EFFECT OF INTRAVESICAL NITRIC OXIDE THERAPY ON CYCLOPHOSPHAMIDE-INDUCED CYSTITIS

arterial chemoreceptors located in the carotid body are an important defense mechanism against systemic hypoxemia. Activation of arterial chemoreceptors increases alveolar ventilation and sympathetic outflow to most vascular beds. During acute exposures to hypoxia, the sympathoexcitatory responses

In the vasculature it is well established that cGMP is involved in the relaxant response to nitric oxide (NO) and NO donors. However, there is an increasing evidence that alternative/additional pathways that are cGMP-independent may also exist. A key criterion for a response to NO or a NO donor drug to be classified as cGMP-independent is lack of (or incomplete) inhibition by the selective inhibitor of soluble guanylate cyclase, ODQ (1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one). In many blood vessels cGMP-independent mechanisms contribute to the vasorelaxation, and in certain vascular beds cGMP-independent relaxation may be the predominant mechanism of action of NO and NO donors. NO donor drugs that generate NO "spontaneously", like authentic NO (i.e. solutions of NO gas), appear to exhibit a larger component of cGMP-independent vasorelaxation than do those drugs that require bioactivation in the tissue. The long lasting inhibition of responses to vasoconstrictors by S-nitrosothiols, persisting after removal of these NO donors, may be a cGMP-independent process, at least in some vessels. The mechanisms involved in the inhibition of vascular growth by NO and NO donors are predominantly cGMP-independent, as are the mechanisms responsible for the effects of NO donors on apoptosis in vascular smooth muscle and endothelial cells. The ability of NO and NO donors to inhibit platelet aggregation has a significant cGMP-independent component. cGMP-independent pathways are most often, though not exclusively, seen at high concentrations (microM - mM) of NO and NO donors. Hence, in relation to the actions of endogenous NO, these pathways may be particularly important in settings when the inducible isoform of NO-synthase is expressed. Furthermore, cGMP-independent pathways are enhanced in animal models of atherosclerosis and ischaemia. This suggests that it may be possible to target cGMP-independent mechanisms with selected NO donors in disease states.

Introduction: Pregnancies complicated by fetal growth restriction (FGR) are known to be associated with a reduced expansion of maternal intravascular space and a lower cardiac output. Therapy with nitric oxide (NO) donors, in addition to plasma volume expansion (PVE) could improve maternal haemodynamic indices and pregnancy outcome.Methods: To evaluate maternal cardiovascular effects of NO donors. We enrolled 52 women with the diagnosis of FGR. Patients were divided into those treated with transdermal patches of NO donors and PVE or a control group. We obtained haemodynamic indices using an USCOM system.Results: At enrolment, the two groups were similar in terms of maternal, fetal and haemodynamic characteristics. In the group treated with NO donors and PVE, we found a significant increase in cardiac output, stroke volume and a decrease of systemic vascular resistance after therapy (see table). At birth the treated group also gave birth to babies with higher birth weight centile.Conclusions: The combined therapeutic approach of NO donor administration and PVE in FGR significantly improves maternal hemodynamic indices. Despite the observation nature of the data, there is suggestion that the use of NO donors together with PVE may also improve pregnancy outcome by increasing the fetal growth.

Activation of M1 macrophages in nonalcoholic steatohepatitis (NASH) is produced by several external or endogenous factors: inflammatory stimuli, oxidative stress, and cytokines are known. However, any direct role of oxidative stress in causing M1 polarization in NASH has been unclear. We hypothesized that CYP2E1-mediated oxidative stress causes M1 polarization in experimental NASH, and that nitric oxide (NO) donor administration inhibits CYP2E1-mediated inflammation with concomitant attenuation of M1 polarization. Because CYP2E1 takes center stage in these studies, we used a toxin model of NASH that uses a ligand and a substrate of CYP2E1 for inducing NASH. Subsequently, we used a methionine and choline-deficient diet-induced rodent NASH model where the role of CYP2E1 in disease progression has been shown. Our results show that CYP2E1 causes M1 polarization bias, which includes a significant increase in interleukin-1β (IL-1β) and IL-12 in both models of NASH, whereas CYP2E1-null mice or diallyl sulfide administration prevented it. Administration of gadolinium chloride (GdCl3), a macrophage toxin, attenuated both the initial M1 response and the subsequent M2 response, showing that the observed increase in cytokine levels is primarily from macrophages. Based on the evidence of an adaptive NO increase, the NO donor administration in vivo that mechanistically inhibited CYP2E1 catalyzed the oxidative stress during the entire study in NASH-abrogated M1 polarization and NASH progression. The results obtained show the association of CYP2E1 in M1 polarization, and that inhibition of CYP2E1 catalyzed oxidative stress by an NO donor (DETA NONOate [(Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate]) can be a promising therapeutic strategy in NASH.

