Mechanisms of direct relaxant effect of sildenafil, tadalafil and vardenafil on corpus cavernosum

3D human foreskin model for testing topical formulations of sildenafil citrate

Sildenafil citrate is an approved drug used for the treatment of erectile dysfunction and premature ejaculation. Despite a widespread application, sildenafil citrate shows numerous adverse cardiovascular effects in high-risk patients. Local transdermal drug delivery of this drug is therefore being explored as an interesting and noninvasive alternative administration method that avoids adverse effects arised from peak plasma drug concentrations. Although human and animal skin represents the most reliable models to perform penetration studies, they involve a series of ethical issues and restrictions. For these reasons new in vitro approaches based on artificially reconstructed human skin or "human skin equivalents" are being developed as possible alternatives for transdermal testing. There is little information, however, on the efficiency of such new in vitro methods on cutaneous penetration of active ingredients. The objective of the current study was to investigate the sildenafil citrate loaded in three commercial transdermal vehicles using 3D full-thickness skin equivalent and compare the results with the permeability experiments using porcine skin. Our results demonstrated that, while the formulation plays an imperative role in an appropriate dermal uptake of sildenafil citrate, the D coefficient results obtained by using the 3D skin equivalent are comparable to those obtained by using the porcine skin when a simple drug suspension is applied (1.17 × 10-10 ± 0.92 × 10-10 cm2/s vs 3.5 × 102 ± 3.3 × 102 cm2/s), suggesting that in such case, this 3D skin model can be a valid alternative for ex-vivo skin absorption experiments.

Inhibition of Cyclic GMP Export by Multidrug Resistance Protein 4: A New Strategy to Treat Erectile Dysfunction?

BACKGROUND

Intracellular cyclic guanosine monophosphate (cGMP) concentrations are regulated by degradation enzymes (phosphodiesterases) and by active transport across the plasma membrane by multidrug resistance proteins (MRPs) 4 and 5.

AIM

To evaluate the functional effect of MRP-4 inhibition and the role of MRP-4-mediated cGMP export in mouse corpora cavernosa.

METHODS

Isometric tension of mouse corpora cavernosa was measured after cumulative addition of MK-571, an inhibitor of MRP-4, or sildenafil, a phosphodiesterase type 5 inhibitor. In addition, the effect of MRP-4 inhibition on cGMP-independent and cGMP-dependent relaxations was studied. In vivo intracavernosal pressure and mean arterial pressure measurements were performed after intracavernosal injection of MK-571. The effect of MRP-4 inhibition on cGMP content was determined using an enzyme immunoassay kit.

OUTCOMES

Measurement of the effect of MK-571 on cGMP content, relaxant responses of mouse corpora cavernosa to cGMP-independent and cGMP-dependent vasodilating substances, and determination of the ratio of intracavernosal pressure to mean arterial pressure after intracavernosal injection of MK-571.

RESULTS

MK-571 and sildenafil relaxed the corpora cavernosa concentration dependently, with sildenafil being the more potent relaxing compound. Furthermore, MK-571 enhanced relaxing responses to cGMP-dependent substances, such as sodium nitroprusside, sildenafil, acetylcholine, and electrical field stimulation, with the latter even under in vitro diabetic conditions. In contrast, cGMP-independent relaxations were not altered by MRP-4 inhibition. Intracavernosal administration of MK-571 significantly increased intracavernosal pressure, with minimal effect on mean arterial pressure. The cGMP analysis showed that MRP-4 inhibition was accompanied by increased cGMP levels.

CLINICAL TRANSLATION

MRP-4, at least when targeted locally in the penis or when combined with a phosphodiesterase type 5 inhibitor, might be a valuable alternative strategy for the treatment of (diabetic) erectile dysfunction.

STRENGTHS AND LIMITATIONS

This study is the first to demonstrate an in vitro direct relaxant and an in vivo pro-erectile effect of the MRP-4 inhibitor, MK-571, on mouse corpora cavernosa. However, the functional effect of MRP-5-mediated export in mouse corpora cavernosa was not explored, which has been suggested to play the predominant role in cGMP export.

