Warfarin-induced changes in procoagulant and anticoagulant proteins.

Dicoumarol was found to be the causative agent of a haemorrhagic disease in cattle following the ingestion of spoiled sweet clover. Vitamin K deficiency in chickens caused bleeding. Dicoumarol was later determined to be a vitamin K antagonist. A more potent form of the drug was produced synthetically and, following its initial use as rat poison, was recognized as a potential anti-thrombotic treatment in humans. The mode of action of a coumarin derivative (i.e. warfarin) is described. The overall effect of high-dose and low-dose warfarin and the possibility of a transient state of hypercoagulability on the introduction and withdrawal of treatment is considered.

Activation of factors XII and VII induced in citrated plasma in the presence of contact surface.

Activated factor XII (XIIa), activated factor VII (VIIa) and factor VII coagulant activity (VIIc) were determined in non-treated and in treated (cold-incubated) citrated plasmas from women in late pregnancy and from norma volunteers. All three activities were higher in the non-treated plasmas from women in late pregnancy than from normal subjects. The incubation of citrated plasmas from women in late pregnancy, on ice for 24 hours, resulted in a many-fold increase of factor XIIa activity, factor VIIa levels and VIIc. The dilution of these plasmas resulted in a sharp decrease of all three activities in the post-incubation mixture, so that in the plasmas diluted 2:1 with buffer all three activities were similar to those in fresh plasmas. Similar incubations of diluted plasmas (1:1) from normal volunteers resulted in no increase of factor XIIa activity, factor VIIa levels and VIIc. However, the presence in the incubation mixture of micellar stearate resulted in a stearate concentration-dependent increase of all three activities in treated plasmas. Levels of factor XIIa activity and factor VIIa in the treated plasmas from both groups of subjects were highly correlated (r = 0.987; p < 0.001). There was also a highly significant correlation between VIIc and factor VIIa levels (0.989; p < 0.001). These results demonstrate that the in vitro increase in factor VIIa levels is due to the activation of the contact system of coagulation and is dependent on the potency of the contact surface. Moreover, VIIc over a wide range of values, observed in the present experiments, can provide an accurate measure of factor VIIa concentration.

Fetal and infant growth and cardiovascular risk factors in women.

OBJECTIVE: To examine whether cardiovascular risk factors in women are related to fetal and infant growth. DESIGN: Follow up study of women born 1923-30 whose birth weights and weights at one year were recorded. SETTING: Hertfordshire. SUBJECTS: 297 women born and still living in East Hertfordshire. MAIN OUTCOME MEASURES: Plasma glucose and insulin concentrations during a standard oral glucose tolerance test; fasting plasma proinsulin and 32-33 split proinsulin concentrations; blood pressure; fasting serum total, low density lipoprotein and high density lipoprotein cholesterol, triglyceride, and apolipoprotein A I and B concentrations; and plasma fibrinogen and factor VII concentrations. RESULTS: Fasting plasma concentrations of glucose, insulin, and 32-33 split proinsulin fell with increasing birth weight (P = 0.04, P = 0.002, and P = 0.0002 respectively, when current body mass index was allowed for). Glucose and insulin concentrations 120 minutes after an oral glucose load showed similar trends (P = 0.03 and P = 0.02). Systolic blood pressure, waist:hip ratio, and serum triglyceride concentrations also fell with increasing birth weight (P = 0.08, P = 0.07, and P = 0.07 respectively), while serum high density lipoprotein cholesterol concentrations rose (P = 0.04). At each birth weight women who currently had a higher body mass index had higher levels of risk factors. CONCLUSION: In women, as in men, reduced fetal growth leads to insulin resistance and the associated disorders: raised blood pressure and high serum triglyceride and low serum high density lipoprotein cholesterol concentrations. The highest values of these coronary risk factors occur in people who were small at birth and became obese. In contrast with men, low rates of infant growth did not predict levels of risk factors in women.

Plasma concentrations of fibrinogen and factor VII in adult life and their relation to intra-uterine growth.

To examine the relation between fetal development and plasma concentrations of fibrinogen and factor VII in adult life we followed up 202 men and women, now aged around 50 years, who had been measured in detail at birth. Plasma concentrations of fibrinogen were related to weight and abdominal circumference at birth. In men, after adjustment for cigarette smoking and current obesity, plasma concentrations of fibrinogen fell by 0.12 g/l (95% CI 0.05-0.19) for each pound increase in birthweight and by 0.10 g/l (95% CI 0.03-0.17) for each inch increase in abdominal circumference. In contrast, analysis of the data for women showed no statistically significant relation between plasma fibrinogen concentration and weight or abdominal circumference at birth. No relation was seen between concentrations of factor VII and measurements made at birth in either sex. These findings suggest that, in men, reduced growth of the liver in fetal life has a long-term influence on fibrinogen metabolism.

Factor VIII, ABO blood group and the incidence of ischaemic heart disease.

