Growth hormone secretion of the neonatal rat pituitaries is stimulated by gamma-aminobutyric acid in vitro

Growth hormone secretion from pituitaries of neonatal rats was stimulated by gamma-aminobutyric acid (GABA) and the GABA agonist muscimol $\text{in vitro}$. This response to GABA was absent after the 9th postnatal day. The stimulation of growth hormone secretion by GABA was antagonized by bicuculline-methiodide and by picrotoxin. Diazepam stimulated while baclophen had no effect on growth hormone secretion. This stimulatory GABA effect might be related to a certain developmental stage of the pituitary GABA receptors or to the lack of hypothalamic regulatory influence(s) in the newborn.