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Related Concept Videos

Adrenergic Antagonists: Pharmacological Actions of ɑ-Receptor Blockers01:22

Adrenergic Antagonists: Pharmacological Actions of ɑ-Receptor Blockers

α-Adrenergic antagonists, known as α-blockers, exert their effects by inhibiting α-adrenoceptors, leading to specific physiological actions. α1-blockers and α2-blockers have distinct pharmacological actions and therapeutic applications.
α1-blockers: These drugs inhibit α1-adrenoceptors on smooth muscle cells, resulting in vasodilation. This vasodilation lowers blood pressure, making α1-blockers valuable in treating hypertension. Additionally, α1-blockers effectively address urinary obstruction...
Adrenergic Antagonists: Chemistry and Classification of ɑ-Receptor Blockers01:17

Adrenergic Antagonists: Chemistry and Classification of ɑ-Receptor Blockers

Adrenergic antagonists, or sympatholytics, inhibit adrenoceptor activation driven by catecholamines or agonists. Based on their adrenoceptor specificity, adrenergic blockers can be categorized into two primary groups: α-adrenergic blockers (α-blockers) and β-adrenergic blockers (β-blockers). α-blockers interact with α1 and α2 subtypes of α-adrenoceptors.
Nonselective α-blockers: Nonselective α-blockers contain haloalkylamine or imidazoline moieties. Phenoxybenzamine, with a haloalkylamine...
Adrenergic Receptors: ɑ Subtype01:31

Adrenergic Receptors: ɑ Subtype

Adrenoceptors are classified into α and ꞵ classes based on their potencies to catecholamine agonists. α-adrenoceptors show the following order of catecholamine potency:
Adrenaline ≥ Noradrenaline >> Isoprenaline
α-adrenoceptors are further divided into α1 and α2-adrenoceptors.
α1-Adrenoceptors: These receptors are located postsynaptically on the effector organs and cause constriction of smooth muscle mediated by activation of phospholipase C—inositol-1,4,5-trisphosphate...
Adrenergic Agonists: Chemistry and Structure-Activity Relationship01:16

Adrenergic Agonists: Chemistry and Structure-Activity Relationship

Adrenergic agonists' structure-activity relationship (SAR) determines their selectivity and efficacy. These agonists comprise a phenylethylamine moiety with an aromatic ring and an ethylamine side chain.
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
Adrenergic Agonists: Indirect-Acting Agents01:25

Adrenergic Agonists: Indirect-Acting Agents

Indirect-acting adrenergic agonists potentiate the effects of endogenous catecholamines through different mechanisms without directly binding to adrenoceptors.
One mechanism involves depleting stored catecholamines by displacing them from synaptic vesicles. These agents, known as "displacers," are transported into vesicles at the expense of noradrenaline. Examples include amphetamine and tyramine, which lack a catechol moiety, resulting in prolonged action, improved oral bioavailability, and...
Adrenergic Receptors: β Subtype01:26

Adrenergic Receptors: β Subtype

β-adrenoceptors have varied sensitivities towards adrenaline, noradrenaline, and isoprenaline. The order of agonist potency is as follows:
Isoprenaline > Adrenaline > Noradrenaline
Neurotransmitter binding to these receptors causes activation of adenylyl cyclase resulting in increased concentrations of cAMP and modulation of calcium ion channels within the cell. They are further classified into β1, β2, and β3 subtypes.
β1-adrenoceptors: β1-adrenoceptors have equal affinities for...

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Receptor Autoradiography Protocol for the Localized Visualization of Angiotensin II Receptors
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Specific α2-adrenoreceptor antagonists induce behavioural activation in the rat.

S L Dickinson1, B Gadie, I F Tulloch

  • 1Reckitt and Colman Psychopharmacology Unit, The School of Medical Sciences, University Walk, Bristol, BS8 1TD.

Journal of Psychopharmacology (Oxford, England)
|January 28, 2012
PubMed
Summary

Selective alpha(2)-adrenoreceptor antagonists like idazoxan induced behavioral activation in rats, but only in habituated animals with low baseline activity. These effects were mild compared to D-amphetamine.

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Area of Science:

  • Neuroscience
  • Pharmacology
  • Behavioral Science

Background:

  • Alpha(2)-adrenoreceptors play a crucial role in regulating neurotransmitter release, including norepinephrine.
  • Antagonists of these receptors can modulate central nervous system activity.
  • Understanding the behavioral consequences of alpha(2)-adrenoreceptor blockade is important for neuroscience research.

Purpose of the Study:

  • To investigate the behavioral effects of specific alpha(2)-adrenoreceptor antagonists in rats.
  • To characterize the conditions under which these behavioral effects manifest.
  • To compare the potency of alpha(2)-adrenoreceptor antagonists with a known stimulant like D-amphetamine.

Main Methods:

  • Administration of three selective alpha(2)-adrenoreceptor antagonists (idazoxan, efaroxan, RX811059) to rats.
  • Observation and quantification of behavioral changes, including locomotion and exploration.
  • Testing in both habituated and novel environments.
  • Comparison with the behavioral effects of D-amphetamine.

Main Results:

  • All tested antagonists induced behavioral activation, characterized by increased locomotion and exploration.
  • These effects were observed only in rats with low baseline activity (habituated animals).
  • Behavioral activation was not observed in novel environments and was significantly weaker than that induced by D-amphetamine.

Conclusions:

  • Selective alpha(2)-adrenoreceptor antagonists can induce behavioral activation in rats, contingent on environmental context and baseline activity.
  • The observed effects suggest a modulatory role of alpha(2)-adrenoreceptors in behavioral control.
  • Potential mechanisms include direct noradrenergic actions or indirect modulation of dopaminergic pathways.