Influence of Nanosilver on Endothelial Function and Vascular Reactivity of Isolated Rabbit Carotid Artery.

There is paucity of information on the effects and mechanism of action of Nanosilver on vascular tone andendothelial function in spite of the upsurge in nanotechnology application in biomedicine. The present study determined theeffect of Nanosilver on vascular reactivity and endothelial function on isolated rabbit carotid artery in standard laboratory20 mL organ bath procedures containing physiological salt solution (PSS) bubbled with 95% O2, 5% CO2. Isometriccontractions were recorded electronically with a 4-channel Grass Polygraph and maintained at 37oC and pH7.4. Cumulativedose response tests to α-receptor agonist phenylephrine (PE) was examined separately, in normal PSS (control) and following20 minutes exposure to varying concentrations of Nanosilver solution [(NAgs) (1.25 and 2.50)] µg/mL in endothelium intact(+E) (control) and endothelium denuded (-E) rings. Contractile responses were analysed with reference to maximalcontractions induced by 8 x 10-2 M K+ in normal PSS. In another experiment, arterial rings were precontracted with EC70 MPE, high and /or low (8, 2 x 10-2) M K+PSS. At stable contractions, cumulative relaxation responses to NAgs was studied.Relaxation responses were analysed with reference to maximal contraction induced by EC70 M PE and/or K+ depolarizationin normal PSS. Following 20 minutes exposure to NAgs, dose relaxation response to acetylcholine (ACh) was also examinedin normal PSS (control), and pre-incubated L-NAME (NO synthase inhibitor) and indomethacin (cyclooxygenase inhibitor)precontracted arterial rings to further determine mechanisms of action. Data were presented as Means ± SEM. Graphs andstatistical analysis were done using GraphPad prism version 7.03 and Student t-test. P-values (P< 0.05) were consideredstatistically significant. The results showed that nanosilver decreased maximum contraction (Emax) and induced attenuatedcontractile and relaxation responses concentration-dependently in +E and -E carotid arterial rings. Also, Nanosilver-inducedrelaxation in α- receptor mediated contraction is endothelium-dependent and showed a biphasic dose-dependent response. Inconclusion, Nanosilver causes attenuation in carotid arterial smooth muscle reactivity with a biphasic dose-dependentrelaxant effect and multiple endothelium-dependent pathways mode of action.