Chronic hypoxia (CH) augments endothelium-derived nitric oxide (NO)-dependent pulmonary vasodilation; however, responses to exogenous NO are reduced following CH in female rats. We hypothesized that CH-induced attenuation of NO-dependent pulmonary vasodilation is mediated by downregulation of vascular smooth muscle (VSM) soluble guanylyl cyclase (sGC) expression and/or activity, increased cGMP degradation by phosphodiesterase type 5 (PDE5), or decreased VSM sensitivity to cGMP. Experiments demonstrated attenuated vasodilatory responsiveness to the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate and to arterial boluses of dissolved NO solutions in isolated, saline-perfused lungs from CH vs. normoxic female rats. In additional experiments, the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, blocked vasodilation to NO donors in lungs from each group. However, CH was not associated with decreased pulmonary sGC expression or activity as assessed by Western blotting and cGMP radioimmunoassay, respectively. Consistent with our hypothesis, the selective PDE5 inhibitors dipyridamole and T-1032 augmented NO-dependent reactivity in lungs from CH rats, while having little effect in lungs from normoxic rats. However, the attenuated vasodilatory response to NO in CH lungs persisted after PDE5 inhibition. Furthermore, CH similarly inhibited vasodilatory responses to 8-bromoguanosine 3'5'-cyclic monophosphate. We conclude that attenuated NO-dependent pulmonary vasodilation after CH is not likely mediated by decreased sGC expression, but rather by increased cGMP degradation by PDE5 and decreased pulmonary VSM reactivity to cGMP. (+info)
The phosphodiesterase 5 inhibitor sildenafil has no effect on cerebral blood flow or blood velocity, but nevertheless induces headache in healthy subjects.
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Cyclic nucleotides are important hemodynamic regulators in many tissues. Glyceryl trinitrate markedly dilates large cerebral arteries and increases cGMP. Here, the authors study the effect of sildenafil, a selective inhibitor of cGMP-hydrolyzing phosphodiesterase 5 on cerebral hemodynamics and headache induction. Ten healthy subjects were included in a double-blind, placebo-controlled crossover study where placebo or sildenafil 100 mg (highest therapeutic dose) were administered on two separate days. Blood velocity in the middle cerebral artery (Vmca) was recorded by transcranial Doppler, and regional cerebral blood flow in the perfusion area of the middle cerebral artery (rCBFmca) was measured using single photon emission computed tomography and xenon inhalation. Radial and temporal artery diameters were studied using high-frequency ultrasound. Blood pressure and heart rate were recorded repeatedly. Headache responses and tenderness of pericranial muscles were scored verbally. Sildenafil caused no significant changes in rCBFmca, Vmca, or in temporal or radial artery diameter, but heart rate increased and diastolic blood pressure decreased significantly compared to placebo. Despite the lack of cerebral arterial dilatation, sildenafil caused significantly more headache than placebo. The present results show that sildenafil 100 mg does not dilate cerebral or extracerebral arteries but nevertheless causes headache, which may be attributed to nonvascular mechanisms. (+info)
Phosphorylation of isolated human phosphodiesterase-5 regulatory domain induces an apparent conformational change and increases cGMP binding affinity.
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Substrate binding to the phosphodiesterase-5 (PDE5) catalytic site increases cGMP binding to the regulatory domain (R domain). The latter promotes PDE5 phosphorylation by cyclic nucleotide-dependent protein kinases, which activates catalysis, enhances allosteric cGMP binding, and causes PDE5A1 to apparently elongate. A human PDE5A1 R domain fragment (Val(46)-Glu(539)) containing the phosphorylation site (Ser(102)) and allosteric cGMP-binding sites was studied. The rate, cGMP dependence, and stoichiometry of phosphorylation of the PDE5 R domain by the catalytic subunit of cAMP-dependent protein kinase are comparable with that of the holoenzyme. Migration in native polyacrylamide gels suggests that either cGMP binding or phosphorylation produces distinct conformers of the R domain. Phosphorylation of the R domain increases affinity for cGMP approximately 10-fold (K(D) values 97.8 +/- 17 and 10.0 +/- 0.5 nm for unphospho- and phospho-R domains, respectively). [(3)H]cGMP dissociates from the phospho-R domain with a single rate (t(12) = 339 +/- 30 min) compared with the biphasic pattern of the unphospho-R domain (t(12) = 39.0 +/- 4.8 and 265 +/- 28 min, for the fast and slow components, respectively). Thus, cGMP-directed regulation of PDE5 phosphorylation and the resulting increase in cGMP binding affinity occur largely within the R domain. Conformational change(s) elicited by phosphorylation of the R domain within the PDE5 holoenzyme may also cause or participate in stimulating catalysis. (+info)
Sildenafil and vardenafil, types 5 and 6 phosphodiesterase inhibitors, induce caspase-dependent apoptosis of B-chronic lymphocytic leukemia cells.
