Graded amounts (0, 50, 500 and 5,000 mg/liter) of
ascorbic acid (AsA) were given in
drinking water to guinea pigs for 21 days to prepare AsA-deficient, low-AsA, moderate-AsA and excess-AsA animals, and the plasma
phospholipid hydroperoxide level and
lipid concentration were quantitatively determined to investigate the
antioxidant effect of AsA in vivo.
Phosphatidylcholine hydroperoxide (
PCOOH) was a predominant
phospholipid hydroperoxide present in the plasma, and the
PCOOH concentration was significantly higher in AsA-deficient, low-AsA and excess-AsA animals (80.4 nM, 54.8 nM and 42.2 nM, respectively) as compared with that in moderate-AsA animals (27.2 nM). Hyperlipidemic plasma characterized as high
cholesterol and high
triacylglycerol concentrations was confirmed in AsA-deficient animals. Molar ratios of plasma AsA and
alpha--tocopherol against 10(4) moles of
phospholipids were significantly lower in AsA-deficient and low-AsA animals (0.6-2.1 and 5.5-8.5, respectively) than in moderate-AsA and excess-AsA animals (14.2-18.0 and 11.2-11.9, respectively). In plasma, a high correlation coefficient (r = 0.979) was observed between
PCOOH and AsA for which there was optimum AsA level to keep the low
PCOOH and such correlation was stronger than that (r = 0.558) observed with
alpha-tocopherol. The results indicated that AsA has an important function to control the
phospholipid hydroperoxide level in plasma and that moderate supplementation of AsA is required to reveal its optimal
antioxidant effect in vivo. The present study also showed that
AsA-deficiency especially invites an increase in plasma
PCOOH together with a hyperlipidemic state which are risk factors in developing
atherogenesis.