Effects of sildenafil on human penile blood vessels

Evaluation of Neutrophil Dynamics Change by Protective Effect of Tadalafil After Renal Ischemia/Reperfusion Using In Vivo Real-time Imaging

BACKGROUND

Neutrophils play a major role in ischemia/reperfusion injury (IRI) in renal transplantation and acute kidney injury. However, it has been difficult to observe changes in neutrophil dynamics over time in living mice kidney. We investigate neutrophil dynamics in IRI in living mice using novel in vivo multiphoton microscope imaging techniques and characterize the renoprotective effects of a selective phosphodiesterase (PDE) 5 inhibitor, tadalafil.

METHODS

Wild-type (WT) and eNOS knockout (eNOS-KO) mice, a model of endothelial dysfunction, were used to establish in vivo real-time imaging in living mouse kidneys. Neutrophils were labeled green with Ly-6G monoclonal antibody, and plasma flow was labeled red with bovine serum albumin. Tadalafil was administered orally 1 h before surgery. Both kidney pedicles were reperfused after 37° warm ischemia for 45 min.

RESULTS

Our novel approach revealed that neutrophils were trapped in glomerulus within a few minutes after reperfusion. They gradually increased over time and Infiltrated neutrophils were observed in the tubular lumen and peritubular capillary. The neutrophils were clearly visualized rolling on peritubular capillary plexus at 3 μm/min. The administration of tadalafil significantly reduced neutrophil influx into the glomerulus in both WT and eNOS-KO mice. Reduced neutrophil infiltration in tadalafil groups, which was confirmed by flow cytometry, resulted in histopathologically decreased tubular injury. The expression of VCAM-1 and KIM-1 was partially prevented by tadalafil.

CONCLUSIONS

Use of a novel technique contributed to elucidation of neutrophil dynamics after reperfusion. Tadalafil has a potential for inhibiting neutrophil infiltration in renal IRI.Supplemental Visual Abstract; http://links.lww.com/TP/C223.

Phosphodiesterase 5 inhibition attenuates cerebral vasospasm and improves functional recovery after experimental subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm is an independent predictor of poor outcome after subarachnoid hemorrhage (SAH). The nitric oxide-cyclic guanosine monophosphate (NO-cGMP) vasodilatory pathway is strongly implicated in its pathophysiology. Preliminary studies suggest that phosphodiesterase 5 (PDE5), an enzyme that degrades cGMP, may play a role because the PDE5 inhibitor sildenafil was found to reduce vasospasm after SAH. However, several questions that are critical when considering translational studies remain unanswered.

OBJECTIVE

To elucidate the mechanism of action of sildenafil against vasospasm and to assess whether sildenafil attenuates SAH-induced neuronal cell death, improves functional outcome after SAH, or causes significant physiological side effects when administered at therapeutically relevant doses.

METHODS

SAH was induced via endovascular perforation in male C57BL6 mice. Beginning 2 hours later, mice received sildenafil citrate (0.7, 2 or 5 mg/kg orally twice daily) or vehicle. Neurological outcome was assessed daily. Vasospasm was determined on post-SAH day 3. Brain PDE5 expression and activity, cGMP content, neuronal cell death, arterial blood pressure, and intracranial pressure were examined.

RESULTS

We found that PDE5 activity (but not expression) is increased after SAH, leading to decreased cGMP levels. Sildenafil attenuates this increase in PDE5 activity and restores cGMP levels after SAH. Post-SAH initiation of sildenafil was found to decrease vasospasm and neuronal cell death and markedly improve neurological outcome without causing significant physiological side effects.

CONCLUSION

Sildenafil, a US Food and Drug Administration-approved drug with a proven track record of safety in humans, is a promising new therapy for vasospasm and neurological deficits after SAH.

A novel method of seminal vesicle preparation in isolated seminal vesicle experiments in the rat: ring preparation

In this study, we evaluated the efficacy of a novel method of seminal vesicle (SV) preparation-ring preparation method-in isolated SV experiments in the rat. Rat SVs were prepared as strips and rings and applied to organ baths. The relaxation responses by sodium nitroprusside or doxazosin and contractile responses by electrical field stimulation (EFS) were recorded in both groups. We compared the proportion of tissues that showed consistent responses to the stimuli-drug or EFS-in both groups. And magnitudes of the contractile or relaxation responses were also evaluated in the two groups. In strip preparations (n=20), six tissues (30%) showed stable responses to drugs and were regarded to be useful. However, in ring preparations (n=20), 13 tissues (65%) showed stable responses (P<0.001). Similarly, consistent contractile responses to the EFS were recorded in eight strips (40%) and 13 rings (65%) (n=20 in each group; P<0.05). The magnitudes of the relaxations by drugs were not different between the two methods (P=0.42) and the contractions by EFS were higher in ring preparations (P<0.05). The ring preparation seems to be better for responses to drugs and EFS compared with the strip preparations and, therefore, might be an alternative technique for in vitro SV experiments.

