Endogenous adenosine increases coronary flow by activation of both A2A and A2B receptors in mice.
To clarify which adenosine receptor subtype(s) are responsible for regulation of coronary flow through endogenous adenosine, coronary vascular responses were examined in isolated hearts from wild-type (WT) and A(2A) knockout (A(2A)KO) mice. Adenosine deaminase inhibitor, erythro-9-hydroxy-nonyl-adenine (EHNA), and adenosine kinase inhibitor, iodotubericidine (ITU), were used to examine the effects of endogenous adenosine. Combined infusion of EHNA and ITU in Balb/c hearts produced comparable increases in coronary flow as exerted by exogenous adenosine while they markedly decreased the heart rate, and these effects were reversed by adenosine receptor antagonist, 8-p-sulfophenyl-theophylline (8-SPT). Similarly, EHNA and ITU increased coronary flow in WT hearts to 422% of baseline, whereas this response was reduced to 144% of baseline in A(2A)KO hearts. Heart rate was equally reduced (approximately 50% of baseline) in both groups. Alloxazine (A(2B) receptor antagonist) abolished EHNA- and ITU-induced coronary flow in A(2A)KO hearts without altering the reduced heart rate. Selective A(1) receptor antagonist, 8-cyclopentyl-1-1,3-dipropylxanthine (DPCPX), reversed EHNA- and ITU-induced decreases in heart rate without altering the elevated coronary flow. These findings suggest that coronary vascular responses to endogenous adenosine mimic those produced by exogenous adenosine and are mediated at least by activation of both A(2A) and A(2B) receptors in isolated mouse hearts.
Talukder
M A Hassan
MA
Departments of Pharmacology, The Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA.
Morrison
R Ray
RR
Ledent
Catherine
C
Mustafa
S Jamal
SJ
D000241:Adenosine / Q000037:antagonists & inhibitors* / Q000378:metabolism* / Q000494:pharmacology; D000243:Adenosine Deaminase / Q000378:metabolism; D058892:Adenosine Deaminase Inhibitors; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1 / Q000172:deficiency / Q000378:metabolism*
D058892:Adenosine Deaminase Inhibitors; D004791:Enzyme Inhibitors; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1; D000248:Adenosine Kinase; D000243:Adenosine Deaminase; D000241:Adenosine