Reticuloendothelial phagocytic activity in high-altitude acclimatized rats

Experiments were undertaken with rats to determine the effects of chronic exposure to a simulated high altitude of 5,000 m on phagocytic activity of the reticuloendothelial system (RES). Phagocytic index (K) was determined by measuring the rate of blood clearance of colloidal carbon given intravenously. K value of the chronically altitude exposed rats was found to be greater than that of the sea level control animals (p less than 0.02), indicating that acclimatization to high altitude stimulated the RES phagocytosis. On analysis of the weights of the liver and spleen, the corrected phagocytic index (alpha) of the high altitude-acclimatized rats was also found to be higher than that of the sea level control animals (p less than 0.05) while the weights of the liver and spleen expressed in percent body weight were not affected by high altitude exposure. The increased number of carbon-containing Kupffer cells in the liver and the increased phagocytic indices (both K and alpha values) suggested that most of the increase in RES phagocytic activity was due to increased RES tissue activity per unit mass of tissue rather than tissue hypertrophy.