EFFECT OF VARIOUS ADRENERGIC RECEPTOR STIMULATING AND BLOCKING AGENTS ON HUMAN GROWTH HORMONE SECRETION

SUMMARY The effects of various adrenergic substances, either alone or in association with alpha and beta blocking agents, on human plasma growth hormone (GH) were studied in 36 normal volunteers. Plasma GH levels were unaffected by i.v. adrenaline (10 μg/min for 30 min) or by propranolol (1·5 mg/min for 10 min). Given together at the same doses, these drugs provoked sharp increases in plasma GH (from 8·5 to > 100 ng/ml; a mean increase of 30±8·02 (s.e.m.)). Reduction of the adrenaline dose to 7 μg/min produced a positive response in four out of six cases. The GH response to propranolol plus adrenaline was suppressed by simultaneous administration of phentolamine, but not significantly altered by glucose and aminophylline. Noradrenaline (7–14 μg/min for 30 min) produced no changes in plasma GH levels in six cases, while its association with propranolol was followed by an increase in only one out of four cases. Phenylephrine and tyramine were without effect, with or without propranolol. In five out of six cases, GH values gradually increased after oral administration of 1 g l-DOPA (from 4·2 to 85 ng/ml; mean, 30·2). This response was totally suppressed by phentolamine. It is considered that stimulation of GH by propranolol plus adrenaline and l-DOPA is mediated by alpha-adrenergic receptors. The possible role of a beta-inhibiting effect is discussed.