Adrenaline (Epinephrine) is a sympathomimetic drug. It causes an adrenergic receptive mechanism on effector cells and mimics all actions of the sympathetic nervous system except those on the facial arteries and sweat glands. Epinephrine also alleviates pruritus, urticaria, and angioedema. Adrenaline may help relieve gastrointestinal and genitourinary symptoms associated with anaphylaxis because of its relaxing effects on the smooth muscle of the stomach, intestine, uterus, and urinary bladder (Farzam et al., 2024; Oyebola, 2011). During reperfusion, adrenaline may counteract cerebral vasoconstriction (Kondo et al., 2022). 

Mechanism of Action

Adrenaline may demonstrate valuable short-term benefits during CPCR, but it is also arrhythmogenic and increases the heart's workload. High doses in many species are considered harmful during CPCR (Rozanski et al., 2012) and have been shown to reduce body tissue oxygen levels in rabbits (Towell et al., 1981). Other catecholamines, such as dopamine and dobutamine, are generally preferred in major pet species if sustained Adrenaline use is anticipated (DeWitt et al., 2016).  Specific receptor effects include:

1. ⍺-1 Sympathomimetic Activity: Smooth muscle contraction, mydriasis

2. ⍺-2  Sympathomimetic Activity: Mixed smooth muscle effects

3. β-1 Sympathomimetic Activity: Increased cardiac chronotropic and inotropic effects (increased heart rate, myocardial contractility, and renin release)

4. β-2 Sympathomimetic Activity:  Bronchodilation

Clinical Applications

There are a variety of potential applications; Adrenaline (Epinephrine) demonstrates a broad spectrum of pharmacologic activity.

Primary Systemic Applications

1. Resuscitation associated with anaesthesia-induced cardiac arrest: ⍺-1 and β-1 activity is beneficial during CPR.

2. Resuscitation outside general anaesthesia:  ⍺-1 and β-1 activity is beneficial during CPR.

3. Anaphylaxis:  ⍺-adrenergic activity reduces vasodilation and increases vascular permeability during anaphylaxis.

4. Bronchospasm: β-2 activity results in bronchodilator.

Secondary Systemic Applications

In human medicine, adrenaline is used for 

1. Type I allergic reactions, including anaphylaxis, hypotension associated with septic shock, 

2. Syncope; 

3. Urticaria, 

 Local Applications

1. Hemostasis, 

2. Rhinitis, acute sinusitis

3. Angioneurotic oedema

4. Open-angle Glaucoma

5. Uterine Relaxation  

6. Prolongation of action of local anaesthetics  

7. Mydriasis during intraocular surgery 

(PubChem, 2024; Farzam et al., 2024).