Preeclampsia is not associated with elevated muscle sympathetic reactivity

Preeclampsia is a serious hypertensive disorder of pregnancy, and historically, it has been widely assumed that this condition is driven by sympathetic nervous system hyperactivity. Based on limited early evidence, researchers often speculated that the peripheral chemoreflex—a sensor system that regulates breathing and blood flow in response to oxygen levels—might be a primary contributor to this sympathetic surge. This study aimed to rigorously test these assumptions by comparing muscle sympathetic nervous system activity (MSNA) and chemoreflex responses in women with preeclampsia against a control group of healthy pregnant women.

The researchers performed a controlled study involving 19 women with preeclampsia and 38 gestational-age-matched pregnant controls. MSNA was directly recorded from the peroneal nerve using microneurography in a subset of participants. The team evaluated sympathetic responses during three specific states: at rest (baseline), during peripheral chemoreflex deactivation (induced by breathing 100% oxygen, or hyperoxia), and during a cold pressor test (which activates nociceptors to stimulate sympathetic activity). They also measured plasma noradrenaline levels and baroreflex function to gain a comprehensive view of how these women regulate their cardiovascular systems.

The study found no significant difference in baseline MSNA between women with preeclampsia and the control group, directly challenging the existing dogma that preeclampsia is characterized by sympathetic neural hyperactivity. While women with preeclampsia did show higher baseline noradrenaline concentrations and a rightward shift in their baroreflex function, their sympathetic responses to both hyperoxia and cold-stress tests were indistinguishable from those of the control group. These results suggest that while sympathetic dysfunction may be present in other forms, such as gestational hypertension, it is not a defining characteristic of preeclampsia.