Intraventricular administration of isatin in rats: antidiuretic, dipsogenic, anorexiant and emetic effects

Isatin, an endogenous indole, has previously been show to be anxiogenic at low doses, and increased in output during stress. Its most potent known in vitro action is inhibition of atriuretic peptide (ANP) receptors. The prese nt study was designed to examine its effects on water and food intake, urin e output and emesis in rats. Intracerebroventricular (ICV) administration o f graded doses of isatin (0.5, 0.1 and 2 mug/rat) induced dose-related incr ease in water intake and decrease in urine output. It also induced a decrea se in food intake and increase in kaolin intake, a model for emesis. All th ese effects were inhibited by ondansetron, a 5-HT3 receptor antagonist, and by pimozide, a dopamine D-2 receptor antagonist, as was earlier reported i n case of the anxiogenic activity of isatin in rodents. The isatin induced responses (anxiety, antidiuresis and polydipsia) are similar to those induc ed by arginine vasopressin and opposite to those induced by atrial natriure tic peptide. Isatin appears to be a nonpeptide endocoid with effects on bot h behaviour and water balance.