SUBCHRONIC APPLICATION OF HUMIC ACIDS AND ASSOCIATED COMPOUNDS PROVOKES HISTOLOGICAL-CHANGES OF GOITER IN THE RAT

1. Different preparations of humic acids, a pyrogallol oxydation produ ct (PYROP) and resorcinol were administered to male and female rats wi th the drinking water for 8 to 14 weeks. 2. By histometrical evaluatio n of the thyroid glands, an increase of the mean epithelial cell heigt h of follicular epithelial cells was established in the 0.1 % humic ac id groups, 0.1 % PYROP group and the 0.004 % resorcinol groups. Female s seemed to be more sensitive than males. Additionally, in some experi ments, a decrease of the mean follicular diameter was found, which was the result of newly formed little follicles. The changes must be cons idered as a precursor of goitre. 3. In one of the experiments, in whic h circulating thyroid hormones were investigated, the serum thyroxine level in the male 0.1 % humic acid group and the free thyroxine index in the female 0.1 % humic group were diminished as compared to the con trol groups.