AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 2 381-R387, Copyright © 1986 by American Physiological Society
Drinking and natriuresis during volume expansion and intracranial angiotensin or carbachol
D. A. Fitts and J. B. Simpson
Two methods of sodium loading were used to counteract the body fluid
dilution resulting from natriuresis and water drinking during sustained
lateral ventricular infusions of carbachol (CBC) or angiotensin II (ANG II)
in rats. It was expected that preventing dilution would also prevent the
precipitous decline of both drinking and natriuresis during the later hours
of CBC infusion. In the first study, rats having isotonic saline as the
sole drinking fluid during CBC infusions drank less fluid and had only
slightly higher plasma osmolality and sodium concentration than rats
drinking water, which showed extreme dilution. In the second study, rats
with only water to drink were given intravenous infusions of 0.15, 0.45, or
1.00 M NaCl solutions at 1.8 ml/h concurrently with the intraventricular
infusions. Significant dilution of plasma was found at the two lower rates
but not at 1.00 M NaCl in CBC-infused rats. Only the latter group showed
both persistent drinking and natriuresis throughout the 4-h infusion
period, and this was not because of elevated plasma osmolality. Infusions
of ANG II generated less severe body fluid dilution and more persistent
drinking in both experiments. The study demonstrates that body fluid
dilution may control the offset of both drinking and natriuresis during
sustained infusions of CBC and that the more persistent drinking to ANG II
vs. CBC probably occurs because of a lesser natriuresis and consequent
fluid dilution.
