryptophan (TP, 2.0 g over 30 min) showed the latter stimulus to be far less potent in eliciting growth hormone (cGH) release. Intravenous injection of L 5 hydroxytryptophan (5 HTP, 10 mg/kg iv) in 5 dogs induced a clear cut rise in cGH, but was accompanied by striking side effects. In 9 dogs, administration of p chlorophenylalanine (PCPA, 100 mg/kg po daily x 5 days), an inhibitor of 5 HT synthesis, did not modify base line cGH and glucose levels, caused a marked decrease of blood 5 HT and resulted in a magnification of the insulin induced cGH release. In 8 dogs, similarly treated with PCPA, administration of 5 HTP (10 mg/kg iv), 10 min before the hypoglycaemic stimulus, blunted the GH secretory response to the latter. Chronic feeding of a TP deficient diet in 5 dogs, was accompanied by a progessive decrease of total and 'free' plasma TP, no significant changes in base line cGH and blood glucose levels and a GH response to the insulin stimulus (0.2 IU/kg iv) almost superimposable to that elicitable in the same animals under normal conditions. TP infusion (2.0 g over 30 min) in 3 TP deficient, dogs, induced a striking reduction of the hypoglycemia induced GH release. Collectively, this study suggests that 5 HT does not have a noticeable effect on base line plasma cGH levels but exerts an inhibitory role in hypoglycemia induced cGH release.
|Titolo:||Inhibitory role of the serotoninergic system in hypoglycaemia-induced growth hormone release in the dog|
|Parole Chiave:||Tryptophan; Animals; Pituitary Gland; Pituitary Gland, Anterior; Fasting; Serotonin; Insulin; Blood Glucose; Fenclonine; 5-Hydroxytryptophan; Dogs; Diet; Female; Male; Growth Hormone|
|Settore Scientifico Disciplinare:||Settore BIO/14 - Farmacologia|
|Data di pubblicazione:||mag-1976|
|Appare nelle tipologie:||01 - Articolo su periodico|