Introduction:
Epinephrine is an agonist at both A and B receptors. It is, therefore a very important vaso – constrictor and cardiac stimulant.
Epinephrine is synthesized from tyrosine in the adrenal medulla and released along small quantities of nor – epinephrine into the bloodstream.
Low doses B effects (vasodilation) predominate while on higher doses a effects (vasoconstriction) is strongest.
Mechanism:
- Epinephrine is a sympathomimetic which are bind to adreno receptor which lies in GPCR.
- GDP dissociates from α subunit of appropriate G protein.
- GTP then binds to this G protein and α subunit dissociates from β – γ
- Activated GTP – bound α subunit then regulate the activity of its effector.
Actions:
(1) Cardiovascular
– Major actions
– Epinephrine strengthens contractility of myocardium and increase its rate of contraction.
– Epinephrine activates B1 receptors on kidneys to cause renin release, an enzyme for production of angiotensin II. i.e. an important vasoconstrictor.
(2) Respiratory
– Causes powerful Bronchodilation.
– Also inhibits the release of allergy mediators such as Histamine from Mast cells.
(3) Hyperglycemia
– It has significant hyperglycemic effect because of increased glycogenolysis in liver, increased release of Glucagon (B2 effect), decreased release of Insulin (a2 effect).
Clinical uses:
- To treat Bronchospasm e.g. in acute asthma and anaphylactic shock.
- A primary treatment of Anaphylaxis, to relieve hyper sensitivity reactions.
- To restore cardiac activity in Cardiac Arrest.
- To facilitate aqueous drainage in chronic open angle Glaucoma.
Adverse effects:
(1) CNS
Anxiety, Fear, Headache, Tremor
(2) CVS
Hypertension, Cardiac arrhythmias, Angina
(3) RESPIRATORY TRACT
Pulmonary edema.
Contradictions:
- Coronary disease – may induce anginal attacks.
- Hyperthyroidism.
- Hypertension.
- Chloroform, Cyclopropane, Halothane anesthesia
Dosage:
(1) IN BRONCHOSPASM
0.4ml 0f 1:1000 sol., SC
(2) IN ANAPHYLAXIS
0.3 – 0.5 mg
Properietary Names of Available Epinephrine:
- Adecaine
- Xylocaine
- Xylodos