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Biomedical subjects

L A Davidson

Publications and source records attributed to L A Davidson.

At least 55 records · Page 3Linked to original sources
PubMed1990

Iron retention from lactoferrin-supplemented formulas in infant rhesus monkeys.

Iron absorption from human milk and infant formula has received much attention, but experimental design problems have been common. In our study, iron retention from human milk, milk-based infant formula (IF) with and without supplemental ferrous sulfate, and IF supplemented with either human or bovine lactoferrin (Lf) was evaluated in infant rhesus monkeys. The exchange of 59Fe (III) Cl3 between the whey, casein, and fat fractions required up to 72 h to reach the same distribution as intrinsic iron, depending on the type of diet. Infant monkeys were intubated with labeled human milk or IF and counted in a whole body counter. Each infant received all five diets and was also intubated with a reference dose of 55Fe (II) ascorbate. There was no significant difference in iron retention (mean +/- SEM) from the experimental diets: human milk 32.5 +/- 5.1%; IF 32.1 +/- 8.0%; IF + Fe 23.0 +/- 3.9%; IF + human Lf 23.5 +/- 3.3%; IF + bovine Lf 22.7 +/- 4.9%. Therefore, infant monkeys absorb and retain iron similarly from human milk and infant formula. Supplementation of infant formula with human or bovine Lf resulted in similar iron retention to that of ferrous sulfate-supplemented infant formula.

Animals↗
PubMed1989

Fe-saturation and proteolysis of human lactoferrin: effect on brush-border receptor-mediated uptake of Fe and Mn.

We have previously characterized a brush-border membrane receptor that facilitates iron uptake from human lactoferrin. The receptor is specific for human and monkey lactoferrin and does not recognize human transferrin or bovine lactoferrin. In this study, iron uptake from lactoferrin fragments was studied, as well as from lactoferrin partially saturated with iron. Brush-border membrane vesicles (BBMV) prepared from infant rhesus monkey small intestine efficiently accumulated iron from lactoferrin half-molecules, although competition experiments showed that intact lactoferrin has a higher affinity toward the receptor. Lactoferrin partially saturated with iron also effectively delivered iron to the receptor, whereas the affinity was lower than for lactoferrin saturated with iron. Lactoferrin also carries a large proportion of human milk manganese, and receptor-mediated uptake of lactoferrin-bound manganese into BBMV was demonstrated, although this complex had lower affinity than that found for iron-lactoferrin. Thus, although the receptor has a preference for intact iron-saturated lactoferrin, partially digested lactoferrin and partially iron-saturated lactoferrin can also deliver iron to the receptor. Therefore, these molecular species, which are likely to occur in the gastrointestinal tract of the infant, may contribute to the high degree of iron absorption from human milk lactoferrin.

Animals↗
PubMed1988

Specific binding of lactoferrin to brush-border membrane: ontogeny and effect of glycan chain.

Bioavailability of iron from human milk is exceptionally high. It has been suggested that lactoferrin, the major iron-binding protein in human milk, may participate in this high iron bioavailability from milk. We examined the interaction of lactoferrin with the intestinal brush-border membrane using the rhesus monkey as a model. Brush-border membrane vesicles were prepared from monkeys of various ages. Binding studies with 59Fe-labeled human and monkey lactoferrin were performed to examine interaction of lactoferrin with the brush-border membrane. Specific saturable binding of lactoferrin was found at all ages studied (fetal, suckling infant, weaned infant, juvenile, and adult). The dissociation constant for lactoferrin-receptor binding was 9 X 10(-6) M. In contrast, no binding of serum transferrin or bovine lactoferrin occurred. Removal of fucose from the lactoferrin glycans resulted in a significant decrease in binding. It was concluded that lactoferrin in milk may function in the process of iron absorption through interaction with a small intestinal receptor and that fucosylated glycans on the carbohydrate chain of lactoferrin are necessary for receptor recognition.

Aging↗
PubMed1987

Persistence of human milk proteins in the breast-fed infant.

