Sequential Mechanisms in the Enhanced Absorption of Vitamin B12 by Intrinsic Factor in the Rat*

Cooper, Bernard A.; Castle, W. E.

doi:10.1172/jci104019

Cited by 111 publications

(57 citation statements)

References 32 publications

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“…It is well established that chelation of calcium by EDTA inhibits IF activity in vitro (8,9,12) and in vivo (26,27). The inhibition of the formation of a complex between the ileal extract and NHGJ-57CoB,2 by sodium EDTA and its reversal by calcium EDTA are consistent with these observations (Table V).…”

Section: Resultssupporting

confidence: 79%

“…Indeed, the mystery of this absorptive process is compounded by the firm attachment of the vitamin to IF, a large carrier protein. It has been shown in man (6) and rat (4,7) that the absorption of B12 is a time consuming process which is probably not energy dependent, for metabolic inhibitors have either no (8) or only a slight inhibitory effect (9).…”

Section: Introductionmentioning

confidence: 99%

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Identification of a macromolecular factor in the ileum which binds intrinsic factor and immunologic identification of intrinsic factor in ileal extracts

Rothenberg¹

1968

J. Clin. Invest.

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Section: Resultssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Identification of a macromolecular factor in the ileum which binds intrinsic factor and immunologic identification of intrinsic factor in ileal extracts

Rothenberg¹

1968

J. Clin. Invest.

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“…The B1,-binding capacity of 125 /Ag (0.05 ml) NFIF was determined by dialysis with Visking casing, as previously described (35). Of 5,000 pg B12 added (Table II) (Figure 3).…”

Section: Methodsmentioning

confidence: 99%

In Vitro Assay for Human Intrinsic Factor*

Sullivan¹,

Herbert²,

Castle³

1963

J. Clin. Invest.

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106

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“…This enhancement was significantly reduced in the absence of calcium and was reversible to a significant degree by disodium ethylenediamine tetraacetate dihydrate (EDTA) (1), suggesting that intrinsic factor action was calcium-dependent. Disodium EDTA reduced the enhancing effect on radio-Bl2 uptake of rat intrinsic factor in loops of small intestine in a living rat; calcium EDTA was without such inhibitory effect (2). Other workers, however, threw doubt on the calcium dependence of intrinsic factor action.…”

mentioning

confidence: 96%

DIVALENT CATION AND pH DEPENDENCE OF RAT INTRINSIC FACTOR ACTION IN EVERTED SACS AND MUCOSAL HOMOGENATES OF RAT SMALL INTESTINE*

Herbert¹,

Castle²

1961

J. Clin. Invest.

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In 1959 it was reported in these pages (1) that hog intrinsic factor concentrate enhanced the uptake of radioactive vitamin B12 (Co60-B12) by everted sacs of rat small intestine in the cold. This enhancement was significantly reduced in the absence of calcium and was reversible to a significant degree by disodium ethylenediamine tetraacetate dihydrate (EDTA) (1), suggesting that intrinsic factor action was calcium-dependent. Disodium EDTA reduced the enhancing effect on radio-Bl2 uptake of rat intrinsic factor in loops of small intestine in a living rat; calcium EDTA was without such inhibitory effect (2). Other workers, however, threw doubt on the calcium dependence of intrinsic factor action. They reported that gastrectomized rats fed radio-B12 bound to rat gastric juice plus large amounts of disodium EDTA (3, 4), and normal rats fed radio-B12 plus disodium or tetrasodium EDTA (5), had normal radio-B12 absorption. These findings, taken with the fact that the in vitro studies did not demonstrate total loss of the effect of intrinsic factor on depletion of calcium, left the concept of the calcium dependence of intrinsic factor action in doubt.The present report presents the results of a study aimed at resolving this uncertainty, and also at strengthening the evidence (6, 7) for the pH dependence of intrinsic factor action. MATERIALS AND METHODSCo'-labeled vitamin B,2 and Co"1-labeled vitamin B,,. Rat intrinsic factor concentrate (RIFC) was prepared as previously described (2).Rat small intestine everted sac system. The homologous system (RIFC, everted sacs of rat small intestine) used by Strauss and Wilson (8-10) was employed.Nonfasting male Sprague-Dawley rats were sacrificed. The small intestine was transected at the pylorus and 25 to 50 ml of 0.9 per cent NaCl was run through it to rinse out particulate content. The small intestine was then stripped free of its mesenteric attachment, transected at its ileal end and everted on a stainless steel rod, 112 cm long and 1.5 mm in diameter, with rounded ends. Beginning with its lower end, the rat small intestine was slipped over the rod until a silk ligature could be placed tightly over the ileal end of the intestine, and held in place by a groove in the rod 2 mm from its end. The intestine was gently and rapidly everted on itself. It was then washed by dipping repeatedly into each of two changes of 200 ml saline, and placed in a petri dish containing 0.9 per cent saline at room temperature.Individual sacs approximately 4 cm long were prepared as described by Wilson and Wiseman (11). After being ligated at each end and slightly distended with Krebs-Henseleit bicarbonate (12) containing 200 mg per 100 ml glucose, each sac was dropped into a separate 50-ml Erlenmeyer flask containing 5 ml incubation medium plus 5,000 Alng of radioactive vitamin B,2 in 0.5 ml of 0.9 per cent saline with or without added RIFC.The amount of RIFC used was prepared from 1/100 of a rat stomach, diluted with 0.9 per cent NaCl to a volume of 0.5 ml. This amount of rat stomach was chosen becau...

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Sequential Mechanisms in the Enhanced Absorption of Vitamin B12 by Intrinsic Factor in the Rat*

Cited by 111 publications

References 32 publications

Identification of a macromolecular factor in the ileum which binds intrinsic factor and immunologic identification of intrinsic factor in ileal extracts

Identification of a macromolecular factor in the ileum which binds intrinsic factor and immunologic identification of intrinsic factor in ileal extracts

In Vitro Assay for Human Intrinsic Factor*

DIVALENT CATION AND pH DEPENDENCE OF RAT INTRINSIC FACTOR ACTION IN EVERTED SACS AND MUCOSAL HOMOGENATES OF RAT SMALL INTESTINE*

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