Progress in hemostasis and thrombosis最新文献

A role of von Willebrand factor-mediated platelet function in porcine atherogenesis is strongly suggested by these studies. This influence of platelet function is probably most important in experimental systems that involve long-term observation and low or moderately elevated levels of serum cholesterol. On the other hand, effects of platelet function on development of atherosclerosis in animals with extremely high serum cholesterol levels are difficult to demonstrate and may be of relatively less importance. These observations are consistent with the results of numbers of recent studies describing the relationship of vascular injury to intimal smooth muscle cell proliferation. There is considerable evidence that lipid-rich intimal lesions occur in hypercholesterolemic animals with no antecedent denudation of endothelium or platelet adherence. It is difficult to ascribe intimal proliferation to platelet effects in this setting. On the other hand, endothelial cells, smooth muscle cells, and monocytes, which are all known to be involved in the atherosclerotic process, can produce mitogenic and chemotactic proteins, including platelet-derived growth factor. Therefore, metabolic aberrations of various kinds, including those initiated by mechanical injury or hypercholesterolemia, may promote proliferation in the vascular wall and resultant lesion development. Data from studies of pigs with vWD suggest a contribution of platelets to this process, but the effects of this contribution are modulated by numbers of variables, most of which are yet to be identified. The control of these multiple variables will be necessary before a clear understanding of the magnitude of the platelet-mediated effects can be gained. This will require carefully defined conditions of hypercholesterolemia, special attention to the immunologic variables and study of properly selected vascular segments under known conditions of flow. This later element will be especially important in the study of vWF-mediated platelet function, since shear forces are a critical determinant of vWF function. Systems that model flow conditions in various segments of the aorta, carotid, and coronary arteries are presently under development for this purpose. Finally, studies examining the molecular basis of vWF-mediated and other platelet functions will probably guide the most productive use of these models. Platelet membrane glycoprotein (GP) receptor Ib and the complex GP IIb and IIIa have been shown in ex vivo studies to be binding sites for vWF molecules.(ABSTRACT TRUNCATED AT 400 WORDS)

At a time when the acquired immunodeficiency syndrome as well as hepatitis and other blood-borne diseases are a threat to patients with bleeding disorders who need treatment with blood products, it is rewarding to realize that a number of these patients can be safely and effectively treated with their own desmopressin-stimulated F.VIII:C and vWF. Desmopressin is clinically useful for treatment of patients with moderate and mild hemophilia. The limits of the clinical indications are established by the nature of the bleeding episode, the resting factor level, the level that must be achieved, and the length of time the level must be maintained to manage any given bleeding episode. In von Willebrand disease, desmopressin can be used more extensively to raise F.VIII:C levels than in classic hemophilia, because fewer of the patients have the severe form of the disease that is unresponsive to desmopressin. Increases in the level of F.VIII:C of about four times the resting value can be expected both in hemophilia and von Willebrand disease, but it must be borne in mind that the range of individual responses is large. Even though it is not easy to correct the prolonged bleeding time, particularly in patients with dysfunctional vWF, this drawback is of clinical relevance only in a minority of cases. A role for the use of desmopressin in acquired diseases of primary hemostasis has been proposed more recently, and experience is more limited than in congenital bleeding disorders. Uremia is probably the most firmly established indication because it has been shown that the bleeding time is often dramatically shortened by desmopressin, and hemorrhages can be stopped or prevented before surgical procedures. The indications for use of the compound in liver cirrhosis and congenital and acquired platelet dysfunctions are promising but much less established from a clinical standpoint. The bulk of available clinical experience is based on intravenous administration. Intranasal and subcutaneous administration have been successfully attempted and might be more convenient in selected circumstances, such as home treatment and the stimulation of blood donors to provide more abundant supplies of F.VIII:C and vWF. However, the responses after intranasal administration are less predictable and consistent than after intravenous administration. Desmopressin has few troublesome side-effects. Mild facial flushing, a small increase in heart rate, and, more rarely, mild headache can occur transiently during infusion. Signs of hyponatremia or cerebral edema are extremely rare, providing that excessive fluid intake is avoided.(ABSTRACT TRUNCATED AT 400 WORDS)

In this chapter, current concepts of eicosanoid biochemistry and function have been summarized. Emphasis has been placed on the importance of ascertaining a complete profile of eicosanoids synthesized by a given tissue under varying conditions of stimulation. The concept of transient intermediates, which are involved in each of the known pathways, was reviewed. Such intermediates can also represent substrate for cell-cell interactions, which have been classified and discussed. Knowledge of the synthetic mechanisms, metabolism, and catabolism of eicosanoids has surpassed our comprehension of their biologic actions. It can be speculated that eicosanoids reinforce or synergize normal homeostatic mechanisms that might proceed less effectively in their absence but occur more efficiently when they are produced. Incomplete comprehension of the functional role of eicosanoids has retarded the development of definitive pharmaceutical approaches toward inhibition or stimulation of eicosanoid production in pathophysiologic situations. With regard to thrombosis, the inflammatory response and host-defense mechanisms, leukotrienes, which have been shown to act on vascular endothelium and smooth muscle, may play an important role in occlusive vascular disease. Since leukotrienes and other hydroxy acids such as 12-HETE are not inhibited by aspirin or nonsteroidal anti-inflammatory agents, development of a unifying concept is difficult. It appears that we are approaching a point in time for reevaluation and reassessment of the role of the eicosanoid pathway in hemostasis and thrombosis. Most importantly, recent eicosanoid research has provided answers to biologic phenomena that were not explicable in the past and also explains why therapeutic trials in occlusive vascular disease were not as successful as predicted on theoretical grounds.