MEASUREMENT OF THE RATE OF ENTRY OF INTACT COLON-DERIVED LACTOSE INTOTHE CIRCULATION - A MODEL FOR ASSESSING GUT UPTAKE OF MOLECULES NOT ENDOGENOUSLY SYNTHESIZED

Background: Results of in vitro studies have documented colonic absorp tion of lactase in the newborn. A stable isotope model was developed f or assessing the entry rate of intact lactose into the portal circulat ion in newborn piglets. Methods: In experiment 1, unlabeled and [D-1-C -13]-lactose were infused into two separate mesenteric veins, and in e xperiment 2, labeled lactose was infused into a mesenteric vein and un labeled lactose was infused into the colon. The C-13-enrichment of pla sma lactose was assessed by high performance Liquid chromatography gas chromatography combined with mass spectrometry. Results: The isotopic estimate of the mesenteric venous infusion rate of lactase was 91% of the theoretical. In the second experiment 13% of the unlabeled lactas e infused into the colon reached the portal circulation. Conclusions: The current study provides the first, direct, in vivo confirmation of colon absorption of intact lactase. The tracer model could be used to evaluate intestinal or colonic absorption of other organic compounds n ot endogenously synthesized, including vitamins or drugs. (C) 1997 Lip pincott-Raven Publishers.