Behavioral and Hormonal Changes in Estrogen-Treated Rats after Repeated Episodes of Dietary Sodium Deficiency

The incidence of hypertension in America is increasing, especially in women. After menopause, women’s blood pressure increases, indicating a possible role of estrogen in the control of blood pressure. Hypertensive patients typically are advised to maintain a low salt diet. However, this diet is difficult to maintain, and many patients exhibit “yo-yo” dieting, in which they alternate between low and higher salt intakes. The impact of alternating dietary sodium remains unclear.

Therefore, the aim of this research was to determine the behavioral and hormonal effects of multiple dietary sodium deprivations on female rats with and without estrogen. We removed the ovaries of female rats, then gave estradiol benzoate (EB) injections or OIL injections twice a week for the remainder of the study. Some rats were maintained on regular sodium diet throughout; others were given one or two alternating 10-day periods of regular and sodium deficient diets. At the end of each 10-day period, rats were given a bottle of water and a bottle of 0.5M NaCl for two hours, and intakes were recorded. On the final day, rats were sacrificed, and ELISAs were used to measure the levels of norepinephrine, epinephrine, vasopressin, and aldosterone in trunk blood. We found that while NaCl intake did not differ between the first and second deprivations, rats drank less water after their second deprivation, and, therefore, a more concentrated solution. However, EB-treated rats drank more water than OIL-treated rats after both deprivations. EB-treated rats had lower norepinephrine, vasopressin, and aldosterone levels than OIL-treated rats, but there was no difference in norepinephrine, epinephrine, or aldosterone between the first and second deprivations. Vasopressin was increased after the second deprivation in both groups, but this did not appear to be specific to diet.

We conclude that there are persistent behavioral changes after repeated episodes of dietary sodium deficiency that are affected by estrogen treatment, but are not likely to be explained by the hormones we measured. In contrast, the observed differences in regulatory hormones may impact blood pressure under baseline conditions, as well as during single or repeated episodes of dietary sodium deficiency, particularly in females with estrogen.