Thyroid Myopathies and the affects of Thyroid Hormone on different fibers

Thyroid Myopathies and the affects of Thyroid Hormone on different fibers

Introduction

Thyroid hormone is a classic endocrine hormone that regulates gene expression by binding to nuclear receptors, controlling multiple physiological processes including metabolism, growth, development, and central nervous system function (1). Thyroid hormone is biosynthesized from tyrosine and is initially produced in the tetraiodinated form thyroxine, or T4, which is then deiodinated to the triiodothyronine T3, which is the active form of the hormone (Figure 1), having greater affinity for the thyroid hormone nuclear receptors (2, 3). By binding to and activating thyroid hormone receptors that regulate transcription of T3-responsive genes, T3 increases basal metabolism, heart rate and contractility, blood flow to peripheral tissues, cholesterol metabolism, lipolysis, and body temperature (4). Although thyroid hormone has been studied for decades and is well-known in the basic science and medical community, the recent discovery of a class of thyroid hormone metabolites known as thyronamines (5) is greatly expanding the potential physiological roles and regulation of thyroid endocrinology.

Thyronamines are decarboxylated derivatives of T4 and iodothyronines (Figure 2). One of these thyronamines, 3-iodothyronamine (T1AM), is a biogenic amine that is found in vertebrate tissues as well as in the circulatory system, and has physiological effects opposite those of thyroid hormone (Figure 3). Intraperitoneal injection of T1AM into mice results in profound hypothermia and bradycardia within minutes, a time scale too rapid to be explained by a transcriptional mechanism (5). In addition, T1AM administration rapidly induces hyperglycemia in mice (6) and triggers a shift in fuel usage toward lipids and away from carbohydrates in both mice and Siberian hamsters (7). Interestingly, while thyroid hormone exerts most of its actions over a period of hours to days, certain rapidly occurring effects of thyroid hormone have been reported but remain poorly understood at the molecular level (8, 9). One intriguing possibility is that these effects are actually due to the rapid, non-transcriptional effects of T1AM and may be a novel mechanism for regulation of thyroid hormone function in response to constantly changing physiological conditions.

Discussion

Thyroid Hormone on different fibers

The muscle maladies of hyperthyroidism were distinguished and incorporate exophthalmic opthalmoplegia, thyrotoxic myopathy, myasthenia gravis and intermittent loss of motion. In hyperthyroidism, 67% patients had neuromuscular side effects, 62% patients had clinical shortcoming in no less than one muscle bunch that connected with free thyroxine (T4) fixations. The clinical indications of perpetual thyrotoxic myopathy are described by dynamic shortcoming in proximal muscles, decay and squandering. Bulbar or respiratory muscle side effects are uncommon. The system of thyrotoxic myopathy is misty. By and large, electromyographic anomalies non-particular and routine histopathological examination demonstrates non-particular changes in muscle biopsy and a few patients have an expanded recurrence of sort 2 fibers. In any case, just not many instances of thyrotoxic myopathy with compelling strength of sort 2 fibers in muscle histological finding have been accounted for. The muscle maladies of hyperthyroidism were distinguished and incorporate exophthalmic opthalmoplegia, thyrotoxic myopathy, myasthenia ...