Exam 1 Ch 37 & 38 Hypothalamic & Pituitary Hormones, Thyroid & Antithyroid Drugs Flashcards
What is Methimazole and what is its mechanism of action?
It is an thioamide (small sulfur-containing thioamide) anti-thyroid drug.
Mechanism of Action: Inhibit thyroid hormone synthesis by blocking peroxidase-catalyzed reactions, iodination of tyrosine residues of thyroglobulin, and coupling of DIT (Diiodotyrosine) and MIT (Monoiodotyrosine). There is an inhibition of the peripheral conversion of T4 to T3 to a much lesser extent.
How are Beta Blockers used for Anti-Thyroid Drugs?
They are an important class of drugs for treatment of thyrotoxicosis. They are particularly useful in controlling tachycardia and other cardiac abnormalities of severe thyrotoxicosis. Propranolol also inhibits peripheral conversion of T4 to T3
What are the actions or uses for iodide salts and iodine in regards to treating hyperthyroidism? What occurs when one takes iodide salts and iodine for more than several weeks?
- Inhibit iodination of tyrosine & thyroid hormone release
- Decreases size & vascularity of hyperplastic thyroid gland
- Because iodide salts inhibit release as well as synthesis of hormones, their onset of action occurs rapidly within 2-7 days–effects are transient
- Thyroid gland “escapes” from iodide block after several weeks of treatment
Which drugs are used to treat hypothyroidism?
Levothyroxine (T4)
Liothyronine (T3)
Which drugs are used to treat hyperthyroidism?
Thioamides (propythiouracil)
Iodide (Lugol Solution)
Beta Blockers (Propanolol)
131 I
How do the hormones released from the anterior pituitary gland differ from those released from the posterior pituitary?
Except for prolactin, hormones released from anterior pituitary stimulate production of hormones by peripheral endocrine gland, liver, or other tissues. Prolactin and hormones released from posterior pituitary (vasopressin and oxytocin) act directly on target tissues.
Hypothalamic factors regulate the release of posterior pituitary hormones.
Which two types of hormones does the thyroid gland secrete, and what are these hormones and their general effects? Are they secreted into ducts or directly into the blood?
- Iodine-containing amino acids: Thyroxin (T4) and Triiodothyronine (T3); they have broad effects on growth development, and metabolism
- Peptide: Calcitonin; important in calcium metabolism
These hormones are secreted directly into the blood; thus the thyroid is part of endocrine system of ductless glands
What happens in thyroid gland after iodide gets actively taken up?
It is highly concentrated and converted to elemental iodine via thyroidal peroxidase
Briefly explain which molecules combine within thyroglobulin to form T3 and T4.
MIT+DIT=T3
DIT+DIT=T4
Why is the binding of T3 more efficient than that of T4, and what does this imply about their activity level?
The 5’ iodine in T4 causes steric hindrance when binding to a receptor. Thus T3, which does not contain this iodine, is more active, as T4 is converted to T3 in target cells, liver and kidneys.
How does methimazole inhibit hormone synthesis?
By blocking peroxidase-catalyzed reactions, iodination of tyrosine residues of thyroglobulin, and coupling of DIT & MIT. It also inhibits peripheral conversion of T4 to T3, but to a much lesser extent.
What happens chemically in thyroglobulin during thyroid hormone synthesis?
Tyrosine residues in thyroglobulin are iodinated to for monoiodotyrosine (MI) or diiodotyrosine (DIT) in a process known as iodine organification
