Alpha-adrenergic vasoconstriction in normal and hypoperfused myocardium during sympathetic nerve stimulation.
Coronary vasoconstriction mediated by postjunctional alpha 1- and alpha 2-adrenergic receptors was studied in normally perfused (control group) and left coronary hypoperfused (stenosis group) hearts of vagotomized, beta-blocked (propranolol) cats. Cardiac sympathetic nerve stimulation was combined with alpha 1- and subsequent alpha 2-adrenergic antagonism (doxazosin and SK&F 104078). Coronary perfusion pressure and heart rate were kept constant within groups; regional myocardial blood flow and cardiac output were obtained by means of microspheres with concomitant measurement of left ventricular myocardial oxygen consumption (MVO2). alpha 1-Adrenergic antagonism alone did not significantly alter blood flow in any wall layer in either group. Subsequent alpha 2-adrenergic antagonism increased epicardial as well as composite transmural flow in the stenosis group (P < 0.025). The inverse correlation between coronary resistance and MVO2 vanished in the stenosis group following alpha 1- and alpha 2-adrenergic antagonism. Maximal first derivative of the left ventricular pressure-time relation (dP/dt) and cardiac output were reduced simultaneously (P < 0.001). Hence, the significance of alpha 1- and alpha 2-adrenergic stimulation of inotropy and cardiac performance are augmented by myocardial hypoperfusion. Furthermore, alpha 2-adrenergic receptors are responsible for epicardial vasoconstriction in hypoperfused myocardium.
Department of Surgery, Haukeland Hospital, University of Bergen, Norway.
J
J
Westby
S
S
Birkeland
S E
SE
Rynning
O L
OL
Myking
J
J
Lekven
K
K
Grong
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002415:Cats; D003326:Coronary Circulation / Q000187:drug effects*; D004558:Electric Stimulation; D006329:Heart Conduction System / Q000502:physiology*; D008297:Male; D010477:Perfusion; D012016:Reference Values; D013564:Sympathetic Nervous System / Q000502:physiology*; D014661:Vasoconstriction
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists