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Questions and Answers
Questions and Answers
Which isomer of compound 1 (L-T4) is listed in the table?
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.
L-isomers of T4 and T3 are more potent than _____ isomers.
D-
What is more important for activity according to the information provided?
What is more important for activity according to the information provided?
- Presence of a carboxylate ion (correct)
- Degree of unsaturation
- Length of the side chain
- Number of atoms in the ring
The activity is maximum with a two-carbon acetic acid side chain.
The activity is maximum with a two-carbon acetic acid side chain.
Match the following terms with their meanings:
Match the following terms with their meanings:
What are the two quantitatively important iodinated amino acids in the thyroid gland?
What are the two quantitatively important iodinated amino acids in the thyroid gland?
Which of the following are iodinated compounds found in the thyroid gland? (Select all that apply)
Which of the following are iodinated compounds found in the thyroid gland? (Select all that apply)
Thyroxine (T4) contains an outer ring and an inner ring. The outer ring only contains one iodine atom.
Thyroxine (T4) contains an outer ring and an inner ring. The outer ring only contains one iodine atom.
Thyroid Replacement Therapy is used for the treatment of ______.
Thyroid Replacement Therapy is used for the treatment of ______.
What is the main storage protein in follicles of the thyroid gland?
What is the main storage protein in follicles of the thyroid gland?
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Study Notes
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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