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Biomedical subjects

R Schmid

Publications and source records attributed to R Schmid.

At least 361 records · Page 20Linked to original sources
PubMed1976

Oxidative metabolism of foreign compounds in rat small intestine: cellular localization and dependence on dietary iron.

Oxidative metabolism of foreign compounds was measured in the intestinal mucosa of male rats. Activities of benzpyrene hydroxylase, p-nitroanisole O-demethylase, and NADPH-cytochrome P-450 reductase and cytochrome P-450 content were 3 to 10 times higher in epithelial cells of the upper villus than in mucosal crypt cells. Villous tip cells of the upper small intestine exhibited much higher cytochrome P-450 content and drug-metabolizing enzyme activity than did tip cells of lower intestinal segments. In rats fed commercial chow diet, cytochrome P-450 content and drug-metabolizing enzyme activity in villous tip cells of duodenal mucosa were higher than in animals fed a semisynthetic diet, but cytochrome b5 and NADPH-cytochrome P-450 reductase were unaffected. On restriction of dietary iron intake, cytochrome P-450 and oxidative enzyme activity fell sharply, but were completely restored in 24 hr by oral iron supplementation, whereas parenteral iron administration was ineffective. These findings suggest that intestinal drug metabolism is localized primarily in the upper villous cells of the proximal intestinal mucosa, that cytochrome P-450 is synthesized in maturing epithelial cells as they migrate from the crypts to the tip of the mucosal villi, and that this process is dependent critically upon absorption of iron from the intestinal lumen.

Animals↗
PubMed1975

Current-voltage studies on the thylakoid membrane in the presence of ionophores.

The reversibility of the binding of ionophores to the thylakoid membrane is studied. While gramicidin binds practically irreversibly, valinomycin and nonactin bind reversibly, however, only a small fraction (about 1%) of the membrane-bound valinomycin or nonactin is active in ion transport. The current-voltage relationship is evaluated under these circumstances. We have found that it is practically linear. This together with the relationship between current and ion concentration agrees qualitatively with the results reported for bimolecular lipid membranes, which contain a large fraction of negatively charged lipids. For the ionophores, valinomycin and nonactin, the binding equilibria (K approximately equal to 10-4) and the turnover numbers (approximately equal to 3-10-4/s) are evaluated for their action on the thylakoid membrane. Possible reasons for the inactivity of the majority of membrane-bound ionophore molecules are discussed.

Anti-Bacterial Agents↗
PubMed1975

Effect of enamel solubility reducing agents on erosion in the rat.

Three experiments performed on Osborne-Mendel rats tested the effects on erosion of the topical application of aluminum, cerium and titanium salts as well as sodium fluoride and sodium mono-fluorophosphate. In two experiments the compounds were applied during the erosion period and in a third trial, the test substances were applied prior to exposure to the erosive agent which was fermented apple juice. While cerium had no significant effects on erosion, aluminum fhloride and titanium chloride significantly increased the severity of erosive tooth destruction. Only sodium fluoride and sodium mono-fluorophosphate were effective in preventing erosion.

Administration, Topical↗
PubMed1975

Specific immunotherapy proposed for hepatitis B virus infection.

Immune response to hepatitis B surface antigen (HBsAg), coinciding with removal of HBsAg from the circulation, has been shown to be a cell-mediated response assessed by leukocyte migration inhibition assay. Immune response to HBsAg is a T-cell dependent phenomenon in the nude mouse model. Immunological tolerance in man appears to stem from the absence of cellular and humoral immune response to HBsAg, causing a chronic carrier state which serves as an epidemiological reservior for the transmission of viral hepatitis type B. Specific immunotherapy in hepatitis may consist of adoptive transfer of immunity to HBsAg. It is proposed to be accomplished by administration of anti-HBs, transfer factor or 'immune-RNA'. The efficacy and safety of 'immune-RNA' administration to chronic carriers can be validated by leukocyte migration inhibition techniques in vitro and in HBsAg positive chimpanzees in vivo.

Animals↗