Differentiation of potent μ- and κ-opiate agonists using heat and pressure antinociceptive profiles and combined potency analysis

Abstract

The antinociceptive profiles of strong μ- and κ-opiate agonists were determined in the tail clip, hot plate (55°C) and tail immersion (48°C and 55°C) tests in mice. All μ- and κ-agonists produced steep dose-response lines in all the tests. Using a combined analysis of potencies for pressure against heat noxia it was possible to diferentiate between μ- and κ-agonists and this paralleled findings in other laboratories using isolated tissue preparations. It was also concluded that qualitative differences between noxia were responsible for the observed differentiation since potency differences for μ- and κ-agonists between tests were maintained even after the intensity of heat and pressure noxia were equated. It was also proposed that use of the combined tail clip and immersion tests may be useful for rapid behavioural classification of novel synthetic μ- and κ-opiate analgesics.