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Anesth Analg 1987; 66:391-394
© 1987 International Anesthesia Research Society
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Effects of U-50488H, a Selective k-Analgesic, on the Minimum Anesthetic Concentration (MAC) of Halothane in the Rat

John S. Althaus, MS, Philip F. VonVoigtlander, DVM, PhD, Cosmo A. DiFazio, PhD, MD, and Edward D. Miller, MD

Upjohn Company, Kalamazoo, Michigan, and the University of Virginia Medical Center, Charlottesville, Virginia.

Abstract

The effects of U-50488H, a selective K-analgesic, on the minimum anesthetic concentration (MAC) of an inhalational agent (halothane) were studied in the rat. U-50488H was given subcutaneously in doses of 3, 10, and 30 mg/kg body weight. The maximal MAC reduction was about 60%. The potency ratio of U-5048SH to morphine in this model was comparable with potency ratios in other analgesic assays. In separate experiments, the percent reduction in halothane MAC with U-50488H at 30 mg/kg was determined during the infusion of naloxone (5 µg·kg–1·min–1 and 1 mg·kg–1·min–1) at doses shown to have reversed a 70% reduction in MAC by 10 mg/kg of morphine. Only when naloxone was infused at 1 mg·kg–1·min–1 was there a significant reversal of the U-50488H-induced reduction in halothane MAC. This observation suggests that the reduction in MAC of halothane with U-50488H was not mediated by a µ-receptor. In conclusion, through the use of a selective pharmacologic tool that stimulates K-receptors we have demonstrated potential utility of K-analgesics as supplements to general anesthesia.

Key Words: ANALGESICS—U-50488H. • POTENCY, ANESTHETIC—MAC • ANESTHETICS, VOLATILE—halothane






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 1987 by the International Anesthesia Research Society.