Vitamin B12 absorption--a study of intraluminal events in control subjects and patients with tropical sprue.
(73/157)
The intraluminal fate of orally administered radioactive vitamin B12 has been studied in control subjects with normal vitamin B12 absorption and those with vitamin B12 malabsorption due to tropical sprue. In control subjects 1 to 21% of the dose was bound to sedimentable material and 37 to 75% was bound to immunoreactive intrinsic factor. In subjects with vitamin B12 malabsorption due to tropical sprue, the results were identical with the control subjects. Bacteriological studies showed a statistically significant correlation between both the number of flora in the jejunum and the number of bacteroides in both the jejunum and ileum and vitamin B12 malabsorption. In patients with tropical sprue who have normal intrinsic factor secretion, the vitamin B12 absorptive defect is not due to binding of the vitamin to bacteria or to alteration to the intrinsic factor vitamin B12 complex in the intestinal lumen. The lesion appears to be one of the mucosal cell receptors or of the cells themselves, possibly caused by bacterial toxins. (+info)
Radioimmunoassay for assessing exocrine pancreatic insufficiency, based on the differential enzymatic degradation of cobalamin-binding proteins.
(74/157)
Pancreatic proteases degrade the protein moiety of the R protein-cobalamin complex but not the intrinsic factor-cobalamin complex. Accordingly, we used these two proteins as substrates in an in vitro enzymatic assay to assess pancreatic function by incubating basal jejunal fluids with a mixture of intrinsic factor and cyano[57Co]cobalamin coupled to R-type protein and then using immunoprecipitation to determine the distribution of isotopically labeled cobalamin bound to the two proteins. With normal jejunal fluids, 91.2 (SD 6.1)% and 4.5 (SD 5.5)% of cyano[57Co]cobalamin was precipitated with antisera to intrinsic factor and anti-R protein, respectively. In the patients' jejunal fluids, the cyano[57Co]cobalamin precipitated with the respective antisera was 5.3 (SD 10.0)% and 96 (SD 6.2)%. In patients with other gastrointestinal problems, the sequestration of cobalamin was indistinguishable from that observed with the normal fluids. The clearcut discrimination this radioimmunoassay provided between abnormal and normal samples was confirmed by parallel comparative chromatographic analysis. (+info)
Laboratory diagnosis of megaloblastic anaemia: current methods assessed by external quality assurance trials.
(75/157)
The results of an Interregional quality assurance scheme for tests in the diagnosis of megaloblastic anaemia were reviewed to assess the methods used. Serum folate assays showed great variation between methods, partly due to limitations in assessment by external quality assurance. Red cell folate assays yielded widely different results and much imprecision due both to the differences in preparation of the haemolysate and to the problems inherent in radioassay of a mixture of folate compounds. Intrinsic factor antibody tests showed appreciable variation in sensitivity. There was considerable inconsistency in the detection of polymorph nuclear hypersegmentation. (+info)
In vitro and in vivo evidences that the malabsorption of cobalamin is related to its binding on haptocorrin (R binder) in chronic pancreatitis.
(76/157)
The intraluminal transport of cobalamin (Cbl) remains controversial in chronic pancreatitis. We have determined the ability of intestinal juice to degrade the digestive holohaptocorrin (R binder) and the binding of endogenous Cbl in basal intestinal juice from 22 chronic pancreatitis patients and 22 controls. The intestinal juice from patients and controls degraded 34.7 +/- 32.3% and 95.2 +/- 7.2% of holohaptocorrin, respectively. This percentage was correlated with the trypsin output but not with the Schilling test. The unsaturated Cbl-binding capacity was similar in both groups. Respectively, 62.5 +/- 26.6% and 19.6 +/- 11.7% of endogenous Cbl was bound to haptocorrin in intestinal juice from patients and controls. These percentages were correlated with the Schilling test and with the ability of intestinal juice to degrade haptocorrin. We concluded that 1) the sequestration of Cbl to haptocorrin is one of the factors responsible for the malabsorption of crystalline Cbl in patients with chronic pancreatitis and 2) enterohepatic circulation of Cbl can be interrupted in some cases of chronic pancreatitis. (+info)
Cobalamin malabsorption in three siblings due to an abnormal intrinsic factor that is markedly susceptible to acid and proteolysis.