Cervical priming before first-trimester surgical abortion is recommended in certain groups of women. Nitric oxide (NO) donors induce cervical ripening without uterine contractions, but the efficacy and side effects are of concern. To evaluate NO donors for cervical ripening before first-trimester surgical abortion, in terms of efficacy, side effects, and reduction of complications. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and POPLINE. We also searched reference lists of retrieved papers. We contacted experts in the field for information on both published and unpublished trials. Randomised controlled trials comparing NO donors alone or in combination with other methods for cervical ripening in first-trimester surgical abortion. Two review authors independently selected and extracted the data onto a data extraction form. We processed the data using Review Manager (RevMan 5) software. We included 9 studies involving 766 participants. There were no serious complications (infection requiring antibiotic treatment, blood transfusion, complications requiring unintended operation, cervical injury, uterine perforation, death or serious morbidity) in the included trials.NO donors were more effective in cervical ripening when compared with placebo or no treatment. Baseline cervical dilatation before the procedure was higher in NO donors group (mean difference (MD) 0.30, 95% confidence interval (CI) 0.01 to 0.58) The cumulative force required to dilate the cervix to 8 mm (MD -4.29, 95% CI -9.92 to 1.35), headache (risk ratio (RR) 1.73, 95% CI 0.86 to 3.46), abdominal pain (RR 0.87, 95% CI 0.50 to 1.50), or patient satisfaction (RR 0.95, 95% CI 0.84 to 1.07) were not different. More nausea and vomiting occurred in the women who received a NO donor (RR 2.62, 95% CI 1.07 to 6.45).NO donors were inferior to prostaglandins for cervical ripening. The cumulative force required to dilate the cervix to 8 mm to 9 mm was higher (MD 13.12, 95% CI 9.72 to 16.52), and baseline cervical dilatation was less (MD -0.73, 95% CI -1.01 to -0.45) in the NO donor group. However, the probability of dilation greater than 8 mm at three hours was higher in the NO donor group (RR 6.67, 95% CI 2.21 to 20.09). Side effects including headache (RR 5.13, 95% CI 3.29 to 8.00), palpitation (RR 3.43, 95% CI 1.64 to 7.15), dizziness (RR 3.29, 95% CI 1.46 to 7.41), and intraoperative blood loss (MD 33.59 ml, 95% CI 24.50 to 42.67) were also higher. However, abdominal pain (RR 0.33, 95% CI 0.25 to 0.44) and vaginal bleeding (RR 0.14, 95% CI 0.07 to 0.27) were less in the NO donor group. No difference for nausea/vomiting in both groups(RR 1.17, 95% CI 0.94 to 1.46). Patient satisfaction was not different.One trial compared a NO donor with a NO donor plus prostaglandin. The cumulative force required to dilate the cervix to 8 mm was higher (MD 14.50, 95% CI 0.50 to 28.50) in the NO donor group. There was no difference in headache (RR 0.88, 95% CI 0.38 to 2.00), abdominal pain (RR 0.14, 95% CI 0.02 to 1.07), or intraoperative blood loss (MD -50, 95% CI -164.19 to 64.19). NO donors are superior to placebo or no treatment, but inferior to prostaglandins for first-trimester cervical ripening, and associated with more side effects.

Nitric oxide (NO) donors are substances that can release NO. Vascular relaxation induction is among the several functions of NO, and the administration of NO donors is a pharmacological alternative to treat hypertension. This review will focus on the physicochemical description of ruthenium-derived NO donor complexes that release NO via reduction and light stimulation. In particular, we will discuss the complexes synthesized by our research group over the last ten years, and we will focus on the vasodilation and arterial pressure control elicited by these complexes. Soluble guanylyl cyclase (sGC) and potassium channels are the main targets of the NO species released from the inorganic compounds. We will consider the importance of the chemical structure of the ruthenium complexes and their vascular effects.

