Renal tubular transport of Diodrast-I131 and PAH in Necturus: evidence for simultaneous reabsorption and secretion

Abstract

Renal plasma clearances were determined in pithed Necturi from samples of cloacal urine and branchial arterial blood. Simultaneous clearance of creatinine and inulin carboxylic acid-C14 corresponded closely. Diodrast-I131 and/or para-aminohippurate (PAH) clearances were less than simultaneous creatinine clearances in about 80% of the Necturi. At low plasma concentrations of Diodrast and/or PAH, Diodrast/ creatinine and/or PAH/creatinine clearance ratios were independent of concentration and exhibited a seasonal variation, approximating 0.2 in ‘winter’ and 0.5 in ‘summer.’ In a random 20% of the animals, however, ratios were greater than unity, approximating 2.0. In both groups of animals the ratios generally approached unity at high plasma concentrations. However, under the conditions of high PAH and low Diodrast concentrations in the group with initial ratios less than unity, the Diodrast ratio approximated 2.0. These data are interpreted as evidence that in Necturus kidney over-all tubular transport of Diodrast and PAH is the net result of simultaneous reabsorption out of and secretion into tubular urine.