Influence of Myocardial Ischemia and Reperfusion on β-Adrenoceptor Subtype Expression

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The effects of ischemic injury and reperfusion on myocardial β-adrenoceptor expression were examined in dogs after 30 min of left anterior descending coronary artery (LAD) ligation. Three sets of six dogs were allocated to either sham ligation (group 1), 30 min ischemia without reperfusion (group II), or ischemia with 1 h of reperfusion (group III). The density of total β-adrenoceptors along with β1- and β2-adrenoceptor subtypes were compared in tissue from the ischemic LAD and nonischemic left lateral zones by using radioligand binding with 125-labeled iodocyanopindolol (ICYP). In the control animals, there was no difference between total β-adrenoceptors (43.8 ± 7.2 vs. 40.7 ± 8.0 fmol/mg protein ± SEM) or percentage β-adrenoceptor subtypes between the two zones. In group II, total β-adrenoceptors increased 19.9% (p = 0.03) in the LAD compared with the lateral zone after 30 min of ischemia Both β-adrenoceptor subtypes increased, but only the increase in β2-adrenoceptor was significant (39.8%; p = 0.02). Animals in group III revealed no difference in total β-adrenoceptors density between LAD and lateral zones (48.3 ± 13.4 vs. 55.2 ± 8.5 fmol/mg protein). Brief myocardial ischemia is associated with an increase in total β-adrenoceptors, attributed predominantly to increased β2-adrenoceptors density. The increase in β-adrenoceptor density is reversible after 1 h of reperfusion.

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