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Nitrates act as donors of nitric oxide (NO), a molecule with a recognized potential for genotoxicity. In order to assess whether chronic long-term nitrate therapy may increase genotoxicity, we evaluated chromosomal damage in peripheral lymphocytes of 27 ischaemic patients undergoing chronic nitrate treatment for vertical line4 years (7.9 +/- 3.1, mean +/- SD) and 18 age- and sex-matched subjects without any previous nitrate treatment. At the same time, after treatment in vitro with 0-20 microM sodium nitroprusside as NO donor, micronucleus induction and cell proliferation were also evaluated using blood from six different healthy donors. The results showed that the frequency of structural chromosomal aberrations was not significantly higher in the drug-treated group than the control [2.1 +/- 1.4 versus 1.6 +/- 1.2 (mean +/- SD); P = 0.23]. The frequency of micronucleated lymphocytes was higher in the nitrate group than in the control group (6.5 +/- 4.6 versus 3.5 +/- 2.9, P=0.01). In vitro treatment indicated a dose-dependent increase in the frequency of micronucleated lymphocytes with increasing SNP concentrations. Cytotoxicity and cell cycle delay, with a statistically significant difference with respect to control culture, were also observed. Our results suggest a possible genotoxic activity of nitrate therapy. Further studies focusing on the possible link between nitrate therapy and genotoxicity are warranted at this point.

Myocardial tissue perfusion is not currently quantified in the clinical setting. Thus the aim of this paper is to review the quantitative information on myocardial perfusion provided by contrast echocardiography. In a circulatory model-without the capillary network interposed between injection and sampling point of contrast-the transit time of microbubbles (source of the echo contrast effect) is inversely related to absolute flow, thus providing accurate quantitation. A similar situation is represented by blood flow inside a vessel or a cardiac cavity, where, if the prerequisites for quantitation are respected, it is possible to measure blood flow by contrast echocardiography. In the coronary circulation, the transit time of contrast microbubbles varies according to their interaction with coronary microcirculation, and to the characteristics of contrast agents as flow tracers. Echo contrast agents with small microbubbles have been injected into the coronary branches of experimental animals, under both coronary autoregulation and maximal coronary dilation, providing good estimates of coronary blood flow. The accuracy of these measurements might improve when new contrast agents, with characteristics closer to those of a flow tracer, are available. If a tracer is injected before a bifurcation, and provided it mixes adequately, the amount of tracer distributed to each branch is proportional to the corresponding blood flow. A similar situation is encountered when an echo contrast agent is injected into the aortic root or into the left main coronary artery. Here, the ratio between myocardial signal intensity in the different perfusion territories reflects the corresponding ratio of blood flows. The validity of this approach has been previously demonstrated in experimental animals and validated in patients with coronary stenoses. The injection of contrast agents into the coronary circulation at baseline and under coronary hyperaemia has the potential for measuring coronary blood flow reserve. However, what is still unclear is whether contrast echo changes reflect changes in coronary blood flow (i.e. flow reserve), coronary blood volume (i.e. coronary recruitment) or both, and also whether they influence the different types of contrast agent. Finally, myocardial contrast echocardiography can provide information on the spatial distribution of myocardial perfusion, i.e. the presence, site and extent of perfused myocardium. Thus, in models where myocardial perfusion may be either present or absent, contrast echo can provide an accurate estimate of perfusion abnormalities.

See article by Wilson et al. [9] (pages 601–607) in this issue. Hypercholesterolemia is reported to be associated both with enhanced oxidative stress, related to increased lipid peroxidation [1], and with augmented susceptibility to coronary vasoconstriction [2]. The abnormal coronary vasoreactivity is mainly attributed to endothelial dysfunction, which in hypercholesterolemic man has been demonstrated by several approaches, including coronary and forearm blood flow response to acetylcholine (ACh) [3,4], and flow-mediated dilation [5]. An increased generation of oxidized LDL is a major factor responsible for the vascular damage related to high cholesterol levels, and oxidative stress leads to increased breakdown and/or reduced bioavailability of NO in a number of experimental and clinical models [6]. F2-Isoprostanes, namely 8-epi-prostaglandin F2α (8-epi-PGF2α), have been recently proposed as reliable markers of oxidative stress in vivo [7,8]. Wilson et al. [9] in their study demonstrate that 8-epi-PGF2α causes a dose-dependent vasoconstriction in vitro, in pig coronary strips obtained from normal and hypercholesterolemic animals. Coronary vasoconstriction induced by 8-epi-PGF2α is shown to be modulated by endothelial NO, being increased after both endothelial denudation and L-NMMA administration in control animals. Hypercholesterolemic vessels (HV), in turn, show an increased coronary vasoconstriction to 8-epi-PGF2α which is comparable to that observed in normal animals following endothelium denudation, specific for 8-epi-PGF2α, not being found with other vasoconstrictor prostanoids, and is attenuated by pretreatment with l-arginine or the NO donor NOR-3. These observations suggest a tonic vasoconstrictor activity dynamically opposed by NO, with the net vasomotor effect resulting from the balance of the two systems. Furthermore, 8-epi-PGF2α in hypercholesterolemic animals … * Corresponding author. Tel.: +39-50-583-288; fax: +39-50-553-461 palombo{at}po.ifc.pi.cnr.it