Physical training increases free radical production and consumes antioxidants. It
has previously been shown that acute exercise markedly increases the susceptibility
of LDL to oxidation but whether such changes are observed during physical training
is unknown. We measured circulating antioxidants, lipids and lipoproteins, and blood
flow responses to intrabrachial infusions of endothelium-dependent (acetylcholine,
ACh, L-N-monomethyl-arginine, L-NMMA) and -independent (sodium nitroprusside, SNP)
vasoactive agents, before and after 3 months of running in 9 fit male subjects. Maximal
aerobic power increased from 53 +/- 1 to 58 +/- 2 ml/kg min (P < 0.02). All circulating
antioxidants (uric acid, SH-groups, alpha-tocopherol, beta-carotene, retinol) except
ascorbate decreased significantly during training. Endothelium-dependent vasodilatation
in forearm vessels decreased by 32-35% (P < 0.05), as determined from blood flow responses
to both a low (10.8 +/- 2.1 vs. 7.3 +/- 1.5 ml/dl min, 0 vs. 3 months) and a high
(14.8 +/- 2.6 vs. 9.6 +/- 1.8) ACh dose. The % endothelium-dependent blood flow (%
decrease in basal flow by L-NMMA), decreased through training from 37 +/- 3 to 22
+/- 7% (P < 0.05). Blood flow responses to SNP remained unchanged. The decrease in
uric acid was significantly correlated with the change in the % decrease in blood
flow by L-NMMA (r = 0.74, P < 0.05). The lag time for the susceptibility of plasma
LDL to oxidation in vitro, LDL size and the concentration of LDL cholestetol remained
unchanged. We conclude that relatively intense aerobic training decreases circulating
antioxidant concentrations and impairs endothelial function in forearm vessels.