Are the blood pressure and endocrine responses of healthy subjects exposedto cold stress altered by an acutely increased sodium intake?

In the study reported here, we examined blood pressure and endocrine respon ses in cold conditions during salt load in young healthy subjects who had p reviously shown increased resting blood pressure during acutely increased s odium intake. Subjects (n = 53) added 121 mmol sodium into their normal die t for 1 week. If their mean arterial pressure had increased by a minimum of 5 mmHg compared to the previous measure they were selected for subsequent experiments. The subjects (n = 8) were given 121 mmol supplemental sodium . day(-1) for 14 days. They were then put into a wind tunnel for 15 min (tem perature -15 degreesC, wind speed 3.5 . ms(-1)). Their blood pressure incre ased (P < 0.05) during the cold exposure, independent of the sodium intake. Their mean (SEM) plasma noradrenaline increased from 3.58 (0.62) nmol . l( -1) to (0.79) nmol . l(-1) (P < 0.05) when the subjects were given a normal diet, and from 2.45 (0.57) nmol . l(-1) to 5.06 (0.56) nmol . l(-1) (P < 0 .05) when the subjects were given an elevated sodium diet. The starting con centrations and the endpoint concentrations were statistically similar. The plasma levels of the N-terminal fragment of pro-atrial natriuretic peptide decreased during the whole-body cold exposure: with the sodium load the ch ange was from 256.6 (25.5) nmol . l(-1) to 208.0 (25.3) nmol . l(-1), and w ith the normal diet, from 205.8 (16.4) nmol . l(-1) to 175.1 (16.1) nmol . l(-1). The haematocrit and red blood cell count increased (P < 0.05) with n ormal and elevated sodium diet in cold conditions, but haemoglobin increase d (P < 0.05) only with high salt in cold conditions. To conclude, acutely i ncreased sodium intake does not change the blood pressure response or hormo nal responses to exposure to acute cold stress in healthy subjects.