Renal function in rats chronically exposed to high altitude

Chronic exposure of rats to a simulated altitude of 18,000 ft (5,500 m) results in severe polycythemia and consequent reduction of the plasma fraction. However, glomerular filtration rate is usually well maintained. This study was conducted to determine whether an increase in effective renal blood flow (ERBF) plays a role in maintaining a normal glomerular filtration rate in the chronically hypoxic rats. Various measurements of renal function were made in conscious trained and chronically catheterized animals. After exposure to high altitude for 30 days, hematocrit ranged from 64 to 77%. Despite this severe reduction in the plasma fraction, however, renal plasma flow decreased by only 25%, primarily owing to an increase in ERBF. The glomerular filtration rate was within the normal range. Since blood pressure remained unchanged, the increase in ERBF must have resulted from renal vasodilation. Acute removal of the hypoxic stimulus did not reverse the increased ERBF, suggesting that the vasodilation may have been of structural origin.