Effect of endorphins on heart rate and blood pressure in adult dogs

Am J Physiol. 1986 May;250(5 Pt 2):H796-805. doi: 10.1152/ajpheart.1986.250.5.H796.

Abstract

To investigate the role of opioids in regulating cardiovascular function, we administered delta-opioid receptor agonists D-Ala-D-Leu enkephalin (DADLE) and D-Ala-Met enkephalinamide (DAME), and mu-opioid receptor agonist, a morphiceptin analogue (MA), intracisternally in 13 unanesthetized, chronically instrumented adult dogs in 2 doses (25 and 125 micrograms/kg). After an initial transient drop, the R-R interval increased (peak approximately 25-60 min) postadministration of opioids. The time course and the magnitude of the change in R-R interval depended on the agonist: delta-agonists induced a more prolonged and marked change in R-R interval than mu-agonists at both doses. Mean arterial blood pressure (MAP) increased initially but dropped toward or even below base line 30 min after opioids administration. Atropine, given intravenously or intra-arterially at peak action of agonist in relatively low doses (0.02 mg/kg), induced an AV block followed by a marked decrease in R-R interval. There was also an increase in MAP after atropine. Naloxone, given intracisternally, reversed both delta- and mu-opioid effects but did not induce changes in the R-R interval without prior administration of opioids. We conclude that in unanesthetized adult dogs 1) both mu- and delta-receptor opioid agonists prolong the R-R interval, and this depends on the type of receptor stimulated; 2) opioids induce slowing in heart rate, possibly by increasing parasympathetic activity to the heart; 3) enkephalin and morphiceptin analogues induce a biphasic response in MAP; and 4) endorphins do not modulate cardiovascular function tonically; we speculate that they can alter the R-R interval and MAP in the presence of stimuli.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Atropine / pharmacology
  • Blood Pressure / drug effects*
  • Consciousness / drug effects
  • Dogs
  • Endorphins* / pharmacology*
  • Enkephalin, Leucine / analogs & derivatives
  • Enkephalin, Leucine / antagonists & inhibitors
  • Enkephalin, Leucine / pharmacology
  • Enkephalin, Leucine-2-Alanine
  • Enkephalin, Methionine / analogs & derivatives*
  • Enkephalin, Methionine / antagonists & inhibitors
  • Enkephalin, Methionine / pharmacology
  • Heart / drug effects
  • Heart Rate / drug effects*
  • Naloxone / pharmacology
  • Naltrexone / pharmacology

Substances

  • Endorphins
  • Naloxone
  • Enkephalin, Methionine
  • Enkephalin, Leucine
  • Naltrexone
  • enkephalinamide-Met, Ala(2)-
  • Enkephalin, Leucine-2-Alanine
  • Atropine
  • morphiceptin