Studies on the mechanism of vitamin B12 absorption: in vivo transfer of vitamin B12 to intrinsic factor

Highley, Derek R.; Ellenbogen, Leon

doi:10.1016/0003-9861(62)90254-0

Cited by 22 publications

(3 citation statements)

References 11 publications

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“…The present schema for vitamin B1n absorption envisages the ingestion of vitamin B12 (actually coenzyme B12 bound to protein [10][11][12][13]), release from its protein bond as a result of proteolytic digestion in an acid medium, binding to intrinsic factor in the stomach or upper portion of the small bowel (14)(15)(16), passage down the small bowel, attachment of the IF-B12 complex to a specific receptor located in the brush border of the ileal epithelial cell (17)(18)(19)(20)(21), and eventual release of the vitamin into the portal circulation unaccompanied by IF (22,23). In addition a factor elaborated by the pancreas may be an obligatory requirement for optimal vitamin Bi2 absorption.…”

Section: Discussionmentioning

confidence: 99%

The Role of the Pancreas in Vitamin B12 Absorption: Studies of Vitamin B12 Absorption in Partially Pancreatectomized Rats

Toskes¹,

Deren²

1972

J. Clin. Invest.

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A iB S T R A C T The effect of partial pancreatectomy(80-90%,) on vitamin Bn absorption was studied in the rat. The absorption of 5 ng of^'Co-labeled vitamin B1u was significantly reduced from 70 ±2.5% (mean +SE) in control and sham-operated rats to 32 ±2.6% in partially pancreatectomized rats. Hog pancreatic extract (0.17 g/kg) improved vitamin B12 absorption from 30.0 to 61.0% in partially pancreatectomized rats but did not alter vitamin B,2 absorption in control rats. Chloramphenicol did not enhance vitamin B12 absorption in partially pancreatectomized rats with pancreatic extractimproved vitamin B12 malabsorption. The partially pancreatectomized rats with pancreatic extract-improved vitamin B12 malabsorption were sacrificed and the stomach and small bowel studied in vitro to further define the pathogenesis of the vitamin B12 malabsorption. Rat gastric intrinsic factor stimulated vitamin B12 uptake by intestinal sacs prepared from partially pancreatectomized rats 3.1-fold. Gastric intrinsic factor prepared from partially pancreatectomized rats was as effective in promoting vitamin B12 uptake by rat intestinal sacs as intrinsic factor prepared from control rats. These data indicate that partially pancreatectomized rats develop an abnormality in the absorption of labeled vitamin B12 which can be corected by pancreatic extract. The vitamin B12 malabsorption is due to neither an alteration in gastric intrinsic factor activity nor an impairment of the intrinsic factor-vitamin B12 receptor in the intestine. It is suggested that in the partially pancreatectomized rats the intrinsic factor-vitamin B12 complex exists in a form which is not available for absorption. INTRODUCTIONAlthough several patients with pancreatic exocrine insufficiency have been noted to poorly absorb vitamin B,2 the importance of normal pancreatic function for optimal vitamin Bi absorption is generally not appreciated 1-5). Furthermore, the pathogenesis of the observed vitamin B12 absorptive defect has not been clarified.The relationship between the pancreas and the intestinal absorption of vitamin B12 was studied by measuring the absorption of this vitamin in rats subjected to partial pancreatectomy. The results demonstrate (a) that the partially pancreatectomized rat has a defect in vitamin B12 absorption, (b) that the administration of hog pancreatic extract restores vitamin B12 absorption to normal, (c) that intrinsic factor extracted from the gastric mucosa -of partially pancreatectomized rats stimulates vitamin Bn absorption in vitro, and (d) that gastric intrinsic factor stimulates vitamin B12 uptake in gut sacs prepared from partially pancreatectomized rats. These data indicate that partially pancreatectomized rats develop a defect in vitamin B12 absorption which is due to neither an alteration in gastric intrinsic factor activity nor to an impairment of the intrinsic factor-vitamin B12 receptor in the intestine.

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Section: Discussionmentioning

confidence: 99%

The Role of the Pancreas in Vitamin B12 Absorption: Studies of Vitamin B12 Absorption in Partially Pancreatectomized Rats

Toskes¹,

Deren²

1972

J. Clin. Invest.

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“…In contrast to free BJ2, which is absorbed from the loop to some extent in the absence of IF, this complexed Bl2 was totally unabsorbable. Only in the presence of a large excess of IF in the loop was such 'sequestered' B12 transferred to IF and subsequently absorbed [77], The quantity of this 'non-IF' binder of the intestinal origin in the rat was quite small, being of the order of several nanograms of B12 in terms of bindingcapacity at a time: yet, several hundred nanogramsofBi2were sequestered in the loop when a large quantity of Bj2 was allowed to remain for more than 10 h. Most of the sequestered B,2 was with desquamated epithelium [77], Highley and Eleenbogen [45] had earlier observed an in vivo transfer of BI2 from non-IF binder to IF in man.…”

Section: Intestinal Bindermentioning

confidence: 99%

Intestinal Mucosa and Vitamin B<sub>12</sub> Absorption

Okuda¹

1972

Digestion

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“…Ή τρί τη ανήκει στίς δεσμευτικές πρωτεΐνες R πού βρίσκονται σέ -39δλα τά υγρά του σώματος, στά ερυθρά και στά λευκά αιμο σφαίρια. Ό Simons148 βρήκε ότι où αναλογίες των τριών δε Η δέσμευση γίνεται κυρίως στό στομάχι, ίσως όμως καί στό λετιτό έντερο93 . *0 Gräsbeck 72 βασιζόμενος σέ μελέτες ύπερφυγοκεντρήσεως βρήκε ότι ò ενδογενής παράγων ελαττώνε ται σέ μέγεθος μετά τ ή σύνδεση του μέ τή βιταμίνη Β 12 .…”

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Συγκριση Μεταξυ Ενος Δεσμευτου Τυπου R (Σιελος) Και Του Ενδογενους Παραγοντα (Γαστρικο Υγρο Ανθρωπου) Στην Ραδιοισοτοπικη Μεθοδο Μετρησεως Της Βιταμινης Β_12 Του Ορου

Σαββοπούλου-Ζαχαράκη¹

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Studies on the mechanism of vitamin B12 absorption: in vivo transfer of vitamin B12 to intrinsic factor

Cited by 22 publications

References 11 publications

The Role of the Pancreas in Vitamin B12 Absorption: Studies of Vitamin B12 Absorption in Partially Pancreatectomized Rats

The Role of the Pancreas in Vitamin B12 Absorption: Studies of Vitamin B12 Absorption in Partially Pancreatectomized Rats

Intestinal Mucosa and Vitamin B<sub>12</sub> Absorption

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