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Application of Dixon's Up-and-Down Design to Estimate the Minimum Alveolar Concentration of Sevoflurane in Rats with Refined Movement Classification
Published on: July 25, 2025
Naltrexone does not affect isoflurane minimum alveolar concentration in cats
Robert J Brosnan1, Bruno H Pypendop, Chalon R Majewski-Tiedeken
1Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. rjbrosnan@ucdavis.edu
Veterinary Anaesthesia and Analgesia
|January 3, 2013
Summary
Naltrexone, an opioid receptor antagonist, did not alter the minimum alveolar concentration (MAC) of isoflurane in cats. This suggests that mu-opioid receptors are not the primary sites for immobility induced by inhaled anesthetics in this species.
Area of Science:
- Veterinary Anesthesiology
- Pharmacology
- Neuroscience
Background:
- Cats exhibit relative resistance to the anesthetic-sparing effects of opioids.
- Opioid receptors are known modulators of anesthetic depth in many species.
Purpose of the Study:
- To investigate the effect of naltrexone, a mu-opioid receptor antagonist, on the minimum alveolar concentration (MAC) of isoflurane in cats.
- To explore the role of mu-opioid receptors in mediating immobility from inhaled anesthetics in felines.
Main Methods:
- A randomized, crossover, placebo-controlled, blinded experimental design was employed.
- Six healthy adult cats were studied twice, receiving either saline or naltrexone (0.6 mg/kg IV) before isoflurane MAC measurement.
- Isoflurane MAC was measured at baseline and after drug administration in a crossover fashion.
Main Results:
- The minimum alveolar concentration (MAC) of isoflurane was 2.03 ± 0.12% in cats.
- Naltrexone administration did not significantly alter the isoflurane MAC compared to saline control.
- Isoflurane MAC remained unchanged from baseline following both saline and naltrexone treatments.
Conclusions:
- Naltrexone does not affect the minimum alveolar concentration (MAC) of isoflurane in cats.
- The findings indicate that mu-opioid receptors are unlikely to be the neuroanatomic sites responsible for immobility induced by inhaled anesthetics in cats.
- This challenges the direct role of mu-opioid receptor-modulated spinal neurons in anesthetic immobility in this species.
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