AJP - Endocrinology and Metabolism, Vol 264, Issue 6 E966-E972, Copyright © 1993 by American Physiological Society
Binding and degradation of 3,5,3'-triiodothyronine and thyroxine by rat intestinal bacteria
J. J. DiStefano 3rd, A. de Luze and T. T. Nguyen
Biocybernetics Laboratory, University of California, Los Angeles 90024.
Intestinal bacteria hydrolyze conjugates of thyroxine (T4) and
3,5,3'-triiodothyronine (T3) secreted in bile, but it is not clear whether
they have any other role in metabolism, storage, transport, or action of
thyroid hormone in the intestines. We have examined aspects of T3 and T4
binding and degradation processes in fresh feces and cecum contents,
obtained from normal control rats and from rats partially decontaminated by
treatment with oral antibiotics for 2-3 wk. Samples were homogenized in
phosphate buffer, fractionated, and subjected to various test conditions
and incubated at 37 degrees C with 125I-labeled T3 (T3*) or T4 (T4*) for 2
or 24 h. Supernatants of high-speed centrifuged incubates were
chromatographed to test for degradation products, and percentage binding
was measured in the pellets. Substantial binding of T3* and T4* was found
in all control rat feces and cecum content samples by 2 h, but binding was
absent or significantly reduced in partially decontaminated rat samples.
Bacterial binding of T3* and T4* were further shown to be competitive with
graded doses of bovine serum albumin. Considerable degradation of T3* and
T4* to labeled iodide (I*) only was also observed in feces and cecum
content samples and was much greater in control rat than in corresponding
partially decontaminated rat samples. Light had no effects in our system
and heat reduced I* production. Propylthiouracil and sodium ipodate had
little effect or equivocal effects, but dithiothreitol substantially
inhibited I* production.(ABSTRACT TRUNCATED AT 250 WORDS)
