The role of glucocorticoids in the postnatal development of ileal active bile salt transport.

The role of glucocorticoids in the regulation of the postnatal development of ileal active bile salt transport was examined in the rat using the villus technique. Ileal taurocholate uptake was initially by passive transport alone on day 14 and 16 which changed to an active and passive transport mechanism at 18 days which persisted thereafter. The Michaelis-Menten constant (Km, mM) was unchanged between days 18 (0.67 +/- 0.12 mM), 20 (0.84 +/- 0.25 mM), 21 (0.49 +/- 0.05 mM), 28 (0.59 +/- 0.06 mM), and 49 (0.50 +/- 0.05 mM) whereas the apparent maximal velocity nmol/mg(dry wt)/min declined after a peak at 18 days (18.17 +/- 1.92 on day 18, 16.14 +/- 1.89 on day 20, 14.65 +/- 0.52 on day 21, 11.40 +/- 0.35 on day 28, and 10.51 +/- 0.32 on day 49). Adrenalectomy performed in sucklings on day 14 with taurocholate transport studies on day 21 and in adults on day 42 studied on day 49 resulted in reductions in uptake at most study concentrations but no change in the Km (1.33 +/- 0.54 in sucklings and 0.75 +/- 0.14 mM in adults) or apparent maximal velocity [11.78 +/- 2.06 in sucklings and 9.24 +/- 0.65 nmol/mg (dry wt)/min in adults]. Treatment of sucklings with corticosterone (5 mg/100 g body weight) on days 10-13 with study on day 14 and 16 did not produce precocious development of ileal active taurocholate transport; however, corticosterone treatment led to apparent increases in ileal permeability to taurocholate in both sucklings and adults. Glucocorticoids appear to play a minor, if any, role in the physiologic postnatal development of ileal active bile salt transport.