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Endocrine Pharmacology > Thyroid and Antithyroid Drugs > Flashcards

Thyroid and Antithyroid Drugs Flashcards

1
Q

Thyroid hormone synthesized in the?

A

Thyroid gland as T4.

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2
Q

Thyroid hormone metabolized to the active form (T3) mostly in?

A

Liver & brain.

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3
Q

Actions of Thyroid Hormone?

A
  1. Growth and development: Especially important in brain. Hypothyroidism is leading cause of mental
    retardation worldwide. Important for development of bones and teeth
  2. Calorigenic: Increased oxygen consumption
  3. Cardiovascular: Increased heart rate and force
    of contraction.
  4. Metabolic: Maintain metabolic homeostasis in
    many organs.
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4
Q

Thyroid hormone is synthesized by sequential?

A

Iodination of thyroglobulin (Tg) followed by proteolysis

but iodinated Tg is very important for storage in the thyroid gland

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5
Q

Thyroid hormone is stored in two forms?

A

3, 5, 3’- Triiodothyronine (T3)

3, 5, 3’, 5’- Tetraiodothyronine (thyroxine, T4)

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6
Q

Iodine, as I– , is taken up against?

A

A concentration gradient and oxidized to I + (exists as hypoiodate, HOI and its enzyme intermediate form EOI) to be used for iodination of Tg.

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7
Q

The ratio of T4 to T3 synthesized in the thyroid gland drops during deficiencies?

A

From 4:1 to 1:3 during iodine deficiency.

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8
Q

Thyroid hormone (both T4 and T3) released into the blood in what ratio?

A

a ~ 10:1 ratio from the thyroid gland in response to thyroid stimulating hormone (TSH).

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9
Q

The ratio of thyroid hormone in tissues is?

A

The ratio is tissues is not the same as the synthesis ratio because of the action of the deiodinases.

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10
Q

Removal of the 5’ iodine from T4 by thyronine

5’-deiodinase produces?

A

The more active T3.

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11
Q

Important sites for producing T3 for export.

A

The liver, kidney and thyroid gland.

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12
Q

The brain, pituitary, heart and skeletal muscle

have the D2 isoform important for?

A

Maintaining intracellular T3.

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13
Q

A third enzyme, thyronine 5-deiodinase produces an?

A

[NOTE: 5 NOT 5’] inactive form (reverse T3 or

rT3) [ found in placenta, skin and brain].

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14
Q

Adequate amounts of thyroid hormone are essential for normal?

A

Fetal brain development. In the first trimester of pregnancy the fetus relies on thyroid hormone derived from the maternal circulation.

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15
Q

T3 and T4 are both metabolized in the?

A

Liver (biotransformation) through glucuronide conjugation and sulfate conjugation pathways that allow excretion of these hormones through the bile.

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16
Q

T3 and T4 are thus subject to?

A

Enterohepatic cycling because glucuronidases secreted by microorganisms in the lower intestine hydrolyze the glucuronide conjugates and release the free hormones to be reabsorbed.

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17
Q

Transport of Thyroid Hormones

A

Thyroxine binding globulin (TBG)
Thyroglobulin (Tg)
Transthyretin (TTR)

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18
Q

Thyroxine binding globulin (TBG) binds?

A

(binds 1:1). T4 bound tighter than T3

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19
Q

Thyroxine binding globulin (TBG) and thyroglobulin (Tg) are?

A

Thyroxine binding globulin (TBG) and thyroglobulin (Tg) are two different proteins. (Do not confuse these two.)

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20
Q

Transthyretin (TTR) binds?

A

(binds 2:1) T(formerly called prealbumin)
Higher levels in blood for TTR than TBG.
TTR also transports T4 in cerebrospinal fluid.

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21
Q

Albumin binds?

A

(binds both T3 and T4) (familial dysalbuminemic hyperthyroxinemia, increased T4)

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22
Q

“Free Hormone” Concept

Thyroid hormones are very?

A

Highly bound to protein in the blood.

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23
Q

“Free Hormone” Concept
Changes in protein levels or changes in the amount of
binding to these proteins can cause?

A

Large changes in total serum hormone levels.

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24
Q

“Free Hormone” Concept

The pituitary senses only?

A

“free” (unbound) hormone and maintains the free level through increased or decreased synthesis.

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25
Q

“Free Hormone” Concept

The hormone signal is?

A

Unbound hormone, not the total amount.

26
Q

“Free Hormone” Concept

Total loss of any one carrier protein?

A

Does not affect the euthyroid state.

27
Q

TSH Action on the Thyroid Gland

Immediate effect & Later effects are?

A
  1. Immediate effect is increased secretion (minutes).
  2. Later effects are iodide uptake, hormone synthesis, proteolysis.
  3. The last effects are hypertrophy and hyperplasia of
    thyroid cells.
28
Q

TSH acts on the thyroid gland through the?

A

TSH receptors (G-protein coupled receptor that stimulates adenylyl cyclase).

29
Q

At higher TSH levels?

A

Phospholipase C is stimulated, resulting in increased PI’s that increase cytosolic Ca2+.

30
Q

Mutations in the TSH receptor can?

A

Result in continuous activation (as in thyroid adenomas) or decreased function (one cause of hypothyroidism).

31
Q

Decreased iodine in the diet causes?

A

Increased TSH leading to thyroid hypertrophy.

32
Q

Severe iodine deficiency can lead to?

