Inhibition of Prolactin Secretion by GABA in Female and Male Rats 1

Abstract

Summary

The effect of GABA on prolactin secretion from the pituitary under physiological conditions in lactating female rats and in normal male rats was investigated. Prolactin was measured by RIA in blood samples taken from lactating mothers by means of an intrajugular silastic catheter, 10-15 days after delivery. GABA in doses of 825 μg, but not 150 μg, microinjected into the third ventricle partially suppressed the serum prolactin rise due to suckling. Aminooxyacetic acid (AOAA), 30 mg/kg ip, which has been reported to produce a sharp increase in GABA content in the CNS, significantly suppressed the prolactin increment during the suckling period. By contrast, in non suckled mothers, GABA or AOAA was ineffective in altering serum prolactin. In normal male rats, GABA and AOAA were able to partially suppress prolactin release due to ether stress. These results clearly show that increments in GABA content in the brain after microinjection of exogenous GABA or following suppression of enzymatic inactivation of the endogenous amino acid were able to inhibit prolactin release under physiological conditions.