Changes in digestive enzyme activities in eel after feeding.

Sequential changes of digestive enzyme activities in gastrointestinal tissue and their contents were examined at 0, 1, 3, 5, and 12h after feeding a paste diet flavoured with the feeding stimulants: alanine, glycine, proline, and histidine. Protease activity in gastric tissue decreased soon after feeding, reaching a minimum level at 3h. The activity in gastric contents maintained low levels in contrast to the tissue. Protease activity in intestinal tissue decreased immediately after feeding and reached a minimum level at 5h. The intestinal content's activity increased after feeding, reaching a maximum level at 5h. Amylase activity in intestinal tissue was approximately constant during the 12h, but the activity in their contents slight increased with time. There was a significant correlation observed between the mount of the intestinal contents and the total activity of protease or amylase in the contents. This suggested that the digestive enzymes were secreted in proportion to the amount of contents in the eel intestine.