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Questions and Answers
Which receptor is responsible for causing hair erection?
Which receptor's action involves increased release of insulin?
Which receptor decreases the release of norepinephrine?
Which receptor is paired with the agonist phenylephrine?
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Which receptor type facilitates generalized vasoconstriction leading to increased peripheral resistance and hypertension?
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Which receptor stimulates glycogenolysis in the liver and skeletal muscles?
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What action is associated with the activation of β3-receptor?
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Which receptor is an antagonist to atenolol?
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Which receptor type primarily mediates the contraction of the dilator pupillae muscle leading to active mydriasis?
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Which receptor's action includes the inhibition of adenylate cyclase activity?
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Which receptor type is involved in both cardiac stimulation and increased lipolysis and free fatty acids?
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Which receptor is coupled to a Gi protein and inhibits the release of norepinephrine from presynaptic terminals?
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Which receptor's activation would most likely lead to bronchodilation?
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Clonidine is an agonist of which receptor?
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Which receptor is associated with increased platelet aggregation?
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Which receptor's mechanism is described as Gq protein coupled and involves increased Ca2+ influx?
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Which receptor facilitates neuromuscular tension by stimulating K+ release from the liver?
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Which receptor type, when activated, results in the relaxation of the gastrointestinal tract and urinary bladder?
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Study Notes
Alpha Receptors
-
α1-receptor:
- Couples with Gq protein, leading to increased production of inositol triphosphate and diacylglycerol, and influx of Ca2+
- Results in:
- Contraction of erector pilae muscle, causing hair erection
- Contraction of dilator pupillae muscle, leading to active mydriasis
- Generalized vasoconstriction, increasing peripheral resistance and hypertension
- Increased viscous salivation
- Constriction of sphincters of the gastrointestinal tract and urinary bladder
- Uterus contraction in pregnant women, and relaxation in non-pregnant women
- Ejaculation
- Facilitates neuromuscular tension, stimulating K+ release from the liver
- Agonist: phenylephrine
- Antagonist: prazosin
-
α2-receptor:
- Couples with Gi protein, inhibiting adenylate cyclase activity and decreasing intracellular cAMP levels
- Results in:
- Sympathetic outflow from the central nervous system
- Presynaptic (autoreceptors) effects:
- Decreased release of norepinephrine
- Acetylcholine release in enteric ganglia, leading to relaxation of the intestinal wall
- Release of renin
- Release of insulin
- Decreased lipolysis in fat cells
- Increased platelet aggregation
- Agonist: clonidine
- Antagonist: yohimbine
Beta Receptors
-
β1-receptor:
- Couples with Gs protein, stimulating the central nervous system and cardiac stimulation
- Results in:
- Increased release of renin
- Lipolysis and free fatty acid release
-
β2-receptor:
- Couples with Gs protein, stimulating adenylate cyclase activity and increasing intracellular cAMP levels
- Results in:
- Generalized vasodilation
- Bronchodilation
- Glycogenolysis in the liver and skeletal muscles
- Increased release of insulin
- Relaxation of the gastrointestinal tract and bladder
- Relaxation of the uterus
- Skeletal muscle tremors
- Agonist: dobutamine, salbutamol, butoxamine
- Antagonist: atenolol
-
β3-receptor:
- Results in:
- Increased lipolysis and free fatty acid release
- Increased thermogenesis
- Agonist: octopamine
- Results in:
-
Presynaptic β2 receptors:
- Increase release of norepinephrine in adrenergic nerve terminals
-
Postsynaptic β receptor:
- Stimulates adenylate cyclase activity, increasing intracellular cAMP levels
Alpha Receptors
-
α1-receptor:
- Increased production of inositol triphosphate and diacylglycerol, and influx of Ca2+
- Mechanism: postsynaptic, Gq protein coupled receptor
- Actions:
- Contraction of erector pilae muscle → hair erection
- Contraction of dilator pupillae muscle → active mydriasis
- Generalized vasoconstriction → increased peripheral resistance and hypertension
- Increased viscous salivation
- Constriction of sphincters of the gastrointestinal tract and urinary bladder
- Uterus: Contracts in pregnant women and relaxes in non-pregnant women
- Ejaculation
- Facilitates neuromuscular tension (stimulates K+ release from liver)
- Agonist: phenylephrine
- Antagonist: prazosin
-
α2-receptor:
- Inhibits adenylate cyclase activity and decreased intracellular cAMP levels
- Mechanism: postsynaptic, presynaptic, and central nervous system, Gi protein coupled receptor
- Actions:
- Sympathetic outflow from the central nervous system
- Presynaptic (autoreceptors):
- Decreased release of norepinephrine
- Acetylcholine release in enteric ganglia → relaxation of the intestinal wall
- Release of renin
- Release of insulin
- Decreased lipolysis in fat cells
- Increased platelet aggregation
- Agonist: clonidine
- Antagonist: yohimbine
Beta Receptors
-
β1-receptor:
- Mechanism: C.N.S stimulation, cardiac stimulation, Gs protein coupled receptor
- Actions:
- Increased release of renin
- Lipolysis and free fatty acid
- Agonist: dobutamine
-
β2-receptor:
- Mechanism: Gs protein coupled receptor
- Actions:
- Generalized vasodilation
- Bronchodilation
- Glycogenolysis in the liver and skeletal muscles
- Increased release of insulin
- Relaxation of the gastrointestinal tract and bladder
- Relaxation of the uterus
- Skeletal muscle tremors
- Agonist: salbutamol, butoxamine
- Antagonist: atenolol
-
β3-receptor:
- Mechanism:
- Actions:
- Increased lipolysis and free fatty acids
- Increased thermogenesis
- Agonist: octopamine
- Presynaptic β2 receptors: increased release of norepinephrine in adrenergic nerve terminals
- Postsynaptic β receptor: stimulates adenylate cyclase activity and increased intracellular cAMP levels
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Description
Learn about alpha 1 and alpha 2 receptors, including their mechanisms and actions in the body, such as hair erection and mydriasis. Understand how they function and their effects.
