Analgesic effect of aprotinin in the rat and its inhibition by naloxone

Newer concepts of analgesia and anesthesia

Intracerebroventricular (ICV) administration of the peptidase inhibitors amastatin, trasylol, bacitracin, or phe-D-ala and systemic administration of phenylmethylsulfonyl fluoride resulted in one or more of the following responses: analgesia, reduced withdrawal severity in opiate tolerant rats, alterations in motor activity and behavior, hypo- and hyperthermia and others; some of these effects were antagonized by naloxone, suggesting participation of opioid and other endogenous peptides. In addition, peptidase inhibitors enhanced analgesic and other responses to opioid peptides given ICV. Peptidase inhibition affords another method of inducing selective pharmacological responses such as pain relief in individuals resistant to other forms of therapy. ICV administration of beta-endorphin in the rat induces general anesthesia that is instantly reversed by systemic naloxone. Extensions of this work include identification of specific neural pathways that mediate anesthesia and characterization of opiate receptor subtype(s) at these sensitive loci. This approach offers the potential for the design of systemically effective opioid peptide anesthetics with little or no secondary effects and rapid reversibility.

Phenylmethylsulfonyl fluoride (PMSF) given systemically produces naloxone-reversible analgesia and potentiates effects of beta-endorphin given centrally

Intraperitoneal (IP) injection of the serine proteinase inhibitor phenylmethylsulfonyl fluoride (PMSF) produced dose-dependent analgesia in Sprague-Dawley rats. AD50 was 2.9 +/- 1.4 (S.E.) mg kg-1, the analgesia was antagonized by naloxone but unaffected by atropine. PMSF significantly enhanced the analgesic effect of beta-endorphin (END) given by intracerebroventricular (ICV) infusion in rats, the enhanced END analgesia was naloxone-reversible. In Swiss-Webster mice the 24-hr LD50 value for PMSF was 215 +/- 55 mg kg-1 IP; autonomic and behavioral responses were similar to those seen in rats with ICV END. These results indicate that systemic PMSF can protect central endorphin(s) from enzymatic destruction. The significant analgesia, low toxicity, naloxone reversibility and minimal anticholinesterase effects suggest the use of PMSF as a parenteral analgesic.