Alpha-adrenoceptor subtypes and regional myocardial blood flow distribution during coronary occlusion in dogs.
The involvement of postsynaptic alpha-adrenoceptors in the distribution of regional myocardial blood flows (RMBFs, microsphere technique) within the left ventricle has been investigated during intermittent coronary artery occlusion in open-chest anesthetized dogs. Two types of RMBFs distribution were assessed: (1) between endocardial (endo) and epicardial (epi) layers (endo/epi ratio) and (2) between nonischemic (NIZ) and ischemic zones (IZ) (IZ/NIZ ratio). Equipressor does of selective alpha 1-(cirazoline after rauwolscine) and alpha 2-(UK-14,304 after prazosin) adrenoceptor agonists were infused in dogs previously submitted to ganglionic and muscarinic blockade. In a control group, aortic pressure was mechanically raised by aortic stenosis to levels similar to those reached with both alpha-adrenoceptor agonists. Cirazoline and aortic stenosis increased RMBFs in IZ and NIZ but did not alter the calculated coronary resistance in NIZ and did not affect endo/epi and IZ/NIZ ratios. In contrast, UK-14,304 preferentially augmented coronary resistance in NIZ, increased IZ/NIZ ratio (both P less than 0.05) but did not affect endo/epi ratio in IZ and NIZ. Thus, we conclude that if transmural distribution of RMBFs (endo/epi ratio) is not preferentially controlled by any alpha-adrenoceptor subtype, postsynaptic alpha 2-adrenoceptors are of importance during coronary occlusion in promoting a favorable redistribution of RMBFs from NIZ towards IZ by inducing a selective NIZ coronary vasoconstriction (ie a "reverse coronary steal").
Département de Pharmacologie, Faculté de Médecine Paris-Sud, Le Kremlin-Bicêtre, France.
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Berdeaux
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Arthaud
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Lambert
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JF
Giudicelli
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D000068438:Brimonidine Tartrate; D003326:Coronary Circulation / Q000502:physiology*; D003331:Coronary Vessels / Q000502:physiology*; D004285:Dogs; D005260:Female; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D000068438:Brimonidine Tartrate; C014282:cirazoline