Thyroid hormones 18- Flashcards
Mechanism of action of thyroid hormones:
« T3 and T4 dissociate from Thyroxine-binding globulin (TBG)
and enter cells by diffusion or active transport.
« Inside the cell, T4 deiodinated to T3
» T3 enters the nucleus and attaches to its nuclear receptor
Drug-receptor complex bind to DNA and promotes
transcription of specific genes — mRNA formation— protein
synthesis (production of various enzymes).
Therapeutic Uses of Thyroid Hormones:
- Replacement therapy in hypothyroidism (levothyroxine)
- TSH suppression therapy in thyroid cancer and nontoxic goiter.
Mechanism of Action of Thioamides
Thioamides inhibit thyroid hormone synthesis by:-
1.Inhibition of oxidation of iodide to iodine.
2.Inhibition of iodination of tyrosine (organification of iodine).
3. Inhibition of coupling of iodotyrosines to T4 and T3.
4. Propylthiouracil in addition reduces conversion of T4 to T3 in the periphery.
Therapeutic uses of thioamides
Used in Treatment of hyperthyroidism:
1. As principal therapy.
2. As adjuvant to 1” to control the disease while waiting its effect.
3. To control the disorder in preparation for surgical treatment.
4. Thyroid storm (PTU inhibits conversion of T4 to T3)
5. In pregnancy:
thioamides used in pregnancy
propylthiouracil and methimazole
Mechanism of action of iodide salts and iodine
- Inhibition of iodide organification
- Reduction of the response of thyroid gland to TSH,
- Inhibition of proteolysis of thyroglobulin — decrease Release of T3&T4.
Adverse effects of thioamides
- No-specific: Allergy, most commonly papular rash and GIT upset
- Agranulocytosis: the most serious but rare and reversible.
- Hepatotoxicity: hepatitis (PTU) & cholestatic jaundice (methimazole)
- Immunological reactions: e.g. vasculitis, lymphadenopathy, a lupus-like reaction,
arthralgia, & polyserositis - Loss of hair, abnormal skin pigmentation
the most serious adverse effect caused by thioamides
agranulocytosis
thioamides causes hepatitis
propyluracil
thioamides causes cholestatic jaundice
(methimazole)
Therapeutic indications of iodine and iodide salts
- Preparation of the patient for thyroidectomy (8gland size & vascularity).
- Thyroid crisis (storm) (inhibit hormone release).
- Prophylactic where goiter is endemic. (Added to salt, water and bread).
Adverse effects of iodine and iodide
- lodism: (dose-dependet, chronic adverse effects) metallic taste, painful salivary glands,
excess salivation, running eyes & nose, sore throat, cough and diarrhea. - Allergic reactions: angioedema, rash, drug fever and ulceration of mucous membranes.
Mechanism of Action: Radioactive iodine
- Oral radioactive iodine is rapidly absorbed & concentrated by thyroid gland
- It emits Beta rays (cytotoxic) which destroy the gland tissue.
Therapeutic uses: Radioactive iodine
- Hyperthyroidism in adults over 45 years
- Hyperthyroidism in patients not fit for surgery
- Recurrence after medical or surgical treatment
- Thyroid cancer.
Adverse effects: Radioactive iodine
- Hypothyroidism (The chief toxic effect).
- Thyroid storm (release of thyroid hormone).
- Patient may require repeated doses.
Used to control peripheral manifestations of hyperactivity of the sympathetic nervous system (tachycardia, tremors and nervousness) occurring secondary to hyperthyroidism.
beta blockers
moa of betablocker as antithyroid agent
- Used to control peripheral manifestations of hyperactivity of the sympathetic nervous system (tachycardia, tremors and nervousness) occurring secondary to hyperthyroidism.
- Propranolol also prevents peripheral conversion of T4 into the more active T3.
Control Of Release of Aldosterone:
1) Renin-Angiotensin System activation by hypovolemia & hyponatremia.
2) Hyperkalemia.
1ry hyperaldosteronism:
Adenoma in Zona glomerulosa “Conn’sgdisease”.
what is escape phenomenon
Prolonged hypervolemia — decrease Sensitivity of distal convoluted tubules (D.C.T.) to the effect of Aldosterone — No Na& Water retention BUT still K excretion.
useful in hyperaldosteronism
Spironolactone
2ry hyperaldosteronism:
Occurs in chronic heart
failure, liver cirrhosis & Nephrotic syndrome.
Mineralocorticoid preparations:
A) Des-Oxy-Corticosterone (D.O.C.)
B) Fludrocortisone Acetate
Pure mineralocorticoid with NO glucocorticoids activity.
Desoxycorticosterone
Used to replace mineralocorticoid activity in Addison’s disease.
