Normal iodide efflux from nonfunctioning nodules of human thyroid glands.

The kinetics of iodide efflux were studied in four benign thyroid nodules and one carcinoma by observing the fractional rate of radioiodide release from slices prelabeled in vitro. The thyroid:medium ratio for iodide (T:M) of the benign nodular tissue was 1.9 +/- 0.3 (mean +/- SE) with a value of 9.1 +/- 3.3 obtained from adjacent normal tissue. Despite the reduction in iodide concentrating activity, the rate constant for iodide efflux (ko) from the nonfunctioning, benign thyroid nodular tissue (0.112 +/- 0.044 min-1) was not significantly different as compared to normal tissue (0.102 +/- 0.033 min-1). In a papillary carcinoma, the efflux of radioactive iodide appeared markedly enhanced. These studies indicate that in non-functioning, benign thyroid adenomas, the reduction in iodide concentrating activity is not the consequence of an increased iodide efflux.