Methylprednisolone accelerates the ontogeny of sodium-taurocholate cotransport in rat ileal brush border membranes

The effect of methylprednisolone on the postnatal maturation of taurocholate transport was studied by using isolated ileal brush border membrane vesicles. Vesicles were prepared from 14-day-old control, 14-day-old methylprednisolone-treated, and untreated 21-day-old rats. Methylprednisolone treatment resulted in a significant stimulation of taurocholate uptake by an inwardly directed Na⁺ gradient when compared with a choline gradient incubation. These differences occurred at 20 seconds and 1, 2, and 5 minutes of incubation (P < 0.05). In 14-day-old controls, uptake was similar for Na⁺ and choline gradients. A plot of active uptake velocity vs. taurocholate concentration (0.1 to 1.0 mmol/L) in 14-day-old controls was linear and approached the abscissa, indicating the absence of active transport. Plots for methylprednisolone-treated rats showed saturability. An inwardly directed Na⁺ gradient stimulated initial taurocholate uptake rates by twofold at 37 ° C (P < 0.01), but not at 4 °C. Glycocholate and glycodeoxycholate inhibited Na⁺-stimulated taurocholate uptake by 50% (P < 0.01) and 20% (P < 0.05), respectively. These data indicate that pharmacologic doses of methylprednisolone accelerate the postnatal acquisition of Na⁺-dependent taurocholate cotransport in rat ileal brush border membranes.