Evaluation of cadaveric pericardium in the rat for the surgical treatment of Peyronie's disease

Objectives. To evaluate the intermediate-term efficacy of cadaveric pericardium (Tutoplast) as a grafting material in the surgical correction of Peyronie’s disease using a rat model. Peyronie’s disease is a connective tissue disorder of the tunica albuginea. When less invasive modalities fail to correct the penile deformity, surgical excision of the plaque and coverage with various grafting materials has been advocated.Methods. Twenty male Sprague-Dawley rats (300 to 325 g) constituted the study population. The animals were divided into two groups: group 1, control rats (n = 10) and group 2, rats that underwent wedge excision of the tunica albuginea and replacement with cadaveric pericardial grafts (n = 10). All rats underwent electrical stimulation of the cavernosal nerve to assess erectile function after 4 months. Tissues obtained after death were stained with trichrome and Verhoff’s van Giesen for collagen and elastic fibers.Results. Erectile function as studied by cavernosal nerve stimulation was not significantly different in either group (P >0.05), and histologic studies of penile cross sections of the pericardial graft group revealed a mild to moderate degree of fibrosis surrounding the patch at 4 months.Conclusions. We found that pericardial cadaveric grafts in a rat model are a suitable tunica albuginea substitute. They allow for penile expansion after cavernosal nerve stimulation and are strong enough to withstand normal intracorporeal pressures. Our early experimental data in the rat support the use of pericardial cadaveric material for coverage of excised Peyronie’s plaques. However, long-term follow-up in humans is mandatory.     

Comparison of cadaveric pericardial,dermal, vein,and synthetic grafts for tunica albuginea substitution using a rat model

OBJECTIVE: To evaluate in an animal model the intermediate and long-term efficacy of cadaveric pericardium, dermis, vein and Gore-Tex per thousand as grafting materials for tunica albuginea substitution after plaque excision for Peyronie's disease. MATERIALS AND METHODS: The study comprised 100 male Sprague-Dawley rats (300-325 g) divided into five equal groups: group 1, sham-operated controls; and groups 2-5 which underwent wedge excision of the tunica albuginea and replacement with either cadaveric pericardium, dermis, vein or Gore-Tex grafts. Ten rats in each group had the cavernosal nerve stimulated electrically to assess erectile function at 4 months, and the remaining 10 rats at 6 months. After death the sampled tissues were fixed in 10% formalin, paraffin-embedded, and stained with Masson's trichrome and Verhoff's van Giesen for collagen and elastic fibres. RESULTS: Erectile function, assessed by cavernosal nerve stimulation, did not differ significantly in any of the groups (P > 0.05). The histological assessment of penile cross-sections showed minimal fibrosis surrounding the patch in the dermal and vein grafts, and moderate to severe fibrosis in the Gore-Tex graft at 4 and 6 months. In the pericardial graft there was a moderate degree of fibrosis at 4 months with only minimal fibrosis at 6 months. CONCLUSIONS: These results show that cadaveric pericardium allows complete penile expansion and is strong enough to withstand normal intracorporal pressures. There was minimal fibrosis in the pericardial, dermal and vein grafts, and moderate fibrosis in the Gore-Tex graft at 6 months. The pericardial graft is a satisfactory grafting material when used for tunica albuginea substitution, including the surgical management of Peyronie's disease.     

Adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis improves age-related erectile dysfunction in the rat

