AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 1 15-R19, Copyright © 1987 by American Physiological Society
Changes in blood volume and plasma sodium concentration after water intake in rats
H. Nose, E. Sugimoto, T. Okuno and T. Morimoto
Changes in blood volume (BV) and Na+ concentration of plasma ([Na+]) were
measured continuously during recovery from thermal dehydration in rats. At
least 5 days prior to the experiments rats were cannulated into both the
jugular vein and the descending aorta. After thermal dehydration (DBT: 36
degrees C, RH: 20%) amounting to approximately 6% of body wt, catheters
were connected to a system for continuous monitoring of BV and [Na+]. Water
was made available and water intake, BV, and [Na+] were recorded at 30-s
intervals for 4 h. The rats took 2-3 ml of water/100 g of body wt in the
first 10 min and then drank 1 ml at 30- to 60-min intervals to reach
equilibrium in 2-3 h. The relations between water intake and delta BV and
between delta[Na+] were analyzed for 2 h after the start of water supply.
BV was unchanged until 18.9 +/- 3.6 min after access to water, whereas
[Na+] started to decrease after 3.6 +/- 0.6 min. The retention ratio of
ingested fluid in the vascular space was 20.8 +/- 2.8%, and the decrease of
[Na+] was 1.5 +/- 0.2 meq X l-1 X ml ingested fluid-1 X 100 g body wt-1.
These results indicate that drinking causes the change of [Na+] more
rapidly than that of blood volume.
