Experiments were designed to determine if changes in rat intestinal bacterial flora
are accompanied by changes in thyroid function. Attempts to modify intestinal bacterial
flora of Sprague-Dawley (SD) rats were made by (a) feeding the non-orally absorbed
antibiotic, kanamycin; (b) insanitary caging. Thyroid function was also compared in
germfree and ex-germ-free animals. Qualitative and quantitative studies of intestinal
bacteria were carried out concurrently; at the end of each study thyroidal radioactive
iodine (RAI) uptakes and plasma radioactivities were determined at three or 24 hours
after radioiodine (Na131I) was administered. Thyroid glands were weighed and total iodine concentration was
measured as well as plasma protein-bound iodine (PBI). Kanamycin lowered the total
aerobic and anaerobic bacterial counts of female rats and this was accompanied by
reduced three hours thyroidal RAI uptakes after 42 and 72 days of treatment Insanitary
caging for four or eight weeks did not change intestinal bacterial flora and there
were no differences in thyroid function. Female germ-free animals had significantly
smaller thyroids than conventional female rats. These studies have shown that reduction
in the intestinal bacterial flora may affect thyroid function - simulating modest
supplementation with iodine.
Intestinal Bacterial Flora - Radioiodine Uptake - Thyroid Function