A

Hypothyroidism and cretinism in adults, or retarded growth and development in children.

33
Q

The preferred method of preventing iodine deficiency?

A

Iodized salt

34
Q

Thyroid hormone acts primarily through binding to?

A

Nuclear receptors.

35
Q

T3 binds to specific receptor proteins?

A

TRα1, and TRβ1 and TRβ2 that bind to specific DNA sequences (thyroid hormone response elements, TRE’s) to increase or decrease DNA transcription.

36
Q

Although T4 can bind to TRα1, and TRβ1 and TRβ2 receptors?

A

It cannot regulate transcription.

37
Q

Actions of T3 are modulated by?

A

Coactivators or corepressors.

38
Q

T3 also binds avidly to?

A

Mitochondrial membranes and activates the mitochondrial adenine nucleotide transporter.

39
Q

Thyroid Hormone Calorigenic Effects Not caused by?

A

Uncoupling. Increased oxygen consumption (heart, skeletal muscle, liver, kidney)

40
Q

Thyroid Hormone Cardiovascular Effects During Hyperthyroidism?

A

Tachycardia, increased stroke volume, cardiac hypertrophy, decreased peripheral vascular resistance, increased pulse pressure.

41
Q

Thyroid Hormone Cardiovascular Effects During Hypothyroidism?

A

Bradycardia, decreased cardiac index, pericardial effusion, increased peripheral vascular resistance, decreased pulse pressure and elevation of mean arterial pressure.

42
Q

Thyroid Hormone Metabolic Effects During

Hyperthyroidism?

A

Increased fatty acid synthesis and fatty acid oxidation, increased bile acid synthesis, decreased cholesterol,
elevated glycolysis and gluconeogenesis.

43
Q

Thyroid Hormone Metabolic Effects During Hypothyroidism?

A

Decreased fatty acid synthesis and fatty acid oxidation, increased cholesterol.

44
Q

Thyroid Disorders Hypothyroidism

A
  1. Myxedema, juvenile myxedema, cretinism
    in adults, simple goiter
  2. Hashimoto’s thyroiditis (autoimune disorder antibodies destroy thyroid gland)
  3. Drug induced hypothyroidism
  4. Congenital hypothyroidism (no gland or ectopic gland), pituitary disease (TSH deficit, radiation induced).
45
Q

Thyroid Disorders- Hypothyroidism Treatment?

A

Administration of thyroid hormone (T4 or T3)

46
Q

Levothyroxine what is it used for and what should be monitored?

A

L-T4
Higher doses required for children
May take several weeks for steady state level
Monitor hormone levels (T4 and T3) (small difference are important)

47
Q

Liothyronine sodium used and types?

A

L-T3 tablets & injectable

48
Q

Liotrix & Thyrolar are?

A

Mixture of T4 and T3

Desiccated animal thyroid preparations - (less desirable, more variable).

49
Q

Thyroid Disorders- Hyperthyroidism:

A
  1. Graves Disease: Autoantibodies directed against
    receptors on thyroid gland stimulate receptors
    and increase hormone production
  2. Toxic nodular goiter (carcinoma)
50
Q

Thyroid Disorders- Hyperthyroidism Treatment:

A

More complex than hypothroidism.

May consist of: Surgery, Radioactive iodine, & Drugs

51
Q

Hyperthyroidism- Antithyroid Drugs

A

Thioureylenes include propylthiouracil & methimazole

52
Q

Propylthiouracil (PTU) & Methimazole Mechanism?

A

These inhibit iodine organification (the peroxidase catalyzed reactions: iodination and coupling).
Propylthiouracil (PTU) also inhibits peripheral conversion of T4 to T3.

53
Q

Propylthiouracil Metabolized?

A

Rapidly absorbed, PTU has shorter plasma halflife

that methimazole.

54
Q

Methimazole Potency?

A

Methimazole is 10 time more potent than PTU.

Methimazole crosses placenta and gets concentrated in fetal thyroid.

55
Q

Propylthiouracil is preferred with?

A

PTU preferred in pregnant patients because of less placental transfer and limited excretion in milk.

56
Q

Propylthiouracil (PTU) & Methimazole Adverse Effects?

A

Minimal number of patients experience adverse reactions (3 to 12%) (agranulocytosis and skin rash)

57
Q

Iodinated Contrast Media is used for and can cause?

A

Used for improved contrast in CT scans cardiac catheterization, etc.
Can cause incident hyperthyroidism in euthyroid individuals.
Can cause thyroid storm in hyperthyroid patients.

58
Q

Large doses of iodine?

A

Inhibit all aspects of iodine metabolism by the thyroid gland. Rapidly blocks release of thyroid hormone.

59
Q

Large doses of iodine are used for?

A

Used in treatment of thyroid storm. Decreases size, vascularity and fragility of the hyperplastic gland. Valuable for pre-operative treatment. Not to be used prior to radioactive iodide treatment (dilution). Works best for preoperative treatment or with other antithyroid drugs. Long-term treatment usually fails.

60
Q

Radioactive Iodine is administered and effects?

A

Na131I is administered orally & concentrated in the thyroid gland.

61
Q

Radioactive Iodine mechanism?

A

Where β-radiation will destroy all or part of the parenchymal cells in several weeks, but not surrounding tissue of thyroid gland. Used in adults 35 years or older, but not in women of child-bearing age.

Endocrine Pharmacology (5 decks)

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