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

The purpose of this study was to examine body fluid adjustments during prolonged resting heat exposure in primates. Rhesus monkeys were acclimated for 35 days at 35 degrees C and 30% rh. Red cell mass, extracellular fluid volume (ECF), and total body water (TBW) were determined with 51Cr, 35SO4, and 3H2O, respectively, prior to and at intervals during heat exposure. Heat acclimation was characterized by a fluid shift from the interstitial compartment. In relation to TBW, interstitial fluid volume and ECF decreased 10.3 and 8.3%, respectively, while plasma volume (PV) and intracellular fluid were increased an average of 5.8 and 3.8%. TBW increased 4.8% during heat exposure. Hematocrit and hemoglobin decreased significantly on day 3 (7.9 and 6.5%) followed by a return toward control values. PV in relation to TBW remained elevated throughout the exposure. An increased drinking (25.0%) was associated with a decrease in caloric intake (30.7%) during heat acclimation. This study has provided a complete body fluid compartment analysis during resting heat acclimation in the rhesus monkey. Our results are consistent with the hypothesis that heat acclimation in primates is characterized by a protein and fluid shift from the interstitial fluid compartment to the cardiovascular system and to the intracellular compartment.