Effect of Isomers of DDD on thyroid and adrenal function in rats

Dietary administration of o,p′-DDD (2,2-bis(2-chlorophenyl, 4-chlorophenyl)-1,1-dichloroethane) at 1.0 and 3.0 g/kg food for 6 weeks increased the thyroid weight of male albino rats by 62 and 81% respectively. The rate of oxygen consumption (measured at 30 °C) and gain in body weight were unaffected by treatment. The rate of loss of 131I from the thyroid gland was significantly faster for both treated groups than for controls. These results suggest that the chronic administration of o,p′-DDD at the doses used resulted in a compensated hypothyroidism in rats. In another experiment, the thyroid weight of female hooded rats given m,p′-DDD (1.0 g/kg food) and p,p′-DDD (1.0 and 3.0 g/kg food) for 24 weeks also increased 112, 94, and 113% respectively above control weight. Ninety-six hours after the administration of thyroxine-131I, significantly greater fecal and less urinary excretion of radioactivity was observed for all treated groups than for the control group. The increase in thyroid weight of the treated rats may be associated with increased hepatic metabolism of thyroxine, but specific effects on the thyroid gland have not been excluded. Although isomers of DDD are reported to induce atrophy of the adrenal cortex and to reduce glucocorticoid secretion in dogs, no effect of the chronic administration of isomers of DDD on adrenal weight or production of either total Δ4-3 ketosteroids or corticosterone in vitro was observed in the case of rats. The rate of metabolism of desoxycorticosterone in vitro by rat liver slices was also unaffected by chronic treatment with o,p′-DDD.