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Autonomous Thyroid Nodules. II. Double Labeling with Iodide Isotopes and Study of Biochemical Constituents of Nodular and Paranodular Tissues

Hospital das Clínicas, University of São Paulo Medical School, and the Radioisotope Laboratory, Institute of Atomic Energy, São Paulo, Brasil

Correspondence: For reprints contact: Geraldo A. Medeiros-Neto, Hospital das Clínicas, Caixa Postal-8091, São Paulo, Brasil.

ABSTRACT

A tracer of ¹²⁵I was administered 3–5 weeks before surgery to ten euthyroid patients with an autonomous solitary thyroid nodule followed by another dose of ¹³¹I 24 hr prior to surgery. The following results were obtained:

1. The concentration of ¹³¹I was higher in the nodular tissue than in the paranodular tissue, but the latter had three times more ¹²⁵I label than the former.

2. The concentration of thyroglobulin per milliliter of nodular homogenate was significantly reduced when compared with the results obtained for the surrounding tissue.

3. The content in the thyroglobulin molecule was evaluated for each isotope. For ¹³¹I the ratio between the nodular and paranodular tissue was 2.8 in 24 hr, but after 3–5 weeks of labeling with ¹²⁵I the surrounding tissue had more label per milligram of thyroglobulin than the nodular tissue.

4. A higher value for the relative concentration of T₃ + T₄ in the nodular tissue at 24 hr was obtained when compared with the same parameter at 3–5 weeks of labeling. Conversely, for the paranodular tissue it was observed that the relative proportion of T₃ + T₄ increased with time with a higher percentage at the ¹²⁵I peak compared with the ¹³¹I peak.

5. The total amount in milligrams of protein per unit of weight in grams of nodular tissue (90.8 ± 9.8) was significantly lower than in the paranodular specimen. There was a significantly higher value for RNA in the former specimen than in the latter, but no difference was found in the DNA-phosphorus content of the two tissues. An increased protein synthesis or turnover is suggested for the nodular tissue by the elevated RNA/DNA ratio found in this tissue. It was concluded that the degree of function per follicle cell of the nodular tissue is considerably greater than the normal thyroid cell in respect either to iodine metabolism or protein biosynthesis, but that to a certain extent the paranodular tissue function is not entirely suppressed.