Effects of Exposure to Simulated High Altitude on Distribution of Body Fluid in Rats and Rabbits

Abstract

To investigate the changes of body fluid balance during the course of adaptation and acclimatization to high altitude, rats and rabbits were exposed to a simulated altitude of 5, 500 m for 14 days. The changes in total body weight, visceral weight, circulating blood and plasma volume, radio-sodium space, and water content and specific gravity of plasma were measured prior to, during and after the exposure. In addition, a restricted feeding experiment corresponding to reduced consumption of food and water at altitude was also performed at sea level environment.
These animals lost their weight at the early stage of the exposure. Main parts of weight changes were broadly muscular and dermal tissue portions. Radio-sodium space was decreased in parallel with body weight until the 4th day of exposure. Plasma volume was decreased in similar pattern to sodium space. Water contents of plasma was clearly decreased at exposure and maintained the low level thereafter during exposure period. On the contrary, plasma specific gravity rose. At the experiment of restricted feeding, plasma water content rose at the 1st day and returned to the initial level at the 3rd day of experiment.
From these results, it seems likely that body water, particularly extracellular water, might be reduced first at the early stage of exposure, followed by partially accompanied reduction of boody fat and another compartments.
Extracellular fluid retained somewhat dehydrated level durnig exposure period. This dehydration was thought to be attribuded to at least 2 causes. The one is apparently reduced intake of food and water and the other cause is not clear yet. However, the experimental evidence that the water content of red cell has gradually risen is of much interest in conjunction with the second factors.