Nitric oxide (NO) is the principal mediator of penile erection. NO is synthesized by a variety of nitric oxide synthases (NOS). It has been demonstrated that a decrease in NOS activity, as observed in aging, is associated with a diminished erectile response. The objective of this study was to determine if adenoviral-mediated gene transfer of eNOS could reverse age-related erectile dysfunction in the rat. Two groups of animals were transfected with adenoviruses: (1) aged rats (60 weeks) with AdRSVbetagal; and (2) aged rats (60 weeks) with AdRSVeNOS. Five days after transfection, these study animals underwent cavernosal nerve stimulation (CNS) to assess erectile function and their responses were compared with young (20 weeks) control rats. Cross-sections of the rat penises transfected with AdRSVeNOS were examined after trichrome staining. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by a galacto-light chemiluminescent reporter gene assay in cavernosal tissues of rats administered AdRSVbetagal. The transgene expression of eNOS was examined by RT-PCR in rats transfected with AdRSVbetagal and AdRSVeNOS. eNOS and iNOS protein levels were measured by Western blot analysis, and cGMP levels were assessed in cavernosal tissue by enzyme immunoassay. Adenoviral expression of the beta-galactosidase reporter gene was observed in cavernosal tissue for up to 30 days, with peak expression registered at 5 days after intracavernosal administration of AdRSVbetagal. Cross-sections of the rat penises transfected with the AdRSVeNOS revealed no pathological (morphological or histological) changes. Five days after administration of AdRSVeNOS, eNOS protein, mRNA and cGMP levels in the corpora cavernosa were significantly increased (P<0. 05), while iNOS protein levels remained unchanged (P>0.05). In conclusion, enhanced expression of eNOS employing an adenoviral vector significantly increased the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the aged rat.     

Implications of nitric oxide synthase isoforms in the pathophysiology of Peyronie's disease

Peyronie's disease is an idiopathic, localized connective tissue disorder of the penis which involves the tunica albuginea of the corpus cavernosum and the adjacent areolar space. Peyronie's disease is characterized by local changes in the collagen and elastic fiber composition of the tunica albuginea. The formation of fibrotic plaques alters penile anatomy and can cause different degrees of bending and narrowing, as well as penile pain and erectile dysfunction. Though long recognized as an important clinical entity of the male genitalia, the etiology of this disease has remained poorly understood. Until recently there have been no studies to examine the role nitric oxide (NO) and nitric oxide synthase (NOS) isoforms may play in the onset and progression of Peyronie's disease. NO is a potent biological mediator with diverse physiological and pathophysiological roles. The purpose of this review is to describe each of the NOS isoforms and their potential roles in the pathophysiology of Peyronie's disease, with particular emphasis on the regulation of endothelial and inducible NOS isoforms.     

Effect of endothelial cell-based iNOS gene transfer on cavernosal eNOS expression and mouse erectile responses

Inducible nitric oxide synthase (iNOS) gene transfer is reported to augment erectile responses in rats, although it is also shown to impair vasorelaxation in cerebral arteries. We investigated the effect of endothelial cell-based iNOS gene transfer on endothelial NOS (eNOS) expression and mouse erectile responses. Human coronary artery endothelial cells (EC) transduced with empty vector (control) or iNOS were grown in culture and transplanted into the corpus cavernosum of severe combined immunodeficient mice. Endothelial NOS expression was compared in control and iNOS-transduced cells grown in the presence or absence of a selective iNOS inhibitor, L-N6- (1-iminoethyl) lysine hydrochloride (L-NIL). At 3-5 days after cell transplantation, we recorded intracorporal pressure (ICP) responses to cavernosal nerve stimulation and measured cavernosal total NO and eNOS protein expression. In this study, EC transduced with iNOS produced significantly more NO than controls but exhibited a twofold downregulation of eNOS protein and mRNA. This effect was reversed by L-NIL. In vivo, the cell-based gene transfer of iNOS led to significantly increased ICP responses, compared to mice transplanted with control ECs. Consistent with the in vitro data, cavernosal lysates had significantly reduced eNOS expression. In conclusion, EC gene transfer of iNOS downregulates EC expression of eNOS by an NOS-dependent mechanism. In the cavernosum of mice transplanted with Inos-transduced EC, nerve-stimulated erectile responses were augmented by the short-term gene transfer. However, our findings suggest that iNOS gene transfer may have deleterious effects on endothelial function if used as a treatment for erectile dysfunction.     

Chronic administration of sildenafil improves erectile function in a rat model of chronic renal failure

The relationship between erectile dysfunction (ED) and chronic renal failure (CRF) has been reported in several studies. This study aimed to investigate whether the chronic use of sildenafil could enhance the erectile capacity in CRF-induced rats. In addition, we assessed the effect of that treatment on certain molecