The return of glomerular filtered albumin to the rat renal vein - The albumin retrieval pathway

Background. Recent studies have demonstrated that the normal glomerular cap illary wall (GCW) is not charge selective to albumin. This means that album in flux across the GCW is high. This has been confirmed in studies where al bumin uptake by the tubules has been inhibited. Therefore, there must be a high capacity postglomerular retrieval pathway in normal kidneys that retur ns filtered albumin back to the blood supply. Methods. This study identifie s the presence of glomerular filtered albumin in the renal vein from the an alysis of the decrease of radioactivity in the venous effluent after the in jection of a pulse of tritium labeled albumin into the renal artery in vivo and in the isolated perfused kidney (IPK). Results. The glomerular filtere d albumin is returned to the blood supply by a high capacity pathway that t ransports this albumin at a rate of 1830 +/- 292 mug/min rat kidney (n = 14 ) (mean SEM). This pathway has been identified under physiological conditio ns in vivo and in the IPK. The pathway is specific for albumin as it does n ot occur for horseradish peroxidase (HRP). The pathway is inhibited in a no n-filtering kidney. The pathway is also inhibited by NH4Cl, an inhibitor of protein uptake. Conclusions. The high capacity retrieval pathway for album in is most likely associated with transtubular cell transport. It is also a pparent that most albuminuric states could be accounted for by the malfunct ioning of this pathway without resorting to any change in glomerular permse lectivity.