Effect of Different Immunostimulants on Digestive Enzyme Activities and Histological Structure in Intestine of Sea Cucumber, Apostichopus japonicus

The activities of digestive enzymes and histological structure were studied in the intestine of sea cucumber Apostichopus japonicus with initial body weight of 21.00 ±2.00 g injected with the same volume solution(400μL, 1.2mg·mL-1)of astragalus polysaccharide, lycium barbarum polysaccharide, cortex phellodendri, radix sophoraflavescens, radix codonopsis, inulin, cecropin,medicated leaven, and hawthorn fruit on the first, third and fifth days at the temperature of 15±0.5℃ to investigate the effect of different immunostimulants on the activities of digestive enzymes and histological structure in the intestines. In the control group, the sea cucumber was injected 400 μL sterile saline individually. The results showed that the sea cucumber administrated with inulin had the maximal protease activity, up to 15.16 μg·g-1·min-1on the third day, significantly different from the control group(7.07μg·g-1·min-1)(P0.05). However, the cortex phellodendri led to inhibit the protease activity. The maximal amylase activity(72.57 U·dl-1)was observed in the sea cucumber infected with medicated leaven, significantly different from the control group(53.2 U·dl-1)(P0.05). There were significant cellulase activities between the inulin group and hawthorn fruit group(P0.05), without significant differences in other groups. The maximal alginase activity was found in the sea cucumber injected with astragalus polysaccharide(2.06 μg·g-1·min-1), followed by in the sea cucumber injected with inulin. During the rearing period, the amylase activity was the most constant, followed by the cellulose activity, and the least by the alginase and protease activities. There were different effects of the immunostimulants on digestive enzyme activities and intestinal histological structure of sea cucumber.