Body fluid and hematologic adjustments during resting cold acclimation in rhesus monkey.

The purpose of this study was to examine body fluid adjustments during prolonged cold exposure in primates. Six male rhesus monkeys were acclimated for 35 days and 6 degrees C and 80% rh. Red cell mass, extracellular fluid volume, and total body water (TBW) were determined with 51Cr, 35SO4, and 3H2O, respectively, prior to and at various intervals during the cold stress. TBW was increased throughout the exposure, whereas changes in extravascular compartments had occurred within the 1st wk of cold exposure, after which they returned to control values. An increased concentration of blood constituents on day 1 was not accompanied by a decrease in cardiovascular volume. Blood volume and plasma volume in relation to TBW were significantly increased on day 3 and remained increased during the remainder of the exposure. These cardiovascular volume changes were accompanied by a significant hemodilution on day 3 and a gradual return to control values. An increased plasma osmolality and expansion of the erythrocytes (decrease in mean corpuscular hemoglobin concentration) were observed throughout the cold stress. These data suggest that the rhesus monkey may be an adequate primate model for studies of body fluid adjustments, especially during prolonged cold exposure, in primates in general, including the human.