AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 3 492-R498, Copyright © 1986 by American Physiological Society
Recovery of blood volume and osmolality after thermal dehydration in rats
H. Nose, M. Morita, T. Yawata and T. Morimoto
Changes in blood volume and fluid intake were assessed continuously during
recovery from thermal dehydration (approximately 6 ml/100 g body wt) in
rats. Catheters chronically implanted into the jugular vein and descending
aorta were connected with the system for continuous monitoring of blood
volume. Changes in blood volume and fluid consumption were recorded for 2-6
h while tap water (TW group) or 0.45% NaCl solution (Na group) was provided
ad libitum. As soon as the fluids became available, the rats in both groups
drank a relatively large volume (2-3 ml/100 g) within 10 min. Thereafter,
Na group consumed approximately 1 ml X 100 g body wt-1 X 30-60 min-1 and
regained almost all water loss in 2 h, whereas TW group drank only
approximately 50% of their water deficit. The percent of ingested fluid
that remained in vascular space was 17% on average in both groups. Thus TW
group replenished 80% of the depleted blood volume, whereas Na group
regained almost all of it. Rehydration for 2 h decreased plasma Na
concentration to the control level in TW group, whereas in Na group the
level remained high. These results suggest that the lower fluid intake in
TW group is due to the dilutional inhibition of drinking and that the
osmoregulation has priority over blood volume regulation in restitution
from thermal dehydration.