Acute effects of a single dose of phosphodiesterase type 5 inhibitor (sildenafil) on systemic arterial blood pressure during exercise and 24-hour ambulatory blood pressure monitoring in heart transplant recipients

BACKGROUND

Arterial systemic hypertension (SH) can be associated with a decrease in endothelium-dependent nitric oxide (NO). Sildenafil increases cyclic guanosine monophosphate (cGMP), a mediator of NO. However, little is known about the effects of PDE5 inhibition on 24-hour ambulatory pressure (ABP) and exercise blood pressure, noreprinephrine (Nor), and exercise capacity, especially after orthotopic heart transplantation (OHT).

METHODS

We studied 22 OHT patients who on the 1st day underwent a cardiopulmonary (CP) self-controlled treadmill 6' walk test (6') and, then, an ECG monitored CP treadmill maximal exercise test (Ex) within 60 and 90 minutes after oral Sildenafil (Sil; 50 mg) or placebo (Pl) given at random, and ABP. We determined at basal position (b), in the last minute of the 6' and at the peak Ex, the HR (bpm), Systolic blood pressure (SBP), and diastolic blood pressure (DBP), (mm Hg), VO2 (mL/kg/min), Slope VE/VCO2, exercise time (ET, min), distance (D; miles), and Nor (pg/mL). Also, after CP tests, 24-h SBP and DBP, the measurements were repeated on the 2nd day when the cross-over was done.

RESULTS

Sil significantly reduced blood pressure in the basal position and during exercise. It also promoted a significant reduction in SBP and DBP during 24 hours, daytime and nighttime. Sil did not change exercise capacity.

CONCLUSION

The NO-cGMP pathway seems to play a role in blood pressure control in OHT. In addition to antihypertensive therapy, PDE5 inhibition may have potential beneficial effects on hypertensive OHT.

Effect of Sildenafil and Rolipram on Adrenergic Responses in Isolated Human and Monkey Corpus Cavernosum

OBJECTIVE

Evaluate and compare effects of phosphodiesterase inhibitors (PDEIs), sildenafil and rolipram, on adrenergic contractile responses of human and monkey cavernosal smooth muscle.

METHODS

Human penises were obtained from patients undergoing gender reassignment surgery. Isolated human and monkey corpus cavernosum (CC) strips were suspended in tissue bath chambers for isometric tension experiments. The effects of the drugs on precontracted monkey and human CC and neurogenic contractions in human CC were investigated.

RESULTS

Both sildenafil and rolipram induced concentration-dependent relaxations of human and monkey CC strips precontracted with noradrenaline (NA). The IC(50) values, determined by reverse regression for nitroglycerin (NTG), isoprenaline, and sildenafil in monkey CC, were, respectively, 1.5+/-0.9x10(-7) M, 3.7+/-0.6x10(-6) M, and 1.7+/-0.7x10(-5) M. Similarly, in human CC muscle, sildenafil was weaker than NTG as a muscle relaxant. Sildenafil, 1.5 microM, reduced neurogenic contractions in human CC due to stimulation of predominantly adrenergic nerves. The suppressant effect of sildenafil on adrenergic transmission was attenuated in CC strips pretreated with N omega-nitro-L-arginine and overcome with a higher stimulus frequency or tetraethylammonium. Rolipram partially inhibited adrenergic excitatory response but without significantly affecting NA-induced contraction.

CONCLUSIONS

Sildenafil and rolipram induced concentration-dependent reversal of human and monkey CC tone mediated by NA. Both PDEIs attenuated contractile adrenergic response of human CC to electrical stimulation. The results also underline the importance of the cyclic adenosine monophosphate-dependent signalling pathway in regulating the tone. PDE4 inhibition in CC is an additional mechanism for erection and potential therapeutic adjunct.

Sildenafil improves the alveolar-capillary function in heart failure patients

BACKGROUND

Sildenafil is used for pulmonary hypertension treatment and its use is safe in chronic heart failure (HF) patients.

AIMS

To analyze the effects of sildenafil on lung mechanics, gas diffusion, exhaled nitric oxide (eNO) at rest and during exercise in chronic HF. We did so to evaluate if sildenafil prevents exercise-induced pulmonary edema formation.

METHODS

We studied 22 chronic HF males. We measured after a single dose of placebo, sildenafil (25 mg) and sildenafil (100 mg), lung diffusion (DLCO), molecular diffusion (DM), pulmonary capillary volume (VC), eNO, all at rest and during exercise, standard pulmonary function, and maximal cardiopulmonary exercise.

RESULTS

At rest sildenafil improved pulmonary mechanics and DLCO from 23.1+/-6.3 ml/mmHg/min to 23.9+/-6.4 (25 mg, p<0.05) and to 25.3+/-6.7 100 mg, p<0.02). Sildenafil (100 mg) prevents edema formation (highest DM/VC during exercise). At rest eNO was low and not affected by tested drugs. With light exercise eNO was higher with sildenafil 100 mg. Peak VO(2) increased with sildenafil from 1376+/-331 ml/min to 1471+/-375 (25 mg, p<0.01) and 1524+/-461 (100 mg, p<0.02). Peak VO(2) increase was related to DLCO improvement.

