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Biomedical subjects

R M Donaldson

Publications and source records attributed to R M Donaldson.

At least 127 records · Page 7Linked to original sources
PubMed1972

Challenges.

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Ethics, Medical↗
PubMed1969

Radioiodination of human intrinsic factor.

Human intrinsic factor (IF) saturated with (60)Co-labeled cyanocobalamin ((60)CoB(12)) was purified and then iodinated with (125)I to yield (125)I-labeled IF-(60)CoB(12) preparations of high specific activity. Sephadex G200 and DEAE-cellulose chromatography of the iodinated IF-(60)CoB(12) complex showed coincidence of the major (125)I and the (60)Co radioactivity peaks. During starch-gel electrophoresis (60)Co radioactivity from noniodinated and iodinated complexes migrated to the same extent while (125)I radioactivity from the iodinated complex migrated slightly further anodally than did the (60)Co radioactivity. After the iodinated complex was mixed with antibody to the IF-B(12) complex (antibody II) the (125)I and (60)Co radioactivity were: (a) precipitated in similar amounts by antiglobulin serum. (b) eluted coincidentally in the 19S region on Sephadex G200, and (c) excluded to the same extent from starch gel during electrophoresis. After equilibrium exchange of IF "blocking" antibody (antibody I) for (60)Co-vitamin B(12) on (125)I-labeled IF. (125)I radioactivity from the IF-antibody I complex: (a) was precipitated by antiglobulin serum, (b) was eluated in the 19S region on Sephadex G200 gel filtration, and (c) migrated slowly towards the anode on starch-gel electrophoresis. Urinary excretion of (60)Co radioactivity in pernicious anemia patients after oral administration of (60)Co-vitamin B(12) bound to freshly prepared (125)I-labeled IF was similar to that obtained with noniodinated intrinsic factor. These results show that iodination of IF-(60)CoB(12) complex does not markedly alter the chromatographic, electrophoretic, antigenic, or absorption-promoting properties of IF.

Antigen-Antibody Reactions↗
PubMed1968

Antibodies to intestinal microvillous membranes. I. Characterization and morphologic localization.

Antibodies (AbMVM) were produced in rabbits to microvillous membranes isolated from hamster small bowel. Incubation of frozen sections of hamster small bowel with fluorescein-labeled AbMVM showed specific reaction with brush borders, but not with other intestinal cellular components. Electron microscopy with ferritin-conjugated AbMVM localized the antigens more precisely to the surface mucopolysaccharide coat of the brush borders. AbMVM also reacted with the brush border of colon and of proximal renal tubules of hamsters but not with those of hamster stomach or gall bladder. It also reacted with the brush borders of some rat and human tissues, but not with those of rabbits. In addition, fluorescent-labeled AbMVM combined specifically with cell walls of some yeasts, but not of several bacteria. AbMVM also contained a weak precipitin to a component of hamster serum, which migrated like prealbumin in immunoelectrophoresis.

Animals↗
PubMed1967

Intrinsic factor-mediated attachment of vitamin B12 to brush borders and microvillous membranes of hamster intestine.

Hamster intrinsic factor (IF) preparations markedly enhanced the uptake of (57)cobalt-labeled cyanocobalamin (B(12)-(57)Co) by brush borders and microvillous membranes isolated from villous absorptive cells obtained from the distal but not the proximal half of hamster intestine. A similar effect was observed with rat and rabbit IF preparations, but IF preparations obtained from man, dog, and hog were ineffective. After fractionation of hamster IF preparations by gel filtration or ion exchange chromatography, the extent to which each fraction enhanced B(12)-(57)Co uptake by brush borders correlated closely with the vitamin B(12) binding capacity of the fraction. IF-mediated attachment of B(12)-(57)Co to brush borders occurred rapidly, was not diminished by removal of glucose or oxygen from the incubation medium, and was not significantly altered when incubation temperatures were reduced from 37 degrees C to 7 degrees C. Marked reduction in uptake occurred, however, in the absence of divalent cations. IF enhanced B(12)-(57)Co uptake by brush borders isolated from the proximal half of the intestine when these proximal brush borders were preincubated with supernatant fluid obtained after centrifugation of homogenates of distal intestinal mucosa at 28,500 g. The factor in this supernate responsible for the effect on proximal brush borders was shown to be particulate in nature upon centrifugation at speeds of 54,500 g or greater. The resultant pellet contained ribosomes and membranous fragments. Prolonged incubation of brush borders with crude saline extracts of hamster gastric mucosa resulted in decreased uptake of B(12)-(57)Co and marked lysis of brush borders with concomitant release of tissue nitrogen. Neither lysis of brush borders nor decreased uptake of B(12)-(57)Co with prolonged incubation was observed when hamster IF was partially purified. Furthermore, uptake of B(12)-(57)Co by brush borders increased with increasing purity of the IF preparation used. These results demonstrate IF-mediated attachment of B(12)-(57)Co to brush borders and microvillous membranes of hamster intestinal cells and provide further support for the presence of a specific receptor for IF-bound vitamin B(12) at the microvillous surface of the intestinal cell. IF-mediated attachment to the intestinal cell surface appears to be facilitated by divalent cations and to result from adsorption rather than an energy-requiring enzymatic reaction. Crude sources of hamster IF contain a factor which causes lysis of brush borders in vitro and which may explain in part the inhibitory effects of IF excess previously observed in vitro.

Adsorption↗