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

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.

• Authors: G G Haddad, H J Jeng, T L Lai
• Journal: The American journal of physiology (Am J Physiol) Vol. 250 Issue 5 Pt 2 Pg. H796-805 (May 1986) ISSN: 0002-9513 [Print] United States
• PMID: 3518492 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

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

Topics

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