Ethanolamine-O-sulfate enhances gamma-aminobutyric acid secretion into hypophysial portal blood and lowers serum prolactin concentrations.

In ovariectomized rats the intraventricular administration of ethanolamine-O-sulfate (EOS, 300 micrograms), a specific, competitive and catalytic inhibitor of gamma-aminobutyric acid (GABA) transaminase, induced 3-4 h later a marked reduction in serum prolactin (PRL) concentrations and a 3- to 4-fold rise in the concentration of GABA in pituitary stalk, but not systemic, plasma. The administration of EOS also resulted in an elevation of GABA concentrations in the hypothalamus. These results demonstrate that GABA in pituitary stalk plasma is derived from the central nervous system and that an abrupt increase in the concentration of GABA in hypophysial portal blood is associated with a suppression of PRL secretion.