ARGININE SYNTHESIS IN MOUSE AND RABBIT NEPHRON - LOCALIZATION AND FUNCTIONAL-SIGNIFICANCE

In the rat kidney, arginine (Arg) synthesis is restricted to the proxi mal tubule with a decreasing intensity from its convoluted (PCT) to it s straight part (PST). The present study was designed to investigate t he pattern of Arg synthesis along the nephron in other mammals, the mo use and rabbit. Micro-dissected representative nephron segments were i ncubated with 0.1 mM L-[ureido-C-14]citrulline in a sealed chamber. Ad dition of arginase and urease to the incubation medium led to the hydr olysis of Arg into ornithine, NH3, and (CO2)-C-14. The latter was trap ped in KOH and counted (results are in fmol Arg . min-1 . mm tubular l ength-1). As in the rat, the main site of Arg synthesis in both specie s was found to be the PCT (mouse, 191; and rabbit, 57). A lower produc tion was observed in rabbit and mouse PST and in rabbit distal segment s. Along the PCT (from 1st to 4th mm after the glomerulus), a steep de crease is observed in mouse (595 and 37, respectively) but not in rabb it (57 and 23). The fate of the newly synthesized Arg probably depends on its site of production. Intracellular arginase activity is known t o be present in the cortical (C) and medullary (OS) PST, in both mouse and rabbit. In rabbit only, arginase activity is also found in the PC T. We observed that a large part of Arg was further hydrolyzed into ur ea and ornithine in CPST and OSPST of mouse (66 and 80%, respectively) and rabbit (40 and 70%) but not in rabbit PCT (8%). Thus Arg produced by PCT in both species is probably released in the cortical blood, wh ereas Arg produced in PST may serve locally to produce urea and ornith ine, and the latter could be used for polyamine synthesis.