RENAL EXCRETION OF ASCORBIC-ACID - EFFECT OF AGE AND SEX

To determine if the lower plasma ascorbic acid concentrations observed in males compared to females, and in the elderly in general, might be due to differences in renal clearances of ascorbic acid, tubular maxi mum reabsorptions (Tm(AA)) and renal thresholds for ascorbic acid were determined on older (10 male, 10 female, aged 70-86 years) and younge r (3 male, 5 female, aged 26-59 years) subjects. The mean Tm(AA) for m en was 1.54 +/- 0.29 and for women 1.39 +/- 0.33 mg/minute/100 mL glom erular filtration rate (p > 0.05). The mean renal threshold for men wa s 1.51 +/- 0.25 and for women 1.26 +/-0. 16 mg/dL (p < 0.02). Neither was affected by age. If differences in Tm(AA) and renal threshold were to explain the lower plasma ascorbic acid concentrations observed in males, both values should have been lower than in females. The ability of women to maintain higher plasma ascorbic acid concentrations than men, and young higher than elderly, cannot be explained by differences in the renal handling of ascorbic acid.