Hypotensive interaction of sildenafil and nicorandil in rats through the cGMP pathway but not by K(ATP) channel activation.

Ishizuka N, Saito K, Akima M, Matsubara S, Saito M.

Chugai Pharmaceutical Co., Ltd., Product Research Laboratory, Tokyo, Japan. ishizukanbh chugai-pharm.co.jp

The possibility that sildenafil citrate can potentiate nicorandil-induced hypotension by increasing cGMP levels of vascular smooth muscle cells was examined using anesthetized rats and isolated aortas. In pentobarbital-anesthetized rats, more than 0.3 mg/kg of sildenafil (i.v.) potentiated intra-aortic (i.Ao.) administration of nitroglycerin-induced hypotension. Hypotension due to nicorandil (100 microg/kg, i.Ao.) was potentiated by sildenafil (1 mg/kg, i.v.), even after glibenclamide treatment, although pinacidil-induced hypotension was not reinforced. Hypotensive responses to neither nitroglycerin (3 microg/kg, i.v.) nor nicorandil (100 microg/kg, i.v.) were potentiated by sildenafil, however. Increases in femoral blood flow due to nitroglycerin (0.1-3 microg, i.a.) were potentiated significantly by sildenafil, but those due to nicorandil (1-30 microg, i.a.) were not. Isolated rat aortas precontracted with phenylephrine were dilated dose-dependently using nicorandil, nitroglycerin, pinacidil or sildenafil. The relaxant effect due to nicorandil and nitroglycerin was reinforced significantly by pretreatment with an ineffective concentration of sildenafil (10(-8) M), but pinacidil was not. After ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) completely blocked relaxation by nicorandil, sildenafil did not increase relaxation. These findings suggest that combination of sildenafil with nicorandil, as well as with nitroglycerin, potentiates the hypotensive response by augmentation of vasodilatation. Synergism of vasodilatation may be linked with NO action, but not with K(ATP) channel-activation.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11138733&dopt=Abstract sildenafil Viagra online



Relative efficacy of sildenafil compared to other treatment options for erectile dysfunction.

Gauthier A, Rutchik DS, Winters CJ, Fuselier AH, Woo H, Prats JL, Bardot S.

Department of Urology, Ochsner Clinic, New Orleans, LA, USA.

OBJECTIVE: We examined and compared the efficacy of sildenafil in patients previously using other agents or devices for erectile dysfunction (ED) treatment. METHODS: We identified 47 patients with organic ED who had tried other therapies (intracavernosal injection therapy [ICIT], intraurethral prostaglandin suppositories [IPS], vacuum erection devices [VEDs], or yohimbine) before using sildenafil. Comparisons of the efficacy of sildenafil to the previously used agent or device were assessed by telephone questionnaire. Responses were compared using nonparametric Wilcoxon rank sum and analysis of variance testing. RESULTS: Sildenafil therapy was no more effective than ICIT or VEDs but was more effective than IPS. No significant difference occurred in response to sildenafil with age. Of 22 patients achieving erections adequate for intercourse with their previous therapy, 14 (63%) achieved equal or improved erections with sildenafil. Of the remaining 18 patients who had erections inadequate for intercourse with previous therapy, 5 (27%) had adequate erections with sildenafil. CONCLUSIONS: Oral sildenafil therapy provides results comparable to those of other available ED treatment modalities. A trial of this drug in this patient population is warranted.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11147477&dopt=Abstract sildenafil Viagra online



The presence and function of phosphodiesterase type 5 in the rat myometrium.

Buhimschi CS, Garfield RE, Weiner CP, Buhimschi IA.

Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University, New Haven, CT 06520, USA. catalin.buhimschi yale.edu

OBJECTIVE: Cyclic nucleotide phosphodiesterases (PDEs) are a diverse enzyme group with multiple regulatory properties and wide tissue distribution. Such activity includes cyclic adenosine (cAMP) and guanosine monophosphate (cGMP) breakdown. The type 5 isoform (PDE-5, cGMP specific) is the target of specific antagonists (ie, sildenafil, Viagra). We tested the hypothesis that PDE-5 is present in rat myometrium and modulates myometrial activity. STUDY DESIGN: Full-thickness uterine wall was collected from nonpregnant (n=3) and pregnant Sprague-Dawley rats on days 10 (n=4), 17 (n=6), 22 nonlabor (n=5), and 22 during term labor (TL, n=4). Preterm labor (PTL, n=3) was induced in some animals on day 16 with 15 mg/kg mifepristone (RU 486). Tissue samples were prepared for Western blotting using a monoclonal antibody against rodent PDE-5. In a second series, cumulative doses of sildenafil (0.005, 0.05, 0.5, 5 mg/kg, intraperitoneal) were administered and the effect on uterine contractility recorded in vivo during term (TL, n=7) and preterm labor (PTL, n=6). Saline solution-injected rats provided temporal control. Uterine contractility was estimated from intrauterine pressure (IP) measured electronically with a sensor tip pressure catheter. Heart rate was recorded simultaneously using electrodes attached to the chest and connected to the same data acquisition system. RESULTS: PDE-5 immunoreactivity was present in the nonpregnant rat uterus and at all gestational times studied, although the expression was unaffected by either pregnancy or the state of labor (preterm or term). A dominant antibody-specific band was identified at 86 kd in the uterine samples, contrasting with lung where the 100-kd PDE-5 isoform was most abundant. Two additional lower molecular weight (55 and 32 kd) bands were also identified as antibody specific. Despite the lack of change in PDE-5 during pregnancy, sildenafil reduced IP during TL and PTL beginning at 0.5 mg/kg. The highest dose of sildenafil reduced IP during both TL and PTL by 45% and 59% of baseline, respectively (two-way analysis of variance, P<.01). This effect was not accompanied by changes in heart rate. CONCLUSION: PDE-5 is constitutively present in the rat uterine wall. There was no observed change in the PDE-5 protein expression throughout pregnancy. In contrast to the lung, the uterus expresses an 80-kd PDE-5 isoform. Sildenafil in pharmacologic doses inhibits mechanical uterine activity and might be of benefit if selectively used for treatment of preterm labor.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=14749671&dopt=Abstract sildenafil Viagra online



Cross-regulation of intracellular cGMP and cAMP in cultured human corpus cavernosum smooth muscle cells.

Kim NN, Huang Y, Moreland RB, Kwak SS, Goldstein I, Traish A.

Department of Urology, Boston University School of Medicine, Boston, Massachusetts, 02118, USA.

The goal of this study was to assess the potential cross-regulation of cyclic nucleotides in human corpus cavernosum (HCC). Incubation of primary cultures of HCC smooth muscle cells with either the NO donor sodium nitroprusside (SNP, 10 microM) or the phosphodiesterase type 5 (PDE 5) inhibitor sildenafil (50 nM) produced little or no changes in the intracellular cGMP levels. Incubation with both SNP and sildenafil produced marked increases in cGMP. Interestingly, incubation of cells with 10 microM of forskolin or PGE(1) produced significant enhancement of cGMP accumulation. These increases were not further enhanced by the addition of SNP and sildenafil. Kinetic analyses of cGMP hydrolysis by PDE 5 showed that high concentrations of cAMP reversibly inhibited the enzyme with a K(i) of 258 +/- 54 microM. The increase in cGMP levels in response to cAMP generating agents is not due to assay artifact since cAMP did not cross-react with cGMP antibody. Our data suggest that cAMP up-regulates intracellular levels of cGMP, in part, by inhibition of PDE 5. We also noted that cGMP down-regulates cAMP synthesis via a mechanism requiring G-protein coupling of adenylyl cyclase. These observations may have important implications in the utility of pharmacotherapeutic agents targeting cyclic nucleotide metabolism for the treatment of erectile dysfunction. Copyright 2000 Academic Press.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11152621&dopt=Abstract sildenafil Viagra online



Sildenafil citrate (Viagra) does not exacerbate myocardial ischemia in canine models of coronary artery stenosis.

