Low Thyroid Hormone Research Articles

Myopathy: As an Initial Presentation of Hypothyroidism in Two cases of Autoimmune Thyroiditis

Although hypothyroidism may cause a wide range of muscle disturbances, an overt myopathy may rarely present as an isolated initial presentation of hypothyroidism. The frequency of myopathy in hypothyroidism ranges from 30 to 80%. The major muscular symptoms are weakness, muscular cramps and myalgia. Laboratorial investigation generally shows increased levels of muscle enzymes and low serum thyroid hormones, with high thyrotrophic-stimulating hormone (TSH) elevated. The electrophysiological study reveals myopathy, neuropathy or mixed pattern. The treatment consists in hormone replacement and the prognosis is good in most of the cases. We report two cases that developed cramps, myalgia, and weakness, one of them presented as a polymyositis-like syndrome. The muscle enzymes were increased with a raised level of TSH. The myopathy was the initial manifestation of hypothyroidism in these cases. Both the patient was treated by replacement of thyroxin with significant clinical and biochemical improvement. DOI = 10.3329/jom.v8i1.1379 J MEDICINE 2007; 8 : 32-36

Thyroxine-enhanced oxidative phosphorylation of rat-liver mitochondria

Documentation of profound changes in serum thyroid hormone concentrations associated with cardiac arrest and resuscitation, as well as other acute emergencies, have spurred evaluation of possible therapeutic thyroid hormone administration. Acute and significant, this state, characterized by abnormally low serum thyroid hormone concentrations, may indicate selective thyroid replacement therapy. In a previous investigation, post-resuscitation infusion of levothyroxine sodium (L-T4) to normalize serum 3,5,3′-triiodothyronine (T3) concentrations was associated with significant reduction of neurologic deficit caused by severe global cerebral ischemia. Since L-T4 has been reported to act directly or via one of its metabolites, most likely T3, this most active form of thyroid hormone was tested. When L-T4 reduced the neurologic deficit, an increase in 3,3′,5′-triiodothyronine (rT3) was also observed. This study therefore determined whether a post-resuscitation treatment with either T3 (n = 8) or rT3 (n = 8) provided protection against global cerebral ischemia comparable to that of L-T4. Global cerebral ischemia was achieved with 9 min of ventricular fibrillation. Following resuscitation, one of three solutions (saline group as a control) was infused for 24 h at rates that reproduced the normal serum T3 concentrations or the rT3 concentrations achieved previously during the L-T4 therapy. The successful elevation of T3 and mimicking rT3 concentrations was assessed and confirmed by radioimmunoassay (RIA). In addition, TSH levels were measured by a novel RIA specific for canine thyroid-stimulating hormone (cTSH). Neurologic deficit was assessed with a well-standardized neurologic deficit examination. In contrast to previous studies using L-T4 infusion, no significant reduction of neurologic deficit was observed. Serum thyroid hormone changes confirmed previously described decreases and in no case did changes in cTSH appear causal in these changes. Thus, we concluded that L-T4 may offer a therapeutic advantage over T3 or rT3.

Thyroid iodine metabolism following partial thyroidectomy in the rat.

Compensatory thyroid hypertrophy, and thyroid iodine metabolism havebeen studied following hemi- and three-quarter thyroidectomy in the rat. Animals have been studied at different time intervals and at two environmental temperatures, 21° and 26° C. The increase in thyroid remnant weight which follows partial thyroidectomy is accompanied by an increase in iodide-trapping ability (thyroid/scrum ratio), and a more rapid turnover of iodine in the thyroid gland. These changes appear to be a good measure of activation of the thyroid remnant after partial thyroidectomy. DURING the course of a study of hypothalamic influences on the pituitary-thyroid axis it became necessary to standardize techniques in the rat for the measurement of the pituitary thyrotrophic hormone (TSH) response to lowered blood thyroid hormone levels. The classical method for studying this response is the demonstration of regeneration of the thyroid gland after partial thyroidectomy. In the following experiments, this method has been further...

THE RELATIONSHIP OF THE THYROID GLAND TO MUSCULAR WORK PERFORMED BY THE ALBINO RAT

1. Muscular work performed by the sciatic nerve‐gastrocnemius muscle preparation in the anæthetised rat is recorded when normal, high, and low thyroid hormone levels are present.2. Hypothyroid animals performed less work than normal animals.3. Hyperthyroid animals performed less work than normal animals.4. Thyroidectomized animals, with iodine added to the diet, performed work at a rate not significantly different from normal animals.5. All animals on which thyroidectomy had been performed, showed a phase of sustained contraction, lasting ¼ to 2 hours, at the commencement of the experiment. This phase was not due to hypocalcæmia, and possibly was not due to defective neuro‐muscular transmission.6. No animal, normal or abnormal in thyroid metabolism under the conditions stated, showed muscular fatigue during the twenty hours of the experiment.