AJP - Renal Physiology, Vol 239, Issue 5 507-F513, Copyright © 1980 by American Physiological Society
Evidence for renal tubular leakage in maleic acid-induced Fanconi syndrome
J. K. Maesaka and M. McCaffery
Micropuncture and microinjection studies were performed in Sprague-Dawley
rats 20 h after subcutaneous injection of buffered maleic acid (MA) or
buffer alone in experimental and control rats, respectively. Collections
were made from earliest and latest accessible portions of proximal tubule
(PT). Lissamine green injections and microperfusion of PT demonstrated
leakage of lissamine green from late PT sites in MA-treated rats, whereas
inulin leakage occurred at a more distal site. Whole kidney GFR was 58%
lower in MA-treated rats despite comparable single nephron GFR in PT of
both groups. Microinjections of PT with [methoxy-3H]inulin resulted in
injected inulin recovery from the contralateral kidney in MA-treated rats
of 24.0 +/- 2.0 compared with 4.7 +/- 0.89% in controls, suggesting that
tubular leakage of inulin accounted for the lower whole kidney GFR. Net
sodium and phosphate transport in early PT was similar in both groups but
was decreased in late PT segments in MA-treated rats. Sodium and phosphate
excretion in final urine were, however, comparable in both groups. The
significantly lower plasma phosphate concentration might account for the
blunted phosphaturia in MA-treated rats. These studies demonstrate a
segmental effect of MA on 1) tubular leakage to lissamine green from late
PT and inulin beyond the late PT, and 2) decreased net sodium and phosphate
transport in the PT.
