A platinum electrode was modified with electropolymerized films of 4-allyl-2-methoxyphenol (eugenol) by its oxidative polymerization from an alkaline solution by cyclic voltammetry. The modified electrode was than used to determine dopamine (DA) in an excess of ascorbic acid (AA) by differential pulse voltammetry. The peak positions as well as relative sensitivity DA/AA were affected by the potential window applied for the polymerization. For polymerization between 0 and 2.2 V, the peak potentials recorded in a phosphate buffer solution (pH 7.4) were -61 and +152 mV vs Ag/AgCl for AA and DA, respectively. After a 5-min equilibration, relative sensitivity DA/AA was 164 and the current sensitivity for DA was 7.9 nA μM(-)(1). The detection limit for S/N = 3 is 0.1 μM. The high selectivity and sensitivity for DA was found to be due to charge discrimination/analyte accumulation and an effect of catalytic mediation of redox sites. Chronocoulometric data reveal that DA is accumulated on the electrode as a monolayer. The electrode is stable, reversible, and free of fouling problems.

Huge advances achieved recently in elucidating the role of NO in plants have been made possible by the application of NO donors. However, the application of NO to plants in various forms and doses should be subjected to detailed verification criteria. Not all metabolic responses induced by NO donors are reliable and reproducible in other experimental designs. The aim of the presented studies was to investigate the half-life of the most frequently applied donors (SNP, SNAP and GSNO), the rate of NO release under the influence of light and reducing agents. At a comparable donor concentration (500 microM) and under light conditions the highest rate of NO generation was found for SNAP, followed by GSNO and SNP. The measured half-life of the donor in the solution was 3 h for SNAP, 7 h for GSNO and 12 h for SNP. A temporary lack of light inhibited NO release from SNP, both in the solution and SNP-treated leaf tissue, which was measured by the electrochemical method. Also a NO, selective fluorescence indicator DAF-2DA in leaves supplied with different donors showed green fluorescence spots in the epidermal cells mainly in the light. SNP as a NO donor was the most photosensitive. The activity of PAL, which plays an important role in plant defence, was also activated by SNP in the light, not in the dark. S-nitrosothiols (SNAP and GSNO) also underwent photodegradation, although to a lesser degree than SNP. Additionally, NO generation capacity from S-nitrosothiols was shown in the presence of reducing agents, i.e. ascorbic acid and GSH, and the absence of light. The authors of this paper would like to polemicize with the commonly cited statement that "donors are compounds that spontaneously break down to release NO" and wish to point out the fact that the process of donor decomposition depends on the numerous external factors. It may be additionally stimulated or inhibited by live plant tissue, thus it is necessary to take into consideration these aspects and monitor the amount of NO released by the donor.

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Most patients with diabetes also have hypertension, a risk factor associated with atherothrombotic disease and characterized by endothelial cell (EC) dysfunction and loss of nitric oxide (NO) bioavailability. Recent studies suggest a possible antihypertensive effect with dipeptidyl peptidase-4 (DPP4) inhibition; however, the underlying mechanism is not understood. In this study, we tested the effects of the DPP4 inhibitor, saxagliptin, on EC function, blood pressure, and soluble intercellular adhesion molecule 1 (sICAM-1) levels in hypertensive rats. Spontaneously hypertensive rats were treated with vehicle or saxagliptin (10 mg·kg(-1)·day(-1)) for 8 weeks. NO and peroxynitrite (ONOO(-)) release from aortic and glomerular ECs was stimulated with calcium ionophore and measured using electrochemical nanosensor technology. Changes in EC function were correlated with fasting glucose levels. Saxagliptin treatment was observed to increase aortic and glomerular NO release by 22% (P < 0.001) and 23% (P < 0.001), respectively, with comparable reductions in ONOO(-) levels; the NO/ONOO(-) ratio increased by >50% in both EC types (P < 0.001) as compared with vehicle. Saxagliptin also reduced mean arterial pressure from 170 ± 10 to 158 ± 10 mm Hg (P < 0.001) and decreased sICAM-1 levels by 37% (P < 0.01). The results of this study suggest that DPP4 inhibition reduces blood pressure and inflammation in hypertensive rats while increasing NO bioavailability.