Oxidative stress can induce abnormal
tryptophan metabolism. The present study was mainly conducted to determine the effect of dietary
tryptophan levels on oxidative stress in the liver of weaned pigs challenged by
diquat. A total of 36 PIC piglets weaned at 21 days of age were randomly allotted to 1 of 3 diets containing dietary
tryptophan levels of 0.18, 0.30, and 0.45% for 14 d. On day 8, the piglets were injected intraperitoneally with sterile
0.9% NaCl solution or
diquat (10 mg/kg
body weight). During the first 7 d of trial, increasing dietary
tryptophan levels enhanced average daily gain (P = 0.09) and average daily feed intake (P = 0.08), and decreased the feed efficiency (P < 0.05) of piglets. The growth performance was decreased by
diquat injection (P < 0.05).
Diquat injection also decreased the activities of the
superoxide dismutase (SOD) and
glutathione peroxidase (GPx) in the plasma and liver (P < 0.05), increased plasma
malondialdehyde (MDA) (P < 0.05) and
urea nitrogen (P < 0.05) concentrations, and enhanced MDA concentration (P = 0.09) and
tryptophan 2,3-dioxygenase (TDO) activity (P = 0.07) in liver of piglets. Increasing dietary
tryptophan levels could attenuate the effects of
diquat injection on the MDA (P = 0.06) concentration and the activities of SOD (P = 0.09) and GPx (P = 0.05) of the liver, and plasma
urea nitrogen (P = 0.06) concentration in the piglet. There was a synergistic role for increasing TDO activity in the liver between dietary
tryptophan levels and
diquat injection (P < 0.05). These results suggest that increasing dietary
tryptophan levels could attenuate the oxidative stress of the liver in weaned piglets intraperitoneally injected with
diquat via enhancing the
antioxidant capacity.