POSSIBLE MEDIATION OF GABA INDUCED GROWTH-HORMONE SECRETION BY INCREASED CALCIUM-FLUX IN NEONATAL PITUITARIES

Gamma-aminobutyric acid (GABA) stimulates growth hormone (GH) secretion from pituitaries of young (less than 20-day old) rats (1,2). Present work revealed that the GH stimulatory effect of GABA was abolished in the absence of calcium and response was attenuated by Nifedipine. The calcium efflux from (CaCl2)-Ca-45 preloaded neonatal pituitaries was enhanced by GABA or by muscimol, and this effect was antagonized by the GABA antagonist picrotoxin. In pituitaries of 21 day old or adult rats GABA stimulated neither GH secretion nor calcium efflux. These results indicate that in neonatal pituitaries GABA influences calcium transport and its GH releasing effect is linked to the presence of calcium.