T3 Catalog Description (100mcg/ml, 60ml)
T3, marketed as Cytomel and also called liothyronine is a synthetic version of the body’s most potent thyroid hormone, triiodothyronine. Liothyronine, the exogenous form of the hormone, is used to treat thyroid deficiency (hypothyroidism). Notable effects include increased basal metabolic rate (BMR), increased protein synthesis including muscle protein synthesis (MPS), and increased sensitivity to catecholamines. Thyroid hormones such as liothyronine and thyroxine (also called T4 or levothyroxine) play a critical role in many physiological processes such as cell growth and differentiation, macronutrient metabolism, cellular energy production, and physiological growth and development. Compared to T4, T3 is faster-acting and has a shorter half-life; this may be due to decreased plasma protein binding to globulins. Compared to liothyronine, thyroxine is approximately 3 times more potent orally, but their relative potency can vary by individual as well as by measurement method.
In the healthy human body with proper thyroid function (euthyroidism), a hypothalamic hormone called thyrotropin releasing hormone (TRH) is released due to a closed feedback-control loop (initiated when blood levels of T3 and T4 drop); TRH induces release of thyroid stimulating hormone (TSH or thyrotropin) from the pituitary, which stimulates the thyroid gland to produce thyroid hormone, primarily T4. In the feedback loop, elevated levels of T3 and T4 in blood plasma halt release of TRH/TSH. This feedback system is collectively known as the hypothalamic-pituitary-thyroid axis. Local deiodination, an enzymatic process controlled by peripheral factors as well as TSH levels, converts T4 to the more-potent T3 “on demand.”
Typical factors contributing to low thyroid hormone levels, diminished functionality, and peripheral issues include iodine deficiency or excess, selenium deficiency, organic issues in one or more portions of the hypothalamic-pituitary-thyroid axis, and illness.
Hypothyroidism is safely and effectively treated with exogenous hormone replacement after a simple diagnostic test of TSH levels (Todd et al, 2009):
Thyroid diseases are common, and most can be safely and effectively managed in primary care. Two of the most common reasons for thyroid function testing are fatigue and obesity, but the vast majority of affected patients do not have hypothyroidism. There is no plausible basis for the assertion that hypothyroidism commonly occurs despite normal thyroid function tests. In primary hypothyroidism all patients, except the elderly and those with ischaemic heart disease, can safely be started on a full replacement dose of thyroxine; the aim is to restore thyroid stimulating hormone (TSH) to normal
The therapeutic benefit of treating hypothyroidism with exogenous administration of thyroid hormones is significant, especially in otherwise-healthy patients; improvement is noted in measures of heart rate variability (sympathetic/parasympathetic activity), physical strength, posture, blood pressure, and lipid parameters.
"Drug Description: Cytomel." RxList.
"Mechanism of Action and Physiologic Effects of Thyroid Hormones." Colorado State University.
Sawin CT, Hershman JM, Chopra IJ. The comparative effect of T4 and T3 on the TSH response to TRH in young adult men. J Clin Endocrinol Metab. 1977 Feb;44(2):273-8.
Köhrle J, Gärtner R. Selenium and Thyroid. Best Pract Res Clin Endocrinol Metab. 23(6):815-27. Review. 2009.
Todd CH. Management of thyroid disorders in primary care: challenges and controversies. Postgrad Med J. 85(1010):655-9. 2009
Lakshmi V, Vaney N, Madhu SV. Effect of thyroxine therapy on autonomic status in hypothyroid patients. Indian J Physiol Pharmacology. 53(3):219-26.2009.