Relations of factor VIII activity, FVIIIC, and von Willebrand factor antigen (vWFAg), with ischaemic heart disease (IHD) were examined in 1393 men aged between 40 and 64 years at entry to the Northwick Park Heart Study (NPHS) who experienced 178 first major episodes of IHD during an average follow-up period of 16.1 years. After allowing for the large factor VIII differences between the main ABO blood groups, FVIIIC was probably associated with IHD incidence, possibly more strongly with fatal than non-fatal episodes. Thus, an increase of 1 standard deviation in FVIIIC raised the risk of fatal IHD by about 28%. vWFAg was also significantly associated with fatal events. The observed relation of FVIIIC with IHD incidence probably underestimates the true strength of the association because of the considerable within-person and laboratory variability in factor VIII measurements. FVIIIC and vWFAg were strongly correlated (r = 0.57) and in statistical terms there may be little to choose between them in long-term studies of IHD. Taking account of evidence that haemophiliacs seem to experience less IHD than expected, high factor VIII levels may contribute to the incidence of IHD by increasing thrombogenic potential. The incidence of IHD was significantly higher in those of blood group AB than in those of groups O, A or B, particularly for fatal events. There was no evidence that the FVIIIC and vWFAg associations with IHD are determined by ABO group. The factor VIII and ABO blood group effects therefore appeared to be independent. Group AB may be a genetic marker of characteristics influencing other indices of IHD risk such as short stature, NPHS men (though not women) of group AB being about 2 cm shorter than those of other groups.

Changes in clot deformability--a possible explanation for the epidemiological association between plasma fibrinogen concentration and myocardial infarction.

This study examined the rheological properties of fibrin gels formed by adding thrombin to plasma samples from 99 subjects with fibrinogen concentrations ranging from 1.45 to 4.14 g/l. A highly significant (r = 0.757; P < 0.001) inverse correlation was observed between plasma fibrinogen concentration and the extent of clot deformability as estimated from the final value of the storage modulus (G') of the fibrin gel when obtained by rheological analysis. A similarly significant correlation (r = 0.844; P < 0.001) was obtained using samples from 47 subjects in which fibrin cross-linking was blocked by addition of 0.1 mM iodoacetamide to inactivate factor XIIIa. The characteristics of the relationship between G' and fibrinogen concentration in the plasma samples was comparable with that observed when the fibrin gel was formed by adding thrombin to purified fibrinogen. These results suggest that the increased risk of myocardial infarction associated with an elevated plasma fibrinogen concentration may, in part, be explained on the basis of a decreased deformability of the fibrin clot formed.

Factor VII-deficient substrate plasmas depleted of protein C raise the sensitivity of the factor VII bio-assay to activated factor VII: an international study.

Plasma from healthy individuals, pregnant women and patients on warfarin were distributed to 3 laboratories supporting major cardiovascular surveys (Northwick Park, Muenster and Houston) for assay of factor VII coagulant activity (VIIc) with their own bio-assays. The mean VIIc in 147 samples agreed to within 1% of standard in Northwick Park and Houston, but was 14% of standard lower in Muenster owing to its more potent standard. In samples with an increased VIIc the Northwick Park assay gave a higher result than the other assays owing to its increased responsiveness to activated factor VII (VIIa). Thus when VIIa concentrations were determined directly with a clotting assay which utilises a soluble recombinant tissue factor, the increase in VIIc with increase in VIIa was considerably greater with the Northwick Park assay than the Muenster assay. This feature of the Northwick Park assay was traced to the virtual absence of protein C in its substrate plasma. Factor Va appears rate-limiting for the coagulant expression of VIIa in test plasma. If the thrombotic response to release of tissue factor is determined by the circulating concentration of VIIa, then the Northwick Park factor VII bio-assay may be preferable to other bio-assays currently employed to estimate risk of acute coronary events.

Fibrinolytic activity, clotting factors, and long-term incidence of ischaemic heart disease in the Northwick Park Heart Study.

Fibrinolytic activity (FA) was measured by dilute blood clot lysis time at entry to the Northwick Park Heart Study in 1382 white men aged 40-64, of whom 179 subsequently experienced episodes of ischaemic heart disease during a mean follow-up period of 16.1 years. There was a significant interaction between age and low FA (p = 0.02) with respect to ischaemic heart disease: a difference of one standard deviation in FA was associated with a difference of about 40% in ischaemic heart disease risk (p = 0.002) in those aged 40-54 at entry. The FA association remained after adjusting for plasma fibrinogen. High fibrinogen concentrations themselves were also associated with ischaemic heart disease, as was high factor VII activity with fatal events. Low FA in younger men may exert a long-term influence by impairing the removal of fibrin deposits that contribute to atherogenesis. Low FA appears to be a leading determinant of ischaemic heart disease in younger men and methods of enhancing fibrinolytic activity, whether by life-style changes or pharmacologically, should be considered.

A six year prospective study of fibrinogen and other risk factors associated with mortality in stable claudicants.

A total of 333 patients with stable intermittent claudication at recruitment were followed up for 6 years to determine risk factors associated with subsequent mortality. Cardiovascular diseases were the underlying cause of death in 78% of the 114 patients who died. The strongest independent predictor of death during the follow-up period was the plasma fibrinogen level, an increase of 1 milligram being associated with a nearly two-fold increase in the probability of death within the next 6 years. Age, low ankle/brachial pressure index and a past history of myocardial infarction also increased the probability of death during the study period. The plasma fibrinogen level is a valuable index of those patients with stable intermittent claudication at high risk of early mortality. The results also provide further evidence for the involvement of fibrinogen in the pathogenesis of arterial disease.

Relation of fetal and infant growth to plasma fibrinogen and factor VII concentrations in adult life.

OBJECTIVE: To determine whether reduced fetal and infant growth are associated with higher plasma fibrinogen and factor VII concentrations in adult life. DESIGN: Follow up study of men born during 1920-30 whose weights at birth and at 1 year had been recorded by health visitors, and men born during 1935-43 whose size at birth had been measured in detail. SETTING: Hertfordshire and Preston, England. SUBJECTS: 591 men born in east Hertfordshire who still lived there and 148 men born in Preston who still lived in or close to the city. MAIN OUTCOME MEASURES: Plasma fibrinogen and factor VII concentrations. RESULTS: Among men in Hertfordshire mean plasma fibrinogen and factor VII concentrations fell with increasing weight at 1 year (from 3.21 g/l in men of less than or equal to 18 lb to 2.93 g/l in men greater than or equal to 27 lb and from 122% of standard to 103%; p less than 0.001, p less than 0.005 respectively). The trends were independent of cigarette smoking, alcohol consumption, body mass index, and social class. Neither plasma fibrinogen nor factor VII concentration was related to birth weight. In men in Preston, however, fibrinogen concentration fell progressively as the ratio of placental weight to birth weight decreased (p = 0.01). CONCLUSIONS: Reduced growth in fetal life and infancy is strongly related to high plasma concentrations of the haemostatic factors fibrinogen and factor VII. This may be a persisting response to impaired liver development during a critical early period.

Antithrombin III and arterial disease.

Cross-sectional studies suggest that both low and high antithrombin III levels are associated with the risk of arterial disease, principally ischaemic heart disease (IHD). The prospective relation between antithrombin III and subsequent death from arterial disease has been investigated in 893 men in the Northwick Park Heart Study. Antithrombin III levels were directly correlated with high rather than low levels of factor VII activity and of plasma fibrinogen. There were more deaths from arterial disease in the low and high thirds of the antithrombin III distribution than in the middle third.

The increased rate of activation of factor XII in late pregnancy can contribute to the increased reactivity of factor VII.

The amidolytic activity of enzymes derived from factor XII (XIIa) was 3-fold higher in plasmas collected during pregnancy than from control subjects. Factor VII coagulant activity (VIIc) and XIIa increased in both kinds of plasmas on incubation on ice for 24 h (cold activation). These increases could be attributed to the decreased potency of C1 inhibitor (C1INH). However, variations in the concentration of C1INH and of factor XII could not explain the differences in VIIc and in XIIa between late pregnancy and control plasmas following cold activation under the same conditions. It is concluded that in vitro the increased amount of contact surface in the late pregnancy plasma promotes a higher rate of generation of XIIa and consequently a higher rate of activation of factor VII. The increased amount of contact surface could also be responsible for the increased concentration of XIIa in non-treated plasma from late pregnancy and could contribute in vivo to the higher reactivity of factor VII in this condition.

Antithrombin III and procoagulant activity: sex differences and effects of the menopause.

Among participants in the Northwick Park Heart Study, antithrombin III activity was lower in pre-menopausal women than in men of the same age. In the women, however, the menopause was associated with a significant increase in antithrombin III, mean levels in these older women then exceeding levels in men of the same age. The occurrence of the menopause was also accompanied by large increases in factor VII coagulant activity, VIIc, and in plasma fibrinogen, these increases being greater in those experiencing a natural menopause than in those whose menopause was artificial. Sex differences in antithrombin III may form part of the explanation for the observed differences between men and women in their experience of ischaemic heart disease (IHD) and also for the contrasting effects of oral contraceptives and of hormone replacement therapy on the risk of thromboembolic disease.

Fat consumption and factor VII coagulant activity in middle-aged men. An association between a dietary and thrombogenic coronary risk factor.

Diet was measured by 5-day weighed inventory to search for an association between fat intake in the general population and factor VII coagulant activity (VIIc), a strong predictor of coronary heart disease. Of 275 men aged 40-59 years registered with a medical practice, 203 (74%) participated and 170 (62%) provided a satisfactory record. After allowance for the increase in fat intake with body size, a statistically significant and positive association was found between dietary fat and VIIc (r = 0.18; P less than 0.05). The correlation coefficient was increased to 0.24 when adjusted for the effect of day-to-day variability in individual fat intake, thereby providing an improved estimate of the true strength of association. The mean difference in VIIc of 12% of standard between men in the highest and lowest quarters of the distribution of fat intake was similar to that reported between men experiencing coronary heart disease and those remaining free. The results support previous experimental fat-feeding studies and suggest that a high fat diet has adverse consequences for blood coagulability and coronary thrombosis.