Cervical priming before first-trimester surgical abortion is recommended in certain groups of women. Nitric oxide (NO) donors induce cervical ripening without uterine contractions, but the efficacy and side effects are of concern. To evaluate efficacy, side effects and complications of NO donors for cervical ripening before first-trimester surgical abortion. We searched the Cochrane Controlled Trials Register, MEDLINE, EMBASE and Popline. We also searched reference lists of retrieved papers. We contacted experts in the field for information on both published and unpublished trials. Randomised controlled trials comparing NO donors alone or in combination with other methods for cervical ripening in first-trimester surgical abortion. Two reviewers independently selected and extracted the data onto a data extraction form. We processed the data using Review Manager (RevMan5) software. We included eight studies involving 718 participants. There were no serious complications (infection requiring antibiotic treatment, blood transfusion, complications requiring unintended operation, cervical injury, uterine perforation, death or serious morbidity) in the trials included.NO donors were ineffective in cervical ripening comparing with placebo or no treatment. The cumulative force required to dilate the cervix to 8 mm (mean difference -4.29, 95% CI -9.92, 1.35), baseline cervical dilatation before the procedure (mean difference 0.21, 95% CI -0.12, 0.53), headache (RR 1.73, 95% CI 0.86, 3.46), abdominal pain (RR 0.87, 95% CI 0.51, 1.50) or patient satisfaction (RR 0.95, 95% CI 0.84, 1.07) were not different. More nausea and vomiting occurred in the women who received a NO donor (RR 2.62, 95% CI 1.07, 6.75).NO donors were inferior to prostaglandins for cervical ripening. The cumulative force required to dilate the cervix to 8-9 mm was higher (mean difference 13.12, 95% CI 9.72, 16.52) and baseline cervical dilatation was less (mean difference -0.73, 95% CI -1.01, -0. 45) in the NO donor group. Side effects including headache (RR 5.13, 95% CI 3.29, 8.00), palpitation (RR 3.43, 95% CI 1.64, 7.15), dizziness (RR 3.29, 95% CI 1.46, 7.41) and intraoperative blood loss (mean difference 33.59 ml, 95% CI 24.50, 42.67) were also higher. However, abdominal pain (RR 0.33, 95% CI 0.25, 0.44) and vaginal bleeding (RR 0.14, 95% CI 0.07, 0.27) was less in the NO donor group. Patient satisfaction was not different.One trial compared a NO donor with a NO donor plus prostaglandin. The cumulative force required to dilate the cervix to 8 mm was higher (mean difference 14.50, 95% CI 0.50, 28.50) in the NO donor group. There was no difference in headache (RR 0.88, 95% CI 0.38, 2.00), abdominal pain (RR 0.14, 95% CI 0.02, 1.07) or intraoperative blood loss (mean difference -50, 95% CI -164.19, 64.19). NO donors are inferior to prostaglandins for first-trimester cervical ripening, and associated with more side effects. NO donors are comparable to placebo and no treatment for cervical ripening.

