Effect of Changing Intestinal Bacterial Flora on Thyroid Function in the Rat

Abstract

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.

Key words

Intestinal Bacterial Flora - Radioiodine Uptake - Thyroid Function

1 Present address: Bionetics Research Laboratories, Kensington, Maryland