CONCLUSION

In chronic HF sildenafil increases exercise performance, improves lung mechanics and gas diffusion and prevents exercise-induced pulmonary edema formation probably by restoring NO pathways.

Early use of vacuum constriction device following radical prostatectomy facilitates early sexual activity and potentially earlier return of erectile function

To assess the efficacy of vacuum constriction devices (VCD) following radical prostatectomy (RP) and determine whether early use of VCD facilitates early sexual activity and potentially earlier return of erectile function. This prospective study consisted of 109 patients who underwent nerve-sparing (NS) or non-nerve-sparing (NNS) RP between August 1999 and October 2001 and developed erectile dysfunction following surgery. The patients were randomized to VCD use daily for 9 months (Group 1, N=74) or observation without any erectogenic treatment (Group 2, N=35). Treatment efficacy was analyzed by responses to the Sexual Health Inventory of Men (SHIM) (abridged 5-item International Index of Erectile Function (IIEF-5)), which were stratified by the NS status. Patient outcome regarding compliance, change in penile length, return of natural erection, and ability for vaginal intercourse were also assessed. The mean patient age was 58.2 years, and the minimum follow-up was 9 months. Use of VCD began at an average of 3.9 weeks after RP. In Group 1, 80% (60/74) successfully used their VCD with a constriction ring for vaginal intercourse at a frequency of twice/week with an overall spousal satisfaction rate of 55% (33/60). In all, 19 of these 60 patients (32%) reported return of natural erections at 9 months, with 10/60 (17%) having erections sufficient for vaginal intercourse. The abridged IIEF-5 score significantly increased after VCD use in both the NS and NNS groups. After a mean use of 3 months, 14/74 (18%) discontinued treatment. In Group 2, 37% (13/35) of patients regained spontaneous erections at a minimum follow-up of 9 months after surgery. However, only four of these patients (29%) had erections sufficient for successful vaginal intercourse and rest of patients (71%) sought adjuvant treatment. Of the 60 successful users, 14 (23%) reported a decrease in penile length and circumference at 9 months (range, 4-8 months) compared to 12/14 (85%) among the nonresponders. However, in control group 22/35 reported decrease in penile length and circumference. Early use of VCD following RP facilitates early sexual intercourse, early patient/spousal sexual satisfaction, and potentially an earlier return of natural erections sufficient for vaginal penetration.

The effects of chronic phosphodiesterase-5 inhibitor use on different organ systems

Phosphodiesterase-5 (PDE-5) inhibitors selectively inhibit PDE-5 enzymes that are present in various tissues like penile tissue, platelets, vascular, and smooth muscle tissue. The drug's actions on these tissues have lead to the successful therapeutic use in patients suffering from conditions such as erectile dysfunction (ED) and pulmonary hypertension. PDE-5 inhibitors (PDE-5i) act on the erectile tissue causing penile smooth muscle relaxation and vasodilatation leading to penile erection. In addition, in particular when used in conjunction with prostaglandin inhibitors, PDE-5i cause vasodilatation in pulmonary vasculature hence decreasing both the pulmonary arterial pressure and resistance. PDE-5i have also shown to mildly decrease blood pressure, increase cardiac index, and increase coronary blood flow in experimental animals as well as in human studies. The Food and Drug Administration (FDA) has approved three PDE-5i for the treatment of ED: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) and one for pulmonary hypertension: sildenafil (Revatio). These agents are highly selective for PDE-5 enzymes as compared to other subclasses of PDE enzymes and have the almost identical pharmacological action but slightly different pharmacokinetics. Only little data exist about long-term use of PDE-5i and their effects on different organ system. This paper reviews the current information available on chronic PDE-5 inhibitor use.

Semiquantitative imaging measurement of baseline and vasomodulated normal prostatic blood flow using sildenafil

The physiologic variability of blood flow to the prostate has not been studied until this time. We report the vasoactive effects of sildenafil and phenylephrine on blood flow of the normal prostate. Sildenafil increases prostate blood flow by approximately 75% and phenylephrine reduces the flow incrementally. Administration of these drugs with dynamic contrast-enhanced magnetic resonance imaging may improve the diagnosis of cancerous tissue because according to the literature, tumor angiogenic vessels lack the vasoactive physiologic response of the normal tissue.

Role of nitric oxide in the relaxation elicited by sildenafil in penile resistance arteries

PURPOSE

We investigated the role of the vascular endothelium and the L-arginine/nitric oxide pathway in the vasorelaxant effect of the phosphodiesterase type 5 inhibitor sildenafil in penile resistance arteries.

MATERIALS AND METHODS

Second or third order branches of the horse deep intracavernous penile artery were mounted in microvascular myographs. The vasodilator effects of sildenafil and the NO donor SNAP (S-nitrosoacetyl-D,L-penicillamine) were evaluated in the absence and presence of the endothelium and inhibitors of the NO/cGMP (cyclic guanosine 3',5'-monophosphate) pathway.

RESULTS

In phenylephrine precontracted, endothelium intact arteries sildenafil elicited potent relaxations that were markedly decreased by the blockade of soluble guanylate cyclase with ODQ (1H-[1,2,4]oxadiazolo[4-3a]quinoxalin-1-one). Endothelium removal and the inhibition of NO synthase with N(G)-nitro-L-arginine (L-NOARG) caused pronounced inhibition of sildenafil elicited relaxations but not of SNAP induced responses. Combined treatment with the cyclooxygenase blocker indomethacin and L-NOARG caused significantly greater inhibition of sildenafil relaxations than that produced by L-NOARG alone. Inhibitors of the cGMP (PKG) and the cAMP (cyclic adenosine 3',5'-monophosphate) dependent protein kinases Rp-8-Br-PET-cGMPS (beta-phenyl-1, N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp-isomer) and Rp-8-CPT-cAMPS (Rp-8-CPT-cAMPS (8-(4-chlorophenylthio) adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer), respectively, inhibited the sildenafil concentration-relaxation curves. The relaxant responses of SNAP were markedly decreased by PKG inhibitor and to a lesser extent by cAMP dependent protein kinase inhibitor.

CONCLUSIONS

The current results demonstrate a potent relaxant effect of sildenafil in penile resistance arteries due in part to cGMP accumulation and to the enhanced effects of basal released, endothelial derived NO acting through PKG activation. Cross-activation of the cAMP signaling pathway by sildenafil is also suggested.

Ca2+-activated K+ (KCa) channels are involved in the relaxations elicited by sildenafil in penile resistance arteries

The aim of the present study was to evaluate the role of K+ channels in the vasorelaxant effect of the phosphodiesterase 5 inhibitor, sildenafil, in isolated horse penile resistance arteries mounted in microvascular myographs. In phenylephrine-precontracted arteries, sildenafil elicited potent relaxations which were markedly reduced by raising extracellular K+, by the non-selective blocker of Ca2+-activated K+ channels (KCa), tetraethylammonium and by the blocker of large- and intermediate-conductance KCa channels, charybdotoxin. Sildenafil relaxant responses were also reduced by the selective inhibitor of large conductance KCa (BK(Ca)) channels iberiotoxin, but not by the blocker of small conductance KCa channels apamin. The inhibitor of the cGMP-dependent protein kinase (PKG), Rp-8-Br-PET-cGMPS, reduced the relaxations elicited by sildenafil but combined treatment with iberiotoxin and Rp-8-Br-PET-cGMPS did not further inhibit these relaxations, compared to the effect of either blocker alone. Iberiotoxin also shifted to the right the relaxations elicited by both the NO donor, S-nitrosoacetyl-D,L-penicillamine (SNAP) and the adenylate cyclase activator forskolin; treatment with both iberiotoxin and Rp-8-Br-PET-cGMPS did cause an additional inhibition. The present results demonstrate that the relaxant effect of sildenafil and NO in penile resistance arteries is due in part to activation of BK(Ca) channels through a PKG-dependent mechanism.

Relaxant effect of sildenafil in the rabbit basilar artery

We hypothesized that sildenafil, inhibitor of phosphodiesterase-5 (PDE-5), interacts with the nitric oxide (NO)-cGMP pathway in the cerebral arteries and shows vasoactive effects. To prove it in the isolated rabbit basilar artery, we compared the effects of sildenafil with other PDE-5 inhibitors, assessed the endothelial dependence of the vasoactive responses, and used modulators of the cGMP and cAMP signaling processes. Sildenafil (10 nM-0.1 mM) induced concentration-dependent relaxations of endothelin-1 (10 nM)-precontracted basilar artery, which were partially inhibited both in endothelium-denuded arteries and in arteries precontracted by depolarization with KCl (50 mM). Endothelin-1 (1 pM-30 nM) induced concentration-dependent contractions that were inhibited by sildenafil (0.1-100 microM). Zaprinast (10 nM-0.1 mM) and MBCQ (1 nM-0.1 mM), PDE-5 inhibitors, induced concentration-dependent relaxations with lower and higher potency than sildenafil, respectively. Sildenafil-induced relaxation was inhibited in arteries preincubated with the NO synthase inhibitor L-NAME (0.1 mM) or the soluble guanylyl cyclase inhibitor ODQ (10 microM). Preincubation with sildenafil (0.1 microM) enhanced the relaxations induced by acetylcholine (0.1 nM-0.1 mM) and the NO donor sodium nitroprusside (0.1 nM-0.1 mM), but not those induced by the cell-permeable cGMP analogue 8-Br-cGMP (1 nM-0.1 mM) and the adenylyl cyclase activator forskolin (0.1 nM-10 microM). These results show that sildenafil has vasoactive effects in isolated cerebral arteries. By enhancing the NO-cGMP signaling pathway in the cerebrovascular wall, sildenafil induces vasodilation, prevents vasoconstriction, and potentiates the effect of other NO-dependent vasodilators.

