Nonspecific microvascular vasodilation during iontophoresis is attenuated by application of hyperosmolar saline

Iontophoretic administration of acetylcholine chloride (ACh) and sodium nit roprusside (SNP) combined with laser Doppler skin blood perfusion measureme nts are used for determination of endothelial-dependent and -independent va sodilation. However, the method is biased by nonspecific vasodilation. The primary aim of this study was to investigate if iontophoresis-induced nonsp ecific vasodilation may be attenuated by addition of high molar concentrati ons of NaCl to the iontophoresis solutions. Secondary we investigated the a pplicability of 5 mol/liter NaCl solution as vehicle for ACh and SNP in thi s method. Skin perfusion changes were determined for iontophoresis of pure vehicles, deionized water and 5 mol/liter NaCl solution, in 12 healthy volu nteers. Responses in skin perfusion to iontophoresis of ACh and SNP dissolv ed in both vehicles were also investigated. Addition of 5 mol/liter NaCl to deionized water significantly attenuated the nonspecific vasodilation and lowered the potential applied over the skin. The inter- and intraindividual coefficients of variation to ACh and SNP responses became, however, higher using hyperosmolar vehicle. During iontophoresis of SNP (in deionized wate r) we were unable to distinguish between SMP and vehicle effects. This stud y shows that the nonspecific vasodilation induced by iontophoresis can be a ttenuated by addition of 5 mol/liter NaCl, possibly due to lower electrical potential over the skin. However, the variability of the method was not im proved. When deionized water was used as vehicle the effect of SNP could no t be differentiated from that of the vehicle. This was not the case for ACh . (C) 1999 Academic Press.