Background-Platelet activation is a feature of many cardiovascular diseases characterized by endothelial dysfunction.The mechanistic relationship between impaired systemic nitric oxide (NO) bioavailability and platelet activation in vivo remains unclear. We investigated whether acute inhibition of NO production in humans modulates platelet activation in vivo and whether exogenous NO would counteract such an effect. Methods and Results-Intravenous injection of the NO synthase inhibitor N G -monomethyl-L-arginine in healthy volunteers resulted in NO synthase inhibition as detected by increased blood pressure and by significantly reduced phosphorylation of platelet vasodilator-stimulated phosphoprotein, an indicator of NO signaling. NO synthase inhibition increased platelet activation as determined by enhanced platelet binding of fibrinogen and surface expression of P-selectin, glycoprotein 53, and CD40 ligand, demonstrating tonic inhibition of platelet activation by NO production in vivo. Sublingual administration of the NO donor glyceryl trinitrate normalized platelet VASP phosphorylation and restored markers of platelet activation to baseline levels. Conclusions-Acute inhibition of endogenous NO production in humans causes rapid platelet activation in vivo, which is reversed by exogenous NO, demonstrating that platelet function in vivo is rapidly regulated by NO bioavailability. Key Words: glycoproteins Ⅲ nitric oxide Ⅲ P-selectin Ⅲ phosphoproteins Ⅲ platelets N itric oxide (NO), generated by NO synthase (NOS), inhibits platelet activation 1 as demonstrated by in vitro experiments such as inhibition of platelet aggregation by endothelial cells 2 or NO donors. 3,4 NO can even reverse agonist-induced activation of glycoprotein IIb/IIIa. 5 Chronic inhibition of NO formation in animal models is associated with impaired fibrinolysis and enhanced thrombin and tissue factor generation. 6 Previous reports described increased platelet activation in disease states with impaired NO bioavailability such as acute coronary syndromes, 7 heart failure, 8 diabetes, 9 and hypercholesterolemia. 10 However, the direct relationship between NO bioavailability and platelet activation in humans remains unclear.NO-dependent phosphorylation of vasodilator-stimulated phosphoprotein (VASP) is an essential regulatory component in the inhibition of platelet activation and correlates with inhibition of fibrinogen binding to glycoprotein IIb/IIIa, 11,12 P-selectin expression, and platelet adhesion. 13 With specific antibodies, VASP phosphorylation provides a sensitive monitor of defective NO/cGMP signaling, and reduced NO bioavailability in several pathophysiological states correlates with reduced VASP phosphorylation. 14 In the present study, we investigated whether acute changes in NO bioavailability in healthy human volunteers would affect platelet activation as determined by activity of the fibrinogen receptor and platelet degranulation. MethodsVenous blood was taken from 12 healthy nonsmoking male donors (age, 29Ϯ1.3 years) resting in a s...