Przyklenk K, Kloner RA.

Heart Institute, Good Samaritan Hospital, and Department of Medicine, University of Southern California, Los Angeles 90017-2395, USA. karinp dnamail.com

OBJECTIVES: Our aim was to determine whether sildenafil citrate (Viagra) unfavorably alters coronary perfusion in canine models of coronary artery stenosis. BACKGROUND: Concern has been raised that sildenafil may exacerbate ischemia in patients with coronary artery disease. However, the effects of sildenafil on coronary perfusion are largely unexplored. METHODS: Using anesthetized dogs, a micromanometer constrictor was applied to either an intact coronary artery (model of stable hypoperfusion: Protocol 1) or a site of arterial injury (model of recurrent platelet-mediated thrombosis: Protocol 2). After monitoring coronary flow for 1 h, dogs received two escalating, clinically relevant doses of sildenafil or placebo. Perfusion was assessed during the initial hour pretreatment, for 1 h following dose 1 and 1 h following dose 2 by measuring the area of the flow-time profile, normalized to baseline flow x 60 min. Interaction between sildenafil and adenosine-mediated inhibition of platelet aggregation was evaluated by in vitro platelet aggregometry (Protocol 3). RESULTS: In Protocol 1, flow-time area was maintained at 50% to 60% of baseline in both placebo- and sildenafil-treated groups. In Protocol 2, controls exhibited an expected modest, temporal adenosine-mediated improvement in flow-time area (from 40 +/- 5% to 61 +/- 7%; p < .05) while in contrast, perfusion in sildenafil-treated dogs remained unchanged (37 +/- 6% vs. 33% to 35% before vs. after treatment). In vitro aggregometry confirmed that sildenafil rendered platelets refractory to the inhibitory effects of adenosine receptor stimulation. CONCLUSIONS: Sildenafil did not exacerbate ischemia in canine models of coronary stenosis. However, in the setting of recurrent thrombosis, sildenafil-treated dogs were apparently unresponsive to the platelet inhibitory effects of endogenous adenosine.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11153753&dopt=Abstract sildenafil Viagra online



Sildenafil-mediated reduction in retinal function in heterozygous mice lacking the gamma-subunit of phosphodiesterase.

Behn D, Potter MJ.

Department of Ophthalmology, University of British Columbia, Vancouver, British Columbia, Canada.

PURPOSE: Retinitis pigmentosa (RP) is a common inherited degenerative retinal disease that has many causes including mutations in the genes coding for cyclic guanosine monophosphate (cGMP) phosphodiesterase 6 (PDE6). Sildenafil (Viagra; Pfizer Pharmaceuticals, New York, NY), a widely used medication for erectile dysfunction, is a specific inhibitor of PDE, with the potential to affect PDE6 in the retina. The purpose of this study was to investigate the retinal effects of sildenafil on knockout mice heterozygous for a mutation causing absence of the gamma subunit of rod PDE6 (PDEG:(tm1)/+). METHODS: Wild-type mice and PDEG:(tm1)/+ mice were subjected to electroretinography (ERG) 1 hour after exposure to one of three treatments: 1) no drug, 2) an intraperitoneal injection of sildenafil at 2 times the equivalent maximal daily recommended dosage for humans, or 3) 10 times this dosage. Control ERGs were also obtained to evaluate the reversibility of changes in retinal function after sildenafil treatment. A minimum of 48 hours elapsed between electroretinogram (ERG) recordings for drug washout and animal recovery. RESULTS: ERGs of the PDEG:(tm1)/+ mice treated with sildenafil showed a reversible, dose-dependent decrease in a- and b-wave amplitudes. Wild-type mice treated with sildenafil did not show significant differences in either a- or b-wave amplitudes compared with untreated control animals. CONCLUSIONS: These findings suggest that sildenafil has a significant impact on retinal function in PDEG:(tm1)/+ mice and may have implications in human carriers of RP. In addition, extension of these results in other model systems could be useful in understanding the mechanisms of RP and other forms of retinal degeneration.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11157892&dopt=Abstract sildenafil Viagra online



