The effect on mechanical pain threshold over human muscles by oral administration of granisetron and diclofenac-sodium.

Previous studies indicate that plasma levels of serotonin (5-HT) and intramuscular prostaglandin E2 (PGE2) participate in determining the mechanical pain threshold and tolerance level to pressure applied on the skin over healthy muscles. Other studies reported gender differences regarding responses to noxious stimuli. The present study aimed to determine whether the mechanical pain threshold of healthy muscles is influenced by oral administration of 5-HT3 or PGE2-inhibitors and if there are any gender differences in this respect. Ten healthy female subjects and 10 age-matched healthy male subjects participated in the study, which was randomized and double blind with crossover design. Granisetron (5-HT3-antagonist), diclofenac-sodium (PGE2-antagonist) and placebo were administered for 3 days. The pressure pain threshold (PPT) was recorded bilaterally with an algometer over certain orofacial, trunk, and limb muscles before and after administration of the antagonists. The PPT over all muscles combined increased after administration of granisetron. There was no change after administration of placebo. The difference between granisetron and placebo was significant for the trapezius and tibialis anterior muscles. Diclofenac-sodium did not influence the PPT and there was no difference compared to placebo. Although the basal PPT values were lower in females, the PPT response to granisetron differed significantly between genders only in the tibialis anterior muscle. In conclusion, the results of this study showed that oral administration of the 5-HT3-antagonist granisetron increased the PPT over healthy trunk and limb muscles but not over orofacial muscles, and that the response in the limb muscles was greater in males.