Effects of laminarin in gastrointestinal tract The effect of laminarin on the integrity of the intestinal mucosa was studied by assays of lactase, maltase and sucrase activities. No difference was observed between the control group and the test group (Figs 4–6). The lactase activity was decreased and the maltase activity was increased between the rats treated for 7days (14days old at sacrifice) and those treated for 14 or 18days (respectively 21 and 25days old at sacrifice).