ANP prevents hypertrophy of adult rat cardiomyocytes. This protective action is shared by BNP and CNP and involves activation of particulate guanylyl cyclase receptors. Antihypertrophic effects of BNP and CNP are mediated through cyclic GMP-dependent protein kinase, but ANP can activate additional pathways independent of cyclic GMP to prevent adult cardiomyocte hypertrophy. These novel findings are of interest particularly since BNP appears to exert antifibrotic rather than antihypertrophic actions in vivo, while CNP is thought to act at least in part via the endothelium.

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Stimulation of cardiomyocyte guanosine 3,5-cyclic monophosphate (cyclic GMP) via endothelial-derived nitric oxide (NO) is an important mechanism by which bradykinin and ACE inhibitors prevent hypertrophy. Endothelial NO dysfunction and cardiac hypertrophy are morbid features of diabetes not entirely prevented by ACE inhibitors. In cardiomyocyte/endothelial cell cocultures, bradykinin efficacy is abolished by highglucose-induced endothelial NO dysfunction. We now demonstrate that antihypertrophic actions of natriuretic peptides, which stimulate cyclic GMP independently of NO, are preserved in cardiomyocytes despite high-glucose-induced endothelial dysfunction. Further, streptozotocin-induced diabetes significantly impairs the effectiveness of acute antihypertrophic strategies in isolated rat hearts. In hearts from citrate-treated control rats, angiotensin II-stimulated [ 3 H]phenylalanine incorporation and atrial natriuretic peptide and ␤-myosin heavy chain mRNA expression were prevented by B-type natriuretic peptide (BNP), bradykinin, the ACE inhibitor ramiprilat, and the neutral endopeptidase inhibitor candoxatrilat. These antihypertrophic effects were accompanied by increased left ventricular cyclic GMP. In age-matched diabetic hearts, the antihypertrophic and cyclic GMP stimulatory actions of bradykinin, ramiprilat, and candoxatrilat were absent. However, the blunting of hypertrophic markers and accompanying increases in cyclic GMP stimulated by BNP were preserved in diabetes. Thus BNP, which increases cyclic GMP independently of NO, is an important approach to prevent growth in the diabetic myocardium, where endothelium-dependent mechanisms are compromised.

Objective-The platelet P2Y12 ADP receptor is a well-known target of thienopyridine-type antiplatelet drugs. This study is the first to describe increased transcriptional expression of a functionally active P2Y12 in response to thrombin in human vascular smooth muscle cells (SMC). Methods and Results-On exposure to thrombin, P2Y12 mRNA was transiently increased, whereas total protein and cell surface expression of P2Y12 were markedly increased within 6 hours and remained elevated over 24 hours. This effect was mediated by activation of nuclear factor B. Preincubation with thrombin significantly enhanced the efficacy of the P2Y receptor agonist 2-methylthio-ADP to induce interleukin 6 expression and SMC mitogenesis. Effects induced by 2-methylthio-ADP were prevented by RNA interference-mediated knockdown of P2Y12 and a selective P2Y12-antagonist R-138727, the active metabolite of prasugrel. In addition, positive P2Y12 immunostaining was shown in SMC of human carotid artery plaques and was found to colocalize with tissue factor, the rate-limiting factor of thrombin formation in vivo. Conclusion-These data suggest that the P2Y12 receptor not only is central to ADP-induced platelet activation but also may mediate platelet-independent responses, specifically under conditions of enhanced thrombin formation, such as local vessel injury and atherosclerotic plaque rupture. Key Words: atherosclerosis Ⅲ thrombin Ⅲ P2Y12 receptor Ⅲ inflammation Ⅲ vascular smooth muscle P 2Y12 ADP receptor antagonists, such as the thienopyridines, are widely used as antiplatelet drugs. 1,2 Besides their role as inhibitors of platelet aggregation, there is increasing evidence that these compounds also exert antiinflammatory actions. Reduced plasma levels of inflammatory markers, such as CD40 ligand, C-reactive protein, P-selectin, and platelet-leukocyte aggregates, have been shown with P2Y12 antagonists in atherothrombotic patients, 3 and platelet P2Y12 has also been shown recently to influence vessel wall responses to injury and thrombosis. 4 Thus far, these effects have been attributed solely to the antiplatelet action and have led to the concept that antiplatelet agents exert their antiinflammatory actions via platelet-related mechanisms. 5 The ADP receptor P2Y12 was originally identified in platelets and in the brain. 6 It is a member of the P2 receptor family, which consists of the ion-channel P2X and the G-protein-coupled P2Y receptors. 7 P2 receptors are activated by the adenine nucleotides ATP and ADP, which can be released from platelets, endothelial cells, sympathetic nerve terminals, and immune cells. 8 P2 receptors have been shown to be involved in a variety of inflammatory processes, such as allergen-driven lung inflammation. 9 In addition, the P2Y12 receptor has been associated with enhanced cell growth in certain brain tumors. 10 Recently, P2Y12 was found to be expressed in vascular smooth muscle cells (SMC), 11 and a role in vessel contraction was suggested. 12 However, no functional changes were seen after thienopyridine tr...

