Renal functional reserve in healthy elderly subjects

Area of Science:

• Nephrology
• Gerontology
• Physiology

Background:

• The renal functional reserve (RFR), an increase in glomerular filtration rate (GFR) following an amino acid (AA) load, is known to be impaired in aged rats.
• The predictive value of RFR for human renal disease progression is debated, but age-related renal hemodynamic alterations may influence kidney disease evolution in the elderly.

Purpose of the Study:

• To compare renal hemodynamics and RFR in healthy young and elderly human subjects.
• To investigate the impact of age on renal hemodynamics before and after an amino acid infusion.

Main Methods:

• Comparison of renal hemodynamics in 15 young (median age 26) and 10 elderly (median age 70) healthy, normotensive subjects.
• Measurement of baseline GFR (using inulin clearance, Cin) and effective renal plasma flow (using para-aminohippurate clearance, Cpah) after 12-hour fasting.
• Assessment of RFR after an overnight amino acid infusion (7% solution at 83 mL/h).

Main Results:

• Elderly subjects had significantly lower median basal GFR (102 mL/min/1.73 m2) and effective RPF (339 mL/min/1.73 m2) compared to young subjects (122 and 647 mL/min/1.73 m2, respectively).
• Despite lower baseline values, GFR increased significantly (P < 0.01) after amino acid loading in both young (median 146 mL/min/1.73 m2) and elderly (median 118 mL/min/1.73 m2) groups.
• Effective RPF also increased significantly after AA load in both groups, though values remained lower in the elderly (349 mL/min/1.73 m2) compared to the young (689 mL/min/1.73 m2).

Conclusions:

• Healthy elderly individuals exhibit reduced baseline renal hemodynamics (GFR and RPF) compared to younger adults.
• The renal functional reserve, indicated by GFR increase post-amino acid load, is preserved in healthy elderly subjects despite lower baseline function.
• Age-related changes in renal hemodynamics do not preclude a significant renal functional reserve in healthy aging.