Phosphorus was imaged in vivo in human cortical and trabecular bone and the T 1 and T* 2 were measured. An ultrashort TE (UTE) pulse sequence (TE ‫؍‬ 70 m) was used with half pulse excitation and radial mapping of k-space from the center out. T* 2 was measured using multiple echo times and T 1 was measured both by saturation recovery and by a method using different RF pulse amplitudes. Seven normal subjects (32-85 years) were examined. Phosphorus was imaged, with a true in-plane resolution of 2.9 ؋ 2.9 mm and a signal-to-noise ratio (SNR) of 19:1, in both cortical and trabecular bone. The mean T* 2 value was 207 ؎ 12 s, and the mean T 1 value was 8.6 ؎ 3.0 sec. Although in vivo phosphorus imaging of bone has been achieved in tissues samples and animals (1-4), translating these results into clinical studies is a challenge and as yet only a single in vivo human imaging example has been presented (5), which required the use of custom-made hardware. The main difficulties arise from the fact that the T 2 of phosphorus in bone is very short, its T 1 is long, and it is present in much lower concentration than protons. In order to address the problem of the short T 2 , we implemented an ultrashort TE (UTE) pulse sequence with a TE of 0.07 ms. Using this sequence we performed exploratory studies in human volunteers to assess the feasibility of imaging phosphorus in both cortical and trabecular bone on a clinical system, as well as measuring its relaxation times. SUBJECTS AND METHODSInstitutional Review Board permission was obtained for this study. All data were acquired on a 1.5T Siemens Sonata MR system (Siemens, Erlangen, Germany) equipped with multinuclear capabilities and high gradient performance (peak 40 mT/m, slew rate 200 T/m/s). A standard phosphorus heart/liver optimized coil was used. This had a large relatively homogeneous RF transmit coil (29 ϫ 29 cm) as well as a smaller (12 ϫ 22 cm) butterfly and (14 ϫ 12 cm) loop coil pair which gave a smaller sensitive reception region. Proton imaging used the transmit coil described above for both transmission and reception. Proton imaging utilized conventional gradient echo images for slice positioning and a T 1 -weighted ultra-short TE acquisition with a TE of 1 ms. Phosphorus ImagingThe basic ultrashort TE (UTE) pulse sequence is based on a ramp-sampled radial acquisition (6,7) and has been used previously for proton imaging (8 -11). The UTE method is a gradient echo-based approach that starts at the center of k-space, consequently there is no "echo" as such and so the use of the term "echo time" (TE) may be confusing. In this context we follow recent convention (8 -11) by using the TE to describe the T 2 weighting of the sequence. The pulse sequence was implemented at the 31 P operating frequency at 1.5T of 25.4MHz. The RF excitation was performed using a half pulse with the data acquisition beginning at the center of k-space and extending radially (see Fig. 1). A second RF half pulse excitation is then performed with a reversed slice selection gradient. During the ...

Objective-Platelet activation is a feature of cardiovascular disease that is also characterized by endothelial dysfunction.The direct relationship between impaired endothelium-derived NO bioavailability and platelet activation remains unclear. We investigated whether acute inhibition of NO production modulates platelet activation in mice and whether specific rescue of endothelial function in diabetes modifies platelet activation. Methods and Results-Intravenous injection of the NO synthase inhibitor N G -nitro-L-arginine methyl ester in wild-type (WT) mice significantly reduced platelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation and increased platelet surface expression of P-selectin, CD40 ligand, and fibrinogen platelet binding, demonstrating that NO production exerts tonic inhibition of platelet activation in mice. Diabetes was induced by streptozotocin injection in WT or endothelial-targeted guanosine 5Ј-triphosphate cyclohydrolase I (GCH)-transgenic (GCH-Tg) mice protected from endothelial dysfunction in diabetes by sustained levels of tetrahydrobiopterin in vascular endothelium. Platelet VASP phosphorylation was significantly reduced in diabetic WT but not in diabetic GCH-Tg mice. P-selectin, CD40 ligand expression, and fibrinogen binding were increased in diabetic WT mice but remained unchanged compared with controls in endothelial-targeted GCH-Tg mice. Key Words: diabetes Ⅲ endothelial nitric oxide synthase Ⅲ platelets Ⅲ endothelial dysfunction T he endothelium plays a crucial role in control of vascular tone by releasing endothelium-derived autocoids, the most important of which is NO, 1 generated by endothelial NO synthase (eNOS). NO also inhibits platelet activation, adhesion and aggregation; reduced NO bioactivity is associated with arterial thrombosis in animal models and in individuals with endothelial dysfunction. 2 The importance of NO in platelet function was shown by in vitro experiments such as inhibition of platelet aggregation by endothelial cells 3 or NO donors. 4,5 NO formation inhibition causes platelet activation, 6 and exogenous NO can even reverse agonist-induced activation of platelet glycoprotein (GP) IIb/IIIa. 7 The finding that platelets adhere to dysfunctional endothelium and that expression of potential adhesion molecules is enhanced under these conditions suggests that NO may modulate platelet activation in vascular disease states. 8 We demonstrated recently that inhibition of systemic NO formation in healthy humans rapidly induces platelet activation, an effect that could be reversed by exogenous NO. 6 Indeed, increased platelet activation is observed in diseases characterized by chronic endothelial dysfunction such as acute coronary syndromes, 9 congestive heart failure, 10,11 diabetes, 12,13 and hypercholesterolemia. 14 In patients with advanced atherosclerosis, impaired endotheliumdependent release of NO leads to reduced platelet cGMP formation. 15 It remains uncertain whether endothelial-derived NO has a more important role in tonic suppression of platelet ...

31P-MR spectroscopy with SLOOP allows a non-invasive, quantitative analysis of cardiac energy metabolism.

The aim of this study was to measure the concentration of creatine in Langendorff perfused rat hearts, both by quantitative 1 H-MRS and by high-pressure liquid chromatography (HPLC). First, the relaxation times and other parameters affecting absolute quantification by MRS were determined. At 11.75 T, the relaxation times of myocardial creatine were T 1 ‫؍‬ 1.1 ؎ 0.29 sec (mean ؎ SD, n ‫؍‬ 5) and T 2 ‫؍‬ 56.4 ؎ 6.2 ms (n ‫؍‬ 9). In phantom experiments the MRS measurements gave accurate values for the known relative concentrations of the detected substances. In glucose-perfused rat hearts, the creatine concentration measured by HPLC was 14.2 ؎ 1.9 mmol/kg wet weight (n ‫؍‬ 8), in good agreement with literature values. The signals of a number of metabolites can be observed in 1 H-MRS spectra acquired in the heart. They reflect the physiologic status of the tissue and may be of diagnostic value. The resonances of lactate and lipids are sensitive indicators of the biochemical status. Reduced oxygen supply leads to an elevated lactate signal (1-5). Alterations of lipid signals after myocardial infarction have been observed in dogs (6 -10), in rats (11), and in humans (12). Due to the important role of creatine in myocardial energy metabolism, the resonance at 3.02 ppm, commonly assigned to total creatine (both phosphorylated and unphosphorylated creatine), is of particular interest (13-16). The purpose of this study was to measure the creatine (Cr) content in isolated rat hearts by quantitative 1 H-MRS and by chemical analysis (HPLC). Phantom experiments were conducted to establish methods for absolute quantification. For the heart measurements, longitudinal and transverse relaxation times at 11.75 T and other relevant parameters intervening in absolute quantification were determined. To assess reproducibility, repeated measurements were performed. Finally, the influence of CHESS water suppression on the Cr-methyl resonance was investigated. MATERIALS AND METHODS Absolute QuantificationThe 1 H-MRS experiments were implemented on a Bruker AMX 500 instrument at 11.75 T. All quantitative measurements used the slice-selective spin-echo pulse sequence shown in Fig. 1. Water suppression was achieved with a binomial refocusing pulse, with adjusted to obtain maximum sensitivity either for creatine ( ϭ 570 s) or TSP ( ϭ 170 s). Additional water suppression could be obtained with three optional CHESS pulses. The slice thickness was always 2.1 mm, the echo time TE 16 ms, the repetition time TR 10 sec. For absolute quantification, a 75-mM solution of 3-(trimethylsilyl) propionic-2,2,3,3-d 4 -acid sodium salt (TSP, Sigma-Aldrich Chemie GmbH, Deisenhofen, Germany) in water, doped with 1 mM Gd-DTPA to shorten relaxation times, was used as external concentration reference. The absolute concentration of Cr was determined from the signal amplitudes A of Cr and TSP:where V Myo and V TSP are the sampled volumes of the myocardium and TSP solution, the factor 3 reflects the relative number of protons contributing to the TSP and Cr peaks, k ...

Based on our data ejaculation does not affect serum PSA concentration in young men, and there seems to be no physiological relationship between ejaculation and PSA level.

Based on our data ejaculation does not affect serum PSA concentration in young men, and there seems to be no physiological relationship between ejaculation and PSA level.

No abstract