Sildenafil-treated Rats Research Articles

Myocardial stretch-induced compliance is abrogated under ischemic conditions and restored by cGMP/PKG-related pathways.

Introduction: Management of acute myocardial infarction (MI) mandates careful optimization of volemia, which can be challenging due to the inherent risk of congestion. Increased myocardial compliance in response to stretching, known as stretch-induced compliance (SIC), has been recently characterized and partly ascribed to cGMP/cGMP-dependent protein kinase (PKG)-related pathways. We hypothesized that SIC would be impaired in MI but restored by activation of PKG, thereby enabling a better response to volume loading in MI. Methods: We conducted experiments in ex vivo rabbit right ventricular papillary muscles under ischemic and non-ischemic conditions as well as pressure-volume hemodynamic evaluations in experimental in vivo MI induced by left anterior descending artery ligation in rats. Results: Acutely stretching muscles ex vivo yielded increased compliance over the next 15min, but not under ischemic conditions. PKG agonists, but not PKC agonists, were able to partially restore SIC in ischemic muscles. A similar effect was observed with phosphodiesterase-5 inhibitor (PDE5i) sildenafil, which was amplified by joint B-type natriuretic peptide or nitric oxide donor administration. In vivo translation revealed that volume loading after MI only increased cardiac output in rats infused with PDE5i. Contrarily to vehicle, sildenafil-treated rats showed a clear increase in myocardial compliance upon volume loading. Discussion: Our results suggest that ischemia impairs the adaptive myocardial response to acute stretching and that this may be partly prevented by pharmacological manipulation of the cGMP/PKG pathway, namely, with PDE5i. Further studies are warranted to further elucidate the potential of this intervention in the clinical setting of acute myocardial ischemia.

Sildenafil-Induced Revascularization of Rat Hindlimb Involves Arteriogenesis through PI3K/AKT and eNOS Activation.

Hypoxia and inflammation play a major role in revascularization following ischemia. Sildenafil inhibits phosphodiesterase-5, increases intracellular cGMP and induces revascularization through a pathway which remains incompletely understood. Thus, we investigated the effect of sildenafil on post-ischemic revascularization. The left femoral artery was ligated in control and sildenafil-treated (25 mg/kg per day) rats. Vascular density was evaluated and expressed as the left/right leg (L/R) ratio. In control rats, L/R ratio was 33 ± 2% and 54 ± 9%, at 7- and 21-days post-ligation, respectively, and was significantly increased in sildenafil-treated rats to 47 ± 4% and 128 ± 11%, respectively. A neutralizing anti-VEGF antibody significantly decreased vascular density (by 0.48-fold) in control without effect in sildenafil-treated animals. Blood flow and arteriolar density followed the same pattern. In the ischemic leg, HIF-1α and VEGF expression levels increased in control, but not in sildenafil–treated rats, suggesting that sildenafil did not induce angiogenesis. PI3-kinase, Akt and eNOS increased after 7 days, with down-regulation after 21 days. Sildenafil induced outward remodeling or arteriogenesis in mesenteric resistance arteries in association with eNOS protein activation. We conclude that sildenafil treatment increased tissue blood flow and arteriogenesis independently of VEGF, but in association with PI3-kinase, Akt and eNOS activation.

Effect of sildenafil citrate on the liver structure and function in obstructive jaundice: An experimental study.

We aimed to investigate the effect of 10 mg/kg sildenafil on the structure and function of the liver in a rat model of obstructive jaundice. Sixty-two male Wistar albino rats were distributed into six different groups. Obstructive jaundice was performed by legating the common bile duct. 10 mg/kg sildenafil citrate in drinking water was delivered orally after the operation before sacrificing them. Rats were sacrificed either after 10 or 28 days according to the study design. The blood and tissue samples from the liver were obtained to perform a biochemical and histopathological analysis to study functional and structural changes in the liver. At the 10th day, there was no difference between the sildenafil-treated and control groups with regard to the aspartate aminotransferase and alanine aminotransferase levels (p=0.423, p=0.661). The alkaline phosphatase total bilirubin levels among the groups were statistically different (p<0.001). At the 28th day, liver function tests except alanine aminotransferase showed significant differences among the groups (p<0.001). Liver function tests did not changed significantly between the 10th and 28th day in sildenafil-treated rats (p>0.05). Significant differences were observed among the groups with regard to cholestasis, fibrosis, inflammation, and necrosis (p<0.001). However, edema increased in the sildenafil-treated group (p<0.001). On the 28th day, the severity of structural changes in the liver after obstructive jaundice, except edema, reduced significantly (p<0.001). The sildenafil-treated groups at different time points didn't show any statistical difference in histopathological changes (p>0.05). Oral administration of 10 mg/kg sildenafil citrate dramatically reverses the biochemical and histopathological liver changes induced by obstructive jaundice in rats.