Desoxycorticosterone
Fludrocortisone Acetate
mineralocorticoid with glucocorticoid action
Fludrocortisone Acetate
cortisol Bound to …………
plasma proteins mainly to Corticosteroids-Binding-Globulin (CBG = Transcortin) & albumin.
effect of CS on ACTH
Suppresses release of corticotropin releasing hormone (C.R.H.) from hypothalamus & Suppresses release of A.C.T.H. from Anterior pituitar
effect of CS on calcium
decrease absorption of calcemia causing hypocalcemia
effect of CS on gastric
increase HCl worsen peptic ulcer
effect of CS on eye
cataract and increase in intraocular pressure
Pharmacological Actions Of Cortisol
1) Negative Feedback effect (A.C.T.H)
2) Organic Metabolism:
3) CNS: EUphoria & DEpression
4) Cataract & increase in intraocular pressure (IOP)
5) 5) Gastric: increase HCl and worsen peptic ulcer
6) Anti-Inflammatory Effect:
7) Anti — Vitamin D
8) Anti-Allergic & Immunosuppressant:
9) Blood
10) Anti-Stress & Anti-Shock effect:
11) Delays Wound Healing:
12) Uricosuric effect:
effect of CS on blood
a. Stimulates erythropoiesis & increases release of RBCs from bone marrow:
= In Cushing’s disease (Hypercortisolemia) — Polycythemia.
= |n Addison’s disease (Hypocortisolemia) — Anemia.
b. Increases circulating P.M.N.L. by their migration from the circulation.
c. Increases number of platelets.
d. T Coagulability of blood.
e. Decreases lymphocytes — Lymphopenea (Catabolic effect on lymphoid tissues).
f. Decreases eosinophils = Eosinopenea.
Therapeutic Uses of Glucocorticoids
A) Replacement therapy in adrenocortical insufficiency (Addison’s disease):
a) Acute Addisonian Crisis: cortisol
b) Chronic Addison’s Disease: cortisone acetate/ mineral: DOCA and fludrocortisone acetate
B) Supplementary & Suppressive therapy
1) Anti-Inflammatory: treat inflammation in:
a.Encephalitis, cerebral edema & Intra-cranial pressure.
b.Rheumatic carditis.
¢. Chronic active hepatitis.
d.Nephritis & nephritic syndrome.
e.Arthritis: Rheumatic, Rheumatoid, Gouty & Osteoarthritis.
2) Allergic diseases: in the skin, eye & bronchial asthma.
3) Immunosuppressive in :
a) Auto-immune diseases:
- Collagen disease: Polyarthritis & systemic lupus erythematosis.
- Blood diseases: Hemolytic & aplastic anemia, thrombocytopenia
- Inflammatory bowel syndrome e.g. ulcerative colitis.
b) Suppress tissue & organ rejection.
4) Suppress lymphoid tissues— Treat lymphoma & leukemia.
5) Suppress A.C.T.H. in adreno-genital syndrome.
6) Suppress hypertrophic scars & keloid formation.
7) Shock & Stress conditions.
8) Hypervitaminosis D & Hypercalcemia.
Adverse Effects of Glucocorticoids:
Abrupt withdrawal after long use — Acute Addisonian Crisis.
Moon face & Buffalo hump
Hyperglycemia — Worsens Diabetes mellitus
Osteoporosis
Hypocalcemia
Delays healing of wounds.
Hypokalemia — Worsens Digitalis toxicity
Na retention: Edema and Hypertension — May lead to HF
weight gain
Immunosuppressant — increase Susceptibility to infection,
Mask manifestations of bacterial & viral infections
Peptic ulceration.
Cataract & increases intra-ocular pressure — Glaucoma.
Teratogenicity
Thromboembolic manifestations.
Contraindications Of Glucocorticoids:
1- Abrupt withdrawal: acute adrenal insufficiency syndrome.
2- Cushing’s disease.
3- Diabetes mellitus.
4- Osteoporosis.
5- Repeated intra-articular injections.
6- Hypertension & Heart failure.
7- Digitalis toxicity.
8- Uncontrolled infection.
9- Peptic ulcer.
10- Thromboembolic diseases.
11- Psychological disturbances.
12- During pregnancy.
13- Glaucoma.
Short acting glucocorticoid
Hydrocortisone (cortisol) & cortisone:
The only glucocorticoid that has no effect on the fetus in pregnancy
Prednisone
Intermediate & long acting CS
Prednisone (intermediate), dexamethasone (long acting)
CS has no mineralcorticoid action
dexamethasone
a somatostatin analogue inhibits ACTH and growth hormone secretion and reduces the circulating levels of cortisol in patients with ACTH-producing pituitary
tumors and is also used in the treatment of acromegaly.
Pasireotide
Pasireotide uses
inhibits ACTH and growth hormone secretion
used in treatment of acromegaly
long-acting dopamine D2 receptor agonist used primarily to treat hyperprolactinemia, also inhibit ACTH release
Cabergoline
Antihistamine (H1-blocker) + Anti-serotonin. }
Suppresses release of A.C.T.H.
Cyproheptadine
Ketoconazole
a. Anti-fungal.
b. Inhibits adrenal steroid hormone synthesis when used in larger doses
c. Useful in Cushing’s disease.
Inhibits 11-B-Hydroxylase enzyme selectively -decrease Synthesis of BOTH Aldosterone & Cortisol »increase ACTH
Metyrapone (Mitopirone):
Test the function of anterior pituitary to secrete A.C.T.H
Metyrapone (Mitopirone):
a- Destruction of adrenocortical cells.
b- Useful in Cushing’s disease & Inoperable adrenocortical carcinoma.
Mitotane
It causes a reduction in the synthesis of all hormonally active steroids. Because it inhibits conversion of Cholesterol — Pregnenolone (First step in steroidogenesis).
Aminoglutethimide