Requisite role of cardiac myocytes in coronary alpha1-adrenergic constriction.
BACKGROUND
Alpha-adrenergic activation in vivo causes constriction of coronary arterioles, but, paradoxically, in vitro these microvessels do not contract to this stimulus. We hypothesized that cardiac myocytes have a requisite role in alpha1-adrenergic coronary arteriolar constriction through the release of myocyte-derived contractile factor(s).


RESULTS
Administration of the alpha1-adrenergic agonist phenylephrine did not constrict isolated coronary arterioles, but constriction was observed to supernatant obtained from phenylephrine-treated cardiac myocytes. Constriction to the supernatant was blocked by administration of an endothelin-A antagonist to the microvessel preparation or an alpha-adrenergic antagonist to the myocytes and was augmented after administration of an adenosine antagonist. Administration of phenylephrine to the myocytes increased endothelin-1 levels in the supernatant, but only to subthreshold concentrations.


CONCLUSIONS
Cardiac myocytes have a requisite role in constriction of coronary resistance vessels to alpha1-adrenergic stimuli, which may be mediated by endothelin-1 and other unidentified myocyte-derived vasoconstrictors.
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226, USA.
C P
CP
Tiefenbacher
D V
DV
DeFily
W M
WM
Chilian
D000241:Adenosine / Q000037:antagonists & inhibitors; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000502:physiology; D003331:Coronary Vessels / Q000502:physiology*; D004285:Dogs; D019332:Endothelin-1 / Q000032:analysis; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology*; D010656:Phenylephrine / Q000494:pharmacology*; D014661:Vasoconstriction / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D019332:Endothelin-1; D010656:Phenylephrine; D000241:Adenosine