CONCLUSION

Inhibition of MRP-4 increases basal and stimulated levels of cGMP, leading to corpora cavernosa relaxation and penile erection. Therefore, in addition to degradation of cGMP, export of cGMP by MRP-4 could contribute substantially to regulating cGMP levels in mouse corpora cavernosa. Boydens C, Pauwels B, Vanden Daele L, Van de Voorde J. Inhibition of Cyclic GMP Export by Multidrug Resistance Protein 4: A New Strategy to Treat Erectile Dysfunction? J Sex Med 2017;14:502-509.

The Relationship between Solubility and Transdermal Absorption of Tadalafil

PURPOSE

The aim of this study was to find a relationship between drug solubility and its transdermal permeation and find the best vehicle composition to improve transdermal permeation of Tadalafil.

METHODS

Pure or binary mixtures of commonly used solvents in pharmaceutical sciences including ethanol, glycerin, N-methyl pyrrolidone (NMP), polyethylene glycol (PEG) 400 and propylene glycol (PG) were evaluated for drug solubility and transdermal delivery through the exercised rat skin employing Franz diffusion cells.

RESULTS

Tadalafil showed higher solubility in NMP compared to the other solvents. The amount of Tadalafil permeation from the pure vehicles was ranked as follow: Ethanol >glycerin >NMP>PEG 400 >PG. Furthermore, the solubility and transdermal delivery from binary mixtures of NMP and PG were higher than that obtained from pure PG, and accordingly, both increased with increasing NMP concentration in the binary solvent mixtures. The Flux values were determined as following order for Ethanol>NMP>glycerin>PG>PEG 400.

CONCLUSION

Generally, increase in Tadalafil solubility resulted in a decrease in its skin penetration rate and amount. However, NMP exhibited substantial drug skin penetration rate and amount accompanying with appropriate drug solvency. In conclusion, the results of this study introduced NMP as a solvent suitable for application in the formulation of topically applied drug delivery systems.

The effects of the combined use of a PDE5 inhibitor and medications for hypertension, lower urinary tract symptoms and dyslipidemia on corporal tissue tone

ED is closely associated with its comorbidities (hypertension, dyslipidemia and lower urinary tract symptoms (LUTS)). Therefore, several drugs have been prescribed simultaneously with PDE5 inhibitors. If a specific medication for ED comorbidities has enhancing effects on PDE5 inhibitors, it offers alternative combination therapy in nonresponders to monotherapy with PDE5 inhibitors and allows clinicians to treat ED and its comorbidities simultaneously. To establish theoretical basis of choosing an appropriate medication for ED and concomitant disease, we examined the effects combining a PDE5 inhibitor with representative drugs for hypertension, dyslipidemia and LUTS on relaxing the corpus cavernosum of rabbits using the organ-bath technique. The effect of mirodenafil on relaxing phenylephrine-induced cavernosal contractions was significantly enhanced by the presence of 10(-4) M losartan, 10(-6) M nifedipine, 10(-6) M amlodipine, 10(-7) M doxazosin and 10(-9) M tamsulosin (P<0.05). The maximum relaxation effects were 47.2±3.8%, 57.6±2.6%, 64.0±3.7%, 76.1±5.7% and 71.7±5.4%, respectively. Enalapril and simvastatin had no enhancing effects. The relaxation induced by sodium nitroprusside alone (39.0±4.0%) was significantly enhanced in the presence of the 10(-4) M losartan (66.0±6.0%, P<0.05). Tetraethylammonium (1 mM) significantly inhibited the enhancement effects of tamsulosin and doxazosin on mirodenafil-induced relaxation (doxazosin: 76.1±5.7% vs 45.3±2.3%; tamsulosin: 71.7±5.4% vs 48.1±3.5%). On the basis of these findings, losartan seemed to induce synergistic effects through an interaction with nitric oxide. In addition, K(+) channel activation could be one of the mechanisms for the synergistic effect of combining mirodenafil with doxazosin or tamsulosin. We believe that the combination of a PDE5 inhibitor with losartan, nifedipine, amlodipine, doxazosin or tamsulosin could be a pharmacologic strategy for simultaneously treating ED and its comorbidities and increasing response rates to PDE5 inhibitors.

