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Questions and Answers
Which isomer of compound 1 (L-T4) is listed in the table?
L-Ala
L-isomers of T4 and T3 are more potent than _____ isomers.
D-
What is more important for activity according to the information provided?
The activity is maximum with a two-carbon acetic acid side chain.
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Match the following terms with their meanings:
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What are the two quantitatively important iodinated amino acids in the thyroid gland?
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Which of the following are iodinated compounds found in the thyroid gland? (Select all that apply)
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Thyroxine (T4) contains an outer ring and an inner ring. The outer ring only contains one iodine atom.
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Thyroid Replacement Therapy is used for the treatment of ______.
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What is the main storage protein in follicles of the thyroid gland?
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Study Notes
Thyromimetic and Antithyroid Agents
- Thyromimetic agents are used to treat hypothyroidism, while antithyroid agents are used to treat hyperthyroidism.
Thyroid Hormones
- Thyroid hormones are iodinated amino acids derived from L-tyrosine, synthesized in the thyroid gland and stored as amino acid residues of thyroglobulin.
- Thyroid gland consists of functional units called follicles, which contain thyroglobulin, a glycoprotein.
- Two main thyroid hormones: thyroxine (T4) and triiodothyronine (T3).
Chemical Structure of T4 and T3
- T4: 3,5,3',5'-tetraiodo-L-thyronine
- T3: 3,5,3'-triiodo-L-thyronine
- Both have an inner ring and an outer ring, with iodine atoms attached to the rings.
Iodinated Compounds of the Thyroid Gland
- In addition to T3 and T4, the thyroid gland contains diiodo-L-tyrosine (DIT) and monoiodo-L-tyrosine (MIT), as well as small amounts of 3,3',5'-triiodo-L-thyronine (reverse T3, rT3) and 3,3'-diiodo-L-thyronine (T2).
- These compounds have no significant hormonal activity.
Biosynthesis of Thyroid Hormones
- Active uptake of iodide by follicular cells
- Oxidation of iodide and formation of iodothyrosines
- Coupling of iodotyrosine residues to form T3 and T4
- Proteolysis of thyroglobulin and release of iodothyronines
- Conversion of T4 to T3 in peripheral tissues
Transport and Metabolism
- Both T4 and T3 are transported in the blood bound to thyroxine-binding globulins (TBG).
- Deiodination is the most important metabolic pathway of the hormone.
- T4 is a prohormone, and its peripheral metabolism occurs in two ways: outer ring deiodination to yield T3, and inner ring deiodination to yield rT3.
Therapeutic Agents
- Thyroid Replacement Therapy: used to treat hypothyroidism
- Natural thyroid hormone preparations
- Synthetic thyroid hormones: L-thyroxine, Liothyronine sodium, and Liotrix
- Antithyroid Drugs: used to treat hyperthyroidism (Thioamides)
Structure-Activity Relationships (SARs)
- Thyroid hormone activity requires aappropriately substituted phenyl-X-phenyl nucleus
- Aliphatic side chain:
- L-isomers of T4 and T3 are more potent than D-isomers
- Carboxylate ion and the number of atoms connecting it to the ring are important for activity
- Optimum chain length is 2C
- Inner ring:
- Substitution of the inner ring affects activity
- Halogenation of the inner ring increases activity
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Description
Learn about thyromimetic agents, antithyroid agents, thyroid hormones, and their functions in the thyroid gland.
