AJP - Endocrinology and Metabolism, Vol 268, Issue 5 E889-E896, Copyright © 1995 by American Physiological Society
Triiodothyronine accelerates maturation of bile acid metabolism in infant baboons
D. S. Lewis, E. M. Jackson and G. E. Mott
Department of Physiology and Medicine, Southwest Foundation for Biomedical Research, San Antonio 78228-0147, USA.
We tested the hypothesis that triiodothyronine (T3) treatment accelerates
the early postnatal maturation of bile acid metabolism in the baboon.
Infant baboons were implanted with 21-day-release pellets containing T3 (n
= 12), a placebo pellet (n = 6), or no pellet (n = 13). T3 treatment
increased plasma T3 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 3H- and 14C-labeled cholic (CA) and chenodeoxycholic acid
(CDCA). T3 treatment increased CA pool size by 47% and CA synthetic rate by
37% but did not significantly affect CDCA pool size or synthetic rate.
Consequently CA-to-CDCA pool size ratio (0.77 vs. 0.42) and biliary
CA-to-CDCA concentration ratio (0.88 vs. 0.46) were higher in the
T3-treated infants than in combined placebo-treated and nontreated control
infants. T3 treatment did not affect the bile acid glycine-to-taurine
conjugate ratio, CA FTR, or CDCA pool size, FTR, and synthetic rate. T3
treatment lowered plasma high-density lipoprotein fraction 2 and 3
cholesterol concentrations by 22 and 40%, respectively. T3 treatment also
increased hepatic low-density lipoprotein receptor mRNA levels but did not
affect plasma low-density lipoprotein cholesterol concentrations. We
conclude that modest elevation of plasma T3 during the preweaning period
increases the CA-to-CDCA ratio at the end of the preweaning period to near
adult values.