Cervical priming before first-trimester surgical abortion is recommended in certain groups of women. Nitric oxide (NO) donors induce cervical ripening without uterine contractions, but the efficacy and side effects are of concern. To evaluate efficacy, side effects and complications of NO donors for cervical ripening before first-trimester surgical abortion. We searched the Cochrane Controlled Trials Register, MEDLINE, EMBASE and POPLINE. We also searched reference lists of retrieved papers. We contacted experts in the field for information on both published and unpublished trials. Randomised controlled trials comparing NO donors alone or in combination with other methods for cervical ripening in first-trimester surgical abortion. Two reviewers independently selected and extracted the data onto a data extraction form. We processed the data using Review Manager (RevMan5) software. We included nine studies involving 766 participants. There were no serious complications (infection requiring antibiotic treatment, blood transfusion, complications requiring unintended operation, cervical injury, uterine perforation, death or serious morbidity) in the trials included.NO donors were more effective in cervical ripening comparing with placebo or no treatment. Baseline cervical dilatation before the procedure was higher in NO donors group (mean difference 0.30, 95% CI 0.01, 0.58) The cumulative force required to dilate the cervix to 8 mm (mean difference -4.29, 95% CI -9.92, 1.35), headache (RR 1.73, 95% CI 0.86, 3.46), abdominal pain (RR 0.87, 95% CI 0.50, 1.50) or patient satisfaction (RR 0.95, 95% CI 0.84, 1.07) were not different. More nausea and vomiting occurred in the women who received a NO donor (RR 2.62, 95% CI 1.07, 6.45).NO donors were inferior to prostaglandins for cervical ripening. The cumulative force required to dilate the cervix to 8-9 mm was higher (mean difference 13.12, 95% CI 9.72, 16.52) and baseline cervical dilatation was less (mean difference -0.73, 95% CI -1.01, -0.45) in the NO donor group. Side effects including headache (RR 5.13, 95% CI 3.29, 8.00), palpitation (RR 3.43, 95% CI 1.64, 7.15), dizziness (RR 3.29, 95% CI 1.46, 7.41) and intraoperative blood loss (mean difference 33.59 ml, 95% CI 24.50, 42.67) were also higher. However, abdominal pain (RR 0.33, 95% CI 0.25, 0.44) and vaginal bleeding (RR 0.14, 95% CI 0.07, 0.27) was less in the NO donor group. Patient satisfaction was not different.One trial compared a NO donor with a NO donor plus prostaglandin.The cumulative force required to dilate the cervix to 8 mm was higher (mean difference 14.50, 95% CI 0.50, 28.50) in the NO donor group. There was no difference in headache (RR 0.88, 95% CI 0.38, 2.00), abdominal pain (RR 0.14, 95% CI 0.02, 1.07) or intraoperative blood loss (mean difference -50, 95% CI -164.19, 64.19). NO donors are superior to placebo or no treatment, but inferior to prostaglandins for first-trimester cervical ripening, and associated with more side effects.

The effect of a nitric oxide (NO) donor on high-voltage-activated Ca(2+) channel currents (I(Ca)) was examined using the whole cell patch-clamp technique in L(6)-S(1) dorsal root ganglion (DRG) neurons innervating the urinary bladder. The neurons were labeled by axonal transport of a fluorescent dye, Fast Blue, injected into the bladder wall. Approximately 70% of bladder afferent neurons exhibited tetrodotoxin (TTX)-resistant action potentials (APs), and 93% of these neurons were sensitive to capsaicin, while the remaining neurons had TTX-sensitive spikes and were insensitive to capsaicin. The peak current density of nimodipine-sensitive L-type Ca(2+) channels activated by depolarizing pulses (0 mV) from a holding potential of -60 mV was greater in bladder afferent neurons with TTX-resistant APs (39.2 pA/pF) than in bladder afferent neurons with TTX-sensitive APs (28.9 pA/pF), while the current density of omega-conotoxin GVIA-sensitive N-type Ca(2+) channels was similar (43-45 pA/pF) in both types of neurons. In both types of neurons, the NO donor, S-nitroso-N-acetylpenicillamine (SNAP) (500 microM), reversibly reduced (23.4-26.6%) the amplitude of I(Ca) elicited by depolarizing pulses to 0 mV from a holding potential of -60 mV. SNAP-induced inhibition of I(Ca) was reduced by 90% in the presence of omega-conotoxin GVIA but was unaffected in the presence of nimodipine, indicating that NO-induced inhibition of I(Ca) is mainly confined to N-type Ca(2+) channels. Exposure of the neurons for 30 min to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), an inhibitor of NO-stimulated guanylyl cyclase, prevented the SNAP-induced reduction in I(Ca). Extracellular application of 8-bromo-cGMP (1 mM) mimicked the effects of NO donors by reducing the peak amplitude of I(Ca) (28.6% of reduction). Action potential configuration and firing frequency during depolarizing current pulses were not altered by the application of SNAP (500 microM) in bladder afferent neurons with TTX-resistant and -sensitive APs. These results indicate that NO acting via a cGMP signaling pathway can modulate N-type Ca(2+) channels in DRG neurons innervating the urinary bladder.

