2015 Volume 69 Issue 1 Pages 36-41
Lactoferrin（LF）has a profound modulatory effect on the adaptive immune system, as well as improves nutritional and physiological conditions. LF is easily degraded by pepsin in the stomach and it is reported that its pepsin hydrolysate may diminish the activity. Some cultured fish have a stomach, and others do not. In this study, we investigated the effects of bovine LF, its pepsin hydrolysate on the physiological dysfunctions of stomachless fish treated with methotrexate（MTX）. Goldfish, weighing about 15 g, was treated intramuscularly with MTX（2.5 mg/kg body weight）three times every other day. In control fish fed a commercial diet, MTX induced severe immune suppression, and an increase in the number of total bacteria and Enterobacteriaceae in the intestinal tract, as well as intestinal damage such as lowered and thickened mucosa and thinned muscularis externa. Pretreatment of LF（oral administration of LF at 200 mg/kg BW/day）for 2 weeks reduced remarkably the deleterious side effects induced by MTX. LF treated at pH 4.0 with 2 ％ porcine pepsin for 2 h at 37 ℃（D4-LF : LF moderate hydrolysate）enhanced the immune response and reduced significantly the physiological dysfunctions of MTX-treated fish. In MTX-treated fish fed LF hydrolysed at pH 2.0 with pepsin（D2-LF : LF severe hydrolysate）, however, little significant improvement of the physiological dysfunctions was found. Oral administration of LF moderate pepsin hydrolysate, that is, reduced the physiological dysfunctions of fish treated with MTX, and its severe pepsin hydrolysate was much less effective than undigested LF. These results suggest that for cultured fish possessing high pepsin activity with low pH in the stomach, administration of enteric-coated LF or simultaneous administration of LF and substances for neutralizing excessive acids in the stomach is more effective.
