CHANGES OF DIGESTIVE ENZYME ACTIVITIES AND FREE AMINO ACIDS IN SIPUNCULUS NUDUS COELOMIC FLUID UNDER ACUTE STRESS OF CD2+

The current study investigated the acute toxicity of Cd2+ to Sipunculus nudus Linnaeus using toxicological methods. To do this, the peanutworms were exposed to Cd2+ stress for 48h at minimum lethal concentration, and the dynamic changes of digestive enzyme activities and free amino acids in their coelomic fluid were analyzed. The results showed that the mortality of peanutworms increased with the increasing Cd2+ concentration. The LC50 of Cd2+ after 24h and 48h were 37.80 mg/L and 22.68 mg/L, respectively. Cd2+ exposure had inhibitory effects on protease and amylase activities in coelomic fluid during the whole experimental period. The lipase activity increased (P0.05) at the early time of the exposure, but inhibited significantly (P0.05) after 24h. The content and composition of free amino acids in coelomic fluid of peanutworms had significant changes during the 48 hours. Each free amino acid and the total amino acid had no significant changes (P0.05) at the first 24 hours, and then the contents of that increased significantly (P0.05) and decreased significantly later at the next 24 hours (P0.05). The total amino acid reached 145.50 mg/100 mL at 36h, twice as initial level. The free amino acids composition had a similar regulation pattern with total amino acid. No significant change was observed at first 24h and then reached peak level after that. The results suggest that acute stress of Cd2+ significantly impact digestive enzyme activities and free amino acids in Sipunculus nudus coelomic fluid with a time-dependent pattern.