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Effect of the Benzodiazepine Derivative, Diazepam, on the Clonidine-Stimulated Human Growth Hormone Secretion

Department of Pharmacology, Institute of Biomedicine, University of Turku, Turku, Finland

Address requests for reprints to: Dr. Markku Koulu, Department of Pharmacology, Institute of Biomedicine, University of Turku, Turku, Finland.

-Aminobutyric acid (GABA) has both stimulatory and inhibitory effect on human GH secretion. We previously reported that the benzodiazepine derivative diazepam, which exerts its main pharmacological effect by facilitating GABA-mediated transmission, is able to reduce the GH response to L-dopa and apomorphine. To establish whether diazepam affects the -adrenergic regulation of GH secretion, the GH response to clonidine (an -agonist) was investigated in seven volunteers after placebo and diazepam premedications.

After placebo pretreatment, clonidine (0.15 mg iv infused over 20 min) significantly stimulated GH secretion: the mean serum GH level rose from a basal level of 4.7 ± 1.1 (±SEM) ng/ml to a maximum of 10.8 ± 1.6 ng/ml (P < 0.025). After 3 days of diazepam treatment, a similar GH response to clonidine was observed; the mean serum GH level rose from a basal value of 2.3 ± 0.3 ng/ml to a maximum of 9.4 ±1.3 ng/ml.

It is concluded that the inhibitory effect of diazepam on human GH secretion is mediated via inhibition of dopaminergic transmission, whereas the -adrenergic control of GH release is not affected. Since diazepam potentiates GABAergic transmission, its effect may reflect the role of endogenous GABA in human GH secretion. (J Clin Endocrinol Metab 56: 1316,1983)

Received October 14, 1982.

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