H. Baker et al., VITAMIN ACTIVITIES IN HUMAN PORTAL, HEPATIC AND FEMORAL BLOOD AFTER VITAMIN INGESTION, International journal for vitamin and nutrition research, 64(1), 1994, pp. 60-67
The dynamics of intestinal absorption, blood concentration and distrib
ution of thiamin, biotin, nicotinate, riboflavin, pantothenate, variou
s folates (folic acid, folinic acid, pteroyltriglutamate), vitamins A,
E, C, B-12, and B-6 were monitored in 12 patients by multiple simulta
neous sampling of brood obtained by combined catheterization of portal
vein, hepatic vein, and femoral artery after vitamin ingestion. All w
ater-soluble vitamins proved elevated after vitamin ingestion principa
lly in portal blood within 10 minutes as compared with hepatic and fem
oral blood. Elevated vitamin levels in portal blood - compared to hepa
tic and femoral blood - remained high even after 120 min. indicating t
hat absorption from the gut was still progressing. In contrast, ingest
ion of the fat-soluble vitamins A and E evoked no elevated vitamin act
ivity in portal blood. Within 10 min. after vitamin ingestion, all fol
ates were converted into reduced and methylated 5-methyltetrahydrofola
te (5-CN3THF) on passage through the gut. At this time, portal blood e
levation of 5-CH3THF persisted before its elevation in hepatic or femo
ral blood. Presumably, the elevation was not due to the flushing of st
ored 5-CH5THF from tissues but rather of folate conversion to 5-CH3THF
upon gut passage. The significance of these findings is discussed.