Effects of sildenafil on nanostructural and nanomechanical changes in mitochondria in an ischaemia-reperfusion rat model.

Sildenafil exerts cardioprotective effects by activating the opening of mitochondrial ATP-sensitive potassium channels to attenuate ischaemia-reperfusion (IR) injury. In the present study, we used atomic force microscopy (AFM) to investigate changes in mitochondrial morphology and properties to assess sildenafil-mediated cardioprotection in a rat myocardial infarction model. To investigate the cardioprotective effects of sildenafil, we used an in vivo Sprague-Dawley rat model of IR. Rats were randomly divided into three groups: (i) sham-operated rats (control; n=5); (ii) IR-injured rats treated with vehicle (normal saline; IR; n=10); and (iii) IR-injured rats treated with 0.75mg/kg, i.p., sildenafil (IR+Sil; n=10). Morphological and mechanical changes to mitochondria were analysed by AFM. Infarct areas were significantly reduced in sildenafil-treated rats (7.8±3.9% vs 20.4±7.0% in the sildenafil-treated and untreated IR groups, respectively; relative reduction 62%; P<0.001). Analysis of mitochondria by AFM showed that IR injury significantly increased the areas of isolated mitochondria compared with control (24150±18289 vs 1495±1139nm(2) , respectively; P<0.001), indicative of mitochondrial swelling. Pretreatment with sildenafil before IR injury reduced the mitochondrial areas (7428±3682nm(2) ; P<0.001; relative reduction 69.2% compared with the IR group) and ameliorated the adhesion force of mitochondrial surfaces. Together, these results suggest that sildenafil has cardioprotective effects against IR injury in a rat model by improving the morphological and mechanical characteristics of mitochondria.

Therapeutic effect of sildenafil on blast-induced tinnitus and auditory impairment

Blast-induced tinnitus, along with associated auditory impairment and traumatic brain injury, is a primary concern facing military service members. To search for treatment, we investigated the therapeutic effects of sildenafil, a phosphodiesterase-5 inhibitor, given its vasodilatory effects and evidence suggesting its beneficial effects on noise-induced hearing loss. Rats were subjected to three consecutive blast exposures at 22psi and were monitored for tinnitus using a gap-detection acoustic startle reflex paradigm. Hearing thresholds and detection were tested using auditory brainstem responses and prepulse inhibition, respectively. Blasted rats were either treated with sildenafil or tap water following blast exposure, while age-matched sham control rats were treated with sildenafil and no blast exposure. Our results showed that sildenafil did not effectively prevent acute tinnitus onset and hearing impairment. Instead, sildenafil significantly suppressed high-frequency tinnitus from 3 to 6weeks after blast exposure and reduced hearing impairment during the first week after blast exposure. Complex results were observed in the startle force data, where sildenafil-treated rats displayed significantly reduced startle force compared to the untreated blasted group, suggesting possible mitigation of traumatic brain injury and suppression of hyperacusis-like percepts. Taken together, sildenafil showed a therapeutic effect on blast-induced tinnitus and audiological impairment in a time-dependent manner. Other regimens such as higher dosage prior to blast exposure and combination with other treatments deserve further investigation to optimize the therapeutic effects.

Saw Palmetto Extract Enhances Erectile Responses by Inhibition of Phosphodiesterase 5 Activity and Increase in Inducible Nitric Oxide Synthase Messenger Ribonucleic Acid Expression in Rat and Rabbit Corpus Cavernosum

