Renal Tubular Transport of Organic Acids: STUDIES WITH OXALATE AND PARA-AMINOHIPPURATE IN THE RAT

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Abstract

The renal handling of oxalate was examined by free-flow micropuncture, intratubular microinjection, and droplet precession techniques in the rat. After the sustained i.v. infusion of [14C]oxalate, the fractional delivery of oxalate from the early portions of the proximal tubule was 120.1±4.4%, indicating net secretion. Fractional delivery rates from the late proximal tubule (124.6±6.1), distal tubule (120.9±2.9), and final urine (126.2±2.9%) were not different from that of the early proximal tubule. Direct intratubular microinjections of oxalate into the early proximal tubule and late proximal tubule yielded urinary recovery rates of 85±3% and 101±2%, respectively, suggesting that oxalate absorption does occur in the mid-portions of the proximal tubule. Droplet precession studies confirmed a secretory flux for oxalate. In contrast to oxalate, para-aminohippurate (PAH), the more traditional marker for organic acid transport, was secreted in the late portions of the proximal tubule and in large measure at a site between the late proximal and distal tubules, presumably the pars recta. Probenecid inhibited PAH secretion but was without effect on net oxalate transport, oxalate absorption, or oxalate secretion.

Authors

E. J. Weinman, S. J. Frankfurt, A. Ince, S. Sansom