Epinephrine is the primary 'fight-or-flight' hormone and works together with norepinephrine to induce its spectacular responses.
Epinephrine works to rapidly mobilize energy-yielding fuels, including glucose from the liver (through glycogenolysis and gluconeogenesis) and fatty acids from adipose tissue.
Epinephrine is secreted from the adrenal medulla in response to hypoglycemia, stress, trauma, or extreme exercise. Its release is largely controlled by the CNS via preganglionic sympathetic fibres.
The biologic effects of the catecholamines are very brief, lasting for only 10 seconds in the case of epinephrine. Enzymes including COMT and MOA convert them to vannilylmandelic acid (VMA), which can be measured in the urine.
Generally, the various adrenoreceptors can bind both epinephrine and norepinephrine, though with different affinities.
Intracellular Effect | location | Physiologic Effect | |
---|---|---|---|
α1 | inc IP3 and DAG lead to inc Ca2+ | peripheral vasoconstriction by SMCs | |
α2 | dec [cAMP] | vasoconstriction in some vessels, Na uptake in the proximal tubule | |
β1 | inc [cAMP] | heart | increases heart rate and contractility |
β2 | inc [cAMP] | arterioles | vasodilation |
β3 | inc [cAMP] |