PURPOSE: Women who develop gestational hypertension have evidence of elevated muscle sympathetic nerve activity (MSNA) in early pregnancy, which continues to rise after diagnosis. Exercise has been shown to play a preventative role in the development of gestational hypertension and has been shown to reduce resting and reflex MSNA in nonpregnant populations. We sought to investigate whether aerobic exercise affected the sympathetic regulation of blood pressure between the second and third trimesters of pregnancy. METHODS: We conducted a randomized controlled trial of structured aerobic exercise (n = 31) compared with no intervention (control, n = 28) beginning at 16 to 20 wk and continuing until 34 to 36 wk of gestation (NCT02948439). Women in the exercise group were prescribed aerobic activity at 50% to 70% of their heart rate reserve, on 3 to 4 d/wk for 25 to 40 min with a 5-min warm-up and 5-min cool-down (ie, up to 160 min total activity per week). At preintervention and postintervention assessments, data from approximately 10 min of quiet rest and a 3-min cold pressor test were analyzed to determine sympathetic nervous system activity and reactivity. RESULTS: MSNA was obtained in 51% of assessments. Resting MSNA burst frequency and burst incidence increased across gestation (main effect of gestational age, p = 0.002). Neurovascular transduction was blunted in the control group (p = 0.024) but not in exercisers (p = 0.873) at the postintervention time point. Lastly, MSNA reactivity during the cold pressor test was not affected by gestational age or exercise (p = 0.790, interaction). CONCLUSIONS: These data show that exercise attenuates both the rise in MSNA and the blunting of neurovascular transduction. This may partially explain the lower risk of developing gestational hypertension in women who are active during their pregnancies.

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