Table 3

Agonist-induced shifts in the NTX ED₂₅ for decreases in rate

4-hr Pretreatment	Dose (mg/kg)	NTX ED₂₅	Post-saline ED₂₅/postagonist ED₂₅	Potency order	n
		mg/kg ± S.E.M.
Saline	1 ml/kg	28.2 ± 1.45			8
Fentanyl	0.03	4.47 ± 1.82	6.3	1	9
	0.056	0.08^* ± 4.27^a,b	352		8
Levorphanol	0.3	0.2 ± 3.86^3-a	141	2	8
	1.0	0.02 ± 2.82^3-a	1410		9
Methadone	1.0	1.86 ± 2.88^3-a	15	3	9
	3.0	0.01 ± 1.48^a,b	2820		8
Morphine	3.0	0.29 ± 5.5^3-a	97	4	7
	10	0.02 ± 2.63^3-a	1410		9
Chronic morphine	15 mg/kg/day	0.002 ± 1.48^3-a	14100		6
Meperidine	10	4.37 ± 3.39	6.5	5	8
	30	0.32^* ± 3.39^3-a	88		8
d-Amphetamine	3.0	14.5 ± 1.66	1.9		8
Dextrorphan	3.0	11.75 ± 2.75	2.4		9
Spiradoline	0.3	7.94 ± 2.88	3.6		9
	1.0				8
	3.0				8
Pentobarbital	18	29.5 ± 1.7	.95		8

Rank potency was determined by linear regression (the dose of agonist producing a 100-fold shift in the ED₂₅ of NTX).