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Type 4 phosphodiesterase (PDE4) inhibitors reportedly induce apoptosis in chronic lymphocytic leukemia (CLL) cells. Following clinical improvement of one previously untreated CLL patient with sildenafil therapy, we evaluated the in vitro induction of apoptosis in CLL cells by 4 PDE5/6 inhibitors, including sildenafil, vardenafil, zaprinast, and methoxyquinazoline (MQZ). After 24 hours of culture, the various PDE inhibitors differed in their ability to induce apoptosis, with zaprinast displaying no killing effect. Normal B cells isolated from control donors were totally resistant to PDE-induced apoptosis. Vardenafil was 3 and 30 times more potent an inducer of apoptosis than sildenafil and MQZ, respectively. Both vardenafil and sildenafil failed to elevate adenosine 3'5' cyclic monophosphate (cAMP) levels, largely excluding an inhibitory effect on cAMP-PDE3, -PDE4, and -PDE7. Vardenafil- or sildenafil-treated B-CLL cells displayed up to 30% intracellular active caspase 3. Drug-induced apoptosis was inhibited by the caspase inhibitor z-VAD.fmk, prevented by interleukin-4 (IL-4), and significantly reduced by stromal-derived factor1-alpha (SDF-1alpha). We conclude that vardenafil and sildenafil induce caspase-dependent apoptosis of B-CLL cells in vitro and thus might be considered in the treatment of CLL patients. However, further in vivo investigations should be warranted. (+info)
Sildenafil (Viagra) induces neurogenesis and promotes functional recovery after stroke in rats.
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BACKGROUND AND PURPOSE: We tested the hypothesis that sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor, promotes functional recovery and neurogenesis after stroke. METHODS: Male Wistar rats were subjected to embolic middle cerebral artery occlusion. Sildenafil (Viagra) was administered orally for 7 consecutive days starting 2 or 24 hours after stroke onset at doses of 2 or 5 mg/kg per day. Ischemic rats administered the same volume of tap water were used as a control group. Functional outcome tests (foot-fault, adhesive removal) were performed. Rats were killed 28 days after stroke for analysis of infarct volume and newly generated cells within the subventricular zone and the dentate gyrus. Brain cGMP levels, expression of PDE5, and localized cerebral blood flow were measured in additional rats. RESULTS: Treatment with sildenafil significantly (P<0.05) enhanced neurological recovery in all tests performed. There was no significant difference of infarct volume among the experimental groups. Treatment with sildenafil significantly (P<0.05) increased numbers of bromodeoxyuridine-immunoreactive cells in the subventricular zone and the dentate gyrus and numbers of immature neurons, as indicated by betaIII-tubulin (TuJ1) immunoreactivity in the ipsilateral subventricular zone and striatum. The cortical levels of cGMP significantly increased after administration of sildenafil, and PDE5 mRNA was present in both nonischemic and ischemic brain. CONCLUSIONS: Sildenafil increases brain levels of cGMP, evokes neurogenesis, and reduces neurological deficits when given to rats 2 or 24 hours after stroke. These data suggest that this drug that is presently in the clinic for sexual dysfunction may have a role in promoting recovery from stroke. (+info)
Acute and chronic effects of T-1032, a novel selective phosphodiesterase type 5 inhibitor, on monocrotaline-induced pulmonary hypertension in rats.
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We examined the hemodynamic property of T-1032 (methyl 2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridylmethoxy)-4-(3,4,5-trimethoxy-phen yl)-3-isoquinoline carboxylate sulfate), a novel selective phosphodiesterase type 5 (PDE5) inhibitor, and evaluated the chronic effect of T-1032 on cardiac remodeling and its related death in monocrotaline (MCT)-induced pulmonary hypertensive rats. T-1032 (1, 10, 100 micro g/kg, i.v.) significantly reduced mean arterial pressure (MAP) and right ventricular systolic pressure (RVSP) without a change in heart rate. The change in RVSP was more potent than that in MAP with 1 micro g/kg T-1032 treatment (RVSP: -8.2+/-1.2%, mean arterial pressure: -5.7+/-1.2%), and reductions in RVSP and MAP reached a peak at doses of 1 and 10 micro g/kg, respectively. In contrast, nitroglycerin (0.1, 1, 10 micro g/kg, i.v.) and beraprost (0.1, 1 micro g/kg, i.v.) did not cause a selective reduction in RVSP at any dose. When T-1032 (300 ppm in diet) was chronically administered, it delayed the death, and significantly suppressed right ventricular remodeling (T-1032-treated: 0.318+/-0.021 g, control: 0.401+/-0.013 g, p<0.05). Our present results suggest that T-1032 selectively reduces RVSP, and resulting in the suppression of right ventricular remodeling with a delay of the death in MCT-induced pulmonary hypertensive rats. (+info)
Increased expression of the cGMP-inhibited cAMP-specific (PDE3) and cGMP binding cGMP-specific (PDE5) phosphodiesterases in models of pulmonary hypertension.