To evaluate whether saw palmetto extract (SPE) relaxes corpus cavernosum and explore the underlying mechanisms. Forty Sprague-Dawley rats and 30 New Zealand rabbits were randomly allocated into 3 SPE-treated groups (low-, middle-, and high-dose) and 1 saline-treated control group. SPE was administered intragastrically for 7 consecutive days. Another 23 rats treated with sildenafil were used to appraise the erectile response to electrical stimulation of nerves in the corpus cavernosum. The erectile functions of rats and rabbits were evaluated 24 hours after the last SPE administration or 15 minutes after intragastric sildenafil. Outcome measures included corpus cavernosum electrical activity recording, phosphodiesterase 5 (PDE5) activity detected by the colorimetric quantitative method, and messenger ribonucleic acid (mRNA) expression level for PDE5 and inducible nitric oxide synthase (iNOS) determined using real-time polymerase chain reaction. In the SPE-treated animals, the relaxant response to electrical stimulation of nerves in the corpus cavernosum, reflected by the amplitude of the electrical activity within the cavernosum, was significantly and dose-dependently augmented. Similar effects were observed in the sildenafil-treated rats. PDE5 activity in rat and rabbit corpus cavernosum tissues was significantly and dose-dependently inhibited in SPE-treated animals, whereas the iNOS mRNA level increased compared with the saline group. PDE5 mRNA, however, was only significantly enhanced in the rats treated with the middle dose of SPE. The results suggest that SPE may have potential application value for the prevention or treatment of erectile dysfunction through an increase in iNOS mRNA expression and inhibition of PDE5 activity in corpus cavernosum smooth muscles.

Sildenafil Alleviates Bronchopulmonary Dysplasia in Neonatal Rats by Activating the Hypoxia-Inducible Factor Signaling Pathway

Bronchopulmonary dysplasia (BPD) is a major cause of morbidity in premature infants receiving oxygen therapy. Currently, sildenafil is being examined clinically to improve pulmonary function in patients with BPD. Based on the pharmacological action of sildenafil, the elevation of cyclic guanosine 3',5'-monophosphate (cGMP) in lung tissue is considered to underlie its beneficial effects, but this mechanism is not understood at the molecular level. Here, we examined the possibility that sildenafil helps the pulmonary system adapt to hyperoxic stress. To induce BPD, fetal rats were exposed to LPS before delivery, and neonates were exposed to hyperoxia, followed by intraperitoneal injections of sildenafil. Alveolarization was impaired in rats exposed to hyperoxia, and alveolarization significantly recovered with sildenafil. An immunohistochemical examination revealed that sildenafil effectively increased vascular distribution in lung tissue. Furthermore, the oxygen sensor hypoxia-inducible factor (HIF)-1/2α and the angiogenic factor vascular endothelial growth factor (VEGF) were highly expressed in the lungs of sildenafil-treated rats. In human small-airway epithelial cells, HIF-1/2α and its downstream genes, including VEGF, were confirmed to be induced by sildenafil at both the protein and mRNA levels. Mechanistically, cGMP in airway cells accumulated after sildenafil treatment because of interfering phosphodiesterase Type 5, and subsequently cGMP activated HIF-mediated hypoxic signaling by stimulating the phosphoinositide 3-kinase (PI3K)-v-akt murine thymoma viral oncogene homolog 1 (AKT)-mammalian target of rapamycin (mTOR) pathway. This study provides a better understanding about the mode of action for sildenafil, and suggests that HIF can be a potential target for treating patients with BPD.

In Vivo Imaging of Neurovascular Remodeling After Stroke

Stroke is one of the leading causes of adult disability throughout the world and, even though neural mechanisms of loss of function have been extensively studied, many aspects of poststroke cerebral responses remain poorly understood. Of particular interest is the mounting evidence of the capacity of the adult brain to reorganize after injury, which is believed to contribute to limitation of the extent of neural dysfunction and to restoration of affected neural functions. Processes such as neuronal plasticity, glial proliferation, and neovascularization may be essential for preservation or recovery of function after stroke and may conceivably go hand-in-hand at nearby and remote sites of active tissue reorganization.1,2 Specifically, the acute initiation of neurovascular remodeling, stimulating the proliferation and growth of existing arteries/arterioles (ie, arteriogenesis) or new capillaries (ie, angiogenesis), may be critical to facilitate the survival and restructuring of neural tissue, which ultimately may contribute to functional recovery at later stages.3 A variety of vascular imaging strategies is available for in vivo detection, characterization, and quantification of these processes, which can significantly aid in elucidation of the role of neurovascular remodeling after stroke, as discussed in this review. Because most of the described imaging modalities are present in experimental and clinical settings, this raises significant opportunities for translational studies. Growth and remodeling of existing and nascent vascular networks in health and disease involve a number of critical steps that have been comprehensively described by Risau4 and Carmeliet.5 Arteriogenesis involves adaptive growth and proliferation of preexisting (collateral) arteries and arterioles in response to increase in intravascular shear forces. The increased shear stress leads to upregulation of cell adhesion molecules, followed by accumulation of monocytes and other leukocytes that release cytokines and growth factors around the proliferating and maturating arteries.6 Although arteriogenic growth of collateral …

