Renal function and control during early altitude acclimatization

Abstract

Renal acclimatization is an important aspect of high-altitude adaption coordinating diuresis, acid-base status, natriuresis, renal hemodynamics and kidney filtration. Renal blood flow, glomerular filtration rate, active renin, plasma aldosterone concentration, NT pro-brain natriuretic peptide (BNP), urine volume, urine microalbumin, HCO3-, PCO2, and PO2, were measured in twenty-four lowlanders (28 ± 7 years; 3 female) at 344 m and again at 4330 m following one (ATL1) and seven (ATL7) days of acclimatization. Renal blood flow decreased significantly from sea-level (931.4 ± 392.3 ml/min) to ATL1 (626.4 ± 364.8 ml/min; p<0.05) however rebound to sea-level values by ATL7 (892.8 ± 334.1 ml/min). Glomerular filtration rate was significantly decreased at ATL7 (86.4 ± 17.4 ml/min at ATL7) compared to sea-level (101.8 ± 21.1 ml/min; p<0.05). Plasma aldosterone concentration was the only hormone measured that reached significance (sea-level 121.7 ± 92.5 vs ATL7 182.7 ± 104.9 mmol/L; p<0.05). Lowlanders produced more urine at high-altitude (ATL1: 680.1 ml/9-hour and ALT7: 756.9 ml/9-hour) compared to sea-level (535.3 ± 277.8 ml/9-hour) reaching significance by ATL7 (p<0.05). Urine microalbumin was not significantly different at any time point. HCO3- was significantly decreased from sea-level (25.8 ± 1.7 mmol/L) and ATL1 (24.6 ± 1.9 mmol/L) compared to ALT7 (19.9 ± 2.0 mmol/L; p<0.05). PCO2 was significantly higher at sea-level (38.4 ± 3.2 mmHg; p<0.05) compared to ATL1 (33.1 ± 3.3) and ATL7 (28.2 ± 2.6 mmHg). PO2 was higher at sea-level (100.6 ± 18.4 mmHg; p<0.05) compared to ALT1 (41.5 ± 7.3 mmHg) and ATL7 (50.7 ± 3.9 mmHg) however increased during ATL7. Our findings suggest glomerular filtration rate decreases with continued high-altitude occupancy. Plasma aldosterone concentration decreases during prolonged hypoxia to cause diuresis. HCO3- excretion occurs to restore the acid-base status, which is evident by late acclimatization (ATL7).