Vardenafil ameliorates calcium mobilization in pulmonary artery smooth muscle cells from hypoxic pulmonary hypertensive mice

BACKGROUND AND AIMS

Vardenafil has been found to be potent in pulmonary hypertension; however, the underlying mechanisms remain poorly understood. To address this issue, we investigated the underlying mechanisms of vardenafil in the contribution of Ca(2+) signaling and mobilization in modifying vasoconstriction of pulmonary arteries in hypoxic mice.

METHODS

Hemodynamic measurements and morphological studies were performed. Muscle tension was measured by PowerLab system. I(Ca,L) was recorded using a perforated patch-clamp technique. [Ca(2+)](i) was measured using a fluorescence imaging system.

RESULTS

Vardenafil greatly inhibited RVSP increases, RV hypertrophy and ameliorated pulmonary artery remodeling in response to chronic hypoxia. Membrane depolarization following 50 mM high K(+)-caused muscle contraction significantly decreased from 101.7 ± 10.1 in the hypoxia group to 81.8 ± 5.0 mg in hypoxia plus vardenafil arteries. Fifty mM high K(+)-elicited increase [Ca(2+)](i) was markedly decreased from 610.6 ± 71.8 in hypoxia cells to 400.3 ± 47.2 nM in hypoxia plus vardenafil cells. Application of vardenafil greatly inhibited the density of I(Ca,L) by 37.7% compared with that in the hypoxia group. Administration of 1 μM phenylephrine to stimulate α(1)-adrenergic receptor resulted in a smaller increase in [Ca(2+)](i) in hypoxia plus vardenafil cells than that in hypoxia cells. One hundred μM ATP-mediated increase in [Ca(2+)](i) was also inhibited in vardenafil-hypoxia group (from 625.8 ± 62.3 to 390.9 ± 38.1 nM), suggesting that internal calcium reserves contribute to neurotransmitter-induced Ca(2+) release from the SR through IP(3)Rs in PASMCs.

CONCLUSIONS

Vardenafil may effectively block Ca(2+) influx through L-type Ca(2+) channel and inhibit the Ca(2+) release from SR through IP(3)Rs, thus enhancing its vasorelaxation of pulmonary arteries under hypoxia conditions.

Intravenous sildenafil as a preconditioning drug against hemodynamic consequences of warm ischemia-reperfusion on the kidney

PURPOSE

We designed an experimental model of renal ischemia-reperfusion to evaluate the preemptive effect of intravenous sildenafil according to the dose administered (0.7 vs 1.4 mg/kg) and the time of administration (30 minutes before ischemia or during ischemia).

MATERIALS AND METHODS

A total of 20 minipigs were divided into groups of 4 each, including group 1-control, group 2-sildenafil 0.7 mg/kg intravenously 30 minutes before vascular clamping, group 3-sildenafil 0.7 mg/kg intravenously during warm ischemia, group 4-sildenafil 1.4 mg/kg intravenously 30 minutes before vascular clamping and group 5-sildenafil 1.4 mg/kg intravenously during warm ischemia. The ischemia-reperfusion model was applied using laparotomy and right kidney vascular clamping for 30 minutes, followed by unclamping and reperfusion for 45 minutes. Renal vascular flow and systemic mean arterial pressure were recorded for 45 minutes after unclamping. Mean values were compared using Student t test with significance considered at p <0.05.

RESULTS

Sildenafil led to a decrease in arterial pressure compared to that in controls, especially at the dose of 1.4 vs 0.7 mg/kg, including 113.77, 109.76, 106.12, 97.41 and 82.85 mm Hg in groups 1 to 5, respectively. Renal vascular flow was significantly higher in groups 2 and 3 than in groups 1, 4 and 5 (112.82 and 111.33 vs 88.25, 87.91 and 84.37 ml per minute, respectively, p = 0.000).