Sildenafil enhances systolic adaptation, but does not prevent diastolic dysfunction, in the pressure‐loaded right ventricle

Right ventricular (RV) failure due to pressure or volume overload is a major risk factor for early mortality in congenital heart disease and pulmonary hypertension, but currently treatments are lacking. We aimed to demonstrate that the phosphodiesterase 5A inhibitor sildenafil can prevent adverse remodelling and improve function in chronic abnormal RV overload, independent from effects on the pulmonary vasculature. In rat models of either pressure or volume overload, we performed pressure-volume studies to measure haemodynamic effects and voluntary exercise testing as clinical outcome after 4 weeks of sildenafil (or vehicle) administration. In the pressure-loaded right ventricle, sildenafil enhanced contractility [end-systolic elastance (mmHg/mL) 247 ± 68 vs.155 ± 71, sildenafil vs. vehicle, P < 0.05], prevented RV dilatation [end-diastolic volume (μL) 733 ± 50 vs. 874 ± 39, P < 0.05], reduced wall stress [peak wall stress (mmHg) 323 ± 46 vs. 492 ± 62, P < 0.05], and partially preserved exercise tolerance [running distance (%) -33 ± 15 vs. -62 ± 12, P < 0.05]. Protein kinase A was not activated by sildenafil and thus did not mediate the observed effects. In contrast, protein kinase G-1 was activated by sildenafil, but hypertrophy was not inhibited. Importantly, sildenafil did not prevent diastolic dysfunction, whereas RV fibrosis appeared to be increased in sildenafil-treated rats. In the volume-loaded right ventricle, sildenafil treatment did not show any beneficial effects. We demonstrate sildenafil to have beneficial, afterload-independent effects on the pressure-loaded right ventricle, but not on the volume-loaded right ventricle. These results indicate that sildenafil may offer a specific treatment for the pressure-loaded right ventricle, although persistent diastolic dysfunction and RV fibrosis could be of concern.

Effect of sildenafil on ventricular arrhythmias in post-infarcted rat hearts

We have demonstrated that activation of ATP-sensitive potassium (KATP) channels can attenuate sympathetic hyperinnervation. Sildenafil, a phosphodiesterase-5 inhibitor, has been shown to provide a preconditioning-like cardioprotective effect via opening of KATP channels. The aim of this study was to investigate whether chronic administration of sildenafil attenuates cardiac sympathetic hyperinnervation after myocardial infarction through activation of KATP channels and to compare it with the nitric oxide donor isosorbide dinitrate. Male Wistar infarcted rats induced by ligation of the anterior descending artery were randomized to either vehicle, nicorandil, sildenafil, isosorbide dinitrate, glibenclamide, or a combination of nicorandil and glibenclamide, or sildenafil and glibenclamide. Myocardial norepinephrine levels revealed a significant elevation in vehicle-treated rats compared with sham-operated rats, consistent with sympathetic hyperinnervation after infarction assessed by immunohistochemical analysis for tyrosine hydroxylase, growth associated factor 43 and neurofilament and by protein expression and mRNA of nerve growth factor. Sympathetic hyperinnervation was reduced after administering either nicorandil or sildenafil. Arrhythmic scores during programmed stimulation in the sildenafil-treated rats were significantly lower than those treated with the vehicle. Furthermore, the beneficial effects of sildenafil-induced were reversed by the addition of either glibenclamide or 5-hydroxydecanoate, implicating mitochondrial KATP channels as the relevant target. Isosorbide dinitrate failed to confer similar antiarrhythmia. 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one, a soluble guanylyl cyclase inhibitor, did not influence the effect of sildenafil on the nerve growth factor. These data indicate that sildenafil after infarction attenuated sympathetic hyperinnervation and arrhythmias by activation of mitochondrial KATP channels through a guanylyl cyclase-cGMP-independent pathway.

