The renal handling of protein excretion

• Main Author: Soliman, Mohamed H. M.
• Published: University of Aberdeen 1967
• Subjects: 616.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635920

Proteinuria has been known for about a century, yet much information concerning the renal handling of protein, particularly by the normal kidney, requires further and more thorough investigation. Since then, some theories have been put forward and assumptions have been made to explain the mechanism of renal function with respect to the glomerular filtration of endogenous or exogenous infused proteins. However, the ways by which these proteins are acted upon by the kidney are still incompletely understood. Although the renal tubular handling of plasma proteins by the diseased kidney has been extensively investigated, this handling is still in need of further study especially in the case of protein not normally present in the plasma, and in the normal kidney. Furthermore, there is some evidence that in proteinuria, the renal tubular reabsorption of plasma proteins is non- selective. Although such a phenomenon is probably operative in the case of plasma proteins, there is evidence that filtered proteins which are not normally present in the plasma may not be reabsorbed at all in the tubules, or only to a limited extent. The most important protein which has been extensively investigated in this respect is haemoglobin, but even attempts to demonstrate histologically that haemoglobin enters the renal tubular cells have yielded equivocal results. In consequence the author's aim was to investigate another important tissue protein and its handling by the normal mammalian kidney. Homologous erythrocyte carbonic anhydrase (C.A.) was chosen for this study for several reasons, the most important of which may be summarised as follows;- (a) C.A. may be detected in the urine of patients suffering from intravascular haemolysis and is absent from those with extravascular haemolysis. (b) It may be easily prepared in fairly good yield and in an immunologically pure state, as a single protein component of homogenous molecular size. (c) The low molecular weight of C.A. is well established (30,000), hence it may be easily filtered through the glomerulus. (d) This enzyme is present neither in normal blood plasma nor in normal urine. Therefore, it was thought that some light might be thrown on the renal tubular mechanism in the case of induced proteinuria, if the clearance of this protein by the normal mammalian kidney were investigated.