Measurement and modeling of nitric oxide release rates for nitric oxide donors.

An accurate model of the nitric oxide (NO)-release rate is essential for predicting the temporal NO-release rate and resulting NO concentrations for NO donors. Knowledge of the NO-release rate and/or the NO concentration is beneficial for assessing the physiological or pathological effects of NO on cell systems. This study describes a method to measure 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 kinetically 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 modeling the NO-release rate. One model parameter, which is the number of moles 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 other model parameter, which is the NONOate first-order decomposition rate 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 spectrophotometry was consistent with the above value for spermine NONOate but was approximately half the above value for diethylamine NONOate. Preliminary experiments using spectrophotometry showed that for both NONOates the decomposition activation energy was approximately 100 kJ/mol. The NO-release rate model for spermine NONOate was applied to a model for predicting the NO concentration in oxygenated solution. The NO concentration was measured in phosphate buffer, culture medium, and Tyrode's solution. Excellent agreement was observed between experimental and predicted NO concentrations.