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.