Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0024523 (malabsorption)
 7,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of bacterial uptake of vitamin B(12), the spectrum of microorganisms capable of such uptake, and the factors involved were the subject of this study. Bacterial uptake of vitamin B(12) was found to be at least a two stage process. A primary uptake phase which was rapid (1 min or less), pH dependent, nontemperature dependent, did not require viable organisms and was insensitive to either the metabolic inhibitor dinitrophenol or to the sulfhydryl inhibitor N-ethyl-maleimide. Protein denaturation (formalin treatment or autoclaving) abolished all B(12) uptake. This primary uptake phase is thought to represent adsorption to binding or "receptor" sites on the cell wall. Second stage uptake was slower, pH and temperature dependent, required living bacteria, and was abolished by either dinitrophenol or N-ethyl-maleimide. This phase is dependent upon metabolic processes and may reflect transfer of B(12) from surface "receptor" sites into the bacterial cell. Although differences among organisms were observed in total 1 hr uptake, number of surface "receptor" sites, and relative avidities for B(12), all organisms except Streptococcus fecalis shared the two stage mechanism. Two Gram-positive organisms. Bacillus subtilis and Group A streptococcus, demonstrated the highest 1 hr vitamin B(12) uptake values; Gram-negative bacteria required 2,000-10,000 the number of organisms for comparable uptake. Binding constants (K(m)) varied from 5.05 +/-1.67 x 10(-10)M for B. subtilis to 6.18 +/-3.08 x 10(-9)M for Klebsiella pneumoniae which approximate the Km for human intrinsic factor (0.38 x 10(-10)M). Competition between bacteria and intrinsic factor for vitamin B(12) may be inferred from the similarity of these constants. These observations suggest that a variety of enteric and nonenteric organisms, not requiring exogenous B(12), may play a role in the pathogenesis of the vitamin B(12) malabsorption found in the intestinal bacterial overgrowth syndromes.
 ...
PMID:Vitamin B12 uptake by intestinal microorganisms: mechanism and relevance to syndromes of intestinal bacterial overgrowth. 499 53

The effect of partial pancreatectomy (80-90%) on vitamin B(12) absorption was studied in the rat. The absorption of 5 ng of (57)Co-labeled vitamin B(12) 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 B(12) absorption from 30.0 to 61.0% in partially pancreatectomized rats but did not alter vitamin B(12) absorption in control rats. Chloramphenicol did not enhance vitamin B(12) absorption in partially pancreatectomized rats with pancreatic extract-improved vitamin B(12) malabsorption. The partially pancreatectomized rats with pancreatic extract-improved vitamin B(12) malabsorption were sacrificed and the stomach and small bowel studied in vitro to further define the pathogenesis of the vitamin B(12) malabsorption. Rat gastric intrinsic factor stimulated vitamin B(12) 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 B(12) 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 B(12) which can be corrected by pancreatic extract. The vitamin B(12) malabsorption is due to neither an alteration in gastric intrinsic factor activity nor an impairment of the intrinsic factor-vitamin B(12) receptor in the intestine. It is suggested that in the partially pancreatectomized rats the intrinsic factor-vitamin B(12) complex exists in a form which is not available for absorption.
 ...
PMID:The role of the pancreas in vitamin B 12 absorption: studies of vitamin B 12 absorption in partially pancreatectomized rats. 500 10

Three patients are described, and they provide further evidence that deficiency of folic acid and vitamin B(12) may sometimes affect small intestinal function. Malabsorption of both xylose and vitamin B(12) returned to normal in one patient after treatment of a megaloblastic anaemia due to dietary deficiency of folic acid. Impaired absorption of vitamin B(12) was corrected by vitamin B(12) therapy in the other two patients. The initial cause of the vitamin B(12) deficiency in one patient was not apparent, but she was taking Gynovlar 21, which may have been an aetiological factor. In the third patient the small intestinal defect was secondary to pernicious anaemia, and in a group of 98 other patients with pernicious anaemia intrinsic factor did not improve vitamin B(12) absorption in six, and only partially corrected absorption in 30. The significance of these observations is discussed.
 ...
PMID:Effect of vitamin B12 and folic acid deficiency on small intestinal absorption. 536 38

A procedure is described for the determination of the separate amounts of two gamma-emitting radioisotopes present simultaneously in large liquid volumes using an annular cell placed over a standard well-type crystal of sodium iodide and a reference source of (137)Cs. This sensitive technique is illustrated with particular reference to the double radioisotope urinary excretion test, using orally administered (57)CoB(12) bound to human gastric juice and (58)CoB(12) simultaneously, for the differentiation between patients with intrinsic factor deficiency and other causes of vitamin B(12) malabsorption.
 ...
PMID:Standardized annular assay of dual radioisotopes on a well type sodium iodide crystal. 543 Apr 23

