Time dependent action of pimozide on deprivation-induced water intake: evidence for a direct drug effect.

Time-response curves were established for the effect of 3 doses of pimozide, a potent and specific dopamine receptor blocker, on deprivation-induced drinking in rats. Injections occurred once every 3 days at intervals of 2, 4, 8, and 16 hr prior to the daily 15 min drinking period. Pimozide produced a significant attenuation in the amount of water normally consumed (on nondrug days) whose degree varied with the proximity of the injection to the drinking period. Only the 2 higher doses (0.5 and 1.0 mg/kg) produced a significant dose dependent effect which was strongest at the 2 hr interval and which gradually weakened by the 8th post injection hr. The relevance of these findings for a direct versus an indirect action of the drug on water intake is discussed.