(77/157)
Three siblings presented in their second year of life with megaloblastic anemia that responded to parenteral cobalamin (Cbl). Schilling tests were less than 1%, correcting to 5 to 15% after addition of hog intrinsic factor (IF). Gastric acid analysis and gastric biopsies were normal by light and electron microscopy. Gastric juice contained less than 3 pmol/ml of Cbl-binding ability due to IF (normal, 10-34 pmol/ml) and less than 2 pmol/ml of IF when measured with a radioimmunoassay (RIA) using normal human IF-[57Co]Cbl and rabbit anti-human IF serum (normal, 17-66 pmol/ml). However, RIA employing rabbit anti-hog IF serum gave values of 4-13 pmol/ml of IF (normal, 11-33 pmol/ml). This material had an apparent molecular weight of 40,000 (normal IF = 70,000). The IF from gastric biopsies appeared normal in terms of Cbl-binding ability, ileal binding, molecular weight, and both RIAs. This IF differed from normal mucosal IF, in that it lost its Cbl-binding ability when incubated at 37 degrees C at acid pH or in the presence of pepsin or trypsin. This loss was retarded when [57Co]Cbl was bound to the IF before these incubations. The stabilizing effects of neutralization and Cbl were also demonstrated in vivo. Schilling tests for the siblings of 0.4, 0.5, and 1.0% increased to 2.7, 5.7, and 4.3% (P less than 0.05), respectively, when the Schilling tests were repeated with the addition of NaHCO3 and cobinamide (which allows Cbl to bind immediately to IF). We conclude that Cbl malabsorption in these children is due to an abnormal IF that is markedly susceptible to acid and proteolytic enzymes which cause a decrease in its molecular weight and Cbl-binding ability and a loss of antigenic determinants that are recognized by the anti-human IF serum. (+info)
Effect of omeprazole on the secretion of intrinsic factor, gastric acid and pepsin in man.
(78/157)
The effect of an intravenous infusion of omeprazole (0.35 mg/kg) and placebo on basal and stimulated (pentagastrin 1.0 microgram/kg/h) secretion of gastric acid, intrinsic factor and pepsin was studied in 10 healthy male subjects. Omeprazole caused a marked inhibition of basal and stimulated acid output. The inhibition of pepsin output was less marked, but also significant. The output of intrinsic factor, however, showed no significant change. The results indicate that acid and intrinsic factor might have different secretory mechanisms within the parietal cell. (+info)
Purification of human intrinsic factor using high-performance ion-exchange chromatography as the final step.
(79/157)
Human intrinsic factor was purified 1430-fold from gastric juice with a yield of 75% using two steps: labile ligand affinity chromatography and high-performance ion-exchange chromatography. Intrinsic factor precipitated in the presence of specific autoantibodies and 15% sodium sulfate, had an estimated Mr of 59 000 in 5% SDS electrophoresis and could bind to the specific ileal receptor in vitro. Its carbohydrate composition could be related to N-lactosaminic and O-glycosidic chains. High-performance ion-exchange chromatography was a mild, rapid and efficient procedure to separate completely intrinsic factor from haptocorrin (another glycoprotein of gastric juice which binds cobalamin) and from other contaminating proteins. (+info)
Serum from patients with pernicious anaemia blocks gastrin stimulation of acid secretion by parietal cells.
(80/157)
We examined 51 sera from patients with pernicious anaemia for their capacity to block maximal gastrin stimulation of acid secretion by isolated rodent gastric parietal cells. 14C-aminopyrine accumulation was used as the index of acid secretion in vitro. Sera from patients with pernicious anaemia gave significantly (P less than 0.005) more block of maximal gastrin stimulation of acid secretion (61.7 +/- 37.8%) than sera from 10 patients with systemic lupus erythematosus (19.6 +/- 17.7%), 10 with scleroderma (34.2 +/- 22.3%), five with rheumatoid arthritis (22.4 +/- 15.6%) or 30 from healthy persons (27.4 +/- 12.8%). Maximal histamine stimulation of acid secretion was not inhibited. The blocking factor was present in serum IgG fractions, and serum and IgG fractions gave parallel dose-response and dilution curves. The serum block was abolished by absorption with gastric mucosal cells and correlated with the presence of parietal cell surface autoantibody. We conclude that serum immunoglobulin in pernicious anaemia can block gastrin stimulation of acid secretion and suggest that this block may be mediated by competition with gastrin for surface receptors on parietal cells. (+info)