Table 1.

Analysis of nociceptin and opioid antinociceptive dose-response curves after spinal administration in amphibians.

Agent	ED50a	95% C.I.b	Slope	95% C.I.	R.P.c
fentanyl	9.8	(6.7–14.1)	38.7	(23.8–53.7)	1.00
DPDPE	11.1	(5.93–20.80)	40.5	(13.7–67.2)	0.88
U50488	48.2	(20.9–111.5)	36.5	(7.0–65.8)	0.20
nociceptin	211.3	(75.5–590.9)	18.5	(12.7–24.3)	0.04
nociceptin1–13 amide	160.5	(7.9–3252.8)	22.4	(−12.2–56.9)	0.06

^ain nmol/animal, spinal administration;

^b95% confidence interval;

^crelative potency compared to fentanyl by the ratio of the ED₅₀ fentanyl/ED₅₀ other agent.