Antithrombotic and vasorelaxant properties of a novel synthetic RGD peptide containing nitric oxide.

We have developed a novel synthetic peptide containing both the antiadhesive Arg-Gly-Asp (RGD) amino acid sequence and a nitric oxide (NO) moiety well known for its vasorelaxant properties. The main objective of this study was to determine whether this hybrid molecule is concurrently effective with regard to antithrombotic and vasorelaxation actions. Studies of in vitro platelet adhesion and of in vivo platelet thrombus formation in the rat demonstrated that the RGD-NO peptide increased the antithrombotic characteristics of the RGD peptide alone. The RGD-NO peptide also caused relaxation of rat aortic rings, while the RGD peptide did not induce relaxation. These characteristics of Ac-RGDC-SNO suggest that this or similar compounds may have potential as effective antithrombotic agents in coronary and peripheral artery disorders.

Platelet aggregation and adhesion during dietary copper deficiency in rats.

The role of dietary copper deficiency in platelet-to-endothelial cell adhesion and in platelet-to-platelet aggregation was studied in vitro. Platelets were obtained from male, weanling Sprague-Dawley rats fed purified diets which were either copper-adequate (CuA, 6.3 micrograms copper/g of diet) or copper-deficient (CuD, 0.3 microgram/g of diet) for 4 weeks. The platelet adhesion study was performed by adding CuA or CuD platelets either suspended in homologous plasma or in Tyrode buffer salt solution (TBSS) to cultured rate endothelial cells. After a one hour incubation at 37 degrees C non-adhered platelets were removed and counted in a microcytometer. Platelet aggregation in platelet rich plasma (PRP) samples was induced by adding ADP (2 x 10(-4)M) and measured in a turbidometric aggregometer. The content of von Willebrand factor (vWF) in platelets and in plasma and the content of fibrinogen in platelets was determined. Platelet adhesion to rat endothelial cells was significantly lower for platelets from CuD rats than for platelets from CuA rats. ADP induced platelet aggregation from CuD rats was significantly higher than platelet aggregation from CuA rats. The content of vWF in platelets and in plasma from CuD rats was significantly lower than in platelets and plasma from CuA rats. However, the amount of fibrinogen in platelets from ++CuD rats was about 4-fold higher than that in platelets from CuA rats while the plasma fibrinogen was lower in CuD rats than in CuA rats. These studies illustrate that copper deficiency diminishes platelet adhesion to endothelial cells but increases platelet aggregability. The results suggest that these physiological alterations may be the result of decreased platelet vWF and increased platelet fibrinogen during dietary copper deficiency.

L-arginine restores cholesterol-attenuated microvascular responses in the rat cremaster.

The role of L-arginine in the reversal of cholesterol-induced endothelial dysfunction was studied in the cremaster muscle microcirculation. In vivo television microscopy was used to measure microvascular diameters and macromolecular leakage. Male Sprague-Dawley rats were fed either a normal chow diet or a diet supplemented with 1% cholesterol and 0.5% cholic acid for 3 weeks prior to in vivo experimentation. The cholesterol diet caused a decreased third-order arteriole dilator response to both acetylcholine and serotonin. This decreased responsiveness occurred in the presence of a higher plasma concentration of L-arginine and an increased ratio of L-arginine to its metabolite L-citrulline. The attenuation to both agonists was reversed by intravenous infusion of the nitric oxide precursor L-arginine (30-mg/kg bolus and 10-mg/kg/min continuous infusion). The cholesterol diet also decreased the postcapillary macromolecular leakage response to serotonin, and again this effect was reversed by L-arginine infusion. D-Arginine infusion had no restorative effect with either agonist in the cholesterol animals. Further experimentation with the nitric oxide production inhibitor N omega-nitro-L-arginine methyl ester demonstrated an inhibition of aretriolar dilation to acetylcholine, but there was no inhibition of dilation or macromolecular leakage to serotonin. Thus, it is probable that serotonin-induced leakage as well as dilation was not caused by stimulation of nitric oxide. These results suggest that L-arginine restores both nitric oxide-dependent and -independent dilation as well as macromolecular leakage in cholesterol-fed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

[Changes of blood flow structure in precapillary microvessels during significant slow-down of flow]. / Izmeneniia v strukture potoka krovi v mikrososudakh prekapilliarnogo tipa pri ego zhachitel'nom zamedlenii.

The experiments were carried out with a special "biological model" in which the rabbits' red blood cell suspension possessing low hematocrit circulated in frogs' mesenterial microvessels. Red blood cell behaviour was investigated in microvessels of 19-45 microns in diameter under conditions of arbitrarily changed flow velocity in mesenterial microvessels. Automatic frame-to-frame analysis of cinematographic films with the texture analysis system (Ernst Leitz, FRG) showed that the velocity fluctuations of individual red blood cells and their radial displacements increased significantly, while their velocity profile became blunt, during slowing-down of flow from 0.7 to 0.2 mm/s. Thus the normal blood flow structure in microvessels becomes disordered under ischemic conditions entailing disturbance of blood rheological properties and creating additionally increased resistance in the vessels.

[Study of the trajectory of erythrocyte movement in microvessels using a method of automatic image analysis]. / Izuchenie traektorii dvizheniia éritrotsitov v mikrososudakh s pomoshch'iu metoda avtomaticheskogo analiza izobrazhenii.

Many physiological and pathological processes in the circulation are related to changes of blood rheological properties. Since blood represents a specific suspension of cells in plasma the mentioned changes are to a great degree dependent on behavior and interaction of red blood cells (RBC). For investigation of blood flow structure in microvessels we developed an algorithm and worked out a program for automatic treatment of RBC movement on the basis of automatic image analysis system "Leitz-TAS" (Ernst Leitz, FRG). The program was based on computation of coordinates of blood cell centers. Further we calculated the following values: the vector of displacements (S), its projection on both axes (dx, dy), their relationship (dy/dx), the relationship of RBC radial coordinate to vessel radius (y/R), and the velocity of RBC movements (V). Proceeding from these data we obtained such parameters, as e.g., the velocity profile, the radial displacements of red cells, etc. by which we could judge on the blood flow regime, the flow structure and changes of blood rheological properties.

[Velocity profiles in the microvessels dependent on the velocity and concentration of erythrocytes]. / Profil' skorostei v mikrososudakh v zavisimosti ot skorosti dvizheniia i kontsentratsii éritrotsitov.

Distribution of velocities of erythrocytes dependent upon their distance from the vascular axis were studied in 25-40 mu large microvessels of the frog mesentery. The method of in vivo cinemicrography with subsequent analysis revealed that with a mean axial velocity of blood flow higher than 0.3-0.4 mm/sec the velocity profile was parabolic, similar to the laminar flow of Newtonian fluids and independent of the erythrocytes concentration in microvessels. With velocities less than 0.3-0.4 mm/sec a chaotic distribution of erythrocytes velocities occurred and the parabolic form of the velocity profiles was rarely observed;--actually only at low erythrocyte concentration (less than 10-11%) in microvessels. The results suggest that an increase in vascular resistance to blood flow must appear during a considerable slow-down of blood flow velocity in microvessels.