Sixty-six male university students were classified as Type A or B on the basis of the Structured Interview of Rosenman and as hostile or non-hostile on the basis of the Cook-Medley scale. Vascular production of prostacyclin and platelet thromboxane in response to a standard vessel injury was evaluated. Basal thromboxane production, measured as the primary… (More)
Unactivated platelets contain about 69% G actin and less than 10% of the contractile proteins in a cytoskeletal core resistant to extraction with 1% Triton X-100. Activation by thrombin leads, within 1 min, to the formation of pseudopodia and contractile gels, accompanied by the reduction of the G-actin content to about 22% and the development of… (More)
We explored the retraction or contraction of platelet-fibrin clots under isometric conditions. In the presence of micromolar calcium clots of normal platelet-rich plasma developed tension at an initial rate of 0.1 to 0.2 g/min per cm2 (initial cross-sectional area). Electron microscopy of clots fixed after attaining a force of 1.6 g/cm2 revealed platelets… (More)
Washed platelets activated by alpha-thrombin, gamma-thrombin, thrombocytin or the ionophore A23187 (ref. 3) lose their disk shape, produce pseudopodia and become cohesive. This cohesiveness is accompanied by the expression of an endogeneous haemagglutinin which, although apparently bound to the platelet membrane, is dependent on cell secretion. The… (More)
Concanavalin A (Con A) has been used to activate platelets, inducing a specific interaction between the glycoprotein IIb-IIIa complex and the cytoskeleton of the activated platelet. In agreement with this, we have shown that Con A activates human platelets, initiating phosphorylation, secretion, and cytoskeletal formation. Con A and cytochalasin B were used… (More)
Inhibition of human platelet aggregation by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE), a novel antagonist of histamine binding, suggested that histamine might serve a critical role in cell function. Phorbol-12-myristate-13-acetate (PMA) or collagen was found to increase platelet histamine content in parallel with promotion of aggregation.… (More)
We previously demonstrated that newly formed intracellular histamine mediates platelet aggregation in response to phorbol-12-myristate-13-acetate (PMA). We now report further investigations of the role of histamine during physiological activation of platelets by collagen. Platelets stirred with collagen produced histamine; the rise in histamine precedes the… (More)
Alpha-adrenergic agonists that promote platelet aggregation were found to reduce ferric heme to ferrous heme. Agents that bind iron in heme inhibited epinephrine-induced platelet aggregation. It is proposed that epinephrine first binds to its receptor and then reduces an adjacent heme group to transmit its agonist stimulus.