Effects of L-arginine and phosphodiesterase-5 inhibitor, sildenafil, on inflammation and airway responsiveness of sensitized BP2 mice

Nitric oxide (NO) levels are elevated in the exhaled breath of asthmatic patients and NO is considered as a biomarker of airway inflammation. However, the functions of NO in the airways are not completely understood. L-arginine, as the substrate of NO synthases, is the precursor of NO which stimulates guanylate cyclase and leads to the formation of cyclic GMP (cGMP). Sildenafil, a phosphodiestérase-5 (PDE-5) inhibitor, prevents the degradation of cGMP. In this study the effects of L-arginine and sildenafil treatment, alone or in combination, were evaluated in ovalbumin-sensitized BP2 mice. These effects concerning the airway responsiveness to inhaled methacholine (MCh) were evaluated by whole-body plethysmography (WBP), the inflammatory response evaluated by bronchoalveolar lavage fluid (BALF) analyses and lung tissue biopsies (eosinophilic inflammation associated with lung remodelling), and NO metabolite measurements (by Griess reaction) in BALF. Ovalbumin sensitization induced: (a) an inflammatory reaction with eosinophil and neutrophil influx in BALF and lung; and (b) an increased bronchial responsiveness to MCh. L-arginine treatment [50 mg/kg intraperitoneally (i.p.), for 7 days] increased the relative amount of eosinophils and neutrophils in BALF, had a tendency to increase the airway responsiveness to inhaled MCh and increased the NO metabolite level in BAL. Sildenafil treatment (20 mg/kg i.p. for 7 days) did not affect the airway responsiveness to MCh and had a lower effect compared with L-arginine on inflammatory reactions. The combination of the two treatments resulted in a dramatic enhancement of the airway responsiveness to inhaled MCh. The relative amount of eosinophils was increased and lung histology showed obvious worsened tissular lesions such as epithelial shedding and hypertrophy, hyperplasia of smooth muscle cells, and fibrosis. These findings are consistent with the notion that NO production plays a role in the development of airway inflammation and hyperresponsiveness of sensitized mice and highlighted the potential risk of the L-arginine dietary complement or PDE5 treatment in asthmatic patients.

Vasopressin V2 (SR121463A) and V1a (SR49059) receptor antagonists both inhibit desmopressin vasorelaxing activity

Although [Arg(8)]vasopressin is a potent vasoconstrictor, it possesses vasorelaxant properties manifested either after vasopressin V1 receptor blockade or directly in some vascular beds. The nature of the receptor involved in the vasorelaxant effect of [deamino-Cys(1) D-Arg(8)]vasopressin (desmopressin), a vasopressin V2 receptor agonist, was studied on rat precontracted aortic rings by the use of highly selective new non-peptide vasopressin receptor antagonists. The present study demonstrates for the first time that desmopressin relaxant effect is antagonized by the vasopressin V2 receptor antagonist SR121463A, but also by the vasopressin V1A receptor antagonist SR49059, suggesting that desmopressin-induced relaxation is mediated by a receptor subtype sharing both V1A and V2 pharmacological profiles.

Contrasting effects of streptozotocin-induced diabetes on the in vitro relaxant properties of adenosine in rat pancreatic vascular bed and thoracic aorta

In the present work, we have studied adenosine-induced vasodilation in streptozotocin-induced diabetic rats and compared it to that observed in normal age-matched or weight-matched animals. Experiments were performed on a vascular bed, the isolated perfused pancreas, and a large vessel, the thoracic aorta, provided from the same animal. Vasodilator activity was assessed, for isolated pancreas, as the increase in flow induced by the infusion of 2 microM adenosine for 30 min, or for noradrenaline-contracted aortae, as the relaxant response to adenosine (1 microM-1 mM). In both preparations the results obtained with selective adenosine receptors ligands (CPA, CGS 21680 and NECA) agreed with the presence of adenosine receptor of A2a subtype. In normal animals, adenosine vasodilator activity on both preparations diminished with advancing age in the rat, while diabetes was associated with a decreased or increased responsiveness to adenosine in pancreatic vascular bed or aorta, respectively. Further, the involvement of nitric oxide (NO), in relaxant responses, was evaluated by the use of the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME). In all groups of animals, the flow rate of isolated pancreas dropped in the presence of 200 microM L-NAME, but was restored by adenosine to the level observed without L-NAME. L-NAME (10 microM) significantly reduced the dilator response to adenosine in aortic rings from diabetic animals, but not in those from normal rats. These results showed that adenosine vasorelaxant activity is significantly but differentially altered by diabetes according to the origin of the vascular preparation, and suggest that NO is involved in the vasorelaxant activity of adenosine in large vessels of diabetic animals. The potential pathophysiological role of adenosine in the vascular complications of diabetes remains to be determined.

New imidazo(1,2-a)pyrazine derivatives with bronchodilatory and cyclic nucleotide phosphodiesterase inhibitory activities

New imidazo[1,2-a]pyrazine derivatives have been synthesized either by direct cyclization from pyrazines or by electrophilic substitutions. The presence of electron donating groups on position 8 greatly enhances the reactivity of the heterocycle towards such reactions on position 3 of the heterocycle. The activities of these derivatives in trachealis muscle relaxation and in inhibiting cyclic nucleotide phosphodiesterase (PDE) isoenzyme types III and IV have been assessed. All compounds demonstrated significantly higher relaxant potency than theophylline. All the derivatives were moderately potent in inhibiting the type IV isoenzyme of PDE but only those with a cyano group on position 2 were potent in inhibiting the type III isoenzyme.

Vanadium levels in French and Californian wines: influence on vanadium dietary intake

An accurate and reproducible method for direct determination of vanadium (V) in wine using graphite furnace atomic absorption spectrometry (GFAAS) is described. This method gave results insignificantly different from those obtained using dry mineralization of wine samples, with a detection limit of 42 pg. A total of 68 wine samples from different regions of France and California were analysed. Vanadium levels ranged from 7.0 to 90.0 micrograms/l in red and from 6.6 to 43.9 micrograms/l in white wines. The method was also adapted to the determination of vanadium levels in 12 grape samples from different varieties after acid mineralization. Vanadium content varied from 2 to 17 micrograms/kg for white and from 5 to 11 micrograms/kg for red varieties. Our data indicate that wine storage conditions may increase vanadium content. The contribution of wine consumption to daily vanadium dietary intake of the French population was estimated to be 11 micrograms/day per individual.