Objective: Hyponatremia occurs not infrequently in hypopituitarism. Arginine vasopressin (AVP)-induced impaired water excretion is found in patients with hypopituitarism and experimental models of glucocorticoid deficiency.
Design: The present study was undertaken to determine whether augmented release of AVP is involved in the development of hyponatremia in elderly subjects with secondary adrenal insufficiency.
Methods: Forty patients with ACTH-deficient, secondary adrenal insufficiency were examined. They were divided into three groups according to the age at which diagnosis was ascertained (group A <20 Years, group B 20-64 Years, and group C>or=65 Years).
Results: Hyponatremia was more manifest in the elderly group than in the other two groups, serum sodium (Na) levels being 124.7 mmol/l in the elderly group, a value significantly less than 141.5 and 133.5 mmol/l in groups A and B. Plasma AVP levels seemed likely to be high compared with the respective hypo-osmolality in plasma in the elderly group, as plasma AVP levels were 1.7 pmol/l despite a mean plasma osmolality of 259 mmol/kg. Such an alteration was less clear in group B and was not found in group A. Therefore, elevation of plasma AVP was apparent in the elderly patients. Hydrocortisone replacement promptly normalized serum Na levels from 125 to 142 mmol/l (P<0.01) and reduced plasma AVP levels from 1.7 to 0.9 pmol/l (P<0.05), which were comparable to the respective plasma osmolality in the elderly patients.
Conclusion: These results indicate that non-suppressible release of AVP is crucially involved in the impaired water excretion and hyponatremia seen in elderly patients with secondary adrenal insufficiency compared with the younger patients, and that exaggerated release of AVP becomes manifest as the subjects grow older.