Adrenergic Receptors Chris Garcia Ryan Roberts

Adrenergic Receptors Have 4 Main Subtypes And Are Located At The Synapse Of Postganglionic Nerves 4 Subtypes: α 1, α 2, β 1, β 2 Postsynaptic: α 1, β 1, β 2 Presynaptic: α 2

Class of G-Coupled Protein Receptors Target of catecholamines Catechol + Amine side chain Dopamine NorepinephrineEpinephrineIsoprenaline

Sympathetic Nervous System Response When catecholamines bind to the adrenergic receptors, generally the sympathetic nervous system is stimulated. - Most sensitive to Norepinephrine > Epinephrine >> Isoprenaline - G q protein coupled -- PLC activated, cleaves PIP 2 -- PIP 2 increases IP 3 and DAG -- IP 3 acts on calcium channels leading to contraction of smooth muscle -- Contraction: Dilation of eyes, Urethral sphincter, Erector pili muscles, Uterus -- Vasoconstriction: increased vascular resistance, blood pressure -- Glycogenolysis and gluconeogenesis from adipose tissue and liverlycogenolysisgluconeogenesisadipose tissueliver -- Na + reabsorption from kidney -- Sweat gland secretion α 1 Receptor: smooth muscle contraction

α 2 Receptor: Inhibition - Most sensitive to Epinephrine ≥ Norepinephrine >> Isoprenaline - G i protein coupled -- Adenylate cyclase inactivated -- AC catalyzes the cyclization of ATP and produces cAMP -- Deactivation of cAMP dependent pathway leads to: -Inhibition of insulin release in the pancreas -Inhibition of norepinephrine through negative feedback -Inhibition of acetalcholine release in parasympathetic NS -Induction of glucagon release from the pancreas -Increased thrombocyte aggregation

β 1 Receptor: Heart - Most sensitive to Isoprenaline > Norepinephrine = Epinephrine - G s protein coupled -- Adenylate cyclase activated -- AC catalyzes the cyclization of ATP and produces cAMP -- Activation of cAMP dependent pathway leads to: -Increased chronotropy: speed at which heart beats -Increased inotropy: force at which heart beats -Increased dromotropy: speed of conduction through the heart -Increased renin secretion in kidneys -Increased ghrelin secretion in stomach

β 2 Receptor: Lungs - Most sensitive to Isoprenaline > Norepinephrine = Epinephrine - G s protein coupled -- Adenylate cyclase activated -- AC catalyzes the cyclization of ATP and produces cAMP -- Activation of cAMP dependent pathway leads to: -Bronchodilation: Smooth muscle relaxation in bronchi -Vasodilation -Inhibit histamine-release from mast cells -Stimulates insulin secretion -Relaxes non pregnant uterus, bladder wall muscles, bronchioles -Contract sphincters of GI tract -Lipolysis in adipose tissue -Glycogenolysis and gluconeogenesis

α 1 Receptor Integration The Inositol Phospholipid (IP 3 ) Dependent Pathway is used as a signal transduction pathway for many hormones including: -antidiuretic hormone (ADH): Induces the synthesis and release of glucocorticoids in adrenal cortex of kidney - Thyrotropin-releasing hormone (TRH): Induces the synthesis and release of TSH in anterior pituitary gland - Thyroid-stimulating hormone (TSH): Induces the synthesis and release of a small amount of thyroxine in the thyroid - Angiotensin II: Induces synthesis and release of Aldosterone in adrenal cortex of kidney -Gonadotropin-releasing hormone (GnRH): Induces the synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in anterior pituitary gland

α Receptor Signaling

β Receptor Signaling

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