1. Few studies have been reported concerning the effect of ageing on renal functional and vascular responses to various stresses during ordinary life. In the present study, we examined the effect of age on changes in renal sodium handling and renal vascular resistance (RVR) in response to standing from a supine position in subjects with normal renal function.
2. We selected 43 healthy males in the second through to the seventh decade of life and gave them a constant dietary sodium intake before the study period. Renal function was estimated by standard clearance methods with the subject in a state of euvolaemia.
3. The mean daily urinary excretion of sodium was 236 ± 22 mEq. Standing from a supine position was associated with significant decreases (P < 0.0001) in creatinine clearance (from 125 ± 18 to 117 ± 19 mL/min per 1.73 m2), sodium excretion (from 178 ± 29 to 97 ± 23 μEq/min) and fractional excretion of sodium (from 1.02 ± 0.19 to 0.60 ± 0.13%). A significant increase (P < 0.0001) in the RVR index (from 0.11 ± 0.03 to 0.14 ± 0.04 units) was noted. Univariate analysis indicated that while the change in RVR associated with standing was significantly diminished (P < 0.05) in older subjects, orthostatic changes in other parameters associated with standing were minimally influenced by age.
4. In conclusion, although the renal vascular response is impaired in advanced age, the renal functional response to orthostasis is otherwise maintained in healthy elderly subjects under conditions of normal sodium intake and clinical euvolaemia.