Epinephrine, also known as adrenaline, is a catecholamine hormone involved in acute stress adaptation, cardiovascular regulation, metabolic mobilization, respiratory signaling, and nervous system activation. It functions as a major component of the sympathetic-adrenal response, preparing the body for rapid increases in physical or psychological demand.
Epinephrine increases heart rate, cardiac contractility, blood flow redistribution, bronchodilation, glycogen breakdown, and glucose release into circulation. The hormone also stimulates lipolysis and enhances availability of metabolic fuel substrates during stress-related conditions. Through adrenergic receptor activation, epinephrine coordinates rapid communication between nervous, cardiovascular, respiratory, hepatic, and muscular systems.
Epinephrine is produced mainly by chromaffin cells of the adrenal medulla. The hormone is synthesized from the amino acid tyrosine through sequential enzymatic steps involving tyrosine hydroxylase, aromatic amino acid decarboxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase.
Cortisol delivered from the adrenal cortex enhances expression of phenylethanolamine N-methyltransferase within medullary tissue, linking glucocorticoid physiology with catecholamine synthesis. After production, epinephrine is stored within secretory granules and rapidly released into circulation during sympathetic activation.
Epinephrine secretion is regulated primarily by sympathetic nervous system stimulation. Preganglionic sympathetic neurons release acetylcholine onto adrenal medullary chromaffin cells, triggering calcium-dependent hormone release. Stress exposure, hypoglycemia, exercise, emotional arousal, low blood pressure, hypoxia, and cold exposure can increase secretion.
Epinephrine acts through alpha-adrenergic and beta-adrenergic receptors distributed throughout cardiovascular, respiratory, hepatic, adipose, skeletal muscle, and nervous tissues. Intracellular signaling involves cyclic AMP pathways, calcium signaling systems, and phosphorylation cascades that rapidly alter metabolic and vascular function. Through these integrated endocrine and autonomic pathways, epinephrine coordinates immediate physiological adaptation during stress and high-energy-demand states.
Catecholamine made in adrenal medulla that rapidly coordinates cardiovascular, metabolic, and respiratory responses.
