PubMed Health⌕ Search

Biomedical subjects

W Burchard

Publications and source records attributed to W Burchard.

7 recordsLinked to original sources
PubMed2002

Hydroxyethyl starch does not cross the blood-brain or the placental barrier but the perineurium of peripheral nerves in infused animals.

Therapy with hydroxyethyl starch (HES) is associated with a high incidence of persistent pruritus due to HES storage in cutaneous nerves. Up to now it has been unknown if HES also accumulates in the extracutaneous peripheral or central nervous system. To study this, five rats including one pregnant one were infused with a single dose (34-150 mg) of HES (70/200/450 kDa molecular weight) conjugated with fluorescein isothiocyanate (FITC). In addition, four sheep were infused with a cumulative dosage of 30 g, 120 g, and 420 g HES (200 kDa), respectively. After 7-13 days, biopsies from the adult rats, four fetal rats and sheep were taken from various organs. The specimens were analyzed by light, electron, and confocal laser scanning microscopy. Typical HES storage vacuoles were found in macrophages of the skin, liver, spleen, lung, and kidney. HES storage in healthy animals was not associated with signs of either inflammation or apoptosis contrary to a previously described animal hemorrhagic shock model. Beyond that, fetus biopsies did not show any storage phenomenon, confirming that HES does not cross the placental barrier. Deposits of HES could be detected in Schwann cells of cutaneous nerve fibers as well as in perineural and endoneural cells of sciatic nerve in one rat (HES 450 kDa) and three of four sheep. No HES storage was found in the central nervous system. Our findings clearly demonstrate that storage of HES is detectable only in small peripheral nerves, suggesting a cutaneous origin of the HES-induced pruritus.

Animals↗
PubMed2001

Structure formation by polysaccharides in concentrated solution.

Molecular structure determination in concentrated solutions is generally considered unfeasible. This conclusion, drawn from experience with linear flexible chains, relates to the complete interpenetration of coils and their ensuing entanglement. Such deep interpenetration is prevented by the obstacles of branching units in branched macromolecules. The present study with branched (and one linear cellulose) polysaccharides demonstrates that different architectures can be distinguished via their different repulsive interactions. The procedure displayed in this article permits the estimation of true molar mass and true radius of gyration at finite concentration c. It furthermore allows, within upper and lower limits, an estimation of the growing size, when association takes place. Results from starches, glycogen, dextran, and cellulose, in aqueous media are discussed. The cellulose was dissolved in a recently developed aqueous cadmium complex. Association can lead to gel formation and/or to phase separation. The former is characterized by repulsive interactions which only slightly decrease when the gel point is approached. Phase separation, on the other hand, results from a decrease of the repulsive interaction induced, for instance, by another polymer. The effect is demonstrated with starches containing different amounts of amylose, where pure amylose forms unstable solutions and precipitates in time as a semicrystalline solid.

Cellulose↗
PubMed1978

Fibrinogen-fibrin transformations characterized during the course of reaction by their intermediate structures. A light scattering study in dilute solution under physiological conditions.

Intermediate structures of human fibrin formed under physiological conditions were investigated by means of light scattering in the course of the polymer/network formation. Very low fibrinogen concentrations (c = 0.03--0.13 mg/ml) were used to lower the polymerization rate, and thrombin at five concentrations (0.0085--0.04 N.I.H./ml) was used for initiation. The light scattering data were evaluated from (i) a Zimm plot, (ii) a Holtzer plot, i.e., hRtheta/Kc vs. h2, and (iii) a Kratky plot, i.e., h2Rtheta/KC vs. h2. In the beginning of the polymerization process rod-like structures are formed. The dimensions of the rod-like monomeric unit in the fibrin polymer are 112 X 3.9 nm and agree with the dimensions of fibrinogen, which also was found to be a thin rod of 105 +/- 10 nm length and 3.9 nm diameter. The mass per unit length, obtained from the asymptote in the Holtzer plot, initially increases only slightly but for high thrombin concentrations increases steeply when a critical length of 1000 nm is exceeded. At this point also the total scattering behaviour changes considerably. The upturn in the Zimm plot and the occurrence of a maximum in the Kratky plot are clear indications for the onset of branching. At low thrombin concentrations the kink in the curve of Mw/Lw against Mw becomes smoothed out because of nonspecific side-by-side aggregation of fibrin strands. The results are discussed and compared with earlier findings by others, and lead to the following conclusions. (i) Fibrinogen is a polymer with some flexibility and can exist in conformations of a stretched rod 105 nm in length, a folded rod of 45 nm in length, and a banana-like conformation of 94 nm circumference. (ii) Under the conditions of the present work, fibrinogen has the thin stretched rod conformation, and has the same dimensions as the repeating unit in the fibrin polymer. (iii) After approx. 10--12 units, end-to-end aggregated monomer branching occurs. (iv) The end-to-end aggregation is promoted by the cleavage of A peptides, branching is caused by the cleavage of B peptides while side-by-side aggregation of strands is caused by nonspecific van der Waals interaction.

Fibrin↗