Jejunal perfusion of simple and conjugated folates in man

The technique of human jejunal perfusion was used to study the process of digestion and absorption of conjugated folates in five healthy volunteers. The test solution of isotonic saline contained equimolar concentrations of purified [3H]pteroylmonoglutamate ([3H]PG-1) and of [14C]pteroylheptaglutamate ([14C]PG-7) which was labeled on the first glutamyl unit. Calculations were made of the luminal disappearance of each labeled folate, and degradation products of [14C]PG-7 were identified in luminal contents obtained 15 and 30 cm from the infusion site. The percentage of disappearance of [3H]PG-1 was 74.7% and of [14C]PG-7 was 52.6% (P less than 0.001)9 Column chromatography of intestinal aspirates demonstrated a spectrum of 14C-labeled folates corresponding to chain lengths from [14C]PG-1 to [14C]PG-7, with distal accumulation of derived [14C]PG-1. Intraluminal hydrolysis of [14C]PG-7 was excluded by finding the compound unchanged after in vitro incubation with intestinal juice obtained by saline perfusion or siphonage. These data indicate that there are separate rates for the luminal disappearance of PG-1 and PG-7, and show that the digestion of PG-7 requires its contact with the intestinal mucosa. The evidence suggests that progressive mucosal hydrolysis is integral to the process of PG-7 absorption in man.