Blood Pressure and Hormonal Responses to Short Whole Body Cold Exposure in Subjects with High Dietary Salt Intake

Abstract

The objective of the present study was to test a hypothesis that a high dietary salt intake potentiates a cold induced increase in blood pressure in normotensive men. Male subjects (n=12) were given 7 g day^-1 sodium chloride during the cold months of the year, divided in 3-4 doses per day and dissolved in water, for 14 days additional to their normal diet which contained on the average 9.7 g sodium chloride per day. The same subjects, having their normal diet, served as controls. The resting blood pressure was measured on the fourteenth day seven times at the intervals of five minutes in a climatic chamber in thermoneutral conditions. Then the subjects, wearing a three-layer winter clothing, moved into a wind tunnel (-15°C, air velocity 3.5 ms^-1) in which they stayed for fifteen minutes and the blood pressure was recorded at the intervals of three minutes. After the cold exposure, the subjects moved back into the climatic chamber for 30 min and the blood pressure was measured as before the cold exposure. Blood samples were drawn before and after the experiment for ion and hormone measurements. A 12 h urine sample was collected just prior to the cold exposure. A significant difference both in systolic (7 mmHg) and in diastolic (7 mmHg) blood pressure was found between a salt load group and control group under thermoneutral conditions, repeatedly measured over 30 min (paired Student’s t-test; p<0.05). During the whole body cold exposure, blood pressure significantly increased both with and without the extra salt load (repeated measures ANOVA, Student-Newman-Keuls; p<0.05). The level to which the mean arterial pressure increased during the exposure was independent of the salt intake and the profile of the mean arterial pressure curve was similar in both groups. The systolic pressure increased by a 25 mmHg in both groups during the cold exposure. The increase in the diastolic pressure was significantly (paired Student’s t-test, p<0.05) higher in the high salt group (18 ± 4 mmHg) than in the control group (12 ± 3 mmHg) thus supporting partly our hypothesis. After the two-week high salt intake, serum Na⁺, K⁺, Cl^-, Hct, and plasma Hb were at the similar level as before the extra salt intake. Plasma renin activity, NT-proANP, ANP, and serum aldosterone were not different between the groups, both before and after the cold exposure. The main findings are: 1) the mean arterial pressure increases to the same level and in the same manner independent of the salt load during a short whole body cold exposure and 2) in cold the diastolic blood pressure increases significantly more in people under a very high salt diet.