TRIIODOTHYRONINE ACCELERATES MATURATION OF BILE-ACID METABOLISM IN INFANT BABOONS

We tested the hypothesis that triiodothyronine (T-3) treatment acceler ates the early postnatal maturation of bile acid metabolism in the bab oon. Infant baboons were implanted with 21-day-release pellets contain ing T-3 (n = 12), a placebo pellet (n = 6), or no pellet (n = 13). T-3 treatment increased plasma T-3 concentrations from 3.0 to 5.0 nmol/l between birth and 15 wk of age. At 15 wk of age, bile acid pool sizes, fractional turnover rates (FTR), and synthetic rates were determined by an isotope-dilution method with H-3- and C-14-labeled cholic (CA) a nd chenodeoxycholic acid (CDCA). T-3 treatment increased CA pool size by 47% and CA synthetic rate by 37% but did not significantly affect C DCA pool size or synthetic rate. Consequently CA-to-CDCA pool size rat io (0.77 vs. 0.42) and biliary CA-to-CDCA concentration ratio (0.88 vs . 0.46) were higher in the T-3-treated infants than in combined placeb o-treated and nontreated control infants. T-3 treatment did not affect the bile acid glycine-to-taurine conjugate ratio, CA FTR, or CDCA poo l size, FTR, and synthetic rate. T-3 treatment lowered plasma high-den sity lipoprotein fraction 2 and 3 cholesterol concentrations by 22 and 40%, respectively. T-3 treatment also increased hepatic low-density l ipoprotein receptor mRNA levels but did not affect plasma low-density lipoprotein cholesterol concentrations. We conclude that modest elevat ion of plasma T-3 during the preweaning period increases the CA-to-CDC A ratio at the end of the preweaning period to near adult values.