SummaryHirudin is a specific, potent inhibitor of thrombin that may be a valuable antithrombotic agent. The aim of this study was to investigate the hypothesis that the haemostatic effects of DDAVP counteract the coagulation defect induced by hirudin. The effect of DDAVP was studied in vivo on the anticoagulant action of recombinant hirudin (CGP39393) in vitro. Blood samples were taken at intervals from 10 normal volunteers infused with DDAVP. Factor VIII: C rose from (mean) 0.68 IU/ml before DDAVP to 2.L9 and 2.16 IU/ml after 30 and 60 min infusion, respectively. Samples taken during DDAVP infusion showed a dose related decrease in the hirudin (0.5 and 1.0 αM) induced prolongation of the APTT that occurred at FVIII: C concentrations of up to twice normal. At higher concentrations of hirudin no effect on the APTT occurred. These results demonstrate that DDAVP infusion elevates factor VIII: C levels with an associated significant reduction in the anticoagulant effect of hirudin in vitro.

SummaryThrombotic diseases increase in incidence with advancing years and this might be partly due to an increased propensity for fibrin formation in older individuals. Accordingly we decided to investigate whether the time taken to generate 50% thrombin activity in vitro varied with the age of the plasma donor. Coagulation was initiated in defibrinated, diluted plasma by contact activation and thrombin activity measured using the chromogenic substrate, S2238. The rate of thrombin generation was assessed by measuring the time taken to reach 50% maximal activity (T50/s). There was a highly significant negative correlation between T50 and age, T50 declining from 93 s at 19 years to 71 s at 65 years (r = −0.637, p <0.0001). A strong negative correlation was demonstrated between T50 and FVII level (r = -0.415, p = 0.0007) and FVIII: C level (r = -0.465, p = 0.0001). Although FVII concentration correlated with age (r = 0.307, p = 0.014) no relationship was seen between age and FVIII :C. These data suggest that coagulation rates in plasma accelerate with age.

No abstract

The association between plasma coagulant activity and the presence of diabetic nephropathy was investigated in 31 patients with Type 1 diabetes, 12 with and 19 without nephropathy, and in 11 healthy subjects. Thrombin generation was assessed by computer assisted chromogenic method and expressed as time (in seconds) to 50% maximal thrombin activity (T50). Factor VIII:C levels related to thrombin activity, glycaemic control, and renal function. Median (IQ) FVIII:C concentration was increased in patients with nephropathy (1590 (1130-1900) IU l-1) compared to those without renal disease and with controls (960 (750-1090); 1020 (810-1100) IU l-1, p < 0.01, respectively). There were no significant differences in T50 values between the groups. FVIII:C correlated with age in all subjects and in the diabetic group (r = 0.33, p = 0.036; r = 0.39, p = 0.031) and inversely with T50 in all subjects and in controls (r = -0.35, p = 0.02; r = -0.62, p = 0.04). In all subjects and in patients, FVIII:C was related to urinary albumin excretion and creatinine clearance. FVIII:C and T50 were not related to HbA1c. The results show that FVIII:C levels are increased in Type 1 diabetes complicated by nephropathy and are related to degree of renal impairment but not levels of glycaemia. No associated enhancement of plasma procoagulant activity was detected.

SummaryTo investigate the effect of increasing FVIII:C in-vivo on coagulation ex-vivo, DDAVP was infused over 15 min in 10 volunteers and in-vitro thrombin generation measured. FVIII:C rose from 0.42 and 0.43 IU/ml before DDAVP to 1.38, 1.73 and 1.78 IU/ml at 15, 30 and 60 min respectively (p <0.001).A computer-assisted thrombin generation test was performed in defibrinated plasma using chromogenic substrate, S2238. Time to reach 50% maximal thrombin activity (T50/s) and lag phase of thrombin generation (lag/s) were measured. Lag shortened from 75 and 60 s before to 45 s during and after infusion (p <0.001). T50 shortened from 78.5 and 76.0 to 62.5, 60.0 and 58.5 s at times 15 (p <0.01), 30 (p <0.001) and 60 (p <0.001) min. FVIII:C correlated inversely with lag and T50 (r = –0.847, p <0.001, r = –0.826, p <0.001, n = 10) respectively.These findings show that acute elevations of FVIII:C in-vivo accelerate in-vitro thrombin production. This work suggests that elevated FVIII:C levels in-vivo may be important in thrombo-occlusive disease.