Augmented Sympathetic Neural Activation in response to Static Handgrip during Early Pregnancy in Humans

Abstract

Pregnancy is a dynamic process with systemic neuro‐vascular adaptations. Normal pregnancy is associated with sympathetic activation and attenuated vasoconstrictor responsiveness to alpha‐adrenergic stimulation, which starts as early as 4 weeks of gestation. However, little is known about changes in the exercise pressor reflex in pregnancy, a robust sympathetic stimulus originating from contracting skeletal muscle. We hypothesized that the muscle sympathetic nerve activity (MSNA) response to isometric muscle contraction would be greater in early pregnant women compared with non‐pregnant women.We measured heart rate (HR), blood pressure (BP), and MSNA in 21 early pregnant women (6–10 weeks of gestation) and 22 age‐matched healthy non‐pregnant women (controls; mid‐luteal phase) during static handgrip (SHG) exercise to fatigue at 40% of maximal voluntary contraction (MVC) force followed by 2 min of postexercise circulatory arrest (PECA). The total SHG time was divided evenly into five stages. We further utilized matched wavelet‐based methodology to extract sympathetic action potential (AP) discharge patterns.Baseline characteristics were comparable between groups. MVC was not different but the time to fatigue was shorter in pregnant women than non‐pregnant women (109±56 vs. 188±76 secs; P=0.003, mean±SD). Supine resting MSNA was greater in pregnant women (burst frequency (BF): 23±10 vs. 14±11 bursts/min; P=0.01) and sympathetic neural discharge was augmented (AP firing frequency: 235±108 vs. 142±87 spikes/min, P=0.04). Mean arterial pressure was not different between groups (80±9 vs. 83±7 mmHg; P=0.3). In response to SHG and PECA, pregnant women exhibited greater increases in MSNA than controls (time × group interaction P=0.03, group P=0.02). At peak exercise and last min of PECA, changes in MSNA BF were greater in pregnant women compared to controls (Δ MSNA at peak exercise: 34±7 vs.19±7 bursts/min; P=0.01, PECA: 25±6 vs.17±7 bursts/min; P=0.03). Similarly, the augmented sympathetic neural response was concomitant with exaggerated AP recruitment (AP firing frequency: group × time interaction P=0.004, group P=0.02 and Δ AP firing frequency at peak exercise: 365±129 vs.193±116 spikes/min; P=0.006, PECA: 241±88 vs.126±55 spikes/min; P=0.03). BP and HR responses to SHG and PECA were not different between groups.In conclusion, early pregnancy is associated with augmented sympathetic neural responses to isometric muscle contraction, which may be attributed to enhanced metabo‐reflex activation. Despite the heightened neural response, vasoconstriction is blunted in early pregnant women. Our findings provide unique mechanistic insight into blood pressure regulation during early pregnancy.Support or Funding InformationSupported by R01HL142605Changes in muscle sympathetic nerve activity (MSNA) burst frequency (BF) in response to static handgrip (SHG), postexercise circulatory arrest (PECA) and recovery.Figure 1Changes in action potential (AP) recruitment in response to static handgrip (SHG), postexercise circulatory arrest (PECA) and recovery.Figure 2