Effects of Salt Intake on Sympathetic Neural and Pressor Responses to Cold Pressor Test in Premenopausal Women with A History of Normal Pregnancy.

Abstract

Excessive salt intake is considered a risk factor for the development of hypertension. Additionally, aberrant neuro-circulatory responses to a cold stimulus are associated with an increased risk of hypertension. This study aimed to determine whether salt loading versus salt reduction would impact hemodynamic and sympathetic neural responses during the cold pressor test (CPT) in premenopausal women with a history of normal pregnancy. Nine healthy premenopausal women [42±3 (SD) yr] were given a standardized isocaloric high salt (HS; 250 mEq sodium/day) or low salt (LS; 50 mEq sodium/day) diet for 1-week each (~2 months apart with the order randomized), while water intake was ad libitum. Laboratory testing was performed following each HS and LS period in the mid-luteal phase of the menstrual cycle. Subjects were in the supine position and beat-by-beat blood pressure (BP), heart rate (HR) and muscle sympathetic nerve activity (MSNA) were continuously measured during 1-minute baseline followed by 2-minute CPT and 3-minute recovery. BP and HR increased during the CPT (both P<0.001); the responses were similar between HS and LS. MSNA increased during the CPT, but the increment (D) was greater during HS than LS (29±6 vs. 15±4 bursts/min; P<0.001). The transduction of MSNA for vasoconstriction during the CPT was lower in HS (P<0.05). Thus, salt loading augments sympathetic neural reactivity to the cold stimulus with similar pressor responses compared to salt reduction, which may be attributed to the blunted neurovascular transduction ─ a compensatory mechanism for hemodynamic homeostasis in premenopausal women with a history of normal pregnancy.