Relaxation of thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) by endothelium-derived 6-nitrodopamine

6-Nitrodopamine is a novel catecholamine released by vascular tissues, heart, and vas deferens. The aim of this study was to investigate whether 6-nitrodopamine is released from the thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) and to evaluate the relaxing and anti-contractile actions of this catecholamine. Release of 6-nitrodopamine, dopamine, noradrenaline, and adrenaline was assessed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The relaxations induced by 6-nitrodopamine and by the selective dopamine D2 receptor antagonist L-741,626 were evaluated on U-46619 (3 nM)-pre-contracted vessels. The effects of 6-nitrodopamine and L-741,626 on the contractions induced by electric-field stimulation (EFS), dopamine, noradrenaline, and adrenaline were also investigated. Both aorta and pulmonary artery rings exhibited endothelium-dependent release of 6-nitrodopamine, which was significantly reduced by the NO synthesis inhibitor L-NAME. Addition of 6-nitrodopamine or L-741,626 caused concentration-dependent relaxations of both vascular tissues, which were almost abolished by endothelium removal, whereas L-NAME and the soluble guanylate cyclase inhibitor ODQ had no effect on 6-nitrodopamine-induced relaxations. Additionally, pre-incubation with 6-nitrodopamine antagonized the dopamine-induced contractions, without affecting the noradrenaline- and adrenaline-induced contractions. Pre-incubation with L-741,626 antagonized the contractions induced by all catecholamines. The EFS-induced contractions were significantly increased by L-NAME, but unaffected by ODQ. Immunohistochemical assays showed no immunostaining of the neural tissue markers S-100 and calretinin in either vascular tissue. The results indicated that 6-nitrodopamine is the major catecholamine released by marmoset vascular tissues, and it acts as a potent and selective antagonist of dopamine D2-like receptors. 6-nitrodopamine release may be the major mechanism by which NO causes vasodilatation.

Analysis of five streptokinase formulations using the euglobulin lysis test and the plasminogen activation assay

Streptokinase, a 47-kDa protein isolated and secreted by most group A, C and G ß-hemolytic streptococci, interacts with and activates human protein plasminogen to form an active complex capable of converting other plasminogen molecules to plasmin. Our objective was to compare five streptokinase formulations commercially available in Brazil in terms of their activity in the in vitro tests of euglobulin clot formation and of the hydrolysis of the plasmin-specific substrate S-2251Õ. Euglobulin lysis time was determined using a 96-well microtiter plate. Initially, human thrombin (10 IU/ml) and streptokinase were placed in individual wells, clot formation was initiated by the addition of plasma euglobulin, and turbidity was measured at 340 nm every 30 s. In the second assay, plasminogen activation was measured using the plasmin-specific substrate S-2251Õ. StreptaseÕ was used as the reference formulation because it presented the strongest fibrinolytic activity in the euglobulin lysis test. The UnitinaseÕ and SolustrepÕ formulations were the weakest, showing about 50 percent activity compared to the reference formulation. All streptokinases tested activated plasminogen but significant differences were observed. In terms of total S-2251Õ activity per vial, StreptaseÕ (75.7 ± 5.0 units) and StreptonaseÕ (94.7 ± 4.6 units) had the highest activity, while UnitinaseÕ (31.0 ± 2.4 units) and StrekÕ (32.9 ± 3.3 units) had the weakest activity. SolustrepÕ (53.3 ± 2.7 units) presented intermediate activity. The variations among the different formulations for both euglobulin lysis test and chromogenic substrate hydrolysis correlated with the SDS-PAGE densitometric results for the amount of 47-kDa protein. These data show that the commercially available clinical streptokinase formulations vary significantly in their in vitro activity. Whether these differences have clinical implications needs to be investigated.

Evaluation of two different oxygen inspiratory fractions on the hemodynamic effects of No-nitro-L-arginine methyl ester in anesthetized dogs

The effect of two different oxygen inspiratory fractions (FiO2 = 21 percent and 100 percent) on the hemodynamic responses induced by N(omega)-nitro-L-arginine methyl ester (L-NAME) was investigated in anesthetized dogs. L-NAME (0.01-10.0 mg/kg), but not D-NAME, induced dose-dependent changes in the hemodynamic parameters of the animals. At the highest dose, L-NAME increased mean arterial blood pressure in both room air (from 86.2 +/- 3.2 to 125.1 +/- 7.8 mmHg) and pure oxygen (from 100.0 +/- 7.5 to 139.0 +/- 3.2 mmHg) ventilated animals. L-NAME also increased systemic and pulmonary vascular resistances. These effects were accompanied by a decrease in cardiac output and bradycardia (37 percent and 31 percent decreases for pure oxygen and room air, respectively). However, there were no significant differences in the responses to L-NAME between the dogs ventilated with FiO2 = 21 percent and those ventilated with FiO2 = 100 percent. L-NAME did not modify blood gas analyses, despite the expected difference in PO2 levels between the two experimental groups of animals (3 times higher in the animals ventilated with pure oxygen). These results indicate that nitric oxide release accounts for the maintenance of hemodynamic function in the anesthetized dog, and that L-NAME-induced effects are not affected by hyperoxemia.

