Table 2.

The effects of the opioid receptor antagonists on 50% paw withdraw threshold (PWT) of naïve rats. Opioid receptor antagonists and corresponding vehicle (PBS, control) were administered intraplantarly into the hind paws of naïve rats. 50% PWTs were measured before and after drug/vehicle treatment. NS: not significant compared with control.

Antagonists (µg)	50% PWT (g)
	Baseline	Treated
Control	25.4 ± 0.6	23.3 ± 1.9
Naloxone (40)	24.3 ± 1.1	21.8 ± 2.1 (NS)
β-Funaltrexamine (50)	24.8 ± 1.2	25.4 ± 0.6 (NS)
Nor-binaltorphimine (76)	25.4 ± 0.6	24.3 ± 1.1 (NS)
Naltrindole (48.7)	25.4 ± 0.6	24.9 ± 0.7 (NS)