Chapter 6: Adrenergic Receptor Agonists and Antagonists Flashcards
What are the 3 classifications of sympathomimetic drugs?
1st Group (Direct Agonists), 2nd Group (Indirect Agonists), 3rd Group (Mixed-Acting Adrenergic Agonists)
Drugs that mimic the physiological and pharmacological actions of the endogrnous catecholamines
Sympathomimetic Drugs
Classification of sympathomimetic drugs that directly binds to and activate adrenergic receptors
1st Group or Direct Agonists
Examples of 1st group or direct agonists
Phenylephrine, Dobutamine
This group enhances the availability of endogenous catecholamines to bind adrenergic receptors
2nd Group (indirect Acting Agonists
Group of drugs that directly activate adrenergic receptors as well as increase the release of NE from adrenergic nerve terminals
3rd Group (Mixed-Acting Adrenergic Agonists)
Main neurotransmitters utilized by the SNS
Epinephrine, Norepinephrine
Parent comound of sympathomimetic amines, consists of benzene ring and ethylamine side
B-phenylethylamine
Sympathomimetic drugs
Epinephrine, Norepinephrine, Dopamine, Isoproterenol
Required for maximum alpha and beta receptor potencies
Catechol nucleus
Any chemical containing catechol
Catecholamines
Modification in phenylethylthalamine that results in reduced B-adrenergic receptor activity
removal of hydroxyl group
Modification in phenylethylthalamine that produces a compound with reduced CNS effects
Substitution of B-carbon atoms
Modification in phenylethylthalamine that produces a drug that is generally more resistant to oxidation by monoamine oxidase
Substitution of a-carbon atom
Modification in phenylethylthalamine that affects a nd B agonistic properties of various drugs
Alkyl substitutions on the amino acid
A type of G-coupled receptor
Adrenergic Receptors
Members of the B-adrenergic receptor family
B1, B2, B3
Activation of this receptor results in stimulation of adenylyl cyclase and increase cAMP
B-adrenergic receptor family
B-adrenergic receptor that increase heart rate and enhance cardiac contractility
B1
B-adrenergic receptor found in the pulmonary airways
B2 receptors
B-adrenergic receptors found in the detrusor muscle of the bladder
B2 and B3 receptors
Members of the a1 receptor family
A1A, A1B, A1D
This receptor family activates phospholipase C
a1 receptor family
Where are a1 receptors located?
vascular smooth muscles
Function of the a1 receptor
smooth muscle contraction
Members of the a2 receptor family
A2A, A2B, and A2C
Activation of these receptor inhibits adenyl cyclase activity, hence, a reduced cAMP levels
a2 receptors
Location of a2 receptors
terminals of postganglionic sympathetic nerve fibers
Activation of this receptor will reduce norepinephrine release from nerve terminals
a2 receptors
This receptor is expressed at the thrombocytes, endothelial cells, and CNS
a2 receptors
Members of the dopamine receptors
D1, D2
Activation of this dopamine receptor is associated with increased cAMP
D1 receptor activation
Activation of this dopamine receptor inhibits adenyl cyclase activity
D2 receptor activation
Provides an important framework for understanding target organ effects of endogenous catecholamines and sympathomimetic drugs
Receptor Selectivity
A potent and selective agonist at A1 adrenergic receptors
Phenylephrine
Drug that can cause an increase in peripheral vascular resistance, hence, an increase in blood pressure
Phenylephrine
An agonist at a1, a2, and b1 adrenergic receptors
Norepinephrine
A potent agonist at a-adrenergic and b-adrenergic receptors
Epinephrine
Produces vasodilation when bound to B2 receptors
Epinephrine
Used for downer patients
Epinephrine
Has competing vasoconstriction and vasodilation effects
Epinephrine
A potent nonselective B1 and B2 receptor agonists that exerts little effect on A-adrenergic receptors
Isoproterenol
Used for hypertensive patients
Isoproterenol
Blocks adrenergic receptors
Adrenergic-Receptor Antagonists
Used in veterinary medicine to reverse sedation caused by a2-adrenergic receptor agonist
A2-Adrenergic receptor Antagonist
Non-selective antagonist that bind covalently to a-adrenergic receptors to produce an irreversible bond
Phenoxybenzamine
Inhibition of reuptake of Norepinephrine at presynaptic nerve terminals is an effect of?
Phenoxybenzamine
What are some exampls of non-seslective a1, a2-adrenergic receptor antagonists?
- Phenoxybenzamine
- Phentolamine
- Phenothiazine tranquilizers
Potent nonselective a-adrenergic receptor antagonists, have profound CNS effect
Phenothiazine tranquilizers
Used in dogs, can antagonize a1 drenergic receptors
Trazodone
A competitive antagonist marked selectivity for a1-adrenergic receptor
Prasozin
Reversible a1-adrenergic receptor antagonists with similar effects to prazosin
Terazosin, Doxazosin, Alfuzosin
A second generation A1 adrenergic receptor antagonist, used for orthostatic hypotension
Tamsulosin
A1 adrenergic receptor antagonist that has higher affinity for A1A and A1D receptors
Tamsulosin
Third generation, highly selective A1 adrenergic receptro antagonist
Silodosin
The prototype for selective A2 adrenergic receptor antagonists
Yohimbine
Yohimbe can be found in the bark of ______ and root of _______
Pausinystalia yohimbe, Rauwolfia root
Demonstrates a degree of antagonistic activity at serotonin receptors
Yohimbine
Belongs to the synthetic group of competitive A2 adrenergic receptor antagonist
Tolazoline
Licensed for reversing xylazine in horses
Tolazoline
A mixed A1 and A2 adrenergic receptor antagonist
Tolazoline
An A2 adrenergic receptor antagonist with an imidazole structure
Atipamezole
Has binding affinity and A2/A1 selectivity ratio higher than those of yohimbine or tolazoline
Atipamezole
Group of beta blockers that can stimulate beta-adrenergic receptors (agonist effect) and oppose catecholamines (antagonistic effect) in a competitive way
Intrinsic Sympathomimetic Activity (ISA)
Drugs considered as partial antagonists
Pindolol, Acebutolol
Cause incomplete activation of B receptors
Partial Antagonists
Inhibit the activation of B-adrenergic receptors in the presence of high levels of Epinephrine and Norepinephrine
Partial Antagonists
Beta blockers used in veterinary medicine
Propranolol, Atenolol, Esmolol, Metoprolol, Carvedilol
Classifications of beta blockers
- Nonselective B-adrenergic receptor antagonists (1st Generation)
- Selective B1-ddrenergic receptor antagonists (2nd Generation)
- Third Generation Nonselective Antagonists