Effect of sildenafil on non-adrenergic non-cholinergic neurotransmission in bovine penile small arteries.

Simonsen U, Contreras J, Garcia-Sacristan A, Martinez AC.

Department of Pharmacology, Faculty of Health Sciences, University of Aarhus, 8000 C, Aarhus, Denmark. us farm.au,dk

The purpose of the present study was to investigate the effect of the phosphodiesterase isoenzyme V inhibitor, sildenafil, on non-adrenergic non-cholinergic neurogenic relaxations of intracavernous isolated penile small arteries. Dense plexes of nerve fibres immunoreactive for neural nitric oxide (NO) synthase were observed in the adventitia-media junction of the penile small arteries. In 5-hydroxytryptamine-contracted preparations, the inhibitor of NO synthase, N(G)-nitro-L-arginine (L-NOARG), and of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), reduced the electrical field stimulation-induced relaxations. Sildenafil and exogenous NO induced relaxations of penile small arteries. Sildenafil enhanced NO and vasoactive intestinal peptide-induced relaxations. Moreover, sildenafil increased the duration of the relaxations elicited by electrical field stimulation in penile small arteries and corpus cavernosum tissue. In the presence of L-NOARG, sildenafil only at supratherapeutic concentrations reduced the prazosin-sensitive contractions elicited by EFS in penile small arteries. Neurogenic NO-mediated and guanylyl cyclase-dependent relaxations of penile small arteries and corpus cavernosum tissue, considered to be associated with the vasodilatation leading to erection, are selectively enhanced by an inhibitor of phosphodiesterase V.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11165227&dopt=Abstract sildenafil Viagra online



In vivo and in vitro investigation of the effects of sildenafil on rat cavernous smooth muscle.

Gemalmaz H, Waldeck K, Chapman TN, Tuttle JB, Steers WD, Andersson KE.

Department of Urology, University of Virginia School of Medicine, Virginia, USA.

PURPOSE: We investigated the effect of sildenafil on rat erectile tissues in vivo and in vitro. MATERIALS AND METHODS: Intracavernous pressure was recorded in pentobarbital anesthetized, male Sprague-Dawley rats and we studied the effect of 100 or 200 microg/kg(-1) sildenafil given intravenously. In an isolated endothelin-1 contracted strip preparation of rat corpus cavernosum we also assessed the effect of sildenafil on the response to electrical field stimulation of the nerves. RESULTS: Electrical stimulation of the cavernous nerve induced a frequency dependent increase in intracavernous pressure of a mean plus or minus standard error of mean 55 +/- 3 mm Hg at 20 Hz, corresponding to a mean of 47% +/- 2% of mean arterial pressure. The 100 microg/kg(-1) dose did not increase intracavernous pressure but significantly increased mean decay time of the pressure response from 16 +/- 3 to 35 +/- 3 seconds (p <0.001). In vitro sildenafil significantly enhanced the amplitude and duration of the relaxation induced by the electrical stimulation of corpus cavernosum strips in a concentration dependent fashion. CONCLUSIONS: In anesthestized rats sildenafil significantly prolonged the decay period of the intracavernous pressure response induced by electrical stimulation of the cavernous nerve but it did not increase the amplitude. Sildenafil enhanced the amplitude and duration of the relaxant response to electrical field stimulation in isolated corpus cavernosum tissue.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11176531&dopt=Abstract sildenafil Viagra online