Longitudinal Magnetic Resonance Imaging of Sildenafil Treatment of Embolic Stroke in Aged Rats

Sildenafil provides restorative therapeutic benefits in the treatment of experimental stroke. The majority of experimental studies on treatment of stroke have been performed in young animals; however, stroke is primarily a disease of the aged. Thus, using MRI, we evaluated the effects of sildenafil treatment of embolic stroke in aged animals. Aged male Wistar rats (18 months) were subjected to embolic stroke and treated daily with saline (n=10) or with sildenafil (n=10) initiated at 24 hours and subsequently for 7 days after onset of ischemia. MRI measurements were performed at 24 hours and weekly to 6 weeks after embolization. MRI and histological measurements demonstrated that sildenafil treatment of aged rats significantly enhanced angiogenesis and axonal remodeling after stroke compared to saline-treated aged rats. Local cerebral blood flow in the angiogenic area was elevated and expansion of the ipsilateral ventricle and, consequently, brain atrophy was significantly reduced in the sildenafil-treated rats. Treatment of embolic stroke in aged rats with sildenafil significantly augments angiogenesis and axonal remodeling, which increased local blood flow and reduced expansion of the ipsilateral ventricle 6 weeks after stroke compared to control aged rats. MRI can be used to investigate brain repair after stroke in aged rats.

Sildenafil treatment in vivo stimulates Leydig cell steroidogenesis via the cAMP/cGMP signaling pathway

Sildenafil citrate (Viagra), a cGMP-selective phosphodiesterase (PDE) inhibitor, is widely used to treat erectile dysfunction and pulmonary arterial hypertension. In contrast to its well established action on erectile dysfunction, little is known on the action of sildenafil on cGMP/cAMP signaling and testicular steroidogenesis. This study was designed to assess the effects of prolonged sildenafil treatment on NO synthase-dependent signaling and steroidogenic function of rat Leydig cells. Male adult rats were treated with Viagra (1.25 mg/kg body wt) daily for 30 days. In our studies, serum testosterone and ex vivo testosterone production significantly increased in sildenafil-treated animals. Human chorionic gonadotropin-stimulated testosterone production and cAMP accumulation were also significantly higher in Leydig cells obtained from sildenafil-treated rats. The expression of soluble guanylyl cyclase (GUCY1) subunits (Gucy1a1, Gucy1b1) significantly increased; cAMP-specific Pde4a, cGMP-specific Pde6c, and dual Pde1c and Nos2 were inhibited and expression of Nos3, protein kinase G1 (Pkg1), and Pde5 remained unchanged. Treatment of purified Leydig cells with NO donor caused a dose-dependent increase in both testosterone and cGMP production. Testosterone and cGMP production was significantly higher in Leydig cells obtained from sildenafil-treated animals. The stimulatory effect of NO donor was significantly enhanced by saturating concentrations of hCG in both Leydig cells obtained from control and sildenafil-treated animals. Occurrence of mature steroidogenic acute regulatory protein also increased in sildenafil treated animals in accord with increased cAMP and cGMP production. In summary, inhibition of PDE activity during prolonged sildenafil treatment increased serum testosterone level and Leydig cells' steroidogenic capacity by coordinated stimulatory action on cAMP and cGMP signaling pathway.

Sildenafil protects against 3-nitropropionic acid neurotoxicity through the modulation of calpain, CREB, and BDNF

In this study we tested whether phosphodiesterase 5 (PDE5) inhibitors, sildenafil and vardenafil, would afford protection against 3-nitropropionic acid (3NP), which produces striatal lesions that closely mimic some of the neuropathological features of Huntington's Disease (HD). The neurotoxin was given over 5 days by constant systemic infusion using osmotic minipumps. Animals treated with PDE5 inhibitors (sildenafil or vardenafil) showed improved neurologic scores, reduced the loss of striatal DARPP-32 protein levels and lesion volumes, and decreased calpain activation produced by 3NP. This protective effect was independent of changes in 3NP-induced succinate dehydrogenase inhibition. Furthermore, striatal p-CREB levels along with the expression of BDNF were significantly increased in sildenafil-treated rats. In summary, PDE5 inhibitors protected against 3NP-induced striatal degeneration by reducing calpain activation and by promoting survival pathways. These data encourage further evaluation of PDE5 inhibitors in transgenic mouse models of HD.

