[Water and electrolyte metabolism in the elderly with cardiovascular disease--hormonal aspects in elderly hypertension].

Study I: A retrospective survey of the data base on serum electrolyte measurements in our hospital (approximately 50,000 cases) revealed that the incidence of hyponatremia increased with age. Its major cause in the elderly hospital inpatients with cardiovascular disease was congestive heart failure, frequently accompanied by renal dysfunction and the use of diuretics. Another interesting finding from this analysis was that the use of potassium sparing diuretics were often associated with hyperkalemia in elderly patients whose renal functions were apparently normal based on the serum creatinine level. Study II: The resting hemodynamics and the plasma levels of various hormones related to water and electrolyte metabolism were compared between normal elderly and young subjects. The resting hemodynamic parameters, including cardiac index and blood pressure, did not differ between the two normal groups. Plasma atrial natriuretic peptide and norepinephrine levels were significantly higher in the elderly, while plasma renin activity and aldosterone levels were significantly decreased. No differences were observed in antidiuretic hormone levels. The same parameters were then compared between normal and hypertensive elderly subjects. Elderly hypertensives had lower cardiac index and higher peripheral resistance than normal elderly subjects. Plasma norepinephrine level and plasma renin activity were lower, but aldosterone level was not significantly lower in hypertensives than in normotensives. There was no difference in antidiuretic hormone. In the elderly group as a whole, atrial natriuretic peptide correlated positively with blood pressure, and negatively with plasma norepinephrine and renin activity. Multivariate analysis showed that the strongest correlation was that with plasma renin activity. These results suggest that the plasma levels of various hormones related to water and electrolyte metabolism were altered with age and hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)