Post-operative mechanical hyperalgesia threshold. Group MC/FC, male/female controlled group received placebo + remifentanil (0.2 µg.kg−1.min−1); Group MD1/FD1, male/female group, received low-dose dexmedetomidine (0.2 µg.kg−1) + remifentanil (0.2 µg.kg−1.min−1); Group MD2/FD2, male/female group received high-dose dexmedetomidine (0.6 µg.kg−1) + remifentanil (0.2 µg.kg−1.min−1). Pain threshold were measured at 30-min, 1, 2, 4, 8 and 24-h time points after surgery. Values were expressed as medians and the error bars indicate the interquartile range. *P<0.05 vs. Group MC, #P<0.05 vs. Group MD1, &P<0.05 vs. Group FC and $P<0.05 vs. Group FD1. MC, male controlled group; FC, female controlled group.