The stimulatory effect of a muscle protein hydrolysate from Atlantic cod,Gadus morhuaL., on Atlantic salmon,Salmo salarL., head kidney leucocytes

This study shows the stimulatory capacity of a cod muscle protein hydrolysate on Atlantic salmon head kidney leucocytes bothin vivoandin vitro. Increased respiratory burst activities were demonstrated in leucocytes after stimulation with a peptide fraction in the molecular weight range 500–3000 Da. The respiratory burst activity was quantified using reduction of nitroblue tetrazolium (NBT) as a measure of superoxide anion production following stimulation with phorbol myristate acetate (PMA) as the trigger.In vitrodose-response studies demonstrated an increased stimulation with increasing concentrations of the peptide fraction (30–1000 μg ml−1). Intraperitoneal injection of the peptide fraction in Atlantic salmon (100 mg kg−1) resulted in enhanced levels of superoxide anion production in head kidney leucocytes 2 and 4 days post-injection when assayed immediately after isolation. Culturing the cells for 18 or 41 h abolished the stimulatory capacity of the peptides. Also, increased levels of the lysosomal enzyme acid phosphatase were measured in the isolated head kidney leucocytes after intraperitoneal injection. Microscopic examination of tissue slices two days after i.p. administration revealed accumulation of FITC-labelled muscle hydrolysate (500–3000 Da) mainly in macrophages and endothelial cells of the kidney.