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Biomedical subjects

G D Wilner

Publications and source records attributed to G D Wilner.

59 records · Page 4Linked to original sources
PubMed1971

Inhibition of collagen-induced platelet aggregation by normal plasma.

Normal plasma has been found to inhibit the platelet aggregation-inducing effect of collagen in a time consuming reaction independent of temperature. Collagen treated with serum and washed has reduced reactivity which can be restored to normal by treatment with 1.5 M sodium chloride. On the basis of this result, it is suggested that inhibition results from adsorption to collagen of a plasma component. The inhibitory plasma component is destroyed at 56 degrees C, is unstable below pH 7, and migrates with the alpha globulins on starch block electrophoresis at pH 8.6. On the basis of ultrafiltration and sucrose density gradient ultracentrifugation studies, a molecular weight in the range of 330,000 is suggested and there may be an additional component of considerably greater size. Partial purification can be achieved by ion exchange chromatography. The purified fraction was completely inactivated by incubation with trypsin. Partially purified fractions inhibit cationic platelet aggregators such as collagen, polylysine, and hexadimethrine but do not affect anionic aggregators such as succinylated collagen and sodium stearate. Normal plasma and serum inhibit succinylated collagen and stearate. Stearate is inhibited by crystalline albumin and Cohn fraction IV-4. It is suggested that plasma proteins may regulate platelet adhesion to collagen and other vessel wall materials.

Adsorption↗
PubMed1968

Activation of Hageman factor by collagen.

Purified acid-soluble and insoluble human collagen accelerated the clotting of plateletpoor plasma in silicone-treated tubes. The clot-promoting effect did not appear to be due to thromboplastic activity since the collagen preparations did not activate factor X in the presence of factor VII and calcium. Instead, collagen appeared to accelerate clotting by activating Hageman factor (factor XII) on the basis of the following findings: collagen increased the clot-promoting activity of partially purified Hageman factor but exerted no further effect in the presence of kaolin, a known activator of Hageman factor; clot-promoting eluates were obtained from collagen exposed to normal, hemophilic, or PTC-deficient plasma but not from collagen exposed to Hageman or PTA-deficient plasma. The collagen molecule itself appeared to be required for the clot-promoting activity since digestion with collagenase or thermal denaturation at pH 2.5 (about 35 degrees C) resulted in very marked reduction in clot-promoting activity. Since thermal denaturation is associated with transformation of collagen structure from triple helical to random coil form, it is suggested that the native form of collagen is essential for the ability to activate Hageman factor. Blockage of the free amino groups by treatment with nitrous acid or dinitrofluorobenzene only slightly reduced the clot-promoting activity of collagen. In contrast, since addition of cationic proteins to collagen markedly reduced pro-coagulant activity it is suggested that negatively charged sites on the collagen molecule are critical for Hageman factor activation. This suggestion is supported by the finding that pepsin treatment of collagen, which removes the predominantly negatively charged telopeptides, results in significant decrease in coagulant activity. Esterification of collagen, which neutralizes 80-90% of the free carboxyl groups, reduced coagulant activity by over 90% and it is suggested that the free carboxyl groups of glutamic and aspartic acids provide the negatively charged sites critical for Hageman factor activation.

Adult↗
PubMed1968

Aggregation of platelets by collagen.

In studying some of the properties of collagen responsible for the ability to aggregate platelets it was found that thermal treatment at pH 2.5 of acid-soluble human collagen resulted in a sharp reduction in relative viscosity and platelet aggregating activity at about 35 degrees C. The reduction in viscosity is known to be associated with structural transition from triple helical to random coil form and it is postulated that the native structure of collagen is essential for its platelet aggregation effect. Blockage of the free amino groups by deamination, N-acetylation, or treatment with dinitrofluorobenzene resulted in over 90% reduction in platelet aggregating activity. Addition of cationic proteins to collagen, removal of the negatively charged telopeptides by treatment with pepsin, or acetylation of the free carboxyl groups did not significantly affect the platelet aggregating activity of collagen. On the basis of these findings it is suggested that the free amino groups and specifically the epsilon amino groups of lysine are critical for the platelet aggregating activity of collagen whereas the carboxyl groups are of relatively little importance.

Blood Cell Count↗