ABSTRACT
The study of individual variability in pain has become an area of research interest globally. Inter-individual variability in pain perception and response is believed to be due to multiple bio-psycho-social factors, including genetic influences. This study was designed to investigate the influence of sex, age and ethnicity on perception and response to experimentally induced pain among a Nigerian adult population in Zaria, Northern Nigeria. Participants included 161 adult volunteers of 20 years and above, drawn from the staff population of selected secondary schools under the Zaria zonal education authority. Experimental pain was induced using the cold pressor test, sub-maximal effort tourniquet model of ischaemic pain, as well as pressure algometry. About 5 ml of blood was collected for determination of blood group, haemoglobin (Hb) genotype, serum concentrations of glutamate, serotonin, electrolytes, Malodealdehyde (MDA), reduced glutathione (GSH) and superoxide dismutase (SOD). Data collected were analysed using parametric (t-test, ANOVA) and non parametric (Mann-Whitney test, Kruskal-Wallis test) analysis. P value ≤ 0.05 was considered significant. Results of the study showed that there was no statistically significant differences in cold pressor pain outcomes and ischaemic pain tolerance between sexes (p > 0.05), but pressure and ischaemic pain thresholds were significantly higher in males than females (p = 0.000). Age difference on ischaemic pain threshold was statistically significant, with older subjects (≥ 50 years) having higher threshold than the younger subjects (p = 0.029). Ethnic differences on experimental pain outcomes showed that Yorubas have significantly higher pressure pain threshold than the Hausas (p = 0.008), while Fulanis have significantly higher ischaemic pain tolerance than those in the others group (p = 0.034). Subjects with normal body mass index (BMI) had a statistically significant higher ischaemic pain tolerance than their obese counterparts (p= 0.012). Effect of handedness showed that right handed subjects have a higher cold pressor pain threshold than left handed ones (p = 0.001). Subjects with the AA haemoglobin genotype were found to have significantly lower cold pressor pain tolerance (p = 0.028) and ischaemic pain threshold (p = 0.043) than the AS subjects. The O- blood group subjects were found to have significantly lower cold pressor pain tolerance when compared to those with O+ (p = 0.025) and A+ (p = 0.019) blood groups, while AB+ subjects have lower ischaemic pain threshold than those with O+ (p = 0.027) and A+ (p = 0.035) blood groups. Result of pain catastrophizing showed that male subjects have a lower pain catastrophizing score than females (p = 0.041). Male subjects have significantly lower serum glutamate concentration than females (p = 0.033). There was significantly higher serum sodium concentration among participants in the 20 - 30 age group than those in the 41 - 50 (p = 0.001) and above 50 groups (p = 0.018), while ethnic variation showed lower serum sodium among Hausas and Fulanis compared to the other ethnic groups. The oxidative stress markers (MDA, GSH and SOD) showed no statistically significant variations by sex, age or ethnicity in the present study. In conclusion, this study showed that perception and response to experimentally induced pain, as well as pain catastrophizing among adult Nigerian subjects in Zaria showed variation by sex, age and ethnicity. Factors such as BMI, blood group, Hb genotype and handedness were also found to influence the outcomes of some experimental pain models.