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1. Chronic hypoxic treatment of rats (to induce pulmonary hypertension, PHT) for 14 days increased cGMP-inhibited cAMP specific phosphodiesterase (PDE3) and cGMP binding cGMP specific phosphodiesterase (PDE5) activities in pulmonary arteries. The objective of this study was to establish the molecular basis for these changes in both animal and cell models of PHT. In this regard, RT-PCR and quantitative Western blotting analysis was applied to rat pulmonary artery homogenates and human pulmonary "artery" smooth muscle cell (HPASMC) lysates. 2. PDE3A/B gene transcript levels were increased in the main, first, intrapulmonary and resistance pulmonary arteries by chronic hypoxia. mRNA transcript and protein levels of PDE5A2 in the main and first branch pulmonary arteries were also increased by chronic hypoxia, with no effect on PDE5A1/A2 in the intra-pulmonary and resistance vessels. 3. The expression of PDE3A was increased in HPASMCs maintained under chronic hypoxic conditions for 14 days. This may be mediated via a protein kinase A-dependent mechanism, as treatment of cells with Br-cAMP (100 microM) mimicked chronic hypoxia in increasing PDE3A expression, while the PKA inhibitor, H8 peptide (50 microM) abolished the hypoxic-dependent increase in PDE3A transcript. 4. We also found that the treatment of HPASMCs with the inhibitor of kappaB degradation Tosyl-Leucyl-Chloro-Ketone (TLCK, 50 microM) reduced PDE5 transcript levels, suggesting a role for this transcription factor in the regulation of PDE5 gene expression. 5. Our results show that increased expression of PDE3 and PDE5 might explain some changes in vascular reactivity of pulmonary vessels from rats with PHT. We also report that NF-kappaB might regulate basal PDE5 expression. (+info)
The effect of vardenafil, a potent and highly selective phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction, on the cardiovascular response to exercise in patients with coronary artery disease.
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OBJECTIVES: The effect of vardenafil, a potent and highly selective phosphodiesterase-5 (PDE5) inhibitor, on symptom-limited exercise time, time to first awareness of angina, and time to ischemic threshold (ST-segment depression > or =1 mm from baseline) during exercise tolerance testing (ETT) was examined in patients with stable coronary artery disease (CAD). BACKGROUND: Erectile dysfunction (ED) is common among men with CAD. PDE5 inhibition is increasingly the preferred treatment option for ED. However, the effect of PDE5 inhibition on exercise-induced ischemia in CAD patients has received limited prospective evaluation. METHODS: In this double-blind, crossover, single-dose multicenter study, 41 men with reproducible stable exertional angina due to ischemic CAD received vardenafil 10 mg or placebo, followed by ETT (5 to 10 metabolic equivalents [METS], Bruce protocol) 1 h postdose. Sublingual nitrate use was prohibited for > or =24 h pre- and postexercise study days. End points included symptom-limited treadmill exercise time, time to first awareness of angina, time to ischemic threshold, and safety. RESULTS: Relative to placebo, vardenafil 10 mg did not alter exercise treadmill time (427 +/- 105 s vs. 433 +/- 109 s, p = 0.39), or time to first awareness of angina (292 +/- 110 s vs. 291 +/- 123 s, p = 0.59), but significantly prolonged time to ischemic threshold (334 +/- 108 s vs. 381 +/- 108, p = 0.0004). At peak exercise, vardenafil 10 mg did not alter blood pressure, heart rate, or rate-pressure product relative to placebo. The most common adverse events (facial flushing and headache) were of mild or moderate intensity, and short-lived. CONCLUSIONS: Vardenafil 10 mg did not impair the ability of patients with stable CAD to exercise at levels equivalent or greater than that attained during sexual intercourse (average of 2.5 to 3.3 METS). (+info)