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Kinetics of the Human Thyroid Trap: Experience in Normal Subjects and in Thyroid Disease

VA Central Office, Washington, D.C.
VA Hospitals, Buffalo, New York and Washington, D.C.

Correspondence: For reprints contact: Marguerite Hays, Dept. of Medicine and Surgery, V.A. Central Office (151), 810 Vermont Avenue, N.W., Washington, D.C. 20420.

ABSTRACT

Kinetics of the thyroid pertechnetate trap were assessed in 85 studies of 39 normal subjects, in five untreated patients with Graves' disease (two of them both before and after treatment), in two hypothyroid patients, and in one patient each with Hashimoto's thyroiditis of recent onset, subacute thyroiditis, and massive anaplastic carcinoma. In normal subjects, the effects of sex, time of day, and the order of experimental sessions were studied. For the analysis, a three-compartment model was assumed for all studies. Data on thyroidal and neck-background pertechnetate were collected with a multi-crystal camera during 40 min after i.v. injection. Input to the two thyroidal compartments in the model—the follicular cell, V₂, and the colloidal plasma-equivalent space, V₃—is a multi-exponential function of plasma radioactivity, V₁, which was measured frequently. None of the model parameters was systematically affected by the sex of the subject, and order of session did not consistently alter any parameter, except for V₃, which was greater in session 2 than in session 1. That increase was not consistent among data subsets, however, and is believed to be spurious. Time of day affected only the exit rate constant from the colloid, ₂₃, which is increased later in the day (P<0.02). Distribution of the normal parameters was more nearly log-normal than normal. After 5% were excluded at the high end and 5% at the low end, the range for a parameter, p, was found empirically to be: antiln (mean ln p - 1.7 s.d. ln p), and antiln (mean ln p + 1.5 s.d. ln p). In Graves' disease, V₂ is increased (P<0.02), but the increases in V₃ and in ₂₁ (the clearance into the thyroid from serum) are much more dramatic (P<10^–8). After treatment, V₃ and ₂₁ fell toward normal. The hypothyroid patients showed no trap activity, and the trap was normal in the patient with early Hashimoto's thyroiditis. The patients with subacute thyroiditis and with anaplastic carcinoma had increases in V₂ V₃, and ₂₁, but the pattern differed from that seen in Graves' disease.