Renal Function

SUZUKf, M. Exercise and Renal Function. Adv. Exerc, Sports Physiol., Vol. 2, Ne.2 pp,45-56, 1996, Reseafch en rcnal functiort cluring cxcrcise is very rare in the sperts niedicine areu because it has no direct bearing en the performance of exercisc. However, the kidncys play an important role in maintnining a constant internal statc, which. whcn disturbed by exercise in a het environment, is normalized by rncans of e]hanced conservntion of vvateT and elcctrolyLes by thc kidneys. It is the purposc ef this articlc to rcview the prcvious literaLurc, te relutc somc of our fbidill:s on rena] function. and to discuss the mechanisms undeTl},ing the changes in renal functien and the roles of the kidncys during and/or following exercise, in relation to exercise intcnsity, duratiom and cxercisc cnvironrnent. Mechanisms undcrlyins, exercise-induced proteinuria in healthy and obese per$ons are furthei distussed. The renal blood flow (RBF) and glomerular fiitration rate {GFR) decreascd from 409.o' and 49%・ of VO!max rcspcctivel)'. depende"t of increase in Lhe intcnsity of exercise, However, RBF and Gi;R were not afreeted by the modificatien of cxcrcise duratien. Urinaiy excretion of many ctcctrolytes was inhibitcd, which might huvc been due tD the dccrease in GFR ip response to exercisc, with increase in thc intensitv of exercise. The rcmaik' uble rcduction ef (]I cuncentration i" lhe urine observcd fellowing exhaustivc cxereise, in particuEar, might have n rolc in the compensation for increase in t]w anion gap in urinc produced by thc excrclse. The RBF and GFR reduce in response to a hot envirenment, The ]oss of water and clectrolytes caused by an incrcasc in sweating and the urinary excretion of watcr and e]ectrolytcs are inhibitedi b}, cnhancenienL oC the rcnin-ungiorensin-aldostcrone CRAA) system during exercise in a hot environment. Response of thc RAA systcm te these condirions was attenuaLeci b)・ rcplaccment of fluids centaining minerals and other eiements. Wuter immersion induced incrcases ln RBF, GFR and lhe extretion of water and eie.ctrelytes into the urine. A light intensity of exercise (undcr about 40% of VOzinax) in water {29.9 l e,6k/') ciid not inhibit thc excretion of water and eiectrolytes inte urine, and p]'oduced only sllght incrcascs in the plasma concentration of catccholamines and aldosLerone, in contrast to the responses lo thc same intensity of cxcrcise on land. The rcsults suggesL LIiat light cxcrcise in water may bc preferred tbr indii,iduals with sympathicotonla, pzticnts with hypertension and obesity ",ho huvc a tenclency to retain wutcr and sodium in the bedy, and have minor nephropathy. '1'he mechanism proposed Lo explain proteinuria of th¢ mixcd glomeru]ar and tubuTar type induced by exhzustive exercise in a healthy person was thzt luctic acid, pyruvic acid and otlier organic acids produced in cxccss b)' ex ¢ rcisc were filtered in tbc glemerulus and renul tubules. and excret ¢d together witb enhanced reabsorption of Cl, and with inhibition of reubsorption of albumii and low molecular weight prutein (LMWP) such as crLM and ,'?2M in tubulaT eel], thcrcby resulting ln the eccurrence of proteinurin vvith both alb-min and LMWE). Howev ¢ r, it was not thought that angiotensin a played an importnnt rele in the occurience ef proteinuria fo]lowing exhaustive cxercise in a healthy pcrson, A modefate lcvc] of cxercise (MI.E) that dose net induces any change in urinary alburnin excretion (UAE) folTowing cxercise in healthy persons is uscd as a provocative test ef difibetic nephropathy (DN). MI,li produccd an increuse in UAE in somc obese persons who shewed highcr lcyels of Hct. serum TC, TG, Apo B and Address for Corrcspondence/ Masato SUZUKI Department of Laboratory Medicine. The Jike{kai University Scheel uf Medicine, 3-25-8 Nishi-shinbashi, MinRto-ku, Tokyo 105, Japan 45 F conccntrations accornpanied by a slightly impaired gTucose tolerance. This rcsutt indicatcd that the MI.E may piovokc a latent Tenal glomcrular abnermality in some obcsc subjecls with n slightly impaired glucosc-fatty rnetaboliSlll.Key vvords: F.xercisc intensity, Rcnal blood now, Heat and watcr envlronments,Water-electrolytcbalance,Excrcisc-inducedpreteinuria lntroduction The kidneys play an important role in maintaining constancy of physiological factors within the body, such as pH, osmotic pressure and electrolytes in plasma, by excreting metabolic wastes and noxious products as well as excreting and reabsorbing water and electrogytes, including Na+, K'i and CI-. These functions are performed by the renal blood fiow (RBF), glomerular filtration rate (GFR), and excretion and reabserption in the tubules. Even if the excretable noxious products were to increase, as a result of increase in metabolic rate, RBF will be reduced during exercise. Physica] exercise has, therefore, a negative effect on the kidneys in terms of maintcnance of renal function. However, in sports medicine, research on renal function in athletes has been given less importance, compared to other areas of study such as the respiratory, circulatory systems and neuro-muscular systems as well as the metabolism of glucose and fats, as it has no direct influence on the performance of exercise. However, exercise is also used in physical therapy for obesity, diabetes mellitus and minor hypertension. In patients with minor nephritis in whom exercise is not restricted, a knowledge of the relation between exercise and renal function is essential, Though microalbuminuria (MAU) is used as useful index for the early detection and diagnosis of diabetic nephropathy (25, 61), physical activity increases excretion of MAU into urine (1, 26) and this knowledge is indispensable for evaluating MAU of diabetic patients, On the other hand, renal function is important in the maintenancc of the fiuid-electrolyte balance, eyen in healthy persons and athletes during exercise in warm conditions or in water. The purpose of this article is to review the previous literature, to present some of our observations on renal function and to discuss the mcchanisms underlying the changes of renal function and the roles of the kidney during and/or