adrenergic receptor

Examples of adrenergic receptor in the following topics:

• Epinephrine and Norepinephrine

  • Its actions vary by tissue type and tissue expression of adrenergic receptors.
  • Epinephrine acts by binding to a variety of adrenergic receptors.
  • Epinephrine is a nonselective agonist of all adrenergic receptors, including the major subtypes α1, α2, β1, β2, and β3.
  • When norepinephrine acts as a drug, it increases blood pressure by increasing vascular tone through α-adrenergic receptor activation.
  • The actions of norepinephrine are carried out via the binding to adrenergic receptors.

• Adrenergic Neurons and Receptors

  • Adrenergic receptors are molecules that bind catecholamines.
  • There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 (a Gq coupled receptor) and α2 (a Gi coupled receptor).
  • Adrenaline or noradrenaline are receptor ligands to α1, α2, or β-adrenergic receptors (the pathway is shown in the following diagram).
  • α1-adrenergic receptors are members of the G protein-coupled receptor superfamily.
  • This schematic shows the mechanism of adrenergic receptors.

• Local Regulation of Blood Flow

  • Generally, norepinephrine and epinephrine (hormones secreted by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive, acting on alpha-1-adrenergic receptors.
  • However, the arterioles of skeletal muscle, cardiac muscle, and the pulmonary circulation vasodilate in response to these hormones acting on beta-adrenergic receptors.

• Agonists, Antagonists, and Drugs

  • Acetylcholine receptor agonists and antagonists can have a direct effect on the receptors or exert their effects indirectly.
  • Muscarinic receptor antagonists bind to muscarinic receptors, thereby preventing ACh from binding to and activating the receptor.
  • Beta blockers (sometimes written as β-blockers) or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists, or beta antagonists, are a class of drugs used for various indications.
  • As beta-adrenergic receptor antagonists, they diminish the effects of epinephrine (adrenaline) and other stress hormones.
  • Beta blockers block the action of endogenous catecholamines—epinephrine (adrenaline) and norepinephrine (noradrenaline) in particular—on β-adrenergic receptors, part of the sympathetic nervous system that mediates the fight-or-flight response.

• Plasma Membrane Hormone Receptors

  • Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
  • When a hormone binds to its membrane receptor, a G protein that is associated with the receptor is activated.
  • G proteins are proteins separate from receptors that are found in the cell membrane.
  • The amino acid-derived hormones epinephrine and norepinephrine bind to beta-adrenergic receptors on the plasma membrane of cells.
  • Describe the events that occur when a hormone binds to a plasma hormone receptor

• Cell Signaling and Cellular Metabolism

  • The activation of β-adrenergic receptors in muscle cells by adrenaline leads to an increase in cyclic adenosine monophosphate (also known as cyclic AMP or cAMP) inside the cell .

• Postganglionic Neurons

  • In the sympathetic division, most are adrenergic, meaning they use norepinephrine as their neurotransmitter.
  • In response to this stimulus, postganglionic neurons—with two important exceptions—release norepinephrine, which activates adrenergic receptors on the peripheral target tissues.
  • The activation of target tissue receptors causes the effects associated with the sympathetic system.
  • The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors.
  • The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.

• Heart Circulation

  • This mechanism is due to beta-adrenergic receptors in the coronary arteries and helps enable the increased cardiac output associated with fight-or-flight responses.

• Classification of Receptors by Stimulus

  • Sensory receptors can be classified by the type of stimulus that generates a response in the receptor.
  • Sensory receptors perform countless functions in our bodies.
  • Cutaneous receptors are sensory receptors found in the dermis or epidermis.
  • Encapsulated receptors consist of the remaining types of cutaneous receptors.
  • A tonic receptor is a sensory receptor that adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that adapts rapidly to a stimulus.

• Ionotropic and Metabotropic Receptors

  • Although both ionotropic and metabotropic receptors are activated by neurotransmitters, ionotropic receptors are channel-linked while metabotropic receptors initiate a cascade of molecules via G-proteins.
  • Two types of membrane-bound receptors are activated with the binding of neurotransmitters: ligand-gated ion channels (LGICs) inotropic receptors and metabotropic G- protein coupled receptors.
  • Examples of metabotropic receptors include glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, most serotonin receptors, and receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides, and endocannabinoids.
  • Since opening channels by metabotropic receptors involves activating a number of molecules in the intracellular mechanism, these receptors take longer to open than the inotropic receptors.
  • While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread throughout the cell.