Histological and ultrastructural changes of the pulmonary tissue in sildenafil-treated rats

Histological and ultrastructural changes of the pulmonary tissue in sildenafil-treated rats

Effects of Sildenafil on Oxidative and Inflammatory Injuries of the Kidney in Streptozotocin-Induced Diabetic Rats

Background: Oxidative stress and inflammation are implicated in the pathogenesis of diabetic nephropathy. Because sildenafil citrate (Viagra®) has variable cardiovascular benefits, including antioxidative and immunomodulating effects, we investigated its influence on oxidative stress and inflammation in diabetic rat kidney. Methods: Streptozotocin-induced diabetic rats received sildenafil (3 mg/kg/day in drinking water) or not (undosed water) for 8 weeks and were compared to age-matched nondiabetic animals. We evaluated 8-hydroxydeoxyguanosine (8-OHdG; for oxidative DNA damage), inducible nitric oxide synthase (iNOS) and nitrotyrosine (for excessive NO production and peroxynitrite formation), and representative chemoattractants [monocyte chemotactic protein-1, MCP-1; for inflammation and monocyte/macrophage infiltrations (ED-1)] in the kidney. Results: Sildenafil-treated rats had a lower kidney-to-body weight ratio than untreated diabetic rats. Urinary albumin excretion in diabetic rats decreased significantly after sildenafil treatment without changes in systolic blood pressure. Sildenafil-treated rats had significantly lower urinary and renal cortical 8-OHdG levels than the nonsildenafil group. Sildenafil administration significantly attenuated the increased renal nitrotyrosine protein expression, positive iNOS and ED-1 staining in glomeruli and tubulointerstitium, and nitrotyrosine staining in tubulointerstitium. Cortical MCP-1 RNA expression in the sildenafil group was significantly lower than in the nonsildenafil group. Conclusions: Sildenafil treatment may attenuate renal damage by ameliorating oxidative and inflammatory injuries in diabetic rats.

Magnetic Resonance Imaging Investigation of Axonal Remodeling and Angiogenesis after Embolic Stroke in Sildenafil-Treated Rats

Interaction between angiogenesis and axonal remodeling after stroke was dynamically investigated by MRI in rats with or without sildenafil treatments. Male Wistar rats were subjected to embolic stroke and treated daily with saline (n=10) or with sildenafil (n=11) initiated at 24 h and subsequently for 7 days after onset of ischemia. T(2)(*)-weighted imaging, cerebral blood flow (CBF), and diffusion tensor imaging (DTI) measurements were performed from 24 h to 6 weeks after embolization. T(2)(*) and fractional anisotropy (FA) maps detected angiogenesis and axonal remodeling after stroke, respectively, starting from 1 week in sildenafil-treated rats. Areas demarcated by MRI with enhanced angiogenesis, elevated local CBF, and augmented axonal remodeling were spatially and temporally matched, and FA values were significantly correlated with the corresponding CBF values (R=0.66, P<4 x 10(-5)) at 6 weeks after stroke. Axonal projections were reorganized along the ischemic boundary after stroke. These MRI measurements, confirmed by histology, showed that sildenafil treatment simultaneously enhanced angiogenesis and axonal remodeling, which were MRI detectable starting from 1 week after stroke in rats. The spatial and temporal consistency of MRI metrics and the correlation between FA and local CBF suggest that angiogenesis, by elevating local CBF, promotes axonal remodeling after stroke.

Sildenafil delays the intestinal transit of a liquid meal in awake rats

Sildenafil slows down the gastric emptying of a liquid test meal in awake rats and inhibits the contractility of intestinal tissue strips. We studied the acute effects of sildenafil on in vivo intestinal transit in rats. Fasted, male albino rats (180-220 g, N = 44) were treated (0.2 mL, iv) with sildenafil (4 mg/kg) or vehicle (0.01 N HCl). Ten minutes later they were fed a liquid test meal (99m technetium-labeled saline) injected directly into the duodenum. Twenty, 30 or 40 min after feeding, the rats were killed and transit throughout the gastrointestinal tract was evaluated by progression of the radiotracer using the geometric center method. The effect of sildenafil on mean arterial pressure (MAP) was monitored in a separate group of rats (N = 14). Data (medians within interquartile ranges) were compared by the Mann-Whitney U-test. The location of the geometric center was significantly more distal in vehicle-treated than in sildenafil-treated rats at 20, 30, and 40 min after test meal instillation (3.3 (3.0-3.6) vs 2.9 (2.7-3.1); 3.8 (3.4-4.0) vs 2.9 (2.5-3.1), and 4.3 (3.9-4.5) vs 3.4 (3.2-3.7), respectively; P < 0.05). MAP was unchanged in vehicle-treated rats but decreased by 25% (P < 0.05) within 10 min after sildenafil injection. In conclusion, besides transiently decreasing MAP, sildenafil delays the intestinal transit of a liquid test meal in awake rats.

