No inhibition by Li+ of thyroxine monodeiodination to 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine (reverse triiodothyronine)

Minor signs and symptoms of toxicity in a young woman in spite of massive thyroxine ingestion

The serum concentrations of thyroxine, 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine were followed during nine days in a case of acute thyroxine intoxication. On admission the concentrations were 11-12 times, 5-6 times and 16 times the normal mean, respectively. There was a striking discrepancy between the high concentrations of active hormones and the minor clinical symptoms.

Thyroid disease and high concentration of serum thyrotrophin in a population sample of women. A 4-year follow-up

In a population study in Göteborg, Sweden, comprising women in the age strata 44, 52, 56, 60 and 66 years, serum thyrotrophin (S-TSH) was determined in 283 women representative of the general population of women of these ages. No women with previously unknown hypothyroidism were found at the clinical examination; 47 (3.7%) were on thyroxine treatment, 9 (0.7%) because of spontaneous hypothyroidism. Sixteen women (1.2%) had markedly elevated S-TSH concentration (less than 14 mU/l). They were studied further by determination of thyroid hormones and circulating antithyroid microsomal and thyroglobulin antibodies, and those with goiter were subjected to fine-needle biopsy of the thyroid gland. They were furthermore followed for four years. Four euthyroid women were given thyroxine because of goiter and abnormal laboratory test results. Of nine individuals with high S-TSH concentration as well as high titers of thyroid antibodies and/or biopsy evidence of autoimmune thyroiditis, seven became hypothyroid within the four years of follow-up. The other two women had consistently elevated basal S-TSH concentration and exaggerated S-TSH response after thyroliberin administration. We conclude that the majority of individuals without previously recognized thyroid disease who have S-TSH concentration above 14 mU/l with the assay used will require thyroxine therapy within a few years. In one woman, however, with multinodular colloid goiter and high titer of antimicrosomal antibodies, the basal S-TSH concentration decreased during follow-up to a high normal value; the S-TSH response to thyroliberin was high borderline. She remained euthyroid during follow-up. The results suggest an annual incidence of spontaneous hypothyroidism of 1-2 cases per 1000 middle-aged females in Swedish west-coast population.

The effects of drugs on tests of thyroid function

Many drugs affect tests of thyroid function through alterations in the synthesis, transport and metabolism of thyroid hormones, as well as via influences on thyrotrophin (TSH) synthesis and secretion. Despite effects on circulating thyroid hormone and TSH levels, few drugs result in important changes in clinical thyroid state, but difficulty in interpretation of thyroid function tests often results. Commonly prescribed drugs including anti-convulsants, non-steroidal anti-inflammatory drugs, beta-adrenoceptor antagonists, steroid hormones and heparin may result in abnormal thyroid function tests in the absence of clinical features of thyroid dysfunction. In contrast, lithium and iodine containing drugs, including radiographic contrast agents and amiodarone, may result rarely in overt thyroid disease.

Evidence for a slow tissue adaptation to circulating thyroxine in patients with chronic L-thyroxine treatment

We measured serum procollagen-III-peptide in 67 women with long-term L-thyroxine treatment and compared the results with age-matched controls. The strong correlation between serum free thyroxine and procollagen-III-peptide concentrations previously found after 6 months of L-thyroxine treatment was not found after long-term treatment. There were slightly higher procollagen-III-peptide concentration values in those chronically treated patients who had high free thyroxine levels but this increase was less marked than in patients previously studied after short-term treatment. An increase in procollagen-III-peptide concentration reflects an increased biosynthesis of collagen III, which is present in connective tissues throughout the body, and our findings may be explained by slow tissue adaptation to increased levels of thyroxine. We conclude that the increased thyroxine levels found in L-thyroxine-treated patients are of less clinical importance than thought previously. We also conclude that peripheral markers of thyroid hormone peripheral effects such as procollagen-III-peptide may be of less use than thought previously due to this slow tissue adaptation to changes in thyroxine concentration.

Urinary excretion of 3-methylhistidine and creatinine and plasma concentrations of amino acids in hyperthyroid patients following preoperative treatment with antithyroid drug or beta-blocking agent: results from a prospective, randomized study

The aim of this investigation was to compare the effects of a beta 1-selective adrenoceptor blocking agent and an antithyroid drug on urinary excretion of creatinine (Cr) and 3-methylhistidine (3-MH) and plasma concentrations of amino acids in hyperthyroid patients. beta-adrenoceptor blocking agents are increasingly used in the treatment of hyperthyroid patients, and the effects on clinical signs and symptoms mainly reflect beta 1-adrenoceptor blockade. The consequences of this treatment on metabolic alterations in hyperthyroidism are not fully known. In the present study, 30 hyperthyroid patients were randomized to preoperative treatment with the antithyroid drug methimazole + thyroxine (group I) or the beta 1-selective adrenoceptor blocking agent metoprolol (group II). Urinary excretion of Cr and 3-MH and plasma concentrations of amino acids were measured at the time of diagnosis, following preoperative treatment and 6 months postoperatively. Serum triiodothyronine (T3) was comparably elevated in the two groups of patients at the time of diagnosis and was normalized during preoperative treatment in group I but remained elevated during preoperative treatment in group II. Urinary excretion of creatinine was lower at the time of diagnosis than postoperatively, suggesting reduced muscle mass during hyperthyroidism. Urinary excretion of Cr increased during preoperative treatment in group I but was not significantly altered during treatment with metoprolol. The 3-MH/Cr ratio, which was higher at the time of diagnosis than postoperatively, indicating accelerated protein breakdown in skeletal muscle during hyperthyroidism, was reduced during preoperative treatment in group I but not in group II.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of thyroid hormone and beta-adrenoceptor blocking agents on urinary excretion of 3-methylhistidine and plasma amino acids in man

