alpha and beta adrenoreceptors

Alpha and Beta Receptors

• epinephrine reacts with both alpha and beta adrenoreceptors

• Alpha receptors stimulation cause vasoconstriction

• Beta receptors stimulation cause vasodilation

• alpha receptors are less sensitive to epinephrine but when activated,they override the vasodilation by beta receptors

• high levels of epinephrine cause vasoconstriction

• low levels of epinephrine will cause vasodilation

alpha 1 receptors

• cause smooth muscle contraction which include blood vessels , skin, gastrointestinal system,renal artery and brain
• induce glycogenolysis and gluconeogenesis in adipose tissue and liver cells
• induce sodium reabsorption in the kidney
• induce sweat glands secretion

alpha 2 receptors

• inhibition of insulin release from pancreas
• induce glucagon release from pancreas
• induce contraction of gastrointestinal tract sphinter

beta 1 receptors

• increase cardiac output : increase HR and increase contraction ( increase ejection fraction)
• renin release from juxtaglomerular cells
• lipolysis in adipose tissue

beta 2 receptors

• smooth muscle relaxation eg: bronchodilator
• dilate arteries to skeletal muscle
• glycogenolysis and gluconeogenesis
• increase renin secretion from kidney
• inhibit histamine release from mast cells

beta 3 receptors

• induce lipolysis