LACK OF HORMONAL INFLUENCES ON THE GABAERGIC STIMULATION OF GROWTH-HORMONE SECRETION IN THE NEONATAL RAT

GABA has been shown to stimulate pituitary growth hormone secretion in the neonatal but not in the adult rat (Acs et al. 1984; 1987). The disapparence of the GH stimulatory effect of GABA was studied in organ-cultured neonatal pituitaries and in pituitaries from rats treated neonatally with various hormones. The responsiveness of organ-cultured neonatal pituitaries to GABA and to TRH was diminished compared to that of the littermate controls. Treatment of the neonatal rats with adrenal and sexual steroids or thyroid hormones had no effect on the GABA elicited pituitary GH secretion. We conclude that the disappearance of GABAergic stimulation of GH secretion in the postnatal development is not influenced by the changes in the hormonal environment.