In a randomized double-blind cross-over trial we gave either 1-deamino-8-D-arginine vasopressin or placebo to 12 patients with uremia, hemorrhagic tendencies, and prolonged bleeding times. After vasopressin infusion, all patients had shortened bleeding times, with the effect lasting for at least four hours in most cases. Platelet count, platelet cyclic AMP levels, platelet retention on glass beads, plasma fibronectin, serum thromboxane B2 and residual prothrombin, hematocrit, and plasma osmolarity were unchanged after vasopressin. A consistent post-infusion increase in factor VIII coagulant activity and, to a lesser extent, in factor VIII-related antigen and ristocetin cofactor accompanied the shortening of bleeding time. In addition, vasopressin induced the appearance in plasma of larger von Willebrand-factor multimers than those present in the resting state. The compound was given to nine additional patients with acute or chronic renal failure and prolonged bleeding times, before major surgery or renal biopsy. In these patients, shortening of the bleeding time was associated with normal hemostasis. Our findings indicate that 1-deamino-8-D-arginine vasopressin can be used for temporary correction of bleeding time and may prevent surgical bleeding in patients with uremia.

We have identified structural attributes required for signal transduction through a seven-transmembrane-domain receptor. Platelets from a patient (AC) with a congenital bleeding disorder had normal shape change but reduced and reversible aggregation in response to 4 M ADP, similar to normal platelets with blocked P2Y12 receptor. The response to 20 M ADP, albeit still decreased, was more pronounced and was reduced by a P2Y 12 antagonist, indicating some residual receptor function. ADP failed to lower the adenylyl cyclase activity stimulated by prostaglandin E1 in the patient's platelets, even though the number and affinity of 2-methylthioadenosine 5 -[ 33 P]diphosphate-binding sites was normal. Analysis of the patient's P2Y12 gene revealed a G-to-A transition in one allele, changing the codon for Arg-256 in the sixth transmembrane domain to Gln, and a C-to-T transition in the other allele, changing the codon for Arg-265 in the third extracellular loop to Trp. Neither mutation interfered with receptor surface expression but both altered function, since ADP inhibited the forskolininduced increase of cAMP markedly less in cells transfected with either mutant P2Y 12 as compared with wild-type receptor. These studies delineate a region of P2Y12 required for normal function after ADP binding.ADP ͉ platelet function disorder ͉ G-protein coupled receptors ͉ platelet aggregation P latelets possess at least two P2 receptors whose combined action is required for full activation and aggregation in response to stimulation by ADP (1, 2). One receptor, P2Y 1 , is coupled to the heterotrimeric GTP-binding protein G q and to phospholipase C-␤; it induces mobilization of cytoplasmic calcium and mediates shape change followed by an initial wave of rapidly reversible aggregation (3, 4). The other, P2Y 12 , is negatively coupled to adenylyl cyclase through G i ; it mediates progressive and sustained platelet aggregation in the absence of shape change (2, 3, 5) and plays an important role in the potentiation of secretion induced by several agonists (6, 7). P2Y 12 is the therapeutic target of ticlopidine and clopidogrel (8), two platelet aggregation inhibitors used for the prevention and treatment of arterial thrombosis (9), and its congenital deficiency results in a bleeding disorder (7,10,11). Platelets deficient in P2Y 12 exhibit normal ADP-induced shape change but only slight and rapidly reversible aggregation, as well as a failure of ADP to inhibit the rise of cAMP levels after stimulation with prostaglandin E 1 (PGE 1 ) (1). The P2Y 12 defect is inherited as an autosomal recessive trait (1), and heterozygous patients display a mild abnormality of platelet function similar to that seen in the relatively common primary secretion defects. These are a heterogeneous group of congenital platelet alterations characterized by reduced platelet secretion despite normal thromboxane production and storage granule content (12). In some of these patients, platelets that produce normal amounts of thromboxane A 2 fail to respond to the agonist b...

