Alpha-2-adrenergic pathways release growth hormone via a non-GRF-dependent mechanism in normal human subjects

Administration of a supramaximal dose of GRF 1-44 (200 micrograms, i.v.) to normal human volunteers increased GH levels while a further bolus of GRF (200 micrograms i.v.) given 2 hours later failed to increase plasma GH levels. In contrast, alpha-adrenergic receptor agonism with either propranolol-adrenaline infusion or clonidine increased plasma GH levels at a time when GH responses to this supramaximal dose of GRF were absent. This indicates that alpha-adrenergic pathways stimulate GH secretion through a non-GRF-dependent mechanism in normal human subjects.