Transmural heterogeneity of postjunctional alpha 2 adrenergic coronary vasoconstriction in hypoperfused cat left ventricle.
OBJECTIVE
The aim was to analyse the influence of coronary postjunctional alpha 1 and alpha 2 adrenergic vasoconstriction in hypoperfused myocardium with special emphasis on transmural distribution of blood flow.


METHODS
The left coronary artery was hypoperfused by means of a clamped shunt line. Sequential selective postjunctional alpha 1 (doxazosin) and alpha 2 (SK&F 104078) adrenergic antagonism was established following beta adrenergic antagonism with propranolol. Regional myocardial blood flow was measured with radiolabelled microspheres during equal coronary perfusion pressures. Experimental subjects were nine pentobarbitone anaesthetised open chest cats.


RESULTS
Left coronary hypoperfusion decreased endocardial blood flow, whereas epicardial flow was unaltered. In this situation alpha 1 adrenergic antagonism did not affect myocardial blood flow. Subsequent alpha 2 antagonism impaired endocardial blood flow, whereas epicardial blood flow was augmented. Mean coronary vascular resistance declined following combined alpha 1 and alpha 2 adrenergic antagonism.


CONCLUSIONS
Coronary alpha adrenergic vasoconstriction is localised mainly epicardially in hypoperfused myocardium and counteracts endocardial hypoperfusion distal to a fixed coronary stenosis. Furthermore, this vasoconstriction is of the postjunctional alpha 2 adrenergic subtype.
Department of Surgery, University of Bergen, Haukeland Hospital, Norway.
J
J
Westby
S
S
Birkeland
J
J
Lekven
K
K
Grong
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D002415:Cats; D003327:Coronary Disease / Q000503:physiopathology*; D003331:Coronary Vessels / Q000187:drug effects*; D017292:Doxazosin / Q000494:pharmacology*; D008297:Male; D012039:Regional Blood Flow / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000502:physiology*
D000317:Adrenergic alpha-Antagonists; D001552:Benzazepines; C054935:SK&F 104078; D017292:Doxazosin