Sex-related differences in the microvascular function of pre-pubertal children

Abstract

There is little research examining the effect of sex on skin blood flow (SkBF) in adults, and less in children. Sex-related differences in SkBF may help explain known thermoregulatory differences between males and females. The purpose of this study is to determine whether there are sex-related differences in the SkBF response to exercise, local heating, and acetylcholine (ACh). Additionally, the role of nitric oxide (NO) was examined. Laser-Doppler fluxmetry was used to assess forearm SkBF. Responses to exercise (30 min cycling, 60%O2max), local heating (44˚C), and ACh iontophoresis were assessed in 12 pre-pubertal boys (age=10.9 ±1.1y, O2max =1665 ± 282 ml·min-1) and 12 girls (age=11.1±1.2y, O2max =1537± 296 ml·min-1), with and without NO synthase inhibition, using Nω-nitro-L-arginine methyl ester (L-NAME) iontophoresis. Exercise-induced increase in SkBF was greater in boys compared with girls (528±290 and 374±192% of baseline, respectively, p=0.03). L-NAME blunted the SkBF response to exercise in boys and in girls (group-by-treatment interaction, p=.82). Local heating-induced SkBF was not significantly different between boys and girls (1445±900% and 1432±582%, respectively, p=.57). The ACh-induced SkBF was not different between the boys and girls, with no difference in the increase in SkBF (673±434% and 558±405%, respectively, p=.18). L-NAME blunted the SkBF response to ACh in boys and girls (group-by-treatment interaction, p=.19). These findings demonstrate that there are no differences between boys and girls in the responses to ACh and to local heating (44˚C). Additionally, the role of NO in the SkBF response appears similar in boys and girls both during exercise and ACh-mediated vasodilation. The greater SkBF response in the boys during exercise may be workload-related. Absolute and relative (%O2max) exercise intensity were not different between the two groups. Therefore, it is possible that the greater SkBF response in boys may be related to their greater workload relative to body mass (p=0.01). Additionally, sex-related factors (e.g., hormones) may interact with the exercise response or other vasodilators may be involved, resulting in the observed sex-related difference in the SkBF response to exercise.