The T4/TBG ratio and the investigation of thyroid function

The relationship between serum thyroxine (T4) and thyroxine-binding globulin (TBG) has been studied in "euthyroid" subjects. The T4/TBG ratios in these subjects has been calculated and compared with those found in patients suffering from myxoedema and thyrotoxicosis. The ratio allows a more precise selection of the borderline cases requiring Thyroid Stimulating Hormone and triiodothyronine assays, particularly when the serum TBG is raised or lowered.

Correlation of free thyroxine index and thyroxine: thyroxine-binding globulin ratio with the free thyroxine concentration as measured by the thyroxine and thyroxine-binding globulin radioimmunoassays

The concentration of thyroxine-binding globulin in the serum can now be measured by a simple and specific radioimmunoassay. Triiodothyronine uptake and measurement of total thyroxine have been combined to yield a free thyroxine index which has been found to correlate with the clinical state of the patients. An estimate of the free thyroxine concentration, as measured by the thyroxine and thyroxine-binding globulin radioimmunoassays, provided a good correlation with the free thyroxine index and the thyroxine: thyroxine-binding globulin ratio. However, the thyroxine: thyroxine-binding globulin ratio is inaccurate when thyroxine-binding globulin concentrations are high or low.

Myxedema coma and normal serum thyroxine

A 76-year-old man who developed the clinical syndrome of myxedema coma was found to have a normal serum thyroxine concentration. Further investigation revealed the presence of a low serum T3 level before and after sodium levothyroxine therapy when the serum T4 value was in the hyperthyroid range. In addition, he demonstrated an inability to release TSH after intravenous administration of TRH and was found to have an enlarged sella turcica. A partial defect in peripheral conversion of T4 to T3 is postulated.

Stimulation of fibroblast biosynthetic activity by serum of patients with pretibial myxedema

Skin fibroblasts from the shoulder and lower extremities of normal individuals, as well as from patients with pretibial myxedema (PTM) were grown in culture. When cells reached the monolayer stage, they were labeled with 3H-glucosamine and tested for hyaluronic acid synthesis in the presence of either serum from PTM patients or normal human serum. All the fibroblasts from the pretibial area synthesized 2 to 3 times more hyaluronic acid when incubated with PTM sera than when incubated in normal human serum. Fibroblasts cultured from skin of the back or prepuce did not respond to PTM sera. This heat-stable, protease-sensitive, and dialyzable, fibroblast-stimulating factor is not a 7S gamma-globulin. The enhanced sensitivity to PTM sera exhibited by fibroblasts from the lower extremities may explain why the lesions in this disease are restricted primarily to that area.

The role of vasopressin in the impaired water excretion of myxedema

The plasma vasopressin response to acute water ingestion was evaluated in 20 patients with myxedema prior to definitive treatment and in eight of these same patients following therapy of their hypothyroidism. Vasopressin levels were elevated and failed to completely suppress following water ingestion in 15 subjects (75 per cent). Two hypothyroid patients with elevated plasma vasopressin levels (10 per cent) had a normal renal response to the water challenge suggesting partial end organ hormonal unresponsiveness. In three (15 per cent) of the five patients with suppressible vasopressin, water excretion was impaired indicating a nonvasopressin-mediated renal defect. In eight patients restudied after achievement of a euthyroid state, vasopressin inhibition and urinary excretion were normal following the oral water load. Although intrinsic renal changes in the hypothyroid state may contribute to the observed defect in water diuresis, the present study suggests a role of endogenous vasopressin in this disorder.

Myxoedema coma. A review

Myxoedema coma is a rare emergency needing prompt recognition and urgent treatment before diagnostic confirmation. The pathyphysiology, clinical features, differential diagnosis, investigations and treatment are described. Triiodothyronine in small doses intravenously with continuous cardiac monitoring is suggested. Slow rewarming, care of the airway and prompt treatment of hypoventilation by assisted ventilation, the use of hydrocortisone and the avoidance of sedatives, vasopressors and overloading are also discussed, as is prevention. This emergency occurs in elderly people often with co-existent disease and thus only close attention to detail will be rewarded with improving results and falling mortality figures.

