Catecholamines can induce adenosine receptor-mediated protection of the myocardium but do not participate in ischemic preconditioning in the rabbit.
The role of catecholamines in ischemic preconditioning is unclear. Accordingly, the effects of tyramine-induced norepinephrine release and alpha 1-receptor blockade were examined. Ischemic preconditioning with a 5-minute coronary occlusion 10 minutes before a 30-minute ischemic interval resulted in only 7.7 +/- 3.1% infarction of the risk area, significantly less than that in control rabbits with isolated 30-minute coronary occlusions (34.4 +/- 3.2%, P < .01). Intravenous infusion of tyramine 10 minutes before 30 minutes of ischemia also protected the heart from infarction to an extent similar to that seen with ischemic preconditioning (6.9 +/- 2.4% infarction). This protection observed with tyramine infusion was eliminated by alpha 1-receptor blockade with BE 2254 (36.8 +/- 2.6% infarction) but was unaffected by beta-blockade with propranolol (10.5 +/- 2.4% infarction). Furthermore, the protection was unaffected when the tyramine-induced hypertension was attenuated by allowing blood to flow into a volume reservoir (3.9 +/- 0.8% infarction, P < .01 vs control value). The nonselective adenosine-receptor blocker PD 115,199 also eliminated tyramine-induced protection (40.2 +/- 5.6% infarction), indicating that adenosine is involved in adrenergic-mediated protection. BE 2254 could not block ischemic preconditioning (3.9 +/- 1.1% infarction, P < .01 vs control value). Therefore, catecholamine release before prolonged ischemia can protect the heart from infarction via the alpha 1-receptor, but adenosine receptor stimulation is also involved. alpha-Adrenergic stimulation does not appear to be critical to the protection observed after ischemic preconditioning.
Thornton
J D
JD
Department of Physiology, University of South Alabama, Mobile 36688.
Daly
J F
JF
Cohen
M V
MV
Yang
X M
XM
Downey
J M
JM
D000241:Adenosine / Q000502:physiology; D000818:Animals; D002395:Catecholamines / Q000502:physiology*; D005260:Female; D008297:Male; D017202:Myocardial Ischemia / Q000503:physiopathology*; D011817:Rabbits; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011983:Receptors, Purinergic / Q000502:physiology*; D013045:Species Specificity; D014439:Tyramine / Q000494:pharmacology
D002395:Catecholamines; D011942:Receptors, Adrenergic, alpha; D011983:Receptors, Purinergic; D000241:Adenosine; D014439:Tyramine