An opioid receptor blocker improved cerebral blood flow, blood pressure, and EEG recovery after brain injury — and the active form outperformed its inactive mirror image.
Improved blood flow and EEGWith opioid receptor blocker given 15 min after brain injury
What the researchers found
Dynorphin A accumulated in injured brain regions after fluid-percussion brain injury in cats. These same regions showed significant decreases in cerebral blood flow. Enkephalin did not accumulate.
The opioid antagonist Win-(-), given 15 minutes after injury, significantly improved multiple outcomes: mean arterial blood pressure increased, EEG amplitude (brain wave activity) improved, regional cerebral blood flow recovered, and both the severity and incidence of brain hemorrhage decreased. Survival after injury was significantly better.
The control was elegant: Win-(+), the mirror-image version of the same drug that cannot bind opioid receptors, had no effect. Neither did saline. This confirmed the benefits came specifically from blocking opioid receptors.
Why it matters
This was strong preclinical evidence that blocking opioid receptors after brain trauma can improve outcomes. The use of an inactive mirror-image control made the results convincing. The findings supported clinical trials of opioid antagonists for traumatic brain injury.
How the study worked
Cats received fluid-percussion brain injury. Treatment groups received Win-(-) (active opioid antagonist), Win-(+) (inactive control), or saline at 15 minutes after injury. Outcomes measured: blood pressure, EEG amplitude, regional cerebral blood flow (using radioactive microspheres), hemorrhage incidence, and survival. Dynorphin and enkephalin were measured in brain regions. Tested in cats, not people.
What this study cannot tell us
Tested in cats, not people. Treatment was given at 15 minutes post-injury, which is faster than typical emergency room arrival. Infarct size and 24-hour mortality were not significantly different from controls, meaning some key outcomes did not improve. Translating large-animal brain injury results to humans is uncertain.
How to read the evidence
Moderate animal study with active vs inactive stereoisomer control — a rigorous pharmacological design.
When this study was published
Published in 1987 — key study driving interest in opioid antagonists for TBI treatment.
The bigger picture
This companion study to RPEP-00021 moved from correlation to treatment. By showing that blocking opioid receptors improved outcomes, it provided direct evidence for opioid peptides as therapeutic targets in brain trauma.
Questions still open
- What is the optimal treatment window for opioid blockers after brain injury?
- Would selective kappa receptor blockers work better?
Common questions
What is a stereoisomer control?
Has this been tried in humans?
Read the original research
Endogenous opioids may mediate secondary damage after experimental brain injury.
The American journal of physiology, 253(5 Pt 1), E565-74
Citation
McIntosh, T K; Hayes, R L; DeWitt, D S; Agura, V; Faden, A I. (1987). Endogenous opioids may mediate secondary damage after experimental brain injury.. The American journal of physiology, 253(5 Pt 1), E565-74.