Platelet aggregation, regulation

NO is found in vivo and regulates various physiological functions including blood pressure, platelet aggregation, and neurotransmission. NO binding to heme proteins... 

Among the local mediators directly produced by endothelium, NO and PGI emerge as two principal regulators of vascular tone and platelet aggregation. Both are sensitive to estrogenic stimuli, and, as mentioned in a previous section, their role is crucial in atherogenesis. How their production is modulated by SERMs is, consequently, an important test of vascular protection. 

Bar J, Lahav J, Hod M, Ben-Rafael Z, Weinberger I, Brosens J (2000) Regulation of platelet aggregation and adenosine triphosphate release in vitro by 17beta-estradiol and medroxyprogesterone acetate in postmenopausal women. Thromb Haemost 84 695-700... 

The antithrombotic effects of NO are also mediated by NO-dependent inhibition of platelet aggregation. Both endothelial cells and platelets contain eNOS, which acts to regulate thrombus formation. Thus, endothelial dysfunction and the associated decrease in NO generation may result in abnormal platelet function. As in vascular smooth muscle, cGMP mediates the effect of NO in platelets. NO may have an additional inhibitory effect on blood coagulation by enhancing fibrinolysis via an effect on plasminogen. 

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