A Simple Solid-Phase Radioimmunoassay for Triiodothyronine

Dissociated thyroxine, triiodothyronine and reverse triiodothyronine levels in patients with familial goitre due to iodide organification defects

The thyroid function of patients with three different types of organification defect was studied. All patients were characterized by a high thyroidal 131I uptake and a positive perchlorate discharge. Patients with Pendred's syndrome who had goitre and congenital nerve deafness were mostly euthyroid with normal circulating thyroid hormone levels. Only two of them had compensated euthyroidism with elevated total T3, high basal TSH and delayed return to basal value with TRH. The patients who were euthyroid with large goitres and normal hearing had elevated total T3 and an exaggerated TSH response to TRH. The thyroid function of these two groups of patients contrasted with that of goitrous cretins, who were clinically hypothyroid with low circulating total T4, increased T3 and decreased rT3 levels. The data suggest that in patients with intrathyroidal iodine deficiency secondary to organification defect, there is preferential T3 production in an effort to maintain euthyroid state, and this is further substantiated in the case of gross thyroid insufficiency either by enhanced peripheral conversion of T4 to T3, or reduced metabolic clearance of T3 and increased clearance of rT3, resulting in elevated T3 and decreased rT3 levels.

Effects of heroin addiction on thyrotrophin, thyroid hormones and porlactin secretion in men

Pituitary-thyroid function in male heroin addicts and addicts after abstinence (ex-addicts) was studied and compared with that of healthy euthyroid men. In heroin addicts the increases in circulating total thyroxine and triiodothyronine levels were accompanied by an increase in the thyroid hormone uptake test. These changes may reflect a quantitative increase in thyroxine binding globulin. Reverse triiodothyronine concentrations in heroin addicts were normal. The thyrotrophin-releasing hormone elicited a diminished thyrotrophin response in heroin addicts which was significantly different from that in control subjects and ex-addicts. An elevation of serum prolactin was noted in heroin addicts, while ex-addicts had normal levels. Gradual recovery of pituitary-thyroid function occurred after heroin withdrawal.

The relationship between circadian variations in circulating thyrotrophin, thyroid hormones and prolactin

Half-hourly blood samples were taken from six clinically euthyroid men over a continuous period of 24 h. Their concentrations of total thyroxine (T4), total triiodothyronine (T3), thyrotrophin (TSH) and prolactin (PRL) were assessed together with the degree of unsaturation of thyroid hormone binding proteins as determined by the thyroid hormone uptake test (THUT). Both T3 and T4 were also measured in urine samples collected serially during the same 24 h period. Significant circadian changes in serum TSH, THUT, serum and urine T4 and serum PRL were demonstrated in all subjects. TSH showed a reciprocal pattern to serum T4, with higher levels during the evening and at night than the daytime. This TSH pattern did not coincide with PRL secretion. Further studies on the same subjects did not show any significant effect of posture, corticosteroid or T4 administration upon circadian changes in TSH. There appeared to be no consistent circadian changes in serum or urinary T3. It seems likely that the TSH circadian rhythm is centrally determined and that free T3 levels are maintained more or less constant by variation in peripheral conversion from T4.

Thyrotoxicosis: relations between clinical state and biochemical changes during carbimazole treatment

The relation between clinical and biochemical changes in thyrotoxicosis were studied in 12 patients with Graves's disease who were being treated with carbimazole. Clinical assessment (using the Crooks-Wayne index) was combined with the measurement of free thyroxine and triiodothyronine indices (FT4I and FT3I) and the assessment of two tissue markers of thyroid hormone action--sex-hormone-binding globulin (SHBG) levels and the thyrotrophin responses to TRH. In general the FT4I and FT3I fell rapidly once treatment was started, and returned to normal in one to four weeks, followed shortly by SHBG levels. The thyrotrophin response returned at this time in two patients, who still had borderline high levels of FT3I and SHBG. The clinical score fell more slowly and variably and was less closely related to any of the biochemical indices than these were to each other. During the early phase of treatment with antithyroid drug the clinical evaluation may be an unreliable indicator of persisting thyroid hormone excess, and when the patient seems clinically but not biochemically thyrotoxic the symptoms should be treated on their own merits with beta-blocking drugs and not with increased doses of antithyroid drugs.

Simple solid-phase radioimmunoassays for total tri-iodothyronine and thyroxine in serum, and their clinical evaluation

1. Simple solid-phase radioimmunoassay methods for total tri-iodothyronine and thyroxine in serum or plasma are described. By using antibodies that are covalently coupled to microcrystalline cellulose, virtually identical assay procedures can be used for the determination of both hormones. An alkaline sodium glycinate buffer provides better assay conditions than the buffers often recommended for thyroid hormone radioimmunoassay. 2. Assay results are unaffected by moderate sample haemolysis. Plasma samples stored at room temperature for more than nine days often show an apparent increase in concentration of both thyroid hormones. 3. Serum tri-iodothyronine and thyroxine concentrations in healthy euthyroid subjects, and in euthyroid pregnant women are reported. In a series of 100 consecutive patients referred to a thyroid clinic the tri-iodothyronine assay discriminated better than the thyroxine assay between hyperthyroid and euthyroid patients. The thyroxine assay was much better than the tri-iodothyronine assay in discriminating between hypothyroid and euthyroid patients.