Several proteins in human milk are postulated to have physiological functions in the breast-fed infant. Therefore, survival of human milk proteins after passage through the gastrointestinal tract of the breast-fed infant was investigated. Fecal samples were collected from exclusively breast-fed term infants and milk samples from their mothers. Soluble proteins in the feces were extracted and analyzed for total protein, nitrogen, lactoferrin, secretory IgA, serum albumin and lysozyme. Significant amounts of lactoferrin and secretory IgA were excreted by the infants and this excretion decreased throughout the study period in a trend similar to the decreasing milk concentrations of these proteins. Gel filtration demonstrated excreted lactoferrin and secretory IgA to be intact. No serum albumin or lysozyme was detected in the fecal extracts. Crossed immunoelectrophoresis showed three human milk proteins to be present in the feces--the third was identified as alpha 1-antitrypsin. Excretion of these proteins indicates the total protein content of human milk is an over-estimation of the protein nutritionally available to the infant.

Breast Feeding↗
PubMed1986

Isolation and characterization of rhesus monkey milk lactoferrin.

Rhesus monkey milk lactoferrin was isolated and its characteristics compared with those of human milk lactoferrin in order to assess the feasibility of using the rhesus monkey as an animal model for the study of iron absorption from milk. Monkey lactoferrin was isolated from pooled monkey milk by two chromatographic steps. Concentration of lactoferrin in milk, determined by rocket immunoelectrophoresis, demonstrated similar concentrations in both human and monkey milk, 1-2 mg/ml. Immunodiffusion of lactoferrins from several species using an antibody raised to money lactoferrin resulted in a cross-reaction only with monkey and human lactoferrin. Lactoferrins from cow, sheep, goat, dog, and rat milk were not recognized by the antibody. Amino acid analysis of monkey lactoferrin showed a composition very similar to human lactoferrin, as well as a similarity in the unusual amino acid sequence at the N-terminal of the protein. The carbohydrate moiety of monkey lactoferrin was investigated and shown to contain monosaccharides in similar proportions to those reported for human lactoferrin. In our opinion, the rhesus monkey is a promising model for the study of the role of lactoferrin in iron absorption in the infant, as well as of the other proposed actions of lactoferrin.

Amino Acid Sequence↗
PubMed1986

Central service as a clinical department.

Central service is a viable, moving, dynamic area that provides service and expertise in finance, production, and clinical care. To recognize and understand its financial and production-based aspects and yet ignore the clinical aspects is to operate ineffectively. Clinical application of the central service area is an operational imperative for materiel management. It is a vehicle for direct participation in clinical care, and it should be developed extensively. By advocating central service as a clinical area, materiel management becomes an integral, clinical part of health care provision.

Central Supply, Hospital↗
PubMed1983

Changes in (Na+ + K+)-ATPase activity associated with stimulation of thymocytes by concanavalin A.

Preincubation of rabbit thymocytes and lymph node cells for 20 h in 10% rabbit serum and subsequent exposure of these cells to concanavalin A resulted in a 70-100% increase in (Na+ + K+)-ATPase activity. The (Na+ + K+)-ATPase activity of rabbit lymph node cells and spleen lymphocytes was increased while that of erythrocytes did not show any response to concanavalin A exposure. Since only inhibition (50%) was observed when crude microsomes from rabbit thymocytes were incubated with concanavalin A, activation of (Na+ + K+)-ATPase appeared to require intact cells. Incubation of rabbit thymocytes in 10% rabbit serum for 20 h resulted in slightly increased fluidity of the innermost lipids of the cell membranes, as measured by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. Fluidity changes did not appear to be the mechanism of activation of ATPase by concanavalin A, since incubation of cells with concanavalin A for 1 h had no effect on membrane fluidity in either freshly isolated or 20-h preincubated thymocytes. Compared with fresh thymocytes, preincubated cells had about twice the number of concanavalin A binding sites. Preincubated thymocytes became temporarily permeable to trypan blue after concanavalin A exposure. The percentage of cells taking up dye reached a maximum of 65% at 45-60 min, but decreased to 18% after a total of 3 h of incubation.

Adenosine Triphosphatases↗