Reversal by β-funaltrexamine and 16-methyl cyprenorphine of the antinociceptive effects of opioid agonists in the mouse and guinea-pig

Add time:09/10/2019    Source:sciencedirect.com

The present study compared the effects of two opioid antagonists, β-funaltrexamine (β-FNA) and 16-methyl cyprenorphine (RX8008M) on the antinociception produced by a range of opioid agonists in the abdominal constriction test in the mouse and the paw pressure test in the guinea-pig. Both antagonists produced large shifts in the dose-response curves to the μ-agonists, morphine and fentanyl, confirming their μ-antagonist activity. Neither antagonist produced any antagonism of the antinociceptive effects of the selective κ-agonists U50488, U69593 and tifluadom, in the mouse. However, RX8008M produced small shifts in the dose-response curves to these agonists in the guinea-pig, which seems more likely to reflect μ-receptor activity of the agonists in the guinea-pig than lack of selectivity of the antagonists. Both β-FNA and RX8008M produced some antagonism of bremazocine, ethyl-ketocyclazocine, proxorphan and butorphanol, indicating that these agonists have a prominent μ-receptor component to their antinociceptive actions.

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