Cyclic AMP-specific and cyclic GMP-specific phosphodiesterase isoenzymes in human cavernous arteries--immunohistochemical distribution and functional significance

OBJECTIVES

It has been well established that male erectile dysfunction is frequently associated with vascular diseases. The normal function of cavernous arteries is considered a prerequisite to maintain sufficient blood flow to the trabecular spaces in order to enable penile erection. Contractility of cavernous arteries is regulated by the peripheral autonomic nervous system and endogenous factors released from the endothelial cell layer. A significant increase of blood flow in the central cavernous arteries is the initial event leading to penile tumescence and rigidity. Besides the significance of the nitric oxide/cyclic guanosine monophosphate (cGMP)-mediated mechanisms, the cyclic AMP (cAMP) signalling pathway is also involved in the regulation of tone of the erectile tissue, and interactions between cGMP- and cAMP-mediated mechanisms have been demonstrated. The aim of the present study was to investigate by means of immunohistochemistry the presence of the phosphodiesterase (PDE) isoenzymes 3, 4 (cAMP-specific PDEs) and 5 (cGMP-specific PDE) in thin sections of human central cavernous arteries (HCA) and their functional significance in the mechanism of vessel tone regulation.

METHODS

Functional experiments were performed using circular segments of HCA and strip preparations of the human corpus cavernosum (HCC). Relaxant effects induced by the cumulative addition of the PDE inhibitors milrinone (PDE3 inhibitor), rolipram (PDE4 inhibitor) and sildenafil (PDE5 inhibitor; 0.01, 0.1, 1 and 10 M) were studied in preparations of HCA and HCC challenged by 1 M norepinephrine (NE). Moreover, immunohistochemistry was carried out in order to evaluate the expression of PDE3, PDE4 and PDE5 in thin sections of HCA.

RESULTS

Milrinone, rolipram and sildenafil dose-dependently reversed the NE-induced tension of the isolated vascular segments and HCC strips with sildenafil being the most effective drug. Neither rolipram nor milrinone reached an EC50 value. Abundant immunoreactivities specific for PDE3, PDE4 and PDE5 were observed in the entire smooth musculature of the wall of HCA and resistance arteries. In addition, immunoreactivity for PDE4 was also detected in the cytoplasm of endothelial cells lining the cavernous arteries.

CONCLUSIONS

The cGMP-dependent relaxation of cavernous arteries is not only dependent on the normal function of the peripheral autonomic nervous system but also on the functional integrity of the vascular endothelium. The expression of the cGMP-specific PDE5 and the ability of the PDE5 inhibitor sildenafil to reverse the adrenergic tension of isolated segments of HCA underline the important role of the NO/cGMP pathway in the control of smooth muscle tone of human trabecular smooth musculature and penile cavernous arteries. Our results also suggest a significance of the cAMP-dependent signaling mechanisms in the regulation of tension of central HCAs. The present findings are also in support of the hypothesis of interactions between the cGMP- and cAMP-mediated signaling pathways in HCAs. Further investigations are indicated in order to outline potential differences between central HCAs and helicine resistance arteries. This may help to understand better the relations between structural and functional changes in the penile erectile tissue in patients with cardiovascular diseases and endothelial dysfunction.

Phosphodiesterase 5 and effects of sildenafil on cerebral arteries of man and guinea pig

Sildenafil (Viagra), a selective inhibitor of phosphodiesterase 5 (PDE5), induces headache and migraine. Although previously supposed to be a "vascular" headache, no significant cerebral artery dilatation was found in vivo. Thus, we hypothesised that PDE5 may not be present or that sildenafil is less effective on the cGMP hydrolysis in cerebral arteries, and that sildenafil may not be an effective dilator of cerebral arteries under baseline conditions. We evaluated the presence of PDE5 mRNA and protein in human arteries. Furthermore, the effects of two selective PDE5 inhibitors, sildenafil and UK-114,542, and a PDE1 inhibitor UK-90,234 on cGMP hydrolysis were investigated in human and guinea pig cerebral arteries. The vasoactive responses of the compounds were evaluated in guinea pig basilar arteries in vitro, with concomitant measurements of cAMP and cGMP. PDE5 was found in human middle cerebral arteries. Sildenafil and UK-114,542 inhibited cGMP hydrolysis concentration-dependently in both species. In guinea pig arteries, sildenafil induced an endothelium-dependent vasodilatation only at concentrations above 10 nM, which was augmented by sodium nitroprusside and attenuated by reduction of cGMP, but was cGMP independent at high concentrations. UK-114,542 was more and UK-90,234 was less potent than sildenafil. In conclusion, PDE5 is present in human and guinea pig cerebral arteries, and is inhibited by sildenafil at micromolar levels. Sildenafil in vitro is a poor dilator of guinea pig cerebral arteries unless a nitric oxide donor is co-administered, corresponding to the previous findings in vivo.

