Abstract
Levothyroxine (T4) is a synthetic form of the endogenous thyroid hormone thyroxine, responsible for regulating metabolism, energy production, and cellular growth. It is commonly studied in endocrine, metabolic, and mitochondrial research to explore the effects of thyroid hormone modulation on lipid metabolism, protein synthesis, and basal metabolic rate.
Although approved clinically for hypothyroidism, the research-grade compound is used for in vitro and in vivo laboratory applications only, under controlled and regulated settings.
Chemical Information
- Chemical Name: Levothyroxine Sodium
- Synonyms: L-Thyroxine Sodium, T4, L-3,3’,5,5’-Tetraiodothyronine
- Chemical Formula: C₁₅H₁₀I₄NO₄Na
- Molecular Weight: 799.86 g/mol
- CAS Number: 25416-65-3
- IUPAC Name: Sodium (2S)-2-amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoate
Mechanism of Action
T4 is a prohormone that serves as the precursor to triiodothyronine (T3), the biologically active thyroid hormone.
When converted by the enzyme 5’-deiodinase, T4 influences numerous physiological processes:
- Increased mitochondrial biogenesis
- Enhanced basal metabolic rate through ATP production
- Regulation of carbohydrate and lipid metabolism
- Upregulation of protein synthesis
- Thermogenic activity in brown adipose tissue
At the cellular level, T4 binds to nuclear thyroid hormone receptors (TRα and TRβ), leading to gene transcription that affects metabolic and growth-related pathways.
Pharmacodynamics
| Parameter | Description |
|---|---|
| Receptor Targets | Thyroid hormone nuclear receptors (TRα, TRβ) |
| Primary Action | Increases metabolic rate and mitochondrial activity |
| Conversion | Peripheral deiodination to T3 (active form) |
| Biological Effects | Enhances lipolysis, glycogenolysis, and oxygen consumption |
| Duration of Effect | Long half-life (~7 days in human physiology; varies by model) |
Pharmacokinetics (Preclinical Context)
| Characteristic | Description |
|---|---|
| Absorption | Complete absorption in oral studies (70–80%) |
| Distribution | Binds strongly to plasma proteins (thyroxine-binding globulin, albumin) |
| Metabolism | Hepatic and peripheral deiodination to T3 |
| Excretion | Renal and fecal (after conjugation) |
| Half-life | ~6–7 days (species-dependent) |
Research Applications
- Endocrine Research: Understanding thyroid hormone signaling and regulation.
- Metabolic Studies: Evaluating effects on basal metabolic rate and energy turnover.
- Mitochondrial Function: T4’s role in mitochondrial respiration and oxidative metabolism.
- Obesity and Lipid Research: Studying thyroid modulation in lipid mobilization.
- Gene Regulation Studies: Exploring thyroid receptor–mediated transcriptional activity.
T4 in Body Composition and Metabolic Research
While Levothyroxine is not approved for human enhancement or bodybuilding, it is studied in research models for:
- Thermogenic effects (increased heat production and calorie expenditure)
- Regulation of fat oxidation and glucose metabolism
- Synergistic interactions with adrenergic agonists (in research settings only)
These effects are purely mechanistic and not intended or approved for clinical or personal use.
Representative Research
1. Brent GA.
Mechanisms of thyroid hormone action. J Clin Invest. 2012;122(9):3035–3043. PubMed: 22945636
2. Mullur R, Liu YY, Brent GA.
Thyroid hormone regulation of metabolism. Physiol Rev. 2014;94(2):355–382. PubMed: 24692351
3. McAninch EA, Bianco AC.
Thyroid hormone signaling in energy homeostasis and lipid metabolism. Biochim Biophys Acta. 2014;1842(10):1454–1463. PubMed: 24722378
Safety and Regulatory Status
- Levothyroxine Sodium (T4) is FDA-approved only as a prescription medication for diagnosed hypothyroidism.
- Research-grade T4 is for in vitro and laboratory research only.
- Improper use may cause thyrotoxicosis, characterized by tachycardia, anxiety, muscle loss, and cardiac strain.
- Use only under controlled research conditions compliant with Good Laboratory Practice (GLP).
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Meta Description (SEO Optimized):
Levothyroxine Sodium (T4, CAS 25416-65-3) is a thyroid hormone analog studied for its role in metabolism, energy regulation, and mitochondrial function. For research use only.
10 Frequently Asked Questions (FAQ)
1. What is T4 (Levothyroxine)?
T4 is a synthetic version of the natural thyroid hormone thyroxine, used in research to study metabolism and cellular energy regulation.
2. What is T4’s CAS number?
25416-65-3
3. How does T4 work in the body?
T4 converts to T3 in tissues, activating thyroid receptors that regulate gene expression and metabolic rate.
4. Is T4 used in bodybuilding?
It is not approved for bodybuilding or weight loss; studied only for metabolic regulation in research.
5. What are T4’s research applications?
Used in studies involving thyroid hormone signaling, metabolism, and mitochondrial energy systems.
6. What receptors does T4 act on?
Nuclear thyroid hormone receptors TRα and TRβ.
7. Is T4 a stimulant?
No. Its effects are hormonal, influencing metabolism indirectly via thyroid receptor activation.
8. How is T4 different from T3?
T4 is a prohormone; T3 is the active form that binds more strongly to thyroid receptors.
9. Can T4 affect fat metabolism?
In research settings, T4 modulates lipolysis and energy expenditure, but it is not a weight-loss compound.
10. Is T4 legal to buy for research?
Yes, Levothyroxine Sodium is available from certified laboratories for research use only—not for human consumption.
Disclaimer
This document is for scientific and educational purposes only.
Levothyroxine Sodium (T4) is a research chemical, not approved for human or veterinary use outside licensed clinical prescription contexts.
