TABLE 1

The ED₅₀ values of propentofylline, dextro-naloxone, and levo-naloxone for blocking dextro-morphine-induced and levo-morphine-induced antianalgesia against levo-morphine-produced TF inhibition

Groups of mice were coadministered i.t. with propentofylline (0.3–98 nmol) and dextro-morphine (33 fmol) or levo-morphine (0.3 nmol) 45 min before i.t. injection of levo-morphine (3.0 nmol). Other groups of mice were pretreated i.t. with dextro-naloxone (0.03–280 pmol) or levo-naloxone (0.03–28 pmol) for 10 min before i.t. injection of dextro-morphine (33 fmol) or levo-morphine (0.3 nmol) injection and were then injected i.t. with levo-morphine (3.0 nmol) 45 min after dextro-morphine injection. The TF response was measured 15 min after levo-morphine injection. The F test was used to test the difference of logED₅₀ between dextro-morphine and levo-morphine pretreatment, which showed no significant difference in present study.