Sildenafil citrate and vacuum constriction device combination enhances sexual satisfaction in erectile dysfunction after radical prostatectomy

OBJECTIVES

To assess the effectiveness of combining sildenafil citrate with a vacuum constriction device (VCD) in men (after radical prostatectomy) unsatisfied with the results of the VCD alone.

METHODS

A total of 31 patients unsatisfied with the early use of VCD alone after radical prostatectomy (mean follow-up of 4.5 months) were instructed to take 100 mg of sildenafil 1 to 2 hours before VCD use for sexual intercourse. Patients used combination therapy for a minimum of five attempts before assessment with the abridged International Index of Erectile Function (IIEF) questionnaire and a visual analogue scale to gauge rigidity. The effect of combination therapy on the total IIEF-5 score and penile rigidity score were assessed.

RESULTS

Of the 31 patients, 7 (22%) had no improvement with the addition of sildenafil with VCD and discontinued the drug, and 24 (77%) reported improved penile rigidity and sexual satisfaction. The IIEF-5 score revealed statistically significant improvement in each domain, and patients reported that sildenafil enhanced their erections 100% of the time. The penile rigidity scores on a scale of 0 to 100 with the VCD alone averaged 55% (range 23% to 85%) for the men and 59% (range 26% to 90%) for their partners. With the addition of sildenafil, it increased to 76% for the men and 82% for their partners. Of the 24 men, 7 (30%) reported a return of natural erections at 18 months using combination therapy, with 5 of 7 reporting erections sufficient for vaginal penetration.

CONCLUSIONS

In this study, the addition of sildenafil with VCD improved sexual satisfaction and penile rigidity in patients unsatisfied with VCD alone after radical prostatectomy.

Peroxynitrite-induced relaxation in isolated canine cerebral arteries and mechanisms of action

The present study was undertaken to determine the vascular actions of peroxynitrite (ONOO(-)), the product of superoxide and nitric oxide (NO), in isolated canine cerebral arteries and to gain insight into its potential mechanisms of action. In the absence of any vasoactive agent, ONOO(-) (from 10(-7) to 10(-6) M) was able to reduce the basal tension. In prostaglandin F2alpha-precontracted canine basilar arterial rings, ONOO(-) elicited concentration-dependent relaxation at concentrations from 10(-8) to 10(-5) M. The effective concentrations producing approximately 50% maximal relaxation (EC(50)) to ONOO(-) were 4.06 x 10(-6) and 4.12 x 10(-6) M in intact and denuded rings, respectively (P > 0.05). No significant differences in relaxation responses were found in ring preparations with or without endothelium (P > 0.05). The presence of either 5 microM methylene blue (MB) or 5 microM 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one (ODQ) significantly inhibited the relaxations induced by ONOO(-). Tetraethylammonium chloride (T-2265) significantly decreased the ONOO(-)-induced relaxations in a concentration-dependent manner. However, ONOO(-) had no effect on rings precontracted by high KCL (P > 0.05). Addition of low concentrations of calyculin A (50 nM) was able to abolish the ONOO(-)-induced relaxation. Furthermore, ONOO(-) significantly inhibited calcium-induced contractions of K(+)-depolarized canine cerebral rings in a concentration-related manner. Lastly, a variety of pharmacological agents and antagonists including L-NMMA, l-arginine, indomethacin, atropine, naloxone, diphenhydramine, cimetine, glibenclamide, haloperidol, etc., did not influence the relaxant effects of ONOO(-) on the rings. Our new results suggest that ONOO(-)-triggered relaxation, on canine cerebral arteries, is mediated by elevation of cyclic guanosine monophosphate (cGMP) levels, membrane hyperpolarization via K+ channel activation, activation of myosin light chain phosphatase activity, and interference with calcium movement and cellular membrane Ca(2+) entry.

Histopathological effects of sildenafil citrate on rat corpus cavernosum

Sildenafil citrate (Viagra) is widely used for the treatment of erectile dysfunction with various etiologies. The aim of the present study was the investigation of histopathological effects of sildenafil citrate on rat corpus cavernosum using tight and electron microscopical techniques. Twenty male rats were divided into two groups. The first group (n = 10) was used as a control and the second group (n = 10) was treated with sildenafil citrate. Penile tissue was collected, fixed with formalin and embedded in paraffin for light microscopy, or fixed with gluteraldehyde and osmium tetroxide and embedded in Epon for electron microscopy. Light microscopical analysis showed that the corpus cavernosum was elongated and the number of blood vessels was increased. The amount of connective tissue in the penis was increased and dense collagen and smooth muscle fibers were observed in treated rats. Electron microscopical analysis showed that stromal structures of the corpus cavernosum (collagen fibers and number of cellular elements) were increased in treated rats. Fibroblasts showed signs of activation and the number of other stromal cells was increased. Immature newly synthesized collagen fibers were observed and penetrated endothelial basement membranes. In addition, endothelial cells also showed signs of activation such as cytoplasmic granules in treated rats, whereas the surface area of blood vessels was increased and basement membranes were thickened. These histopathological changes due to treatment with sildenafil citrate indicate that prolonged use of sildenafil citrate may increase the risk of fibrosis in the penis.

