Nov 27, 2010

Adrenergic Receptors..Pharmacology

Two types of receptor sites are theorized to explain adrenergic effects.
  • Alpha-receptors are associated mainly with increased contractibility of vascular smooth muscle and intestinal relaxation.
  • The alpha1 is located at postsynaptic effector sites to stimulate transmitter release in smooth muscle. For example, the smooth muscle of peripheral blood vessels is contracted in alpha1 stimulation.
  • The alpha2 receptor site is located presynaptic on axon terminals to inhibit the release of nor-epinephrine (the transmitter). The effects of alpha2 stimulation results in relaxation of the intestinal tract--motility and tone are decreased.
  • Beta-receptors are associated with vasodilation and relaxation of nonintestinal smooth muscle and cardiac stimulation.
  • Beta1 Stimulation of beta1 receptor sites results in cardiac stimulation and lipolysis.
  • Beta2 Stimulation of beta2 receptor sites causes bronchodilation, relaxation of blood vessels (usually in skeletal muscles), and muscle glycogenolysis.
Alpha Receptor Site: Important features of the site include in order of importance:
  • An anionic site - which binds the positive ammonium group.
  • One hydrogen bonding area
  • A flat area non-polar area for the aromatic ring.
Beta Receptor Site: Important features of the site include in order of importance - also see the graphic on the left:
  • An anionic site - shown as Asp anionic negative acid group which binds the positive ammonium group.
  • Two hydrogen bonding areas - shown as two Serine with alcohol (OH) groups hydrogen bonding to the phenol OH groups of the NE.
  • A flat area non-polar area for the aromatic ring.
  Receptor Subtype
NE, EP, dobutamine, xamoterol
atenolol, metoprolol.
 Adipose tissue
  beta1, beta 3?

Vascular Smooth Muscle
 beta 2
 EP, salbutamol, terbutaline, salmeterol
Airway Smooth Muscle
  beta 2
 terbutaline, salbutamol, salmeterol and zinterol,
 Smooth muscle contraction
 alpha 1
 NE, EP, phenylephrine, oxymetazoline)
prazosin, doxazocin
 Inhibition of
transmitter release Hypotension, anaesthesia, Vasoconstriction
 alpha 2
clenbuterol, alpha-methylnoradrenaline, dexmedetomidine, and mivazerol, clonidine, clenbuterol
yohimbine, idazoxan, atipamezole, efaroxan, and rauwolscine

Receptor Sites
 vasodilation (b2)
 iris dilation
 cardioacceleration (b1)
 intestinal relaxation
 intestinal relaxation (b2)
 intestinal sphincter
 uterus relaxation(b2)
 bladder sphincter contraction
 bronchodilation (b2)


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