THE STIMULATORY EFFECT OF A MUSCLE PROTEIN HYDROLYSATE FROM ATLANTIC COD, GADUS-MORHUA L, ON ATLANTIC SALMON, SALMO-SALAR L, HEAD KIDNEY LEUKOCYTES

This study shows the stimulatory capacity of a cod muscle protein hydr olysate on Atlantic salmon head kidney leucocytes both in, vivo and in vitro. Increased respiratory burst activities were demonstrated in le ucocytes after stimulation with a peptide fraction in the molecular we ight range 500-3000 Da. The respiratory burst activity was quantified using reduction of nitroblue tetrazolium (NET) as a measure of superox ide anion production following stimulation with phorbol myristate acet ate (PMA) as the trigger. In vitro dose-response studies demonstrated an increased stimulation with increasing concentrations of the peptide fraction (30-1000 mu g ml(-1)). Intraperitoneal injection of the pept ide fraction in Atlantic salmon (100 mg kg(-1)) resulted in enhanced l evels of superoxide anion production in head kidney leucocytes 2 and 4 days post-injection when assayed immediately after isolation. Culturi ng the cells for 18 or 41 h abolished the stimulatory capacity of the peptides. Also, increased levels of the lysosomal enzyme acid phosphat ase were measured in the isolated head kidney leucocytes after intrape ritoneal injection. Microscopic examination of tissue slices two days after i.p, administration revealed accumulation of FITC-labelled muscl e hydrolysate (500-3000 Da) mainly in macrophages and endothelial cell s of the kidney. (C) 1996 Academic Press Limited