Sildenafil effects on exercise, neurohormonal activation, and erectile dysfunction in congestive heart failure: a double-blind, placebo-controlled, randomized study followed by a prospective treatment for erectile dysfunction

BACKGROUND

Erectile dysfunction (ED) is common in patients with congestive heart failure (CHF). ED reduces quality of life, and it may affect compliance, thereby impairing the success of CHF treatment.

METHODS AND RESULTS

In the first phase (fixed-dose double-blind, randomized, placebo-controlled, two-way crossover study), we studied in 23 men with CHF the effects of 50 mg sildenafil on exercise and neurohormonal activation. Patients underwent a treadmill 6-minute cardiopulmonary walking (6'WT) test followed by a maximal cardiopulmonary exercise test (ET). In the second phase, patients received sildenafil, taken as required for ED. Sildenafil reduced the heart rate (HR) (bpm) before the 6'WT (from 75+/-15 to 71+/-14, P=0.02) and ET (from 75+/-15 to 71+/-15, P=0.02); the systolic blood pressure (mm Hg) before the 6'WT (from 116+/-18 to 108+/-18, P=0.004) and ET (from 116+/-15 to 108+/-17, P=0.001); the diastolic blood pressure before the 6'WT (from 69+/-9 to 63+/-11, P=0.01) and ET (from 70+/-8 to 65+/-10, P=0.004); and the Ve/VCO2 slope during the 6'WT (from 32+/-7 to 31+/-6, P=0.04) and ET (from 33+/-8 to 31+/-5, P=0.03). Sildenafil attenuated the HR increment during the 6'WT (P=0.003) and ET (P=0.000). Sildenafil increased the peak *O2 from 16.6+/-3.4 to 17.7+/-3.4 mL/kg per min (P=0.025) and the exercise time from 12.3+/-3.4 to 13.7+/-3.2 minutes (P=0.003). Sildenafil improved most scores of International Index of Erectile Function.

CONCLUSIONS

Sildenafil was tolerated and effective for ED treatment in CHF, and improved the exercise capacity. The reduction of HR during exercise with sildenafil could theoretically decrease the myocardial oxygen consumption during sexual activity.

Relaxation induced by milrinone and rolipram in human penile arteries and veins

We studied the relaxant effects of milrinone, an inhibitor of phosphodiesterase 3, and rolipram, an inhibitor of phosphodiesterase 4, on contracted human penile dorsal artery and deep dorsal vein. Vascular rings from 12 multi-organ donors were suspended in organ baths for isometric recording of tension. Both milrinone and rolipram inhibited (100%) the contraction induced by noradrenaline and shifted the relaxation-response curves to the cAMP forming agents prostaglandin E(1) and forskolin to the left. The findings indicate that the cAMP pathway appears to be a main determinant of relaxation in human penile vessels.

Sildenafil and T-1032, phosphodiesterase type 5 inhibitors, showed a different vasorelaxant property in the isolated rat aorta

The vasorelaxant effects of sildenafil and T-1032 [methyl-2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridinylmethoxy)-4-(3,4,5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate], two phosphodiesterase type 5 inhibitors, were examined in the isolated rat aorta. Sildenafil and T-1032, both of which have almost the same potency and selectivity regarding phosphodiesterase type 5 inhibitory activity, produced a similar, moderate, relaxation at 10(-10) to 10(-7) M (sildenafil: 66.8 +/- 13.7%; T-1032: 77.9 +/- 10.8% at 10(-7) M). However, sildenafil, but not T-1032, produced further relaxation at the higher concentrations (sildenafil: 102.0 +/- 0.6%; T-1032: 81.0 +/- 7.2% at 10(-4) M, P < 0.05). Sildenafil also produced a more potent relaxation than did T-1032 at the high concentrations (10(-5) and 10(-4) M) in endothelium-denuded aortic rings and in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor (3 x 10(-4) M). Moreover, the high concentrations of sildenafil, but not of T-1032, caused a rightward shift of the concentration-response curve for calcium chloride in K(+)-depolarized endothelium-denuded preparations. In the ligand binding assay for the L-type Ca(2+) channels, the affinities of sildenafil at 10(-5) M for binding sites of nitrendipine and (--)-desmethoxyverapamil [(--)- D888] (35.2 +/- 3.3% and 35.8 +/- 1.9%, respectively) were higher than those of T-1032 (11.8 +/- 4.0% and -13.1 +/- 1.3%, respectively, P < 0.05). Regarding cyclic nucleotide levels, both phosphodiesterase type 5 inhibitors increased cGMP levels at 10(-6) M. However, sildenafil, but not T-1032, further increased cGMP levels at the higher concentrations (sildenafil: 15.7 +/- 2.7 pmol/mg protein; T-1032: 5.6 +/- 0.6 pmol/mg protein at 10(-4) M, P < 0.05). These results suggested that high concentrations of sildenafil had additional vasorelaxant properties through mechanisms other than phosphodiesterase type 5 inhibition. Sildenafil-induced relaxation appears to be due to inhibition of the external Ca(2+)-dependent cascade for contraction and/or to an increase in cGMP levels. In contrast, T-1032 only showed a vasorelaxant property due to phosphodiesterase type 5 inhibition. In conclusion, T-1032 appears to be a specific phosphodiesterase type 5 inhibitor compared with sildenafil and a useful compound to examine the physiological function of phosphodiesterase type 5.

