SIGNIFICANCE OF CHLORIDE CHANNEL ACTIVATION IN THE GAMMA-AMINOBUTYRIC-ACID INDUCED GROWTH-HORMONE SECRETION IN THE NEONATAL RAT PITUITARY

Growth hormone (GH) secretion of the neonatal pituitary is stimulated by tau-aminobutyric acid (GABA) (1,2). Since in most cases GABA is kno wn to act by increasing postsynaptic membrane permeability to chloride ions we tested the importance of chloride channel activation in the G H stimulatory effect of GABA in the neonatal pituitary. In the absence of chloride in the superfusion medium GABA was without effect on GH s ecretion of the neonatal pituitaries and its effect was attenuated by chloride channel inhibitors. The effect of growth hormone releasing ho rmone (GHRH) on GH secretion was attenuated in the chloride-free media , but it was not affected by simultaneous administration of chloride c hannel blockers. The present study indicates that GH stimulatory effec t of GABA in the neonatal pituitaries might involve chloride channel a ctivation probably resulting in secondary activation of calcium channe ls.