AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 2 237-G242, Copyright © 1986 by American Physiological Society
Role of thyroxine on postnatal development of ileal active bile salt transport
J. E. Heubi
The role of thyroid hormone on the postnatal development of ileal active
taurocholate transport uptake was measured by an in vitro incubation
technique in Sprague-Dawley rats. In 16-day-old rats treated with
pharmacological doses of L-thyroxine (50 micrograms X 100 g body wt-1 X
day-1 on days 10-13), ileal active transport appeared precociously whose Km
was 1.60 +/- 0.48 mM and Vapp (apparent maximal velocity) was 8.09 +/- 1.14
nmol X min-1 X mg dry wt-1, while age-matched shams had only passive
diffusion of taurocholate. To determine whether enhanced endogenous
secretion of thyroxine was capable of stimulating development of ileal
active taurocholate transport, thyrotrophic stimulating hormone (TSH) (0.5
U/100 g body wt twice daily) was given on days 10-13, with uptake measured
on day 16. Following TSH treatment, only passive transport for taurocholate
was observed in the ileum; uptake rates were consistently higher than those
for untreated controls at each study concentration. Thyroidectomy performed
at age 14 days with uptake measured at age 21 days did not ablate
development of ileal active transport but resulted in a significant
reduction (P less than 0.001) in the Vapp (7.39 +/- 1.10 nmol X min-1 X mg
dry wt-1) and a significant increase (P less than 0.014) in Km (1.72 +/-
0.53 mM) compared with age-matched controls. Thyroid hormone does not
appear to be obligatory for the postnatal development of ileal active
taurocholate transport.
