The effects of injection of various purinoceptor agonists into the hypothalamic paraventricular nucleus in water-loaded and ethanol-anesthetized rats were investigated. Adenosine triphosphate (ATP), beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) and beta,gamma-imidoadenosine 5'-triphosphate (AMP-PNP) potently decreased the outflow of urine in a time- and dose-dependent manner. The ED50 values were approx 70 and 37 nmol for ATP and AMP-PCP, respectively. Adenosine diphosphate (ADP), AMP and adenosine reduced the outflow of urine much less than ATP. Adenosine triphosphate induced concomitant increases in the osmotic pressure of the urine and in the level of arginine-vasopressin (AVP) in plasma. The antidiuretic effect of ATP was blocked by prior injection of quinidine (a P2-purinoceptor antagonist) into the paraventricular nucleus, but not by the prior injection of theophylline (a P1-purinoceptor antagonist). The effect of ATP was also blocked by intravenous injection of an AVP(V1V2)-receptor antagonist, d(CH2)5-D-Tyr(Et)VAVP. The results suggest that ATP injected into the paraventricular nucleus may stimulate a purinoceptor, releasing AVP and inducing the antidiuretic effect through renal AVP(V2) receptors.