Direct measurement of actual levels of nitric oxide (NO) in cell culture conditions using soluble NO donors

Endogenous nitric oxide (NO) reduces sympathetic vasoconstriction by attenuating neuronal excitability in the brain stem and inhibition of postganglionic neurotransmission. We studied whether this modulation of sympathetic circulatory control by NO may be altered during chronic administration of NO donor drugs in pigs. Nitrate tolerance was induced by oral administration of isosorbide dinitrate (ISDN, 4 mg/kg per day for 4 weeks) in eight pigs. Four of them were chronically instrumented for the measurement of mean arterial blood pressure and cardiac output in the conscious state. ISDN treatment caused hemodynamic tolerance to NO donors and significantly increased the hypotensive responses to pharmacologic ganglionic blockade in conscious pigs. In general anesthesia, ISDN-treated animals and age-matched controls (n=5) had similar baseline renal sympathetic nerve activity and in both groups neither inhibition of NO synthases (NOS) nor administration of NO donors to the brain stem by intracerebroventricular (i.c.v.) infusions caused significant changes in baseline renal sympathetic nerve activity. However, whereas sympathoexcitatory responses to glutamate (0.5 mL, 0.1 mol/L, i.c.v.) or electrical stimulation of somatic nerve afferents were significantly potentiated by central NOS inhibition and attenuated by NO donors in controls, these treatments no longer had significant effects in ISDN-treated pigs. Furthermore, reflex sympathetic activation in response to intravenous NO donor treatment was more pronounced in nitrate tolerant animals, which suggests loss of central sympathoinhibitory effects of NO. Subsequent histology on brain stem slices with NADPH-diaphorase as NOS marker revealed significant reduction of NOS density in ISDN-treated pigs. Long-term administration of organic nitrates reduces the number of NO-producing neurons in the brain stem and causes loss of inhibitory effects of NO on sympathetic excitability. This component of tolerance to organic nitrates may be important in patients confronted frequently with sympathetic activation caused by mental and/or physical stressors.

Comparison of the mechanisms underlying the relaxation induced by two nitric oxide donors: Sodium nitroprusside and a new ruthenium complex

We investigated the role of nitric oxide (NO) in inflammatory hyperalgesia. Coinjection of prostaglandin E2 (PGE2) with the nitric oxide synthase (NOS) inhibitor NG-methyl-L-arginine (L-NMA) inhibited PGE2-induced hyperalgesia. L-NMA was also able to reverse that hyperalgesia. This suggests that NO contributes to the maintenance of, as well as to the induction of, PGE2-induced hyperalgesia. Consistent with the hypothesis that the NO that contributes to PGE2-induced sensitization of primary afferents is generated in the dorsal root ganglion (DRG) neurons themselves, L-NMA also inhibited the PGE2-induced increase in tetrodotoxin-resistant sodium current in patch-clamp electrophysiological studies of small diameter DRG neurons in vitro. Although NO, the product of NOS, often activates guanylyl cyclase, we found that PGE2-induced hyperalgesia was not inhibited by coinjection of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylyl cyclase inhibitor. We then tested whether the effect of NO depended on interaction with the adenylyl cyclase-protein kinase A (PKA) pathway, which is known to mediate PGE2-induced hyperalgesia. L-NMA inhibited hyperalgesia produced by 8-bromo-cAMP (a stable membrane permeable analog of cAMP) or by forskolin (an adenylyl cyclase activator). However, L-NMA did not inhibit hyperalgesia produced by injection of the catalytic subunit of PKA. Therefore, the contribution of NO to PGE2-induced hyperalgesia may occur in the cAMP second messenger pathway at a point before the action of PKA. We next performed experiments to test whether administration of exogenous NO precursor or donor could mimic the hyperalgesic effect of endogenous NO. Intradermal injection of either the NOS substrate L-arginine or the NO donor 3-(4-morphinolinyl)-sydnonimine hydrochloride (SIN-1) produced hyperalgesia. However, this hyperalgesia differed from PGE2-induced hyperalgesia, because it was independent of the cAMP second messenger system and blocked by the guanylyl cyclase inhibitor ODQ. Therefore, although exogenous NO induces hyperalgesia, it acts by a mechanism different from that by which endogenous NO facilitates PGE2-induced hyperalgesia. Consistent with the hypothesis that these mechanisms are distinct, we found that inhibition of PGE2-induced hyperalgesia caused by L-NMA could be reversed by a low dose of the NO donor SIN-1. The following facts suggest that this dose of SIN-1 mimics a permissive effect of basal levels of NO with regard to PGE2-induced hyperalgesia: (1) this dose of SIN-1 does not produce hyperalgesia when administered alone, and (2) the effect was not blocked by ODQ. In conclusion, we have shown that low levels of NO facilitate cAMP-dependent PGE2-induced hyperalgesia, whereas higher levels of NO produce a cGMP-dependent hyperalgesia.

