The present study was designed to investigate the effects of grape see
d tannins on rat intestinal alkaline phosphatase (AP), sucrase and dip
eptidyl peptidase IV (DPP IV) activities. An experiment was performed
in vivo by dietary supplementation with 2% tannins; this diet was test
ed on an experimental group of rats; a control group received a diet w
ithout tannins. After 31 days, tannins intake significantly decreased
middle-jejunal AP from 123 to 45 mU/mg protein and sucrase activities
from 310 to 195 mU/mg protein, while no significant difference appeare
d at the duodenal stage (p < 0.05). Ileal DPP IV activity was also sig
nificantly reduced (p < 0.05) from 190 to 110 mU/mg protein after tann
in intake. Using in vitro experiments on purified brush border membran
es, AP activity was found to be inhibited by grape tannins; this inhib
ition was prevented by the detergent Triton X-100. The addition of pan
creatic-biliary (PB) juice to the incubation medium prevented or rever
sed the tannin-inhibited enzyme activity. The present data indicate th
at in the duodenal lumen, alkalinity and detergency from the PB secret
ion neutralized the ability of tannins to inactivate brush border hydr
olase activities and suggest that enzyme inhibition took place once bi
le salts were reabsorbed while moving down the gut. This was confirmed
by in vitro experiments where sucrase and DPP IV activities inhibited
by grape seed tannins were largely recovered after the addition of PB
juice to the incubation medium.