Developmental Aspects of Renal β-Amino Acid Transport I. Ontogeny of Taurine Reabsorption and Accumulation in Rat Renal Cortex

Abstract

Summary: Newborn Sprague-Dawley rat pups were found to have reduced net tubular reclamation of the β-amino acid taurine in vivo. The reabsorption of this compound increased between the 2nd and 4th week of life and the excreted taurine fell despite a rise in glomerular filtration rate indicative of increased transport with maturation. Kidney cortex in vivo accumulated taurine from plasma against a large chemical gradient. Newborn cortex slices in vitro accumulated taurine to higher levels at steady state at <0.4 mM, but uptake was less efficient at higher taurine concentrations. Further metabolism of taurine by cortex slices was not found at any age. Accumulation in adult and newborn cortex was greatest at 10–15 mEq/liter K in the external medium. Slices from younger animals had slightly higher pH optima for uptake and temperature elevation increases uptake more in neonatal than in adult kidney. Speculation: If the newborn rat is in part dependent on the transfer of taurine from mother to pup via milk, the process of weaning may require greater renal tubular reabsorption in order to maintain tissue and plasma pools of taurine. The improved reabsorption of taurine found in 4-week-old and adult animals may reflect maturational changes brought about by the reduction in dietary taurine (and other sulfur containing amino acids) after weaning.