MEASUREMENT AND MODELING OF NITRIC-OXIDE RELEASE RATES FOR NITRIC-OXIDE DONORS

An accurate model of the nitric oxide (NO)-release rate is essential f or predicting the temporal NO-release rate and resulting NO concentrat ions for NO donors. Knowledge of the NO-release rate and/or the NO con centration is beneficial for assessing the physiological or pathologic al effects of NO on cell systems. This study describes a method to mea sure the temporal NO-release rate from NO donor compounds utilizing a modified ultrafiltration cell. For this study, the NO-release rates of spermine NONOate and diethylamine NONOate were measured and kinetical ly modeled at pH 7.4 and 37 degrees C. An advantage of this method is that complete dissolution of the NONOate was not necessary for modelin g the NO-release rate. One model parameter, which is the number of mol es of NO released per mole of decomposed NONOate, is 1.7 +/- 0.1 and 1 .5 +/- 0.2 for spermine and diethylamine NONOate, respectively. The ot her model parameter, which is the NONOate first-order decomposition ra te constant, is 0.019 +/- 0.002 min(-1) and 0.47 +/- 0.10 min(-1) for spermine and diethylamine NONOate, respectively, as determined from NO concentration profiles. The decomposition rate constant measured by s pectrophotometry was consistent with the above value for spermine NONO ate but was approximately half the above value for diethylamine NONOat e. Preliminary experiments using spectrophotometry showed that for bot h NONOates the decomposition activation energy was similar to 100 kJ/m ol. The NO-release rate model for spermine NONOate was applied to a mo del for predicting the NO concentration in oxygenated solution. The NO concentration was measured in phosphate buffer, culture medium, and T yrode's solution. Excellent agreement was observed between experimenta l and predicted NO concentrations.