Figure 4. Duration of stimulation-enhanced hyperalgesia.

Separate groups of rats were tested for stimulation-induced hyperalgesia at increasing intervals of one hour after ET-1 (100 ng) administration (1 – 4 hours, panels A – D). (Note: groups are designated by the time of the last measurement since ET-1 administration.) Each group was tested at five minute intervals for 15 minutes (Readings 1 – 4), similar to the 5 minute interval 30 minute group shown in Fig. 3B (replotted in this figure for comparison). Two-way repeated measures ANOVA with one within-subjects factor (time) and one between-subjects factor (group) was performed for each of the four experiments. The 1 hour, 2 hour, or 3 hour groups each showed a significant main effect of time (F3,30=32.035; p<0.001), (F3,24=36.971; p<0.001), and (F3,30=29.956; p<0.001), respectively, but not a significant group × time interaction (F3,30=0.210; p=0.832), (F3,24=0.653; p=0.533), and (F3,30=0.558; p=0.592), nor a significant main effect of group (F1,10=0.118; p=0.738), (F1,8=0.196; p=0.669), and (F1,10=0.826; p=0.385). Thus, while there was an overall change over time for these three groups, there was no significant difference between the groups. The 4 hour group showed a significant main effect of time (F3,24=7.286; p<0.001) as well as a significant group × time interaction (F3,24=15.808; p<0.001), but not a significant main effect of group (F1,8=1.539; p=0.250). Based on the significant interaction, separate one-way repeated measures ANOVAs were performed for each of the two groups. The effect of time for the four hour group was not significant (F3,9=1.800; p=0.217), indicating that stimulation-enhanced hyperalgesia was no longer present at the four hour time point. See Fig. 3B for the ANOVA result for the 30 minute group.