KIDNEY-FUNCTION DURING EXERCISE IN HEALTHY AND DISEASED HUMANS - AN UPDATE

Exercise induces profound changes in renal haemodynamics and protein e xcretion. The rate of ultrafiltration across the glomerular capillary is determined by the imbalance between the transcapillary hydraulic an d colloid osmotic pressure gradients. Despite a major reduction in the renal plasma flow, the filtration fraction can double with maximal ex ercise, preserving the transfer of metabolites or substances through t he glomerulus. Tubular processes and excretion rates are modified by e xercise. Despite large increases in plasma lactate during strenuous ex ercise, renal excretion plays a limited role in lactate metabolism. Ap parently, the mechanism of transcellular transport of lactate is satur ated during severe exercise. Urea reabsorption is enhanced during prol onged exercise, and this process may act to limit the dehydration of a n individual. As uric acid transport is also carrier-mediated, it appe ars that there is no saturation of the carrier system during prolonged exercise. Postexercise proteinuria is directly related to the intensi ty of exercise rather than to its duration. This excretion of excess p roteins is a transient state with a half-time decay of about 1 hour. T he increased clearance of plasma proteins suggests an increased glomer ular permeability and a partial inhibition of tubular reabsorption. St udies suggest that exercise decreases the glomerular electrostatic bar rier and facilities transfer of macromolecules. Postexercise proteinur ia appears to be age-dependent. Nephropathy is a common observation in the diabetic patient. In young and adult diabetic patients, exhaustiv e physical exercise does not provoke an enhanced dysfunction of the ki dney to what is already found in healthy individuals. Heart and kidney transplant patients have a lesser postexercise proteinuria as compare d with healthy individuals.