How Anesthesia Triggers Stress Hormones and Opioid Release in Horses | Research

The takeaway

Thiopentone/halothane anesthesia in ponies triggered release of endogenous opioids, ACTH, cortisol, and stress hormones, with higher halothane causing more cardiovascular depression.

11 ponies studied
Comparison of two halothane protocols showed higher constant doses produced more cardiovascular depression

What the researchers found

Anesthesia triggered release of endogenous opioids, ACTH, vasopressin, cortisol, and catecholamines, with constant higher halothane producing more cardiovascular depression.

Why it matters

Understanding how anesthesia triggers opioid and stress hormone release helps veterinarians manage surgical pain and cardiovascular risks in horses, and has parallels to human anesthesiology.

How the study worked

Eleven ponies received thiopentone/halothane anesthesia. Six were maintained at constant 1.2% halothane, five at variable 0.8-1.2%. Blood hormones and cardiorespiratory parameters were monitored.

What this study cannot tell us

Small veterinary study with 11 ponies. Two treatment groups with different protocols. Results may not directly apply to other species or anesthetic combinations.

How to read the evidence

Preliminary — small veterinary study with only 11 animals split across two treatment groups.

When this study was published

Published in 1995. Thiopentone/halothane protocols have largely been replaced by newer agents, but the physiological principle of anesthesia-triggered stress hormone release remains relevant.

The bigger picture

Surgery triggers a massive stress response. Understanding how anesthesia itself activates endogenous opioid and stress hormone release helps anesthesiologists manage pain and cardiovascular stability during surgery, in both veterinary and human medicine.

Questions still open

Does the endogenous opioid release during anesthesia provide meaningful pain relief, or is it purely a stress marker?
How do modern anesthetic protocols compare in their stress hormone triggering effects?

Common questions

Does anesthesia trigger the body's own pain-relieving chemicals?

Yes. This study showed anesthesia triggers release of beta-endorphin and other endogenous opioids as part of the stress response, alongside cortisol and adrenaline.

Is this relevant to human anesthesia?

The stress hormone response to anesthesia is similar across mammals. Human anesthesiologists also manage anesthesia-induced hormonal changes, though specific drug protocols differ.

Read the original research

Pituitary-adrenal activity and opioid release in ponies during thiopentone/halothane anaesthesia.

Research in veterinary science, 58(1), 35-41

View on PubMed ↗

Citation

Luna, S P; Taylor, P M. (1995). Pituitary-adrenal activity and opioid release in ponies during thiopentone/halothane anaesthesia.. Research in veterinary science, 58(1), 35-41.