Effects of age and low sodium diet on glomerular filtration rate, plasma renal flow, urinary aldosterone excretion rate and ability of renal sodium conservation in the elderly

Zygmunt Chodorowski¹, Przemyslaw Rutkowski², Boleslaw Rutkowski², Jacek Sein Anand¹

Summary
The objective of the study was to assess the effects of age and low-sodium diet (Na + < 10 mmol/24 h) on glomerular filtration rate, effective renal plasma flow, 24 h urinary aldosterone excretion rate and renal sodium conservation ability in the elderly.
The research was carried out in two patient groups: a control group (I) of 23 healthy subjects (11 women) aged 18-39 years (mean 30 years) and a study group of 22 clinically healthy subjects (10 women) aged 66-83 (mean 73 years). None of the subjects had any abnormal changes in the kidneys, liver, cardiovasular or edocrine organs. In statistical analysis Student´s t and paired tests were used. In the elderly on normal sodium diet (Na+ ave 150 mmol/24 h) glomerular filtration rate was decreased by 39.5%, 51Cr clearance by 38.1%, 125J-hippurate clearance by 47.9% and 24-hour urinary aldosterone excrection rate by 35.8%; filtration fraction was elevated by 15.7%. The results were statisticalyy significant as compared with those of group I. A fouir-day dietary sodium intake had no effect on the renal function parameters; however, in the elderly subjects it reduced 24-hour urinary sodium excretion by 26.5%, and in the control group by 65.9%. This difference indicated an increased urinary sodium loss in the elderly group. Additionally, low sodium diet increased the urinary sodium aldosterone excretion in both groups; however, this increase was lower in the elderly subjects.

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