Response of exercise‐onset vasodilator kinetics to L‐citrulline supplementation during different phases of the menstrual cycle

The purpose of this study was to determine whether L‐citrulline (CIT) supplementation during the follicular and luteal phases of the menstrual cycle would present differential effects on vasodilator kinetics in dynamically contracting muscle. Twenty‐four women were studied during the follicular (day 15 after onset of menses, n = 13) or the luteal phase (day 25 after onset of menses, n = 11). Supplementation with CIT (6g/day) or placebo occurred 7‐days prior to testing in a crossover design across two menstrual cycles. Forearm vascular conductance (FVC) was calculated from blood flow and mean arterial pressure measured continuously during handgrip exercise performed at 10% maximal grip strength. FVC was calculated for each duty cycle (contract:relax, 1:2s) and expressed as a change from baseline (ΔFVC) before being fit with a monoexponential model. Amplitude of the ΔFVC response and the number of duty cycles for ΔFVC to reach 63% of steady‐state amplitude (τΔFVC) were derived from the model. Analysis of variance showed no difference in the amplitude of ΔFVC between CIT and placebo (p = .45) or between menstrual cycle phases (p = .11). Additionally, τΔFVC was not different (p = .35) between CIT and placebo in women tested during the follicular (6 ± 3 versus 5 ± 3 duty cycles) or luteal phase (9 ± 1 versus 8 ± 1 duty cycles) although τΔFVC was found to be slower for women tested during the luteal as compared to the follicular phase (8 ± 4 versus 5 ± 3 duty cycles, p = .02). These results indicate that exercise‐onset vasodilator kinetics is unaltered with CIT supplementation in young healthy women irrespective of menstrual cycle phase.