CONCLUSIONS

The effect of intravenous sildenafil as a preemptive drug against the hemodynamic effects of renal ischemia-reperfusion is dose dependent. The 0.7 mg/kg dose significantly increased reperfusion renal vascular flow with a small decrease in arterial pressure compared to the 1.4 mg/kg dose.

Chuanxiongzine relaxes isolated corpus cavernosum strips and raises intracavernous pressure in rabbits

It has been shown that there are many Chinese traditional herbals that can enhance sexual activity. Chuanxiongzine is a vasoactive ingredient that has been isolated and purified from Ligusticum chuanxiong Hort. In previous studies, it has been found that chuanxiongzine was effective in relaxing rabbit corpus cavernosum smooth muscle. We determined the effects of chuanxiongzine on relaxation of isolated corpus cavernosum strips in vitro and on increase of intracavernous pressure (ICP) in vivo in rabbits. Chuanxiongzine caused a concentration-dependent relaxation of phenylephrine precontracted isolated corpus cavernosum strips (EC₅₀ 1.58 × 10⁻⁴ mol l⁻¹), which were endothelium independent and NO independent. However, the guanylyl cyclase inhibitor 1-H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one significantly shifted the chuanxiongzine concentration–response relationship to the right. Although there was no significant difference in the level of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) in isolated corpus cavernosum strips treated with chuanxiongzine or vehicle, chuanxiongzine caused a significant rise in the level of cGMP and cAMP in isolated corpus cavernosum strips pretreated with the activator of adenylyl cyclase forskolin and the source of NO sodium nitroprusside. In an in vivo study, chuanxiongzine dose-dependently raised ICP after the intracavernous injection of its cumulative doses (0.5, 1, 2 and 5 mg kg⁻¹). The ICP increased from baseline to 19.1±3.7, 24.8±2.1, 30.2±4.8 and 39.7±6.1 mm Hg, respectively, and the duration of tumescence ranged from 8.5±2.8 to 22.9±7.3 min. Our results show that chuanxiongzine can relax isolated corpus cavernosum strips of rabbits in vitro and increase ICP of rabbits in vivo, which is neither endothelium dependent nor NO dependent, but may be partly mediated by the inhibition of cAMP phosphodiesterase or cGMP phosphodiesterase.

Vardenafil-induced relaxation and cyclic nucleotide levels in normal and obstructed rat urinary bladder

OBJECTIVE

To study the effects of the phosphodiesterase-5 inhibitor, vardenafil, on contraction and cyclic nucleotide levels in isolated detrusor preparations with and without mucosa, from control rats and rats with partial urethral obstruction (PUO) and intact mucosa.

MATERIALS AND METHODS

Female Sprague-Dawley rats were divided into groups subjected to PUO for 14 days (six), and sham-operated control rats (12). Detrusor preparations were mounted in organ baths and effects of increasing concentrations of vardenafil (1 nm to 100 microm) assessed on carbachol-activated (1 microm) preparations, and on contractions induced by transmural activation of nerves (electrical field stimulation, EFS). Levels of cGMP and cAMP were determined using radioimmunoassays.

RESULTS

Vardenafil caused concentration-dependent relaxations of carbachol-contracted detrusor, the mean (sd) of which at 100 microm was 91 (4)% in control and 100% in PUO rats. The -log 50% inhibitory concentration (IC(50)) was 4.41 (0.08) and 4.73 (0.05) (P < 0.01), respectively. Removing the mucosa increased the relaxant effect of vardenafil at 1-10 microm (P < 0.05) although -log IC(50) values were unaffected compared to the control. The cGMP levels ( pmol/mg protein) in control preparations increased from 2.5 (0.6) to 5.0 (0.8), and from 1.4 (0.2) to 7.2 (1.3) in obstructed bladders. In mucosa-denuded preparations the cGMP content increased from 0.6 (0.1) to 1.6 (0.4) in response to vardenafil. In control rats, the levels of cAMP increased from 12.8 (2.5) to 18.9 (0.9) (P < 0.05) after vardenafil. In mucosa-denuded preparations the cAMP levels after vardenafil increased from 16.5 (2.11) to 37.8 (3.4) (P < 0.01). In PUO bladders, the tissue content of cAMP increased from 12.6 (2.4) to 20.6 (3.4) (P < 0.01). Vardenafil concentration-dependently inhibited nerve-induced contractions in all groups studied. At 100 microm 19 (3)% of the control contraction remained, vs 8 (1)% for preparations from obstructed rats, and 11 (4)% in mucosa-denuded preparations.

