Effect of a rickets-inducing diet and vitamin D metabolites [25-OH-D 3 and 1,25(OH) 2D 3] on transmembrane transport systems in rat kidney

Abstract

We previously demonstrated that feeding rats Steenbock and Black's rickets-inducing diet (deficient in vitamin D and with an altered Ca:P ratio) produces remarkable changes in the metabolic picture of the intestinal mucosa, kidney, and liver and in the transmembrane transport systems of D-glucose in intestinal and renal brush-border membrane vesicles. We have now investigated the effect of both 25-hydroxyvitamin D 3 and 1,25-dihydroxyvitamin D 3 on Na +-dependent D-glucose and citrate transport and on calcium, phosphorus, and citrate content in rat serum and kidney. Na +-dependent D-glucose uptake, which decreased in rachitic rat jejunum brush-border membrane vesicles, returned to control values after 25-hydroxyvitamin D 3 or 1,25-dihydroxyvitamin D 3 administration, while in kidney normal D-glucose transport was restored only after 1,25-dihydroxyvitamin D 3 treatment. Na +-dependent citrate uptake was lowered in rachitic rat renal brush-border membrane vesicles and both 25-hydroxyvitamin D 3 and 1,25-dihydroxyvitamin D 3 proved to be ineffective in restoring to normal values. The in vitro addition to vesicle preparations of calcium or phosphate, citrate, 1,25-dihydroxyvitamin D 3, or valinomycin did not show a selective influence on D-glucose and citrate transport.