Thyroxine

Also known as:  L-Thyroxine;  Levothyroxine;  T4;  Oroxine;  Thyroxin;  Tetraiodothyronine

Thyroxine is the primary Hormone synthesized and secreted by the Thyroid Gland - Thyroxine comprises 80% of the Thyroid Hormone secretions.  Thyroxine is less potent than Triiodothyronine (T3).

Thyroxine is the second most prescribed Pharmaceutical Drug (based on the number of prescriptions dispensed in the USA during 1999).

Other functions of Thyroxine are listed in the topic for Thyroid Hormones.  Most of the functions of Thyroxine occur after it has been converted within the body to Triiodothyronine (T3).

Cardiovascular System

 Thyroxine may help to prevent Cardiovascular Diseases:  ^[1]

 Thyroxine may help to prevent Atherosclerosis.  ^[2]

 Thyroxine may improve Heart function in Hypothyroidism patients.  ^[3]

Metabolism

 Thyroxine may help to control the body's Basal Metabolism (BMR).  ^[4]

 Hypothyroidism occurs as a result of low Thyroxine levels and supplemental Thyroxine is used for the treatment of Hypothyroidism.  ^[5]

Metabolism

 Thyroxine (Percutacrine Thyroxinique applied topically) is used in France to stimulate weight loss in specific areas of the body (in persons afflicted with Obesity) and is reported to be very effective. 

Hormones

 Some of the body’s Thyroxine content is converted to Triiodothyronine (T3).  ^[6]

Proteins

 Thyroxine accelerates the synthesis and breakdown of Proteins - Endogenous.  ^[7]

Amino Acids

 Thyroxine may lower elevated Homocysteine levels (especially in Hypothyroidism patients).  ^[8]

Amino Acids

 Tyrosine is an essential cofactor (along with Iodine) for the production of Thyroxine within the body - Tyrosine comprises 35% of Thyroxine.  ^[9]

Electromagnetic Radiation

 Sunlight may stimulate the production of Thyroxine. 

Enzymes

 5'-Deiodinase catalyzes the conversion of Thyroxine to Triiodothyronine (or Reverse T3).

Minerals

 Iodine is a cofactor for the production of Thyroxine from Tyrosine.  ^[10]

Polyphenols

 Genistein may enhance the production of Thyroxine.  ^[11]

Proteins

 Thyroid Binding Globulin (TBG) binds to and functions as a storage vehicle for 99.6% of the body's Thyroxine within the Thyroid Gland (i.e. only 0.4% of the body's Thyroxine exists in its "free" state).  ^[12]

Thyroid Hormone Precursors

 Thyrotrophin (released by the Pituitary Gland) stimulates the secretion of Thyroxine from the Thyroid Gland - this activity is under the control of a Negative Feedback Mechanism.  ^[13]