Endogenous opioid peptides in the caudal ventrolateral medulla tonically inhibit blood-pressure-lowering neurons through delta and kappa receptors — a constant opioid contribution to maintaining normal blood pressure.
Tonic opioid restraint of depressor neuronsBlocking brainstem opioid receptors caused blood pressure to drop, revealing constant opioid suppression of the depressor system
What the researchers found
Naloxone injection into the caudal ventrolateral medulla caused dose-dependent blood pressure drops. Delta and kappa receptor antagonists reproduced this effect; mu antagonist did not.
Why it matters
This study reveals that the body's natural opioid peptides play a constant role in maintaining blood pressure through the brain. This could be relevant to understanding blood pressure disorders.
How the study worked
Anesthetized rabbits received bilateral microinjections of opioid antagonists (naloxone, ICI 174864, nor-binaltorphimine, beta-funaltrexamine) into the caudal ventrolateral medulla. Blood pressure and heart rate were continuously monitored.
What this study cannot tell us
Animal study in anesthetized rabbits. Anesthesia itself affects blood pressure regulation. Results may differ in conscious animals or humans.
How to read the evidence
Preliminary animal study in anesthetized rabbits. Demonstrates a tonic mechanism but anesthesia may alter baseline activity.
When this study was published
Published in 1991. The role of brainstem opioid systems in cardiovascular regulation is now well-established.
The bigger picture
Blood pressure regulation is continuous and involves multiple brainstem systems. The finding that opioid peptides constantly restrain the depressor system adds an important piece to the blood pressure puzzle and is relevant to understanding hypotension and blood pressure instability.
Questions still open
- Is this tonic opioid suppression altered in hypotensive disorders?
- Could dysfunction of this system contribute to orthostatic hypotension?
Common questions
What does tonic inhibition mean?
Why delta and kappa but not mu?
Read the original research
Endogenous opioids tonically inhibit the depressor neurones in the caudal ventrolateral medulla of rabbits: mediation through delta- and kappa-receptors.
Neuropharmacology, 30(4), 383-90
Citation
Drolet, G; Morilak, D A; Chalmers, J. (1991). Endogenous opioids tonically inhibit the depressor neurones in the caudal ventrolateral medulla of rabbits: mediation through delta- and kappa-receptors.. Neuropharmacology, 30(4), 383-90.