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

In the study reported here, we examined blood pressure and endocrine responses in cold conditions during salt load in young healthy subjects who had previously shown increased resting blood pressure during acutely increased sodium intake. Subjects (n = 53) added 121 mmol sodium into their normal diet 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 (temperature--15 degrees C, wind speed 3.5.ms-1). Their blood pressure increased (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 5.61 (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 concentrations 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 change was from 256.6 (25.5) nmol.l-1 to 208.0 (25.3) nmol.l-1, and with 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 normal and elevated sodium diet in cold conditions, but haemoglobin increased (P < 0.05) only with high salt in cold conditions. To conclude, acutely increased sodium intake does not change the blood pressure response or hormonal responses to exposure to acute cold stress in healthy subjects.