CONCLUSION

In normal rats, vardenafil relaxed carbachol- and inhibited EFS-induced contractions of detrusor preparations with and without urothelium, and in PUO rats with urothelium. Relaxations were accompanied by increases in both cAMP and cGMP content. It is proposed that vardenafil-induced relaxation of rat detrusor, also in obstructed and mucosa-denuded preparations, is mediated via cAMP.

Effect of the phosphodiesterase 5 inhibitors sildenafil, tadalafil and vardenafil on rat anococcygeus muscle: functional and biochemical aspects

1. The anococcygeus muscle is part of the erectile machinery in male rodents. Phosphodiesterase (PDE) 5 inhibitors enhance and prolong the effects of cGMP, which has a key role in penile erection. The aim of the present study was to provide a functional and biochemical comparison of the three PDE5 inhibitors, namely sildenafil, tadalafil and vardenafil, in the rat anococcygeus muscle. 2. Muscle strips were mounted in 4 mL organ baths and isometric force recorded. Levels of cGMP were measured using an enzyme immunoassay kit. Western blots were used to determine PDE5 protein expression. 3. The PDE5 inhibitors concentration-dependently relaxed carbachol-precontracted anococcygeus muscle; however, vardenafil was more potent (pEC(50) = 8.11 +/- 0.05) than sildenafil (7.72 +/- 0.06) or tadalafil (7.69 +/- 0.05). Addition of N(G)-nitro-l-arginine methyl ester (100 micromol/L) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L) to the organ baths caused significant rightward shifts in concentration-response curves for all PDE5 inhibitors. 4. Sildenafil, tadalafil and vardenafil (all at 0.1 micromol/L) caused leftward shifts in the glyceryl trinitrate (GTN) concentration-response curves (by 4.0-, 3.7- and 5.5-fold, respectively). In addition, all three PDE5 inhibitors significantly potentiated relaxation responses to both GTN (0.01-10 micromol/L) and electrical field stimulation (EFS; 1-32 Hz), with vardenafil having more pronounced effects. 5. All three PDE5 inhibitors reduced EFS-evoked contractions in a concentration-dependent manner over the concentration range 0.001-1 micromol/L. There were no significant differences between the effects of the three PDE5 inhibitors. 6. Vardenafil (0.01-0.1 micromol/L) was more potent in preventing cGMP degradation in vitro than sildenafil (0.01-0.1 micromol/L) and tadalafil (0.01-0.1 micromol/L). 7. Under control conditions, the expression of PDE5 was higher in the anococcygeus muscle than in the corpus cavernosum. 8. In conclusion, PDE5 inhibitors enhance exogenous and endogenous nitric oxide-mediated relaxation in the rat anococcygeus muscle. The potency of vardenafil was greater than that of either sildenafil or tadalafil.

[PDE5 inhibitors. A new option in the treatment of ureteral colic?]

BACKGROUND

PDE5 inhibitors represent the gold standard in the medical therapy of erectile dysfunction (ED). Promising results have been published regarding further urological indications such as treatment of ureteral colic. The aim of the present study was to evaluate the functional effects of the PDE5 inhibitors sildenafil (SIL), vardenafil (VAR), and tadalafil (TAD) on tissue tension and cyclic nucleotide levels of human ureteral smooth muscle segments in vitro.

METHODS

Relaxant responses of human ureteral smooth muscle were investigated in vitro using the organ bath technique. Cyclic nucleotides cAMP and cGMP were determined by specific radioimmunoassays.

