Effects of a Gamma Aminobutyric Acid (GABA) Derivative, Baclofen, on Growth Hormone and Prolactin Secretion in Man

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Abstract
In 2 groups of 6 normal subjects each, we have investigated the effects of oral administration of a gamma aminobutyric acid (GABA) derivative, baclofen [β-(4-chlorophenyl)-gamma aminobutyric acid, Lioresal, Ciba-Geigy] on growth hormone (GH) and prolactin (PRL) secretion in response to insulin hypoglycemia and arginine infusion, respectively. Administration of baclofen, 30 mg daily for 4 days, caused a significant reduction of GH response to hypoglycemia (mean peak values decreased from 30.7 ± 6.30to 21.5 ± 5.74 ng/ml, P < 0.01) and to arginine infusion (21.8 ± 2.94 vs. 13.6 ± 2.16 ng/ml, P < 0.05). In contrast, the responseof PRL to the above stimuli was increased after baclofen administration: mean peak plasmalevels increased from 22.0 ± 4.01 to 30.1 ± 3.85 ng/ml, P < 0.05, in the insulin tolerance test, and from 22.6 ± 4.83 to 36.7 ± 6.60 ng/ml, P < 0.05, after arginine infusion. The pattern of plasma free fatty acids (FFA) and blood glucose was not changed by baclofen treatment during either of the tests. The mechanism whereby baclofen alters GH and PRL secretion is still hypothetical. One possibility is that the drug inhibits dopamine release from the dopaminergic nerve endings in the central nervous system. Although its mode of action seems to differ in many respects from that of GABA, baclofen has a number of pharmacological effects also shown by GABA. The results of this study therefore suggest that GABA might physiologically restrain GH secretion and enhance PRL release in man.

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