Plasma arginine vasopressin level in hypothyroid women in relation to dietary sodium supply.

INTRODUCTION A disturbed regulation mechanism of arginine vasopressin secretion in response to plasma osmolality and volaemia changes occurs in hypothyroidism. The aim of this study was to determine plasma arginine vasopressin concentration in hypothyroid women under conditions of a low sodium diet and in an upright position. MATERIAL AND METHODS Twenty-six women with primary hypothyroidism and 24 healthy women (control group) were investigated. In all the patients, the plasma arginine vasopressin and serum sodium and potassium levels, as well as plasma osmolality, were measured first under basal conditions, i.e. after three days of a normal sodium diet (120 mmol sodium per day) in a horizontal position, and next after three days of a low sodium diet (10 mmol Na per day) in an upright position. In hypothyroid patients, the investigations were repeated after a euthyroid state as a result of L-thyroxine treatment had been attained. RESULTS An increase of vasopressinaemia, measured under basal conditions as well as after three days of the low sodium diet, was shown in untreated hypothyroid patients compared to the control group. The arginine vasopressin plasma level normalised after a euthyroid state had been attained. As a result of the low sodium diet and the upright position, a significant increase of arginine vasopressin secretion was observed in the control group and hypothyroid women in the euthyroid state. No significant increase of this neuropeptide level in untreated patients was shown while applying the low sodium diet and upright position. Plasma osmolality and natraemia were decreased in the untreated hypothyroid patients. No correlation between vasopressinaemia and plasma osmolality was shown. CONCLUSION The plasma arginine vasopressin level is increased in hypothyroid women, and does not change in the upright position under the influence of a low sodium diet.