RESULTS

Relaxing effects of ureteral muscle tension were observed in the rank order VAR>SIL>TAD. While only VAR significantly elevated cGMP levels 3.3-fold over control, no increase for cAMP levels was observed.

CONCLUSIONS

Our data provide evidence that cGMP is involved in the control of the normal function of the smooth musculature of the human ureter. Our findings suggest the potential of using selective inhibitors of PDE isoenzymes in the treatment of ureteral colic.

Mechanisms of the relaxant effect of vardenafil in rat penile arteries

The aim of the present study was to investigate the mechanisms underlying the vasorelaxation induced by the selective phosphodiesterase 5 (PDE5) inhibitor vardenafil in rat penile small arteries. Segments of the rat dorsal penile artery were mounted in microvascular myographs for isometric tension recording. Concentration-response curves for vardenafil (1 nM-3 microM) and other PDE inhibitors (sildenafil, rolipram and milrinone) were constructed by adding cummulative concentrations of the drugs to arteries precontracted with phenylephrine. The effect of mechanical endothelial cell removal and of selective blockers of the nitric oxide (NO)/cGMP pathway and K+ channels were evaluated on the vardenafil relaxant responses. Vardenafil was the most potent of the four PDE inhibitors tested that maximally relaxed penile arteries, pD2 and maximum relaxation being 6.96+/-0.08 and 97+/-1% (n=48), respectively. Blockade of guanylate cyclase with ODQ (5 microM), mechanical removal of the endothelium or inhibition of NO synthase with l-NOARG (100 microM) markedly reduced vardenafil-induced relaxations, without altering maximum response. Inhibitors of both the cGMP-dependent (PKG) and the cAMP-dependent (PKA) protein kinases, Rp-8-Br-PET-cGMPS (5 microM) and Rp-8-CPT-cAMPS (50 microM), respectively, both reduced vardenafil relaxant responses and the later abolished that of rolipram. Vardenafil-elicited relaxation was reduced by the selective inhibitor of the large-conductance Ca2+-activated K+ channels (BK(Ca)), iberiotoxin (30 nM) and also by the ATP-sensitive K+ channel (K(ATP)) inhibitor, glibenclamide (1 microM). Vardenafil induces a potent vasodilatation in rat penile arteries that is partially dependent on the endothelium and the NO/cGMP pathway and involves activation of both BK(Ca) and K(ATP) channels.

Combination of alfuzosin and tadalafil exerts in vitro an additive relaxant effect on human corpus cavernosum

INTRODUCTION

Phosphodiesterase type 5 (PDE5) inhibitors, such as tadalafil, are a first-line treatment for erectile dysfunction (ED). Nevertheless, some patients do not respond to this treatment. Clinical data suggest that the addition of alpha1-adrenoceptor blocker, such as alfuzosin, commonly prescribed for lower urinary tract symptoms suggestive of benign prostatic hyperplasia, may be of benefit. Aim. Evaluation of the effect of alfuzosin, tadalafil or the combination of both on human corpus cavernosum.

METHODS

Human cavernosal tissues were obtained from 10 patients undergoing penile surgery. Strips contractility was studied in organ baths. Concentration-response curves to tadalafil were generated on norepinephrine (NE, 1-10 microM)-precontracted strips in the presence of alfuzosin or vehicle. Frequency-response curves (FRC) to electrical field stimulation (EFS, 0-64 Hz, 3 ms, 10 seconds, 300 mA) were generated in the presence of vehicle, alfuzosin, tadalafil, or both drugs combined. EFS (20 Hz, 1 ms, 10 seconds, 300 mM)-induced nitrergic relaxation on NE-precontracted strips was studied in the presence of vehicle, alfuzosin, tadalafil, or both drugs combined.

MAIN OUTCOME MEASURES

Functional measurement of cavernosal smooth muscle relaxation in the presence of tadalafil and alfuzosin.

