Superficial nephron tubular-vascular relationships in the rat kidney.

Silicone rubber injections of methyl salicylate-cleared rat kidneys were performed. In 50 of 56 injections of superficial nephrons with their accompanying blood supply, the efferent vessel and early proximal tubule were closely approximated. In 18 of 21 tubular injections filling through the pars recta, the proximal tubule folded upon itself with early and late proximal segments, in close contact, located over their parent glomerulus, and the midproximal segments separate and located over their parent interlobular artery. The distribution of blood was serially through the early-late proximal region above the glomerulus via a long unbranched efferent vessel, via branches over the capsular surface, via capillaries down through the midproximal region, then into the interlobular vein. The observed anatomical pattern of the superficial nephron appears to permit direct functional interactions between the juxtaposed early and late proximal tubule, and in turn may effect midproximal function via the distribution of blood (modified by early proximal) from the efferent vessel to midproximal convolutions. In addition, the relationship between specific segments of the proximal tubule and specific portions of the postglomerular peritubular blood supply may be important in determining the distribution of peritubular physical forces to these nephrons.