Muscimol inhibits ADH release induced by hypertonic sodium chloride in rats

The effect of the GABA-agonist muscimol on ADH release induced in rats by administration of hypertonic sodium chloride solutions was studied by means of intracerebroventricular and intraperitoneal injections of the drug. Injected by the intracerebroventricular route, muscimol produced a significant reduction of plasma ADH concentration not only in animals treated with hypertonic sodium chloride, but also in unstimulated animals. Following intraperitoneal administration larger doses were required to produce such an effect, thus suggesting a central site of action for the effect of muscimol on ADH release. Bicuculline, given intraperitoneally before muscimol injection, completely blocked ADH inhibition induced by muscimol, thus suggesting a specific involvement of GABAergic receptors. These findings indicate that GABAergic mechanisms may be involved in the regulation of body fluids in the rat by affecting ADH release.