AJP - Heart and Circulatory Physiology, Vol 248, Issue 3 382-H388, Copyright © 1985 by American Physiological Society
Local endogenous opiate activity in dog myocardium: receptor blockade with naloxone
J. L. Caffrey, J. F. Gaugl and C. E. Jones
The participation of endogenous opiates in myocardial performance and
coronary blood flow was investigated. Heart rate, left ventricular
contractile force (LVCF), left coronary blood flow (LCBF), and left
ventricular oxygen extraction were monitored in anesthetized dogs before
and after intracoronary opiate receptor blockade with naloxone. LVCF
consistently increased in a dose-dependent fashion following intracoronary
naloxone. The increasing LVCF was accompanied by significant increases in
LCBF and myocardial oxygen consumption, without changes in heart rate.
Rapid onset of responses suggested the presence of endogenous opiates
operating locally within the myocardium. Similar effects did not follow
right atrial injection of naloxone, ruling out a systemic mechanism.
Furthermore, naloxone injected into the isolated left anterior descending
artery selectively increased contractile force in that perfusion territory
while the adjacent untreated circumflex territory showed no change. The
administration of dynorphin into the coronaries produced a depression of
LVCF qualitatively consistent with these effects. The effect of dynorphin
was subsequently reversed with naloxone. These results support the concept
that endogenous opiates participate in the regulation of myocardial
function through local mechanisms at the myocardial level.
