Effects of gamma-aminobutyric acid (GABA), aminooxy acetic acid (AOAA), a GABA transaminase inhibitor, and gamma-hydroxybutyric acid (GHB) on the release of serum growth hormone (GH), prolactin (PRL), luteinizing hormone (LH) and hypothalamic somatotropin release inhibiting hormone (SRIF) content were investigated in urethane or pentobarbital anesthetized Sprague-Dawley male rats. Intraventricular injection of GABA caused a dose-related increase in serum GH and hypothalamic SRIF. In another study, intraperitoneal administration of AOAA produced a significant increase in both serum GH and hypothalamic SRIF. Furthermore, levels of serum GH and hypothalamic SRIF elevated significantly after intraperitoneal GHB administration. Pretreatment with L-DoPA diminished GHB induced serum GH increase and hypothalamic SRIF content. These results showed that GABA and GHB stimulated GH secretion accompanied by increased hypothalamic SRIF. GHB administration caused a significant increase in serum PRL in urethane-anesthetized rats but not in pentobarbital anesthetized rats. Pretreatment with L-DoPA completely inhibited the GHB-induced serum PRL increase in urethane anesthetized rats. Intraperitoneal administration of GHB caused a decrease in serum LH. Preadministration with L-DoPA inhibited GHB induced decrease of serum LH in urethane but not in pentobarbital anesthetized rats. Thus, the GH release induced by GABA or GHB may be partly ascribed to the inhibition of hypothalamic SRIF release. GHB-induced GH release might be mediated by inhibition of dopaminergic mechanism because pretreatment with L-DoPA inhibited GH release after GHB administration. However the mechanism of the GHB-induced serum PRL and LH releases was not clarified in this investigation.