No abstract

Bennett and Ratnoff(1972) reported that in haemophiliacs the coagulant activity of factor VIII(F VIII:C) disappeared faster than the factor VII-related antigen (F VIIIR:AG). We decided to investigate this phenomenon with radiolabelled factor VIII. This also allowed us to study the behaviour of various factor VIII fractions after infus i on. Human factor VIII was purified from cryoprecipitate, labelled with 125 I by “the lactoperoxydase-glucose oxydase method, mixed with a human albumin solution and sterilized by filtration through a Millipore filter. F VIII:C,F VIIIR:AG,F VIIIR:WF assays, gelchromatography, crossed Immunoelectrophoresis and PAGE studies were carried out. No significant changes due to the procedure were observed. The radiolabel in the plasma after in vivo administration was for more than 95% bound to F VIIIR:AG as demonstrated with immunoadsorption with an antiserum prepared against a subunit of factor VIII purified by PAGE. About 1.5–6% of free 125 I was also present. Yield and survival were studied in 6 normal volunteers. The yield was somewhat lower (79%) than expected after transfusion. The survival curve was biphasic showing half lives of hours and 20 hours. In 4 haemophiliacs the yield and disappearance were essentially similar. The F VIII:C in these patients who also received cryoprecipitate of 20 donors disappeared with the same kinetics as the radiolabel. Evidence was obtained indicating that the highest molecular weight forms of factor VIII disappeared more rapidly, while losing the F VIIIR:WF, than the lower molecular weight forms. Radio label in cryoprecipitate showed a biphasic, more rapid disappearance ; label in cryosupernatant plasma disappeared slower.

VK 744 — a dipyridamole analogue — is an inhibitor of primary aggregation of platelets in vitro. In this paper we describe the in vivo effects in human male volunteers. A dose of 1500 mg VK 744 prolonged the kaolin‐stypven time and inhibited ADP aggregation. Administration of 500 mg three times daily during 48 hrs in a paired coded investigation produced a slightly significant prolongation of the kaolin‐stypven time. Side effects prevented continuation of the trial. The inhibition by indomethacin was not enhanced by combination with VK 744.

No abstract

Adenosine is taken up tino intact washed human blood platelets by two independent carrier-mediated processes. The ‘low Km system’ has a Km of 9 uM, a V of 792 pMol/min/109, is energy dependent and has a Q10 of 1.71. This system is competitively inhibited by papaverine and dipyridamol. The high Km system has a Km of 9.4 mM, as V of 106 nMol/min/109 is also energy dependent and has a Q10 of 1.31. This system is competitively inhibited by adenine, that has a very high affinity (K1 = 5,8 uM).Evidence is presented that the low Km system transports adenosine in such a way, that it is directly incorporated into nucleotides. Adenosine transported by way of the high Km system arrives unchanged inside the platelets. At low concentrations all this adenosine is deaminated. At higher concentrations (5 mM) part of it is converted into adenine nucleotides and part of it is present in an unchanged form. Only a relatively small part is deaminated at high adenosine concentrations.The high Km system is inhibited by purines. The low Km system is only inhibited by purine ribosides. The presence of a double uptake mechanism and metabolic pathway has direct bearing on experiments that have been effected about the relation between adenosine transport and inhibition of ADP aggregation.