Abstract-Two unrelated patients with a congenital bleeding diathesis associated with a severe defect of the platelet ADP receptor coupled to adenylate cyclase (P2 CYC ) have been described so far. In one of them, platelet secretion was shown to be abnormal. We recently showed that platelets with the primary secretion defect (PSD; characterized by abnormal secretion but normal granule stores, thromboxane A 2 production, and ADP-induced primary wave of aggregation) have a moderate defect of P2 CYC . Therefore, the interaction of ADP with the full complement of its receptors seems to be essential for normal platelet secretion, and PSD patients may be heterozygotes for the congenital severe defect of P2 CYC .In this study, we describe 2 new related patients with a severe defect of P2 CYC and the son of one of them, who is to be considered an obligate heterozygote for the defect. The 2 patients with the severe defect had lifelong histories of abnormal bleeding, prolonged bleeding times, abnormalities of platelet aggregation and secretion, lack of inhibition of adenylate cyclase by ADP, and a deficiency of platelet-binding sites for

Type I von Willebrand disease (vWD) is characterized by equally low plasma concentrations of von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor (RiCof) and by the presence of all vWF multimers in sodium dodecyl sulfate (SDS)-agarose gel electrophoresis. For 17 patients (13 kindreds) diagnosed with these criteria, we have studied the platelet contents of vWF:Ag and RiCof and the changes of these in plasma after DDAVP infusion. Platelet vWF:Ag and RiCof were normal in four kindreds (called “platelet normal” subgroup); following 1-deamino- 8-D-arginine vasopressin; plasma vWF:Ag, RiCof and the bleeding time (BT) became normal. In six kindreds, platelet vWF:Ag and RiCof were equally low (platelet low); after DDAVP, plasma vWF:Ag and RiCof remained low, and the BT was prolonged. In three additional kindreds, platelets contained normal concentrations of vWF:Ag, but RiCof was very low (platelet discordant); even though a complete set of multimers was found in plasma and platelets, there was a relatively small amount of large multimers. After DDAVP, plasma vWF:Ag became normal, but RiCof remained low and the BT was very prolonged. These findings demonstrated that there can be an abnormal vWF (RiCof less than vWF:Ag) even in type I vWD, coexisting with a complete set of vWF multimers (platelet discordant); that the abnormal vWF can be shown more clearly in platelets than in plasma or else in plasma after DDAVP infusion; and that DDAVP normalizes the BT only in those patients with normal platelet levels of both vWF:Ag and RiCof (platelet normal).

Activation of the P2Y(1) nucleotide receptor in platelets by ADP causes changes in shape and aggregation, mediated by activation of phospholipase C (PLC). Recently, MRS2500(2-iodo-N(6)-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate) was introduced as a highly potent and selective antagonist for this receptor. We have studied the actions of MRS2500 in human platelets and compared these effects with the effects of two acyclic nucleotide analogues, a bisphosphate MRS2298 and a bisphosphonate derivative MRS2496, which act as P2Y(1) receptor antagonists, although less potently than MRS2500. Improved synthetic methods for MRS2500 and MRS2496 were devised. The bisphosphonate is predicted to be more stable in general in biological systems than phosphate antagonists due to the non-hydrolyzable CP bond. MRS2500 inhibited the ADP-induced aggregation of human platelets with an IC(50) value of 0.95 nM. MRS2298 and MRS2496 also both inhibited the ADP-induced aggregation of human platelets with IC(50) values of 62.8 nM and 1.5 microM, respectively. A similar order of potency was observed for the three antagonists in binding to the recombinant human P2Y(1) receptor and in inhibition of ADP-induced shape change and ADP-induced rise in intracellular Ca(2+). No substantial antagonism of the pathway linked to the inhibition of cyclic AMP was observed for the nucleotide derivatives, indicating no interaction of these three P2Y(1) receptor antagonists with the proaggregatory P2Y(12) receptor, which is also activated by ADP. Thus, all three of the bisphosphate derivatives are highly selective antagonists of the platelet P2Y(1) receptor, and MRS2500 is the most potent such antagonist yet reported.

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Low vitamin B(6) plasma levels, an independent risk factor for thrombosis, are frequent in patients with IBD, especially those with active disease.

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