Calcium hopantenate, a GABA agonist, induces elevation of plasma beta-endorphin-like immunoreactivity levels in rats

Abstract

The effects of calcium hopantenate (HOPA) on plasma beta-endorphin-like immunoreactivity (beta-En-LI) levels in rats have been studied. HOPA (1.5 g/kg) was injected ip, and the animals were serially decapitated. The plasma beta-En-LI levels were measured by radioimmunoassay. Effects of HOPA on beta-En-LI release from the anterior pituitary were also investigated by means of an in vitro experiment. The beta-En-LI content in the hypothalamus and pituitary gland did not change significantly after HOPA injection. The plasma beta-En-LI levels increased significantly in a dose-related manner with a zenith at 30 min after HOPA injection. Effects of HOPA on plasma beta-En-LI levels were prevented with the pretreatment of bicuculline. The beta-En-LI release from the anterior pituitary was enhanced with the addition of HOPA to the medium, and HOPA's effects were blocked with an addition of bicuculline to the medium. These findings suggest that HOPA acts on the anterior pituitary to stimulate beta-En-LI release, and its effects are mediated via GABA receptor.