The injection of a hypertonic saline solution (0.2 M NaCl) into the lateral preoptic area of the rat produced an increase in water intake that was further increased by the injection of angiotensin II (4 ng) into the subfornical organ. An increase in arterial pressure was also observed. Increase in heart rate was noted after injection of 0.2 M NaCl into the lateral preoptic area. 2. The injection of hypertonic NaCl into the subfornical organ increased water intake and the injection of 4 ng of angiotensin II into the lateral preoptic area augmented this effect. The injection of 0.2 M NaCl into the subfornical organ did not affect blood pressure or heart rate, whereas the injection of angiotensin II into the lateral preoptic area resulted in an increase in these parameters. 3. Intravenous perfusion of angiotensin II (40 ng microliters-1 min-1) caused increased water intake, arterial pressure and heart rate. Dehydration of the lateral preoptic area by 0.2 M NaCl resulted in a summation of effects for water intake alone. 4. Intravenous perfusion with 0.5 M NaCl caused an increase in water intake which was further increased after the injection of angiotensin II (4 ng) into the subfornical organ and angiotensin II (4 ng) into the lateral preoptic area. Arterial pressure and heart rate also increased, remaining unchanged when angiotensin II was injected into the subfornical organ or into the lateral preoptic area. 5. These results suggest interactions between the two areas in the regulation of cardiovascular and thirst mechanisms. However, cardiovascular regulation and the regulation of body fluids may be stimulated by physiological responses to separate mechanisms.
