title: Noradrenergic modulation of human pancreatic growth hormone-releasing factor (hpGHRF1-44)-induced growth hormone release in conscious male rabbits: involvement of endogenous somatostatin.
abstract: To clarify the role of noradrenergic neurons in the regulation of GH secretion, the effects of iv administered noradrenergic antagonists were investigated in freely moving, conscious male rabbits. During a 6-h observation period (1030-1630 h), control rabbits manifested pulsatile GH secretion with surges between 1030-1200 and 1415-1630 h. Phenoxybenzamine, (POB), an alpha-adrenergic blocker (5 mg/kg, twice), abolished the episodic GH surges; propranolol, a beta-adrenergic blocker (2.5 mg/kg, twice), did not. The bolus injection (1 or 10 micrograms) of synthetic human pancreatic GH-releasing factor (hpGHRF) with 44 amino acid residues (hpGHRF1-44) resulted in significant rises in the plasma GH of control animals. The plasma GH responses to hpGHRF1-44 were significantly larger in propranolol-treated than control rabbits. In contrast, POB completely suppressed the hpGHRF1-44-induced GH release. The injection of antisomatostatin (SRIF) serum into POB-treated rabbits did not yield a disinhibition of the episodic GH surges but restored the plasma GH rises after hpGHRF1-44 injection. These results indicate that noradrenaline++ plays an important role in regulating GH secretion in the rabbit. We propose that alpha-noradrenergic blockade suppresses GH release not only by inhibiting the release of hypothalamic GHRF but also by stimulating the secretion of SRIF and that beta-noradrenergic blockade enhances GH release by inhibiting the release of SRIF from the hypothalamus.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects; D003243:Consciousness / Q000502:physiology; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D008297:Male; D010179:Pancreas / Q000502:physiology*; D010187:Pancreatic Hormones / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011863:Radioimmunoassay; D013004:Somatostatin / Q000502:physiology*
chemical_list: D010187:Pancreatic Hormones; D010446:Peptide Fragments; D010643:Phenoxybenzamine; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D011433:Propranolol