Angiotensin ii: a humoral mediator for the gastric sodium
monitor.
Duggan, K. A., V. Z. C. Ye, D. M. Jones, and G. J. Macdonald.
University Department of Medicine, Prince Henry Hospital, Sydney,
Australia
APStracts 2:0176F, 1995.
Natriuresis in direct response to a gastric sodium stimulus (upper gut
sodium monitor ) has paradoxically only been demonstrated in man and
animals on a low sodium diet preceding each study. It is possible
that the low sodium diet itself induces or suppresses systems which
mediate or oppose the ensuing natriuresis. In this study we sought to
determine whether a system activated by this diet, the renin
-angiotensin system mediates the natriuretic response. Specifically we
sought to show whether changes in the circulating concentration of
angiotensin II (Ang II) may mediate the renal response to stimulation
of the gastric sodium monitor. Male New Zealand white rabbits were
randomly assigned to low (0.008%) or normal (2.2%) sodium diets.
After one week on the experimental diet they received a sodium load
intragastrically or intravenously and plasma Ang II was measured at
0, 5, 10, 30, 60 and 120 minutes. Urine was collected for 4 hours
after the sodium load and plasma sodium measured at 0, 2 and 4 hours.
Urinary sodium excretion was greater in the four hours after gastric
than after intravenous sodium administration (p<0.025) in the
rabbits on the low sodium diet. No significant difference was noted
in the rabbits on the normal sodium. In rabbits on the low sodium
diet there was an immediate and significant decline in plasma Ang II
after sodium administered both intragastrically (p<0.025) and
intravenously (p<0.05). This decrease was greater after
intragastric than intravenous sodium (p<0.0025) and the
difference was still evident at 120 minutes (p<0.05). No
significant difference in plasma Ang II was found in the normal diet
group. We conclude therefore that a prolonged decrease in Ang II
concentration may play a role in mediating the natriuretic response
to the gastric sodium monitor.
Received 13 March 1995; accepted in final form 8 September 1995.
APS Manuscript Number F83-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95