Augmented sympathetic neural responses to a cold pressor test during salt loading in healthy premenopausal women

Abstract

BackgroundExcessive salt intake is considered a risk factor for the development of hypertension. Previous studies have demonstrated that augmented neural and pressor responses to a cold stimulus are associated with an increased risk of hypertension. This study aimed to determine whether salt loading impacts sympathetic neural responses during the cold pressor test (CPT) in healthy young and middle‐aged women.MethodsNine healthy premenopausal women [42±3 (SD) yr] were given a standardized isocaloric high‐salt (HS; 250 mEq sodium, 100 mEq potassium, and 1000 mg calcium per day) or low‐salt diet (LS; 50 mEq sodium, 100 mEq potassium, and 1000 mg calcium per day) for 1 week each (~2‐month apart with the order randomized), while water intake was ad libitum. Twenty‐four‐hour urine was collected and 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 BP, heart rate (HR) and muscle sympathetic nerve activity (MSNA) were measured during baseline, 2‐minute CPT, and 3‐minute recovery. Blood sample was taken to calculate the change in plasma and blood volume by using the Dill’s equation. Salt sensitive was defined as more than 10% changes in mean arterial pressure between HS and LS, and below this cutoff was defined as non‐salt‐sensitive.ResultAll subjects were non‐salt‐sensitive (salt sensitivity range: −7.78 to 6.49%). Urine osmolality and 24‐h urine sodium were higher during HS than LS (572±174 vs. 443±153 mOs/kg and 150.8±72.1 vs. 65.2±38.5 mmol/day, both P<0.05). Plasma and blood volume increased by 6.9±1.8% (p=0.006) and 4.3±1.2% (p=0.008) in HS compared with LS. Baseline systolic and diastolic BP (103±12 vs. 105±10 mmHg and 59±6 vs. 69±9 mmHg), HR (66±10 vs. 63±9 bpm), or MSNA (burst frequency: 14±11 vs. 16±10 bursts/min and total activity: 156±118 vs.184±115 a.u./min) did not differ between HS and LS (all P>0.05). Systolic and diastolic BP and HR increased during the CPT (all P<0.001) with no salt effects (all P>0.05). MSNA increased during the CPT in both conditions (both P<0.001), but the increases in burst frequency and total activity were greater during HS than LS (Δ burst frequency: 26±20 vs. 14±15 bursts/min and Δ total activity: 644±480 vs.368±402 a.u./min, P=0.042 and 0.002 for interaction, as figure ).ConclusionSalt loading augments sympathetic neural responses to the cold pressor stimulus with no significant impact on blood pressure responses in healthy premenopausal non‐salt‐sensitive women. Whether similar results can be obtained in salt‐sensitive women remains to be determined.Support or Funding InformationThe Harry S. Moss Heart Trust awardChanges (Δ) from baseline in muscle sympathetic nerve activity (MSNA) burst frequency, total activity, mean arterial pressure and heart rate during cold pressor test (CPT) and recovery in high salt and low salt diet. Values are means ± SD. *, high salt vs low salt at P<0.05.Figure 1