The iodine requirement and influence of iodine intake on iodine metabolism and thyroid function in the adult beagle.

Various aspects of iodine metabolism were studied in adult beagles maintained at iodine intake levels ranging from 480 to 20 mug/day. On the basis of changes in radioiodine metabolism, the minimum daily iodine requirement of the adult beagle was found to be 140 mug. Although striking changes were observed in radioiodine metabolism when iodine intake was reduced to 90mug/day, serum T4 and T3 levels were unaffected. Marked reductions in serum T4 occurred in dogs restricted to an iodine intake of 50 or 20 mug/day, but even at these low levels of iodine intake there were only slight reductions in serum T3 concentration and a eumetabolic state was maintained. Prolonged iodine deficiency (8-12 months) resulted in variable patterns of thyroid histology, which were related to differences in thyroidal 127I content and in the rate of release of radioiodine from the thyroid. The heterogeneity in thyroid morphology and iodine kinetics did not, however, have a significant effect on serum T4 and T3 levels.