To assess the dilatory effectiveness of nitric oxide donors in resistance arteries of patients with arterial hypertension in comparison with that in those of normotensive controls. Endothelium-dependent vasodilation has been demonstrated to be impaired in arterial hypertension. Besides disturbances in endothelial nitric oxide production a reduced vasodilatory effectiveness of nitric oxide might contribute to this phenomenon of endothelial dysfunction. We therefore investigated the dilatory responsiveness of resistance arteries to exogenous nitric oxide by means of administration of the nitric oxide donors glycerol trinitrate (GTN), isosorbide dinitrate (ISDN) and sodium nitroprusside (SNP) in hypertensive patients. Forearm blood flow was measured by venous occlusion plethysmography at rest and during intra-arterial infusion of nitric oxide donors at increasing doses in 11 patients with arterial hypertension and in 10 age-matched normotensive controls. Forearm blood flow at rest was comparable in the two groups and was dose-dependently increased by administration of either nitric oxide donor. In patients with arterial hypertension, blood flow responses to infusions of organic nitrates were significantly impaired over the entire dose-response curve compared with those of normotensive controls (220 nmol/min GTN 13.1 +/- 1.3 and 8.6 +/- 0.3 ml/min per 100 ml tissue; 212 nmol/min ISDN 9.9 +/- 0.7 and 5.8 +/- 1.0 ml/min per 100 ml tissue). Blood flow responses to infusion of the nitric oxide donor SNP were also profoundly impaired in the hypertensive patients, the extent of which impairment equalled that found with the organic nitrates. Within the entire set of normotensive and hypertensive subjects, maximal flow responses to either nitric oxide donor were inversely correlated with mean arterial blood pressure. Dilation of resistance arteries in response to infusion of nitric oxide donors is impaired in hypertensive patients and the degree of this impairment depends critically on the severity of arterial hypertension. The reduced effectiveness of nitric oxide appears to be independent of the class of nitric oxide donor and thus of the mode of intravascular nitric oxide generation. These findings are likely to have important implications not only for our understanding of the pathophysiological mechanisms of endothelial dysfunction but also for nitric oxide donor therapy in arterial hypertension.

The positive contractile effect of nitric oxide (NO) donors was studied on isolated rat ventricular cardiomyocytes within a range of a positive force/frequency relationship. We determined whether the observed effect depended on cGMP. The NO donors S-nitroso-acetyl-D,L-penicillamine (SNAP) and N-[4-[1-(3-aminopropyl)-2-hydroxy-2-nitrosohydrazino]butyl]-1,3-propanediamine (spermine-NONO) increased contractile responsiveness transiently in a concentration- and frequency-dependent manner. The influence of NO donors on cGMP levels was enhanced under beating conditions. The positive contractile effect of NO donors was inhibited by adenosine 3',5'-cyclic monophosphothioate Rp diastereomer (Rp-cAMPS), but not by bisindolylmaleimide. Inhibition of the soluble guanylyl cyclase (sGC) by 1 H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ) inhibited the positive contractile effect of NO donors. Direct activation of sGC by 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC1) or addition of 8-bromo cGMP increased cell contractility comparably to NO donors. Inhibition of G(alphas) proteins by NF441 inhibited the positive contractile effect of NO donors. In contrast, NO donors did not potentiate the positive contractile effect of forskolin. These results demonstrate that the positive contractile effect of NO donors on rat ventricular cardiomyocytes working in a range of a positive force/frequency relationships is enhanced. It is mediated by NO-dependent stimulation of the sGC interacting with G(alphas) proteins.