AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 4 638-R643, Copyright © 1986 by American Physiological Society
Canine renal responses to atrial stretch or intravenous saline are not attenuated at night
K. L. Goetz and B. C. Wang
Primates develop a diuresis and natriuresis in response to stimuli that
increase central blood volume. However, the renal response is markedly
attenuated when these same experimental stimuli are applied at night. The
purpose of the present study was to determine whether a quadruped,
specifically the dog, also demonstrates attenuated renal responses to
similar stimuli given at night. Two experimental protocols were performed
on conscious dogs at night: 1) left atrial distension by partial mitral
valve obstruction and 2) intravenous saline administration. Results from
these experiments were compared with results from comparable experiments
performed on the same dogs during the day. Each experimental intervention
produced increases in urine flow and sodium excretion and decreases in
urine osmolality during both day and night experiments (all P less than
0.05). The responses obtained during the night did not differ significantly
from those obtained during the day. Thus the dog does not demonstrate an
attenuated renal response to central volume expansion during the night.
This contrasts with the adaptive response in primates that serves to
minimize fluid loss when the intrathoracic blood pool is increased during
prolonged recumbency at night. Presumably quadrupeds, with trunks
horizontal both day and night, do not require nocturnal adaptive mechanisms
to conserve body fluids.
