You can also use enhancer cells (modified USP2 dissolution model), see the following publication by Pankaj R. Rege and al: Development in release testing of topical dosage forms: Use of the Enhancer Cell(TM) with automated sampling. Journal of Pharmaceutical and Biomedical Analysis 17(8):1226-33, september 1998
For the quantification of nitric oxide you can use a method that determines nitric oxide concentrations based on the enzymatic conversion of nitrate to nitrite by nitrate reductase followed by colorimetric detection of nitrite (Griess Reaction) , you can find assay kit for determination of nitric oxide in biological samples (urine, serum, plasma..)