Sildenafil inhibits agonist-evoked rat uterine contractility: influence of guanylyl cyclase inhibition

Sildenafil shows a potent relaxant effect on corpus cavernosum smooth muscles by prolonging cyclic guanosine monophosphate (cGMP) actions. We investigated whether this inhibitory effect of sildenafil was also displayed on the uterine musculature. Isolated uteri of non-pregnant rats were used to measure the possible sildenafil-induced inhibition of contractions evoked by various oxytocic agents, viz., prostaglandin E2, oxytocin and acetylcholine. The relation of these effects to sildenafil action on cGMP was also examined, using methylene blue as a guanylyl cyclase inhibitor. Sildenafil (30 and 100 nM) was found to shift to the right the non-cumulative concentration-response curves of the test agonists in a concentration-dependent manner. The shift was accompanied by a reduction in the maximal response of the tissue to all uterine stimulants selected. Sildenafil also elicited a marked concentration-dependent increase in EC25 of prostaglandin E2, oxytocin and acetylcholine, as compared to their respective control values. Preincubation of the uterine strip with methylene blue (10 microM) reduced the inhibitory effects of sildenafil on oxytocin- and acetylcholine-evoked contractions, at submaximal concentrations of each agonist. The results suggest that sildenafil inhibits the uterotonic potentials of various oxytocic agents and that this effect could be probably related to the drug's action on cGMP.

Inhibition of neuroeffector transmission in human vas deferens by sildenafil

Sildenafil (0.1 - 30 microM), a cyclic GMP phosphodiesterase 5 (PDE 5) inhibitor, induced inhibition of electrically evoked contractions of ring segments of human vas deferens from 34 vasectomies. Zaprinast (0.1 - 100 microM), another PDE 5 inhibitor, and the nitric oxide (NO) donor sodium nitroprusside (SNP) (0.1 - 100 microM) had no effect on neurogenic contractions. The inhibition induced by sildenafil was not modified by the inhibitor of guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) (1 - 30 microM) but it was abolished by the K(+) channel blockers tetraethylammonium (TEA, 1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM). Sildenafil, zaprinast and SNP did not affect the contractions induced by noradrenaline. SNP (10 microM) caused elevation of cyclic GMP levels that was potentiated by sildenafil (10 microM) and zaprinast (100 microM). ODQ (10 microM) inhibited the increase in cyclic GMP. Sildenafil inhibits adrenergic neurotransmission in human vas deferens. The inhibition is not related to accumulation of cyclic GMP but is probably due to activation of prejunctional large-conductance Ca(2+)-activated K(+) channels.

Relaxation induced by cGMP phosphodiesterase inhibitors sildenafil and zaprinast in human vessels

BACKGROUND

Sildenafil is currently used in the treatment of erectile dysfunction. However, assessment of direct effects of sildenafil on coronary arteries and on arteries used as coronary grafts is unknown. This study was designed to investigate the effects of sildenafil on contracted human coronary, internal mammary, and radial arteries obtained from multiorgan donors. The observations were extended to forearm veins. Zaprinast was included in this study for comparison.

METHODS

Segments of left coronary, internal mammary, and radial arteries, and forearm veins were obtained from 16 multiorgan donors. Vascular rings were suspended in organ bath chambers and isometric tension was recorded. Then the effects of sildenafil, zaprinast, and sodium nitroprusside on precontracted vessels were studied.

RESULTS

Sildenafil (10(-8) - 3 x 10(-5) mol/L) caused concentration-dependent relaxation in the internal mammary arteries, radial arteries, and forearm veins. In the coronary arteries, sildenafil had a modest relaxant effect. In addition, sildenafil amplified the relaxation induced by sodium nitroprusside in all four vessels. Relaxation was unaffected by the inhibitor of nitric oxide synthase NG-monomethyl-L-arginine (10(-4) mol/L). Compared with zaprinast, sildenafil was eight to ten times more potent in terms of EC50 values.

CONCLUSIONS

The direct relaxant effects of sildenafil together with its synergistic interaction with nitric oxide donors should be considered in patients undergoing coronary bypass surgery, patients with low blood pressure, and patients receiving antihypertensive regimes.