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A2A-adenosine receptor reserve for coronary vasodilation
J C Shryock1, S Snowdy, P G Baraldi
1Department of Medicine, University of Florida, Gainesville 32610, USA.
Circulation
|August 26, 1998
Summary
Adenosine
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Receptor Biology
Background:
- Adenosine is a potent coronary vasodilator.
- It increases coronary blood flow via A2A-adenosine receptors (A2A-AdoRs).
- A large reserve of A2A-AdoRs may explain adenosine's high potency.
Purpose of the Study:
- To test if a large A2A-AdoR reserve explains adenosine's potent coronary vasodilation.
- Investigate the role of spare receptors in adenosine-mediated vasodilation.
Main Methods:
- Used an irreversible A2A-AdoR antagonist to inactivate receptors.
- Compared agonist-induced coronary conductance before and after receptor inactivation.
- Studied three agonists: CGS21680, adenosine, and CCPA.
Main Results:
- Calculated agonist equilibrium dissociation constant (KA) and EC50 values.
- Determined that half-maximal responses occurred when only 1.3% to 9% of A2A-AdoRs were occupied.
- Demonstrated significant receptor reserves for all three agonists.
Conclusions:
- Large receptor reserves for A2A-AdoR agonists were confirmed.
- These reserves explain the high potency of adenosine in causing coronary vasodilation.
- Receptor reserve explains vasodilation without systemic effects.