THYROID-FUNCTION IN RATS WITH IODINE DEFICIENCY IS NOT FURTHER IMPAIRED BY CONCURRENT, MARGINAL ZINC-DEFICIENCY

The hypothesis tested was that Zn deficiency aggravates impaired thyro id function as induced by I deficiency. In two separate experiments ma le rats were fed on diets either deficient in Zn or in I, or deficient in both. An identical, restricted amount of food was given to each ra t so that body-weight gain of the experimental groups was comparable. Zn deficiency was evidenced by reduced tibial Zn concentrations. I def iciency was evidenced by goitre, reduced urinary I excretion, reduced plasma thyroxine concentrations and reduced absolute amounts and conce ntrations of thyroxine in the thyroid. Zn deficiency had no effect on the raised thyroid weight as induced by I deficiency. Zn restriction f rom 184 mu mol Zn/kg diet to 31 mu mol Zn/kg diet, but not to 92 mu mo l Zn/kg diet, significantly lowered plasma thyroxine concentration. Th ere were no interrelated effects of Zn and I deficiencies on thyroid h ormone levels. These results indicate that marginal Zn deficiency does not influence thyroid hormone metabolism in I deficiency.