Effects of L-tryptophan and melatonin on the serum glucose level and antioxidant capacity in the hepatopancreas of Chinese mitten crab (Eriocheir sinensis)

In order to investigate the effects of L-tryptophan and melatonin on the serum glucose level and antioxidant capacity in the hepatopancreas of Chinese mitten crab (Eriocheir sinensis), the female crabs with the average body weight of (16.58±2.20) g were randomly allocated into 8 groups (the processing experiments of L-tryptophan and melatonin had 4 groups respectively). Each experimental period was 30d. (1) The feeding experiment of L-tryptophan: crabs were fed with diet which added 4 levels of L-tryptophan, and the L-tryptophan percently for the diet were 0.36% (basal diet, namely control group), 0.47%, 0.73% and 1.05% (named diet 1, 2, 3 and 4, respectively). The serum glucose level and T-AOC and the capacity of SOD in the hepatopancreas were determined. (2) The injection experiment of melatonin: on the 1^st and 15^th days, crabs were injected with saline (control group namely C) and different doses of melatonin which were 10^–6 mol/crab (μM), 10^–9 mol/crab (nM) and 10^–12 mol/crab (pM). Then hemolymph and hepatopancreas were collected separately for the determination of the serum glucose level and T-AOC and the capacity of SOD in the hepatopancreas on the 1^st and 15^th days. In addition, we analyzed the serum glucose level on the 30^th day. The results showed that different levels of L-tryptophan had no significant effect on serum glucose level, and its value was approximately (4.62±0.20) mmol/L. The diet which contained 0.73% L-tryptophan could significantly increase the capacity of SOD (82.86±1.07) U/mL. Injection of melatonin into crabs resulted in hyperglycemia in a dose-dependent manner on the 1^st day. Among them, the serum glucose level of μM reached up to (7.56±0.36) mmol/L, which was significantly higher than other three groups. Moreover, the injection of MT played an important role in promoting the T-AOC and the capacity of SOD, but only effective on the 1^st day. Compared with C, pM and nM, the the T-AOC and the capacity of SOD of μM was higher than those significantly. In summary, 0.73% L-tryptophan can improve the antioxidant capacity of crabs, but the effects on the serum glucose level are not obvious. The injection of 10^–6 mol/crab melatonin can improve the serum glucose level and antioxidant capacity of Chinese mitten crab for short time (1 d).