Effect of peripherally administered atriopeptin III on water intake in rats.

1. Extracellular fluid deficits of 33% were produced in male Long-Evans rats by peritoneal dialysis. The conscious, unrestrained animals were then infused I.V. for 30 min with atriopeptin III at doses of 0.01, 0.1, 0.5 and 1.0 micrograms/min. At 5 min into the infusion, the rats were offered water and subsequent intakes were monitored. Since atrial natriuretic peptide (ANP) causes hypotension, one group of control animals was given an injection of diazoxide sufficient to match this fall in blood pressure. 2. A similar group of rats was prepared for measurement of plasma ANP achieved by infusion. 3. Relative to the saline-infused controls, atriopeptin III did not reduce water intake. Indeed, intake was increased at the highest dose of 1.0 micrograms/min. 4. Relative to the diazoxide controls, water intake was influenced by atriopeptin III in a dose-dependent manner, the greatest attenuation being observed at infusions of 0.1 microgram/min. 5. Infusion of atriopeptin III at 0.1 microgram/min caused plasma ANP levels to rise from 252 +/- 21 to 532 +/- 136 pg/ml (n = 9, P less than 0.05) at 15 min. The lowest dose (0.01 microgram/min) caused no detectable increase in plasma levels. 6. It is concluded that, in groups of hypovolaemic rats matched for blood pressure, atriopeptin III caused a dose-related reduction in water intake.