Hormonal control of postnatal development of renal tubular transport of weak organic acids

We have postulated that the maturation of the renal transport mechanism for weak organic acids is controlled by thyroid and adrenal hormones. Administration of T3 and T4 (20 micrograms/100 g body wt. for 3 days) to immature rats enhanced by approximately 50% the accumulation of p-aminohippurate (PAH) in renal cortical slices of 5- to 30-day-old rats. The effect of T3 was lower, while T4 had no effect, in 50- and 105-day-old animals. Enhancement of PAH transport became apparent 24 h and disappeared by 9 days after the end of hormone treatment. Administration of a booster dose of T3 (1 microgram/100 g body wt.) on day 9 brought the level of PAH accumulation to values similar to those observed 24 h after the end of the initial 3 days of T3 administration. Dexamethasone administration (80 mg/100 g body wt. for 3 days) affected PAH uptake only in cortical slices obtained from 5-day-old rats. Changes in PAH accumulation did not correlate with changes in kidney weight or protein synthesis, indicating that they were mediated by the hormones rather than being consequent to growth.