Journal of Applied Physiology, Vol 42, Issue 6 915-922, Copyright © 1977 by American Physiological Society
Immersion diuresis in dogs
J. T. Davis and A. B. DuBois
The mechanism of diuresis during the 1st h of immersion was investigated
using anesthetized dogs. Four different experiments were carried out.
First, left atrial transmural pressure was measured before, during, and
after immersion. The data suggest that, although the left atrium may or may
not be stretched depending on the conditions of immersion, the amount of
diuresis is independent of the amount of left atrial stretch, and therefore
a causal relationship between diuresis and left atrial stretch could not be
established. Second, bilateral cervical vagotomy was carried out. Immersion
diuresis sometimes occurred despite this vagotomy, suggesting that the left
atrial stretch reflex was not participating in those cases. Third,
negative-pressure breathing was carried out to simulate the negative
transthoracic pressure associated with uncompensated immersion. The average
left atrial transmural pressure did not change. A slight hemodilution and a
moderate diuresis occurred. There was no correlation between changes in
left atrial transmural pressure and changes in urine ouput. Fourth, blood
studies were done on splenectomized dogs subjected to immersion.
Hemodilution occurred and was most marked in dogs which had had their
kidneys removed. The hemodilution is sufficient to explain the early phase
of the immersion diuresis. The data suggest that, in anesthetized dogs,
hemodilution is the probable initiator of diuresis upon immersion and that,
in dogs, left atrial stretch is unrelated to diuresis during immersion or
negative-pressure breathing.