RESULTS

The relaxation induced by tadalafil (10(-10) to 10(-5) M) on precontracted strips was enhanced by alfuzosin at both 10(-8) and 10(-7) M. The combination of alfuzosin (3.10(-8) M) and tadalafil (10(-7) M) was more efficient to inhibit FRC-induced contractions than each compound alone. The combination of tadalafil (10(-6) M) and alfuzosin (10(-8) M) increased the relaxation induced by EFS and its effect was greater than tadalafil alone. In addition, the combination of tadalafil (10(-6) M) and alfuzosin (10(-7) M) prolonged EFS-induced relaxation to a greater extent than each compound alone.

CONCLUSIONS

In vitro, the combination of alfuzosin and tadalafil is more efficient than each compound alone to relax adrenergic tone or to enhance nitrergic relaxation of the human corpus cavernosum. Such a combination deserves further investigation in placebo-controlled studies to evaluate its benefit in ED patients who are not sufficiently improved by PDE5 inhibitors.

Sildenafil improves immediate posttransplant parameters in warm-ischemic kidney transplants: experimental study

OBJECTIVE

To evaluate in an experimental model the effects of the PDE5 inhibitor sildenafil on kidney grafts autotransplanted after a period of 45 minutes of warm ischemia and 60 minutes of hypothermic pump perfusion.

METHODS

Nine laboratory large-white pigs were divided into two groups. Group A (n = 4): oral dose of 100 mg sildenafil was administered 1 hour before the surgery. Group B (n = 5): no sildenafil given. Right single nephrectomy was completed after a 45-minute period of warm ischemia by complete vascular clamping. Before the autotransplant, all kidneys were submitted to a 60-minute period of hypothermic pulsatile perfusion. Renal flow, arterial pressure, and renal vascular resistance were recorded in real time for 60 minutes after autotransplant. Nitric oxide levels were determined in blood samples of the renal vein at predefined intervals. Optical and electronic microscopy was performed on all organs at the end of the procedure.

RESULTS

Renal vascular flow was significantly higher and renal vascular resistance significantly lower in the sildenafil group compared with the non-sildenafil group. No significant differences were observed in systemic arterial pressure values between both groups. Nitric oxide levels were significantly higher for all periods in the sildenafil group. No differences were observed in histological studies.

CONCLUSION

Our experimental work suggested a positive effect of sildenafil on the immediate posttransplant outcome of warm-ischemic kidneys without systemic secondary effects.

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.

In vitro effects of PDE5 inhibitors sildenafil, vardenafil and tadalafil on isolated human ureteral smooth muscle: a basic research approach

Cyclic nucleotide phosphodiesterase (PDE) isoenzymes are key proteins regulating intracellular cyclic nucleotide turnover and thus smooth muscle tension. Several in vitro studies have indicated that the cyclic GMP and cyclic AMP-mediated signaling may play a role in the control of human ureteral muscle. The aim of the present study was to evaluate the functional effects of PDE5 inhibitors sildenafil (Sil), vardenafil (Var) and tadalafil (Tad), as well as nitric oxide (NO)-donating agent sodium nitroprusside (SNP) and non-selective muscarinic antagonist butylscopolamine (BSC) on the tension induced by KCl and the turnover of cyclic nucleotides in isolated human ureteral smooth muscle. In vitro relaxant responses of human ureteral smooth muscle to the PDE5 inhibitors mentioned above were investigated using the organ bath technique. Cyclic nucleotides cAMP and cGMP were determined by means of specific radioimmunoassay following incubation of the tissue with Sil, Var, Tad and SNP. The tension induced by KCl of the ureteral tissue was dose dependently reversed by the drugs with the following rank order of efficacy: SNP > Var >or= Sil > Tad > BSC. R(max) values ranged from 25 +/- 9% (SNP) to 5 +/- 3% (BSC). Relaxant responses were paralleled by threefold to fourfold increase in tissue levels of cGMP. Our results indicate that PDE5 inhibitors can reverse the tension of isolated human ureteral smooth muscle via cGMP-mediated pathways. Nevertheless, further studies are indicated in order to evaluate as to whether there might be a use for PDE5 inhibitors in the treatment of ureteral stone disease.