Epinephrine
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.
- effects on the cardiovascular system
- effects on the kidneys
- effects on carbohydrate metabolism
- effects on lipid metabolism
- adrenergic receptors
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.
Effects on the Cardiovascular System
- stimulates the heart via β1 receptors to increase heart rate (IF), conduction rate (ICa), and force of cardiomyocyte contraction
- causes arteriolar constriction through α1 receptors and contstricts veins to increase venous return
Effects on Renal System
- decreases renal GFR
- increases Na-H exchanger and Na-K pump in the proximal tubule, increasing Na reabsorption via α2 receptors and inhibition of adenylate cyclase/cAMP. This is akin to the effetcs of Ang II.
Effects on Carbohydrate Metabolism
- works on pancreatic beta cells to inhibit insulin secretion and keep blood glucose levels elevated
- increases glycogenolysis and gluconeogenesis in muscle (and liver?)
Effects on Lipid Metabolism
- Increases action of hormone-sensitive lipase in adipose tissues, liberating FFAs and DAG.
Adrenergic Receptors
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] |