Assessment of heme oxygenase-1 (HO-1) activity in the cavernous tissues of sildenafil citrate-treated rats

To assess heme oxygenase-1 (HO-1) activity in the cavernous tissue of sildenafil citrate-treated rats. One hundred and ninety-two Sprague-Dawley male rats, divided into four equal groups, were investigated. Group 1, the control group, received regular animal chow; group 2 received sildenafil citrate by intragastric tube; group 3 received sildenafil and HO inhibitor (zinc protoporphyrin, ZnPP); and group 4 received sildenafil and nitric oxide synthase (NOS) inhibitor L-nitroarginine methyl ester (L-NAME). Twelve rats from each group were killed after 0.5 h, 1 h, 2 h and 3 h of drug administration. Then HO-1 activity, cGMP levels and NOS enzymatic activity in the cavernous tissues were estimated. In cavernous tissue, HO-1 activity, NOS enzymatic activity and cGMP concentration increased significantly in sildenafil-treated rats compared to other groups throughout the experiment. Rats receiving either HO or NOS inhibitors showed a significant decrease in these parameters. HO-1 cavernous tissue activity and NOS enzymatic activity demonstrated a positive significant correlation with cGMP levels (r = 0.646, r = 0.612 respectively; P < 0.001). The actions of PDE5 inhibitor sildenafil citrate in the cavernous tissue are partly mediated through the interdependent relationship between both HO-1 and NOS activities.

Sildenafil induces revascularization after rat hindlimb ischemia in association with resistance arteries outward remodeling.

Background: Angiogenesis has a key role in ischemic diseases. Sildenafil inhibits phosphodiesterase 5, increases intracellular cGMP content and thus induces vasodilation. As its effects on the peripheral vasculature in ischemic conditions are unknown, we investigated the consequences of a long-term treatment with Sildenafil on post-ischemic revascularization. Methods and results: In Sildenafil-treated rats (25mg/kg/d) left femoral artery was ligated. After 7 or 21 days, vascular density and blood flow were evaluated in legs and expressed as ischemic (left)/non-ischemic (right) (L/R) leg ratio. At 7 and 21 days, the L/R ratio was 33±2% and 54±9% in controls, respectively. Sildenafil increased this ratio to 47±4% and to 128±11%, respectively. Blood flow and arteriolar density followed the same pattern. At seven days, Sildenafil–induced revascularization was associated with activation of the PI3-kinase-Akt-eNOS pathway. After 21 days, this pathway was down-regulated. HIF1 and VEGF level was not affected by Sildenafil in the ligated leg, despite revascularization suggesting that arteriogenesis predominated over angiogenesis. Indeed, Sildenafil induced outward remodeling (arteriogenesis) in resistance arteries. Conclusion: Chronic Sildenafil increased local blood flow and collateral arteries growth in association with activation of the PI3K-AKT-eNOS pathway after ligature of the femoral artery.

Lack of synergistic effect of molsidomine and sildenafil on development of pulmonary hypertension in chronic hypoxic rats

The present study addressed whether combined treatment with a phosphodiesterase type 5 inhibitor, sildenafil, and a nitric oxide donor, molsidomine, prevents development of pulmonary hypertension in chronic hypoxic rats. Two weeks of hypoxia increased right ventricular systolic pressure, and right ventricular and lung weight. Treatment with either sildenafil (10 mg/kg/day) or molsidomine (15 mg/kg/day) in drinking water reduced right ventricular systolic pressure and weight, while lung weight was unchanged. Combining sildenafil and molsidomine did not have additional effects compared to molsidomine alone. The number of muscularized pulmonary arteries with diameters below 50 μm was increased in vehicle and sildenafil-treated, but not in molsidomine-treated hypoxic rats. Acetylcholine relaxation was blunted in arteries from vehicle and molsidomine-treated, but not in sildenafil-treated rats. In conclusion, both sildenafil and molsidomine blunts pulmonary hypertension and right ventricular hypertrophy in chronic hypoxic rats, but no synergistic effects were observed.