epinephrineneurotransmitters

Epinephrine, also known as adrenaline, is a catecholamine that functions both as a neurotransmitter in certain brain circuits and as a circulating hormone released by the adrenal medulla. It is synthesized from tyrosine and stored in chromaffin granules; its production is upregulated by the stress response and sympathetic activity. In the brain, epinephrine acts as a neuromodulator in select pathways, though norepinephrine plays a larger role as a CNS neurotransmitter.

Epinephrine exerts its effects by binding to adrenergic receptors, a family of G protein–coupled receptors including alpha1, alpha2, beta1, beta2, and beta3. Receptor activation triggers diverse responses: beta1 increases heart rate and contractility; beta2 promotes bronchodilation and vasodilation in skeletal muscle; alpha1 induces vasoconstriction in certain vascular beds; alpha2 modulates neurotransmitter release. The overall outcome depends on receptor subtype distribution and tissue context, with signaling largely mediated by cyclic AMP or calcium pathways.

Physiological roles include preparation for the fight-or-flight response, rapid adjustments in cardiac output, airway diameter, and vascular tone, and metabolic effects such as glycogenolysis and lipolysis. In the brain, epinephrine can influence arousal and attention, but its central actions are generally secondary to those of norepinephrine. Peripherally, it primes tissues for immediate action during stress.

In clinical practice, epinephrine is used for anaphylaxis, cardiac arrest, and as a vasoconstrictor in local anesthesia. It is rapidly metabolized by catechol-O-methyltransferase and monoamine oxidase, with a short plasma half-life. Routes of administration include intramuscular, subcutaneous, and intravenous delivery, tailored to the clinical situation.