Stimulative effect of skipjack tuna soluble extract on pepsin-like protease in the stomach of rockfish (Sebastes schlegelii) using an in vitro perfusion method

The effect of intra-gastric infusion of skipjack tuna (Katsuwonus pelamis) muscle soluble extract and of carnosine, anserine and histidine, on pepsin-like protease activity was studied in the isolated, externally batch-cultured stomach of the rockfish (Sebastes schlegelii). Stomach was isolated from the fish, then intragastrically infused with the above solutions or with a balanced saline solution (control solution) as the stimulant at 0.1 mL/min for 6 h. Intra-gastric efflux was collected for measurement of pepsin-like protease activity. Skipjack tuna soluble extract, but not carnosine, anserine or histidine alone caused significant enhancement of pepsin-like protease activity during the infusion. Pepsin-like protease activity from skipjack tuna soluble extract responded immediately after infusion and was kept for 150 min after infusion. Stomach motility at the end of infusion was also observed. These results suggest that isolated stomach can receive mucosal side stimulants in vitro. It is likely that some effective components for stomach digestion in fish exist in skipjack tuna soluble extract.