Salt intake impacts sympathetic neural control but not morning blood pressure surge in premenopausal women with a history of normal pregnancy

Salt intake may alter blood pressure (BP) regulation, but no study has investigated the impact of salt reduction versus salt loading on morning blood pressure surge (MBPS) and sympathetic neural control in premenopausal women with a history of normal pregnancy. Nine healthy women (42 ± 3 yr; mean ± SD) were given a low-salt diet (LS; 50 mEq sodium/day) and high-salt diet (HS; 250 mEq sodium/ day) for 1 wk each (~2 mo apart with the order randomized), while water intake was ad libitum. Ambulatory BP at 24 h was measured, and the percent change in blood volume (BV) was calculated following LS and HS. MBPS was defined as the morning systolic BP (averaged for 2 h after wake-up) minus the lowest nocturnal systolic BP. Beat-by-beat BP, heart rate, and muscle sympathetic nerve activity (MSNA) were measured during supine rest. Signal averaging was used to characterize changes in beat-by-beat mean arterial pressure and total vascular conductance following spontaneous MSNA bursts to assess sympathetic vascular transduction. Ambulatory BP and MBPS (32 ± 7 vs. 26 ± 12 mmHg, P = 0.208) did not differ between LS and HS. From LS to HS, BV increased by 4.3 ± 3.7% (P = 0.008). MSNA (30 ± 20 vs. 18 ± 13 bursts/100 heartbeats, P = 0.005) was higher, whereas sympathetic vascular transduction was lower in LS than HS (both, P < 0.01). Changes in MSNA from LS to HS were correlated to percent changes in BV (r = -0.673; P = 0.047). Thus, salt intake affects sympathetic neural control but not MBPS in premenopausal women with a history of normal pregnancy. The underlying mechanisms remain unknown; however, alterations in sympathetic vascular transduction may, in part, contribute.