Effects of drinking and central angiotensin II stimulation on organ blood flow in conscious rats

While the hemodynamic response pattern accompanying feeding behavior has been well characterized, there is less information about the hemodynamic changes associated with drinking. In the present study, we have measured organ blood flows in conscious, unrestrained rats during schedule-induced drinking behavior, using the tracer microsphere technique (diameter of spheres 15 +/- 3 microns; labels: 141Ce, 113Sn). In addition, we determined the hemodynamic response pattern following intracerebroventricular (i.c.v.) injection of 100 ng angiotensin II (ANG II) (a dose known to be dipsogenic) in rats that were not allowed to drink during the experiment. The hemodynamic responses during drinking behavior included (a) significant increases in blood flow through the kidney, stomach and small intestine, (b) a decrease in blood flow through skeletal muscle, and (c) no significant changes in the rest of the organs. ANG II i.c.v. elicited (a) significant decreases in blood flow through the kidney, stomach, small intestine and skin, (b) a significant increase in blood flow through the liver (hepatic artery), and (c) no significant changes in blood flow through the brain, heart, lung (bronchial arteries), colon, skeletal muscle (biceps) and testis. We conclude that spontaneous drinking behavior in rats is associated with a characteristic hemodynamic drinking response, which resembles a classical feeding reaction. In non-drinking rats the hemodynamic response pattern following ANG II i.c.v. was different from the drinking response, providing further evidence, that the behavioral and cardiovascular effects of the neuropeptide can be dissociated.