Protein binding of cardiac glycosides in disease states

Digitoxin in 97% bound to serum albumin and digoxin only to the extent of 24%. Hypoalbuminaemia significantly changes the protein binding of digoxin in Kwashorkor serum and the binding of digitoxin in patients with chronic active hepatitis and the nephrotic syndrome. Sprue patiens with normal albumin values have normal binding of digitoxin. Preliminary data in patients with thyrotoxicosis and myxoedema show digitoxin binding within the normal range. The effect of uraemia per se on digitoxin binding is controversial as both normal and slightly decreased values have been reported. In uraemic patients on treatment with haemodialysis, heparin administration has been shown to be a powerful serum binding displacing agent for both digitoxin and digoxin, the mechanism probably being a heparin-induced release of free fatty acids. Patients with a significant decrease in serum protein binding of digitoxin or digoxin should be maintained on a total serum concentration lower than usually considered within the therapeutic range.

Rapid diagnosis of thyroid disease using carbonic-anhydrase immunoassay

Erythrocyte carbonic-anhydrase-I (C.A.I.) concentration was measured by radial immunodiffusion in 30 thyrotoxic patients and 15 myxoedemic patients, the results being compared with those found in a control group of 90 euthyroid individuals. In thyrotoxicosis the erythrocyte-C.A.I. concentration was found to be below 10-29 mg/g haemoglobin, whereas the normal range varied from 11-1 to 22-5 mg C.A.I./g Hb. Low values were found in 4 patients with triiodothyronine(T3)-toxicosis. In myxoedema, the mean erythrocyte-C.A.I. concentration, though elevated at 20-37 mg/g Hb, fell within the normal range. In pregnancy, the erythrocyte-C.A.I. concentration rose with time, the mean value at tern being 20-6 +/-S.D. 3-3 mg/g Hb. In a group of women taking oral contraceptives, a low erythrocyte-C.A.I. concentration was noted--an effect which was most obvious among those taking low-oestrogen contraceptives. It is suggested that erythrocyte-C.A.I. estimation provdes a rapid screening test for thyrotoxicosis.

The separation of plasma lipoproteins using gel electrofocusing and polyacrylamide gradient gel electrophoresis

Polyacrylamide gel electrofocusing and gradient electrophoresis have been used to separate the lipoproteins in whole plasma and in fractions prepared by sequential flotation in the ultracentrifuge and by precipitation with dextran sulphate and manganous chloride. After the two-dimensional separation, high density lipoproteins appear as a zone showing noticeable heterogeneity with respect to both isoelectric point and molecular weight. Low density lipoproteins are resolved as a compact spot while very low density lipoproteins are visible as a long horizontal streak across the top of the electrophoresis gel. The implications of the technique for the analysis of lipoprotein patterns in pathological plasmas are discussed.

Two patients with premyxoedema

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[Assay of serum creatine phosphokinase in primary hypothyroidism. Comparison with other thyroid gland function tests in 32 cases. Value of isoenzyme studies]

Serum-creatine phosphokinase levels were measured in 32 cases of primary hypothyroidism in adults and compared with the results of other thyroid function test. C.P.K. elevation appeared to be almost completely uniform (31 out of 32 cases) and marked, reaching six times the normal value. This elevation is more marked in 18 myxoedematous patients than in 14 with those with hypothyroidism of mixed aetiology. Close correlation does not seem to exist between the elevation of C.P.K. and the lowering of serum thyroxine. The elevation of C.P.K. above the upper limits of normal seemed more constant than lengthening of the achilles reflex time, a rise in serum cholesterol, or a rise in other enzymes of muscular origin, such as the glutampopyruvic and glutamo-oxalocetic transaminases, lactodehydrogenase and hydroxybutyric dehydrogenase. In 8 cases of hypothyroidism, the isoenzymic study of serum C.P.K. by electrophoresis on cellulose acetate confirmed that the molecular structure was of the muscle type MM. The advantage of such a study shows that a structure MB found in the case of myocardial infarction in a patient with hypothyroidism deserves to be stressed.

[Prolactinemia in primary hypothyroïdism : basal and dynamic studies--signification of galactorrhea associated with myxedema (author's transl)]

PRL and TSH were measured by radioimmuno-assay in 14 persons wth myxoedema aged 16 to 65 years. Three of them had galactorrhea. In 13 patients the circadian rhythm of PRL was studied, and in 8 patients PRL was measured after TRH administration. All these patients have a high value of serum TSH, with a mean value +/- SEM of 29,4 (24,3 - 35,6) mU/ml. Values of serum PRL were comprised in normal ranges with a mean value +/- SEM of 126(196 - 238) mU/ml. The circadian rhythm of PRL is not altered, since mean values of serum PRL are more elevated at 4 am than 8 am with highly statistical significance. After THR administration the PRL response is normal or exaggerated.