Objective-Diabetes is associated with vascular remodeling and increased thrombin generation. Thrombin promotes vascular smooth muscle cell (SMC) mitogenesis and migration via protease-activated receptors (PAR)-1, PAR-3, and PAR-4. We investigated the effect of high glucose on expression and function of vascular thrombin receptors. Methods and Results-In human vascular SMCs, high glucose (25 versus 5.5 mmol/L) induced a rapid and sustained increase in PAR-4 mRNA, protein, and cell surface expression. PAR-1 and PAR-3 expression were not changed. High glucose pretreatment (48 hours) enhanced thrombin or PAR-4 -activating peptide but not PAR-1-activating peptide evoked intracellular calcium mobilization, migration, and tumor necrosis factor ␣ gene expression. This enhancement of thrombinstimulated migration and gene expression by high glucose was abolished by endogenous PAR-4 knockdown. PAR-4 regulation was prevented by inhibition of protein kinase (PK)C-␤ and -␦ isoforms or nuclear factor (NF)B. Nuclear translocation of NFB in high glucose-stimulated SMCs led to PKC-dependent NFB binding to the PAR-4 promoter in a chromatin immunoprecipitation assay. Furthermore, in situ hybridization and immunohistochemistry confirmed high abundance of PAR-4 in human diabetic vessels as compared with nondiabetic vessels. Key Words: diabetes mellitus Ⅲ thrombin Ⅲ vascular muscle Ⅲ protease-activated receptors C hronically elevated plasma glucose levels in diabetes are associated with cardiovascular complications such as vascular remodeling and poor outcome after revascularization. 1,2 At the cellular level, hyperglycemia is a potent stimulus for the proliferation and migration of vascular smooth muscle cells (SMCs), 3 which are major factors contributing to vascular remodeling and accelerated atherosclerosis. 4 In addition, diabetes represents a hypercoagulable state associated with enhanced thrombin generation and increased risk of thrombotic complications. 5 Thrombin is the central component of the coagulation cascade that becomes activated when vascular injury allows contact between blood-borne components and tissue factor-expressing cells such as fibroblasts and SMCs. 6 However, the overwhelming majority of total thrombin generated is released by the thrombus after clotting is completed, 6,7 indicating functions beyond coagulation. Conclusion-HighThrombin can exert direct coagulation-independent actions such as SMC migration and proliferation through activation of a unique family of G protein-coupled receptors, the protease-activated receptors (PARs). 8 PARs are activated through proteolytic cleavage of the extracellular N terminus, which unmasks a new N terminus that acts as a tethered ligand to autoactivate the receptor. 9 Synthetic hexapeptides mimicking this tethered ligand can elicit most of the biological actions of thrombin independently of receptor cleavage. Of the 4 PARs identified to date, PAR-1, PAR-3, and PAR-4 are activated by thrombin, whereas another receptor, PAR-2, is activated by other proteases such as activa...

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Orellanine is rapidly concentrated in the kidneys in a relatively soluble form and cannot be detected in urine, blood and dialysis fluids at the time when first symptoms appear.