The kinetics of chondroitin 4-sulfate release from stimulated platelets and its relation to thromboxane A2 formation and granule secretion

1. In platelet rich plasma (PRP), chondroitin 4-sulfate release from platelets occurred after stimulation with ADP (5µM), collagen (5-10µM). Release started within 60 s and maximum release (0.7-2.0 mg/l) was reached within 180 s. TXA2 formation and dense granule release reached a maximum within 90 s after stimulation. 2. Using washed platelets (1.5 x 10**8 cells/ml), the platelet responses were faster. Release of chondroitin 4-sulfate and TXA2 started within 20-30 s after thrombin addition (100 mU/ml). Maximum release was reached within 60 s in both cases. Dense granule release started in the first 5 s of stimulation (34.6 ñ 12.4 por cento) reaching maximum secretion (74.4 ñ 8.7 por cento) within 60 s. 3. Our results demonstrate that maximal chondroitin 4-sulfate release occurs after the dense granule release reaction in both PRP and washed platelets. This observation suggests that chondroitin 4-sulfates is unlikely to be stored in the dense granules but may be stored in the alfagranules

Measurement of plasma verapamil levels by high-performance liquid chromatography

1. We have developed an alternative procedure for the measurement of verapamil levels in human plasma by reverse-phase high performance liquid chromatography with fluorimetric detection. 2. Prior to assay, plasma is submitted to a double extraction procedure, using first n-heptane in alkaline medium and then an acid phosphate buffer. Flecainide, a compound not related to verapamil, is used as internal standard. Mean recoveries of 70 and 63 per cent were obtained for verapamil and flecainide, respectively. 3. The sensitivity (5 ng/ml), reproducibility (inter-assay per cent CV = 1.7-8.7; intra-assay per cent CV = 2-4) and high recovery during sample clean-up make this method useful for the quantitation of verapamil in therapeutic monitoring and pharmacokinetic studies. 4. The method is illustrated with the pharmacokinetic results obtained for 14 healthy male volunteers who received a single 240 mg dose of the commercially available tablets of Dilacoron Retard 240 mg. The mean values for the area under the curve from 0 to 24 h (AUC[0-24]), maximum achieved concentration (Cmax) and time to achieve the maximum concentration (Tmax) were 863 ng h-1 ml-1, 112 ng/ml and 4 h, respectively

Effects of Phoneutria nigriventer venom on rabbit vascular smooth muscle

1. The effects of Phneutria nigriventer venom (PNV) on rabbit vascular smooth muscle have been investigated. De-endothelialized vascular strips were superfused in a cascade system with oxygenated (95 per cent O2 + 5 per cent CO2) Krebs solution at 37 degrees C. 2. Phoneutria nigriventer venom (0.3-30 micrograms) produced dose-dependent and short-lived contractions of both venous (cava, mesenteric and jugular veins) and arterial (pulmonary and mesenteric arteries) tissues. 3. Methysergide (5.0 microM) did not significantly affect PNV-induced contractions in venous tissues (cava and mesenteric veins) or pulmonary artery, indicating that serotonin is not involved in the contraction. This was confirmed when PNV was dialyzed (24-48 h) since the contracting activity was still observed on the above tissues. In addition, the spasmogenic activity induced by dialyzed PNV was greatly reduced by incubating the venom with trypsin. 4. Neither tetrodotoxin (3.0 microM) nor phenoxybenzamine (0.05 microM) significantly affected PNV-induced contractions, suggesting that voltage-dependent sodium channel activation or endogenous catecholamine release from autonomic nerve endings on the vascular walls do not play a role in the response to PNV. 5. Our results demonstrate that PNV contains non-dialyzable components, probably peptides, that are responsible for the contractile activity on rabbit veins and pulmonary artery strips

Biovailability of four pharmaceutical formulations of metronidazole tested on normal healthy volunteers

1. Single doses of four metronidazole formulations (the unmarketed Trichomol, 200 mg, 200 mg, 400 mg, 500 mg, and the commercially available Flagyl, 400 mg) were administered to 14 healthy adult male volunteers in order to determine their pharmacokinetic profiles. 2. Plasma metronidazole concentrations were measured by high pressure liquid chromatography. The results were plotted against time and the curves obtained were used to calculate pharmacokinetic parameters ( area under the curves, maximun achieved concentration and time at which it occurred, elimination constant, and half-life). 3. Trichomol formulations of 200 mg and 500 mg significantly differed from the 400 mg formulation with respect to area under the curve and maximum concentration. Trichomol 400 mg and Flagyl 400 mg showed no significant differences in maximum concentration or area under the curve. No differences were observed in half-life or time of appearance of maximum concentration among formulations. 4. Good correlations occurred between maximum concentration, area under the curve and amount of metronidazole ingested, indicating a linear pharmacokinetic profile. 5. We conclude that Trichomol 400 mg proved to be bioequivalent to the commercially available reference Flagyl 400 mg according to U.S. Food and Drug Adminsitration requirements