Effects of alpha- and beta-adrenergic agonists and antagonists on growth hormone secretion in man

The adrenergic system is involved in the neural control of GH secretion with both stimulatory and inhibitory influences mainly mediated via GHRH and/or somatostatin modulation. To throw further light on adrenergic neuroregulation of somatotrophic function in man, the effect of various catecholamine agonists and antagonists on basal or GHRH-stimulated GH secretion was studied. Twenty-one adult males aged 20-30 years underwent the following studies: 1. clonidine (CLON), alpha 2-agonist, (15 micrograms/min infused i.v. from 0 to +10 min) alone and preceded by yohimbine (YOH), alpha 2-antagonist, (30 mg orally at -50 min); 2. GHRH (GHRH 44, 1 microgram/kg i.v. bolus at 0 min) alone and preceded by YOH; 3. CLON alone and combined with methoxamine (METHOX), alpha 1-agonist, (1 mg/min infused i.v. from -10 to +10 min); 4. GHRH alone and combined with i.v. infusion of phentolamine (PHEN), alpha 1/alpha 2-antagonist, (0.5 mg/min from -60 to +30 min); 5. GHRH alone and combined with i.v. infusion of salbutamol (SAL), beta 2-agonist, (10 micrograms/min from -5 to +15 min). The GH response to CLON was inhibited by YOH (area under the response curve, mean +/- S.E.: 672.6 +/- 143.0 vs. 219.6 +/- 16.7 micrograms/l/h, P less than 0.05) but was not modified by METHOX (278.4 +/- 94.1 vs. 216.7 +/- 115.5 micrograms/l/h). On the other hand, YOH was unable to affect the GH response to GHRH (339.3 +/- 19.1 vs. 518 +/- 172.8 micrograms/l/h).(ABSTRACT TRUNCATED AT 250 WORDS)