The excretion in the urine of (58)Co after an oral dose of (58)Co vitamin B(12) given together with intrinsic factor has been found to be reduced in a number of patients with psoriasis, eczema, and other less common dermatoses. There is a correlation between the abnormality and the extent of the rash. A reduced glomerular filtration rate was found in a few of the patients in whom it was measured, and this must have been responsible, at least in part, for the reduced excretion of vitamin B(12) in these patients, but abnormal vitamin B(12) excretion also occurred in the absence of impaired renal function. Our evidence is insufficient to show whether malabsorption or increased tissue utilization of vitamin B(12) was the explanation in other cases. Certainly a number of patients had steatorrhoea, and in these it is most likely that malabsorption was the major factor. In patients without steatorrhoea a lone malabsorption of vitamin B(12) cannot be excluded. A decreased serum concentration of vitamin B(12) was found in only one of the patients.
 ...
PMID:Vitamin B12 excretion in patients with various skin diseases. 547 89

The intrinsic factor content of 263 samples of gastric juice was determined by immunoassay using charcoal absorption and by immunoelectrophoresis on acrylamide gel. There was good correlation between the results of the two techniques and, with a few exceptions, both made it possible to predict which patients would have malabsorption of radioactive vitamin B(12). Of the two methods, immunoassay using charcoal absorption generally gave the higher readings. Further study showed that this could not be attributed to the recognized difference in the principles of the two methods but that it was more likely to be due to the dissimilarity of the experimental conditions.
 ...
PMID:A comparison of two methods for the immunoassay of intrinsic factor. 560 77

The effects of ranitidine, a new potent histamine H2-receptor antagonist, on gastric intrinsic factor (IF) secretion and protein-bound cobalamin absorption were evaluated in 6 patients with duodenal ulcer, before, during and after discontinuation of ranitidine therapy. Oral ranitidine (150 mg twice a day) resulted in a non significant decrease of IF concentration and IF output but was responsible for malabsorption of protein-bound cobalamin. This malabsorption was reversible upon discontinuation of ranitidine. These results indicate that occurrence of cobalamin deficiency cannot be excluded during long-term ranitidine treatment and emphasize the need for careful follow-up in these patients.
 ...
PMID:[Effect of ranitidine on secretion of gastric intrinsic factor and absorption of vitamin B 12]. 613 42

A 57-year-old woman developed dementia and peripheral neuropathy 16 years after a partial gastrectomy (Billroth II). Serum cobalamin was 198 pmol/l (reference interval 150-550), and the vitamin B12 absorption test (Schilling) showed decreased absorption (1.7% without and 2.2% with intrinsic factor). In spite of 20 months' therapy with vitamin B12, the neurological symptoms progressed. Folate deficiency was suggested by a very low erythrocyte folate and a slightly abnormal FIGLU test. There were no other signs of general malabsorption. A few months' treatment with folic acid significantly improved the massive neurological manifestations which were verified neurophysiologically as well as histologically. A common role of vitamin B12 and folate in the development of neuropathy is suggested.
 ...
PMID:Reversible dementia and neuropathy associated with folate deficiency 16 years after partial gastrectomy. 625 53

The traditional radioimmunoassay for gastric intrinsic factor, in which this protein is measured on the basis of immunoreactivity rather than function, is of no value for identifying intrinsic factor that binds cobalamin but does not bind to the ileal receptor site, or for detecting animal intrinsic factor, which does not cross react with human intrinsic factor. Accordingly, we have applied a radioassay for the intrinsic factor receptor protein to measure the functional activity of intrinsic factor in gastric juice. The receptor protein reagent was partly purified from guniea pig ilea and its interaction with intrinsic factor--CN[57Co]-cobalamin was determined by precipitation with sodium sulfate at a final concentration of 150 g/L. Results of this assay were comparable with results obtained for intrinsic factor by radioimmunoassay. The receptor protein did not bind immunoreactive intrinsic factor that was functionally abnormal. This functional radioassay for intrinsic factor is not species specific and will be of value when specific antiserum to intrinsic factor is not available and when cobalamin malabsorption is to be evaluated in patients who are secreting normal amounts of immunoreactive intrinsic factor.
 ...
PMID:Functional activity of intrinsic factor measured by using solubilized receptor protein. 628 8

This review focusses on research performed by the author and coworkers. The absorption, turnover and excretion of cobalamin and the pathogenesis of cobalamin deficiency states are described and the laboratory tests used to diagnose these states are discussed. Topics dealt with in detail include: overall turnover, daily need, enterohepatic circulation and excretion of cobalamin and other corrins . The soluble proteins mediating cobalamin transport and their cellular receptors are described and their nomenclature, isolation, structure and mode of action, the role of calcium in the membrane transport, the evolution of these systems and the analogies with transport systems for other substrates are discussed together with deficiency states, especially fish tapeworm anemia and familial selective vitamin B12 malabsorption with proteinuria. Folate deficiency is a relatively rare cause of megaloblastic anemia in Scandinavia but common in North America and explanations for this difference are suggested. The methods of assaying cobalamin in serum and plasma and the performance of radiovitamin B12 absorption tests are critically evaluated. The measurement of intrinsic factor in gastric juice, serum, amniotic fluid and urine is described.
 ...
PMID:Biochemistry and clinical chemistry of vitamin B12 transport and the related diseases. 632 50


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>