Possible importance of thyroidal iodine compartments in the adaptation of thyroid hormone secretion to antithyroid drugs.

Abstract

Rats with either normal thyroid glands, hyperplastic goiters or colloid goiters were given 125I in the drinking water for 28 days. A single injection of 131I was then given and 4 hr later further hormone biosynthesis was blocked with propylthiouracil. During the following seven days the various isotopes of protein-bound iodine (PBI) in serum were measured. In rats with normal glands, the 131I-PBI derived from the young label declined rapidly while the 127I-PBI stayed nearly constant. The 125I-PBI (old label) declined at an intermediate rate. In hyperplastic goiters the 131I-PBI and the 125I-PBI declined at the same rate and only slightly faster than the 127I-PBI. In colloid goiters the 127I-PBI and the 125I-PBI declined very little and at an identical slow rate, while the 131I-PBI concentration dropped nearly at the same fast rate as in normal glands and in hyperplastic goiters. The data suggest that the two labels are distributed in different compartments of intrathyroidal hormone. The young label (131I)...