Alpha 2-adrenoceptor-mediated coronary vasoconstriction persists after exhaustion of coronary dilator reserve.
The effect of intracoronary administration of the selective alpha 2-adrenoceptor agonist B-HT 920 on coronary resistance was tested in 14 open-chest dogs before and after exhaustion of coronary dilator reserve. Under both conditions B-HT 920 increased coronary resistance to the same extent: 27 +/- 4% before and 32 +/- 3% after. Administration of B-HT 920 did not affect cardiovascular haemodynamics significantly, although after exhaustion of coronary dilator reserve left ventricular dP/dtmax decreased slightly by 12 +/- 5%. While efferent cardiac sympathetic discharge remained constant during control conditions it increased by 27 +/- 7% when B-HT 920 was administered into a stenotic coronary artery. We conclude that, in contrast to observations made on alpha 1-adrenoceptors, activation of coronary alpha 2-adrenoceptors may have deleterious effects after exhaustion of coronary dilator reserve because these receptors mediate a comparable constriction in well- and under-perfused coronary vessels. Thus they are unlikely to favour a redistribution of coronary blood flow into under-perfused myocardial regions. In addition, this unfavourable effect of B-HT 920 on coronary perfusion after coronary dilator reserve has been exhausted may be further exacerbated by an increase in efferent sympathetic discharge.
Deussen
A
A
Heusch
G
G
Thämer
V
V
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D003331:Coronary Vessels / Q000502:physiology*; D004285:Dogs; D010101:Oxygen Consumption / Q000187:drug effects; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; C024763:talipexole