AJP - Heart and Circulatory Physiology, Vol 256, Issue 6 1651-H1658, Copyright © 1989 by American Physiological Society
Effect of enkephalins on cardiac output and regional blood flow in conscious dogs
C. L. Rosen, A. Cote and G. G. Haddad
Department of Pediatrics, Columbia University, College of Physicians and Surgeons, New York, New York 11791.
To investigate the effects of enkephalins on cardiac output and regional
blood flow, we administered D-Ala-D-Leu-enkephalin (DADLE) intracisternally
(ic) to 14 chronically instrumented unanesthetized dogs. Measurements were
made at base line, 20, 45, and 75 min after DADLE (25 or 125 micrograms/kg)
and 15 min after naloxone (5 micrograms/kg ic). After 125 micrograms/kg
DADLE, all animals developed hypoventilation, bradycardia, and decreased O2
consumption without hypotension. Cardiac output decreased (-34%), but brain
blood flow increased (+110%). Blood flow decreased to the diaphragm (-38%),
heart (-21%), skeletal muscle (-40%), skin (-67%), pancreas (-79%), and
gastrointestinal tract (-26%). After 25 micrograms/kg DADLE, there were no
consistent changes in cardiac output or regional blood flow. Four
additional animals (without DADLE) were exposed to altered inspired gases
to reproduce the blood gas changes after DADLE. These animals developed
hyperventilation without bradycardia and increased brain (+114%) and
diaphragm (+649%) blood flow. We conclude that centrally administered
enkephalins produce 1) a parallel decrease in ventilation, heart rate, O2
consumption, and cardiac output and 2) a major blood flow redistribution,
primarily dictated by the effects of opioids on ventilation, heart rate,
and metabolism.
