Table 1

ED50 values (mg/kg) for different opioid agonists either alone or after pretreatment with various doses of NTX in the 50°C water antinociceptive assay

AgonistsED501-a(95% CL)
BaselinePretreatment Naltrexone Dose (mg/kg)
0.0032(DR)1-b0.01(DR)0.032(DR)0.1(DR)0.32(DR)
Alfentanil0.046 (0.037–0.057)0.21  (0.16–0.27)(4.5)0.56  (0.53–0.59)(12)2.2    (2.1–2.5)(49)
EKC0.020 (0.013–0.030)0.035 (0.024–0.051)(1.7)0.073 (0.071–0.077)(3.7)0.18   (0.13–0.26)(9.0)0.51  (0.32–0.81)(25)
U69,5930.045 (0.027–0.074)0.11  (0.08–0.13)(2.4)0.20   (0.15–0.26)(4.4)0.53  (0.29–0.95)(12)
U50,4880.62 (0.44–0.88)1.3   (1.2–1.4)(2.0)2.2    (1.8–2.7)(3.6)6.6   (5.4–8.0)(11)
Bremazocine0.0089 (0.0050–0.016)0.015  (0.0074–0.030)(1.7)0.033 (0.020–0.056)(3.7)0.064 (0.046–0.090)(7.2)
Enadoline0.0057 (0.0035–0.0090)0.0096 (0.0062–0.015)(1.7)0.015 (0.010–0.023)(2.6)0.045 (0.028–0.071)(7.9)
  • 1-a ED50 values were the mean of individual ED50 values (n = 4) and 95% CL were confidence limits (P < .05).

  • 1-b DR were dose ratios relative to corresponding base-line ED50 values.