The aim of this investigation was to study the effect of beta-adrenoceptor blockade on alterations in protein metabolism induced by administration of 3,5,3'-triiodothyronine (T3) to man. Urinary excretion of 3-methylhistidine and plasma concentrations of amino acids were measured in seven healthy subjects following 1 weeks's administration of T3 alone or T3 in combination with the selective beta 1-adrenoceptor blocking agent metoprolol or the non-selective beta-adrenoceptor blocking agent propranolol. Urinary excretion of 3-methylhistidine and plasma concentrations of valine, methionine, lysine, tyrosine, phenylalanine, isoleucine, leucine, and total essential and branched chain amino acids increased following administration of T3, probably in part reflecting accelerated muscle proteolysis. Neither metoprolol nor propranolol normalized 3-methylhistidine excretion or plasma concentrations of amino acids during T3 treatment. The results indicate that metabolic alterations induced by T3 and giving rise to enhanced 3-methylhistidine excretion and elevated concentrations of plasma amino acids are not normalized by beta-adrenoceptor blockade.

The effect of beta-adrenergic blockade on the myopathic changes in experimental hyperthyroidism in rats

Hyperthyroidism is frequently associated with myopathy. Beta-blocking agents, which are increasingly used in the treatment of hyperthyroidism, have been reported to have a possible beneficial effect on thyrotoxic myopathy. We have studied the myopathic changes in experimental hyperthyroidism in rats and the effect of the beta-blocking agents metoprolol and propranolol on these changes. During experimental hyperthyroidism, conversion of type 1 to type 2 fibres and accumulation of intracellular lipid, increased amounts of mitochondria, and reduced size of muscle fibers were noticed. None of these changes were prevented by metoprolol or propranolol. The results indicate that histochemical and morphological changes in skeletal muscle induced by thyroid hormone are not mediated by beta-receptors. The results of this investigation make dubious a beneficial effect of beta-blocking agents on thyrotoxic myopathy.

Increased erythrocyte sodium efflux during overfeeding without evidence of mediation by circulating catecholamines or thyroid hormone

Ten slightly obese middle-aged men were instructed to increase their energy intake 25% during a period of 1 week, which was preceded by a control period of seven days. Body weight increased by 0.67 kg (SD 0.60) indicating good compliance with the regimen. Transmembrane sodium fluxes were determined with the use of 22Na. The pre-diet erythrocyte sodium content was 9.7 mmol/L (SD 0.8) decreasing to 8.9 mmol/L (SD 1.1) (P less than 0.05) during overfeeding. The Na-efflux rate constant increased from 0.40 h-1 to 0.54 h-1 (P less than 0.05). Urinary excretion of catecholamines and concentrations of catecholamines and insulin in plasma and of thyroxine, triiodothyronine, and reverse T3 in serum did not change. Thus, overfeeding seems to enhance the total Na efflux in erythrocytes from slightly obese men. There were no measurable changes in thyroid hormone or catecholamine levels leaving the regulatory mechanisms unexplained.

Glucose turnover, gluconeogenesis from glycerol, and estimation of net glucose cycling in cancer patients

A double isotope method was used in patients with progressive malignancy and in control patients to measure: glucose turnover, conversion rate of carbon skeleton of glycerol into glucose, and the interorgan cycling of glucose carbons (Cori-cycle plus alanine-glucose cycle). [U-14C]glycerol and [6-3H]glucose were given intravenously as a single dose injection. The time course of the specific radioactivities of [6-3H] and [U-14C]glucose was followed in blood. The pool size and the turnover rate of glucose were increased in the cancer group as compared with the control patients. The net recycling of glucose carbons was not increased in the cancer group, despite the increased turnover of glucose. The alterations in the metabolism of glucose did not correlate with the plasma levels of insulin or thyroid hormones (T4, T3, rT3) neither in the entire cancer group nor in those cancer patients who were repeatedly investigated at different intervals of time. The turnover rate of glucose in the cancer patients correlated inversely to their body weight index. The gluconeogenesis rate, given as the fractional conversion rate of the injected radioactive dose of [14C]glycerol, or as mol glucose . kg body weight-1 . day-1, was increased in the cancer group, but still contributed only 3% of the glucose turnover rate in both cancer and control patients. We conclude that an increased gluconeogenesis from glycerol is not significant in terms of energy expenditure in patients with progressive malignancy, as has previously been concluded for the gluconeogenesis from alanine. It seems that increased turnover of glucose may contribute to inappropriately high energy expenditure in cancer patients.

Lithium therapy and thyroid function: a long-term study

Seventy-three patients who had been continuously receiving lithium carbonate for 6 months or more had their thyroid function evaluated clinically and biochemically. Goitre was found in 37%, exophthalmos in 23%, positive thyroid auto-antibodies in 24% and abnormal TRH tests in 49%. It would appear that thyroid failure due to lithium is usually dependent on antibody mediated damage. It is unlikely that lithium has a direct effect on the hypothalamic-pituitary axis.