Inhibitory effect of phentolamine on diazepam-induced growth hormone secretion and lack of effect of diazepam on prolactin secretion in man.

Phentolamine, a postsynaptic noradrenergic (NA) receptor blocker, inhibits diazepam-induced growth hormone (GH) secretion in man. In order to study the effect of phentolamine on six healthy subjects with a diazepam (10 mg i.v.)-induced GH increase greater than 7.5 ng/ml, it was necessary to test 11 subjects. The six diazepam GH responders showed a significantly higher (p less than 0.01) GH stimulation after diazepam alone than after diazepam plus phentolamine (60 mg i.v.). The inhibitory effect of phentolamine suggests that NA alpha receptors are involved in the diazepam-induced GH increase. Prolactin secretion after administration of diazepam (10 mg i.v.) was only slightly elevated in comparison with placebo (i.v.), suggesting that diazepam does not have an agonistic effect on dopamine (DA) receptors.

Comparison of growth hormone stimulation induced by desimipramine, diazepam and metaclazepam in man.

A comparison of the effect on growth hormone (GH) stimulation in men (n = 6) of desimipramine (DMI), a tricyclic antidepressant, and of the benzodiazepine derivatives diazepam and metaclazepam with that of a placebo, showed that only DMI caused a significant (p less than 0.01) GH stimulation. After DMI, all six subjects showed a GH stimulation greater than 7.5 ng/ml, whereas after diazepam or metaclazepam, only three of the six subjects showed GH stimulation greater than 7.5 ng/ml, and the other three showed only a very small change, or no change at all in GH secretion. Higher GH stimulation occurred after diazepam (10 mg i.v.) than after diazepam (10 mg p.o.). No dose-dependent difference in GH stimulation after metaclazepam (10 and 30 mg p.o.) was apparent. No side effects appeared after administration of DMI during the test period (180 min); however, after administration of the benzodiazepine derivatives, sedative effects were clearly noted. DMI thus causes reliable GH stimulation in healthy male subjects, whereas GH stimulation could only be measured in some of the subjects after diazepam and metaclazepam.