Neuroendocrine regulation of growth hormone secretion in sheep. VII. Effects of GABA.

The effects of intravenous (i.v.) or intracerebroventricular (i.c.v.) administration of gamma aminobutyric acid (GABA) on plasma growth hormone (GH) concentrations have been examined in sheep. Intravenous administration of GABA resulted in a rapid, significant (P < 0.001) increase in plasma GH. Administration of 10 mg of GABA i.c.v. produced a significant (P < 0.001) increase in GH release. By contrast, 100 mg given i.c.v. was inhibitory and resulted in a decrease (P < 0.05) in plasma GH levels. Concurrent administration of somatostatin (0.5 microgram/min i.v. over 1 h) did not alter the plasma GH response to 10 mg GABA given i.c.v. These data are consistent with the concept of dual sites of action for GABA in regulating GH release in sheep, but the exact mechanism through which this effect is mediated remains unclear.