Renal filtration, transport, and metabolism of low-molecular-weight proteins: A review
Despite general recognition that the kidneys play an important role in the plasma turnover and in the maintenance of adequate plasma levels of small proteins, the study of the renal handling of these substances still constitutes one of the most underdeveloped areas of research in renal physiology. Nevertheless, recent advances in the field have been considerable and are the subject of the present review. Without attempting to be all inclusive, we will analyze the evidence regarding the extent, pathways, and mechanisms of the renal accumulation, filtration, absorption, and metabolism of small proteins. A final section will then deal with the renal turnover and the homeostatic role of the kidney in the maintenance of adequate plasma levels of these substances. A critical appraisal of the methods used to estimate glomerular sieving coefficients and renal turnover rates of small proteins will be given in some detail, because a correct determination of these parameters is essential to an understanding of the kidney's role in the disposal of circulating small proteins.