Effects of the ovarian cycle on sympathetic neural outflow during static exercise

We compared reflex responses to static handgrip at 30% maximal voluntary co ntraction ((MVC) in 10 women (mean age 24.1 +/- 1.7 yr) during two phases o f their ovarian cycle: the menstrual phase (days 1-4) and the follicular ph ase (days 10-12). Changes in muscle sympathetic nerve activity (MSNA; micro neurography) in response to static exercise were greater during the menstru al compared with follicular phase (phase effect P = 0.01). Levels of estrog en were less during the menstrual phase (75 +/- 5.5 vs. 116 +/- 9.6 pg/ml, days 1-4 vs, days 10-22; P = 0.002). Generated tension did not explain diff erences in MSNA responses (MVC: 29.3 +/- 1.3 vs. 28.2 +/- 1.5 kg, days 1-4 vs. days 10-12; P = 0.13). In a group of experiments with the use of P-31-N MR spectroscopy, no phase effect was observed for H+ and H2PO4- concentrati ons (n = 5). During an Ischemic rhythmic handgrip paradigm (20% MVC), a pha se effect was not observed for MSNA or H+ or H2PO4- concentrations, suggest ing that blood flow was necessary for the expression of the cycle-related e ffect. The present studies suggest that, during static handgrip exercise, M SNA is increased during the menstrual compared with the follicular phase of the ovarian cycle.