Figure 6.
Effect of pretreatment with naloxone on the antinociceptive action of pentoxifylline or morphine in zymosan-induced writhing response in mice and knee joint incapacitation in rats. Mice or rats were pretreated with vehicle (saline, S) or naloxone (N; 2 mg kg−1). After 15 min, they were pretreated with pentoxifylline (PTF; 1.6 mg kg−1) or morphine (5 mg kg−1) i.p., and 30 min after that, zymosan (1 mg mouse−1) was injected i.p. into mice, or intra-articularly into rats (1 mg cavity−1). The number of writhes in mice was determined during the following 30 min (panel a), and paw elevation times were measured before and after zymosan administration, over a 60-min period, until the 4th h (panel b). Bars on panel b show means of maximal values obtained between 3rd and 4th hour after zymosan intra-articular injection. Results are expressed as means±s.e.m. for groups of 6 mice and 5–6 rats. Asterisks indicates statistically significant differences comparing the group injected with zymosan and pretreated with pentoxifylline and saline or morphine and saline with the group injected with zymosan and pretreated with saline (*P<0.05; **P<001). #Symbols indicates statistically significant differences comparing groups injected with zymosan and pretreated with morphine and naloxone with the group injected with zymosan and pretreated with morphine and saline (#P<0.001).