Sex Differences In Microvascular Function In 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. PURPOSE: 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. METHODS: Laser-Doppler flowmetry was used to assess forearm SkBF. Responses to exercise (30 min cycling, 60%V˙O2max), local heating (44°C), and ACh iontophoresis were assessed in 15 pre-pubertal boys (age=10±1y, VO2max=1.66±0.25 l/min) and 10 girls (age=10±1y, VO2max=1.58±0.35 l/min), with and without NO synthase inhibition, using L-NAME iontophoresis. Three-way (group, time, treatment) repeated measures ANOVA was used to examine sex-related differences in the SkBF response during exercise and in the SkBF-ACh dose response. A two-way (group, treatment) repeated measures ANOVA was used to examine local heathing-induced increase in SkBF. RESULTS: Exercise-induced SkBF was greater in boys compared with girls (654±355 and 316±182% of baseline, respectively, p=<.0001). L-NAME blunted the SkBF response more in boys than in girls (group-by-treatment interaction, p=.004). Local heating-induced SkBF was not significantly different between boys and girls (1705±739% and 1488±600%, respectively, p=.35), with no effect of L-NAME. The maximal ACh-induced SkBF was similar in boys and girls (650±420% and 612±411%, respectively). L-NAME similarly blunted the SkBF response in boys and girls (group-by-treatment interaction, p=.52). CONCLUSION: These findings demonstrate that while maximal SkBF and the vasodilatory response to ACh stimulation are similar in boys and girls, boys display a greater increase in SkBF during exercise of similar intensity. Further, the role of NO in the SkBF response appears greater in boys than girls only during exercise. Since absolute and relative exercise intensity was similar in the two groups, it is suggested that sex-related factors (e.g., hormones) may interact with the exercise response or with other vasodilators, resulting in different SkBF response.