Adaptations in autonomic nervous system regulation in normal and hypertensive pregnancy - Brooks 2022

During a normal pregnancy, there is a rise in basal sympathetic nerve activity (SNA) which counteracts primary vasodilation. However, this increase in SNA can impair baroreflex control of heart rate and SNA, leading to increased mortality due to peripartum hemorrhage. Pregnancy-induced hypertensive disorders further elevate SNA, which likely contribute to hypertension. However, the mechanisms underlying this process are not well understood. In a normal pregnancy, increased levels of angiotensin II stimulate SNA in specific hypothalamic sites, including the subfornical organ, paraventricular nucleus, and arcuate nucleus, though this has yet to be proven. Additionally, increased production and actions of the neurosteroid allopregnanolone during pregnancy inhibit the rostral ventrolateral medulla (RVLM), which is a key brainstem site that transmits excitatory inputs to spinal sympathetic preganglionic neurons. This leads to a suppression of baroreflex function, but the overall increase in basal SNA suggests that excitatory influences dominate in the RVLM. However, much remains to be understood about the other sites and factors that contribute to increased SNA during normal pregnancy, as well as the underlying mechanisms for excessive sympathoexcitation in hypertensive pregnancy disorders such as preeclampsia that can be life-threatening.

Brooks VL, Fu Q, Shi Z, Heesch CM. Adaptations in autonomic nervous system regulation in normal and hypertensive pregnancy. Handb Clin Neurol. 2020;171:57-84. doi: 10.1016/B978-0-444-64239-4.00003-5. PMID: 32736759; PMCID: PMC9261029.