Skin blood flow responses to acetylcholine and local heating at rest and 60%V O2max, and associated nitric oxide contribution, in boys vs. girl

Abstract

To determine sex-related differences in the skin-blood-flow (SkBF) response to exercise, local heating, and acetylcholine (ACh) in children. Additionally, the contribution of nitric oxide (NO) was examined. Methods: Forearm SkBF during local heating (44˚C), ACh iontophoresis, and exercise (30 min cycling, 60% OV 2max) was assessed, using Laser-Doppler fluxmetry, in 12 boys and 12 girls (7–13 yrs old), with and without NO synthase inhibition, using Nω-nitro-L-arginine methyl ester (L-NAME) iontophoresis. Results: Local-heating-induced and ACh-induced SkBF increase were not different between boys and girls (Local heating: 1445±900% and 1432±582% of baseline, , p=.57; ACh: 673±434% and 558±405% of baseline, respectively, p=0.18). Exercise-induced increase in SkBF was greater in boys than girls (528±290 and 374±192% of baseline, respectively, p=0.03). L-NAME blunted the SkBF response to ACh and during exercise (p<0.001), with no difference between sexes. Summary: SkBF responses to ACh and local heat stimuli were similar in boys and girls, while the increase in SkBF during exercise was greater in boys. The apparent role of NO was not different between boys and girls. It is suggested that the greater SkBF response in the boys during exercise is related to greater relative heat production and dissipation needs during this exercise intensity. The response to body-size-related workload should be further examined.