An unstable [ti/2 at 37°= 32 L 2 (SD) sec] intermediate, thromboxane A2, was detected in the conversion of prostaglandin G2 into 841-hydroxy-3-oxopropyl)9,12L-di- Recently the hemiacetal derivative of 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid (PHD) and 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) were found to be the major metabolites of prostaglandin G2 (PGG2) in suspensions of human platelets (1, 2). Conversion of PGG2 into PHD was suggested to occur by rearrangement of the endoperoxide structure followed by incorporation of one molecule of H20 (1)

Incubation for a short time of arachidonic acid with the microsomal fraction of a homogenate of the vesicular gland of sheep in the presence of 1 mM p-mercuribenzoate followed by extraction and silicic acid chromatography yielded two prostaglandin endoperoxides. The structures of these compounds, i.e., 15-hydroperoxy-9a,11a-peroxidoprosta-5,13-dienoic acid (prostaglandin G2) and 15-hydroxy-9a,lla-peroxidoprosta-5,13-dienoic acid (prostaglandin H2), were assigned mainly by a number of chemical transformations into previously known prostaglandins. The new prostaglandins were 50-200 times (prostaglandin G2) and 100-450 times (prostaglandin H2) more active than prostaglandin E2 on the superfused aorta strip. The half-life of the prostaglandin endoperoxides in aqueous medium (about 5 min) was significantly longer than that of "rabbit aorta-contracting substance" released from guinea pig lung, indicating that none of the prostaglandin endoperoxides is identical with this factor. Addition of 10-300 ng/ml of the endoperoxides to suspensions of washed human platelets resulted in rapid aggregation. Furthermore, platelet aggregation induced by thrombin was accompanied by release of material reducible by stannous chloride into prostaglandin F2a, thus indicating the involvement of endogenous prostaglandin endoperoxides in platelet aggregation.

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We studied whether hemostatic abnormalities contribute to the increased risk of stroke in patients with nonvalvular atrial fibrillation. Hemostatic function was studied in four agematched groups: 20 patients with nonvalvular atrial fibrillation and a previous ischemic stroke, 20 patients with nonvalvular atrial fibrillation without a previous stroke, 20 stroke patients with sinus rhythm, and 40 healthy controls. Both groups with nonvalvular atrial fibrillation had significantly higher concentrations of von Willebrand factor, factor VM:C, fibrinogen, D-dlmer (a fibrinolytic product), /3-thromboglobulin, and platelet factor 4; a significantly higher fibrinogen/antithrombin ratio; and significantly higher spontaneous amidolytic activity than the healthy controls. Prekallikrein levels were significantly lower in both groups with nonvalvular atrial fibrillation. Stroke patients with sinus rhythm had normal hemostatic function, normal concentrations of platelet-related factors, and a slightly increased concentration of fibrinopeptide A compared with the healthy controls. Both groups with nonvalvular atrial fibrillation differed from the stroke patients with sinus rhythm as they did from the healthy controls. No difference in hemostatic function was seen between the nonvalvular atrial fibrillation patients with and without a previous ischemic stroke. Thus, alterations in hemostatic function may contribute to the increased risk of stroke in patients with nonvalvular atrial fibrillation. (Stroke 1990^1:47-51) N onvalvular atrial fibrillation (NVAF) afflicts 2-4% of 70-year-old people, and its prevalence increases with age. 1 NVAF is an important risk factor for stroke. In the Framingham Study, NVAF was associated with a 5-6 times higher incidence of stroke compared with an age-, sex-, and blood pressure-matched control group without NVAF. 2Left atrial thrombosis causing stroke by arterial embolism has been thought to be the main pathogenetic mechanism in the association between NVAF and stroke. However, the precise mechanism is difficult to determine in individuals with NVAF. As pointed out in recent studies, a considerable proportion of strokes are probably due to atherothrombosis. 3 -4 Generalized atherosclerosis might be the common cause of both NVAF and stroke, thereby explaining the association. If this is true, it can be assumed that there are higher concen-

Methods were developed for quantitative determination of the three major metabolites of arachidonic acid in human platelets, i.e., 12L-hydroxy-5,8,10,-14-eicosatetraenoic acid (HETE), 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid (PHD). Aggregation of washed platelets by thrombin was accompanied by release of 1163-2175 ng/ml of HETE, 1129-2430 ng/ml of HHT, and 998-2299 ng/ml of PHD. The amount of PGG2 (prostaglandin G2) produced as calculated from the sum of the amounts of its metabolites (HHT and PHD) was 2477-5480 ng/ml. In contrast, the amounts of PGE2 (prostaglandin E2) and PGF2. (prostaglandin F2.) released were approximately two orders of magnitude lower. In this system, the prostaglandins thus exert their biological action through the endoperoxides, which are almost exclusively metabolized to nonprostanoate structures and only to a small extent to the classical prostaglandins.Platelets from subjects given aspirin produced less than 5% of the above mentioned amounts of HHT and PHD, whereas the production of HETE was stimulated about 3-fold. This provides additional evidence for our earlier proposal tHamberg, M., Svensson, J., Wakabayashi, T. & Samuelsson, B. (1974) Proc. Nat. Acad. Sci. USA 71, 345-3491 that the anti-aggregating effect of aspirin is through inhibition of PGG2 formation.In a recent paper (1) we showed that the prostaglandin endoperoxides, PGG2 and PGH2, in low concentrations induce aggregation of human platelets and that they are released during thrombin-induced aggregation. Together with the known effects of inhibitors of prostaglandin biosynthesis on platelets, this indicated a physiological role of endoperoxides in platelet function and gave information on the mechanism of action of, e.g., aspirin (1, 2). With a similar technique, it was also demonstrated that aggregation induced by collagen, epinephrine, and arachidonic acid was accompanied by release of the intact endoperoxides (3).We recently studied the transformation of [ [5,6,8,9,11,12,14,Arachidonic acid was prepared as previously described (5). [3,3,4,4-2H4]PGE2 and [3,3,4,4-2H4]-PGF2a were generously provided by Dr. U. Axen, The Upjohn Co., Kalamazoo, Mich. Thrombin (TopostasinO) was purchased from Hoffmann-La Roche Co.Quantitative Determination of 12L-Hydroxy-6,8,10,14-Eicosatetraenoic Acid (HETE). 5,6,8,9,11,12,14,

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The endoperoxide prostaglandin G2 (PGG2) induced platelet aggregation as well as the platelet release reaction (release of ADP and serotonin) when added to human platelet-rich plasma. Formation of a metabolite of PGG2 [8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid] and a lipoxygenase product [12L-hydroxy-5,8,10,14-eicosatetraenoic acid] accompanied the release reaction caused by aggregating agents such as collagen, ADP, epinephrine, and thrombin. Indomethacin inhibited the release reaction and PGG2 formation induced by these agents but had no effect on PGG2-induced release reaction. The aggregating effect of PGG2 was abolished by furosemide, which is a competitive inhibitor of ADP-induced primary aggregation. These data indicate that the aggregating effect of PGG2 is due to release of ADP and that PGG2 synthesis is required for induction of the release reaction by various aggregating agents.A subject with a hemostatic defect due to abnormal release mechanism [decreased aggregation with epinephrine (second wave) and collagen and normal platelet ADP] had a deficiency of the cyclo-oxygenase that catalyzes formation of PGG2. Normal aggregation and release reaction were obtained with added PGG2.It is concluded that the endoperoxide (PGG2) is essential in normal hemostasis because of its role in initiating the release reaction required for aggregation by collagen and the second wave of aggregation caused by, e.g., ADP.

SUMMARY Coagulation factor VIII, von Willebrand factor, antithrombin, fibrinogen, plasminogen activator capacity, and inhibitors of fibrinolysis, including a recently discovered fast inhibitor of tissue plasminogen activator, were measured three to six months after myocardial infarction in 116 male and 32 female patients aged < 45 and in 136 age and sex matched random controls. Plasma concentrations of fibrinogen and the fast inhibitor of tissue plasminogen activator were raised in male patients (with or without correction for orosomucoid levels, blood group distribution, tobacco and alcohol consumption, and weight/height index) and plasminogen activator capacity was reduced. In female patients the concentrations of factor VIII, von Willebrand factor, the fast inhibitor of tissue plasminogen activator, aC2-antiplasmin, and Cl inhibitor were significantly increased. The increase in factor VIII concentrations depended strongly on a persisting inflammatory response. Multivariate analysis indicated that a combination of fibrinogen and tissue plasminogen activator inhibitor concentrations gave the best independent discrimination between male patients and controls. For female patients the best combination was von Willebrand factor and tissue plasminogen activator inhibitor. Male patients with multiple vessel atheromatosis at coronary angiography had higher fibrinogen concentrations than those with atheromatosis of a single vessel. Atheromatosis was defined as sharp-edged, plaque-like, or irregular indentations, often multiple, into the vessel lumen without features suggesting fibromuscular hyperplasia.Several mechanisms have been suggested to explain the pathogenesis of ischaemic heart disease. According to the thrombogenic theory of atherogenesis,l hypercoagulability may be a prerequisite not only for the development of thrombotic complications but also for the pathogenesis of atherosclerosis. Impaired fibrinolysis at the onset and during the course of myocardial infarction is viewed mainly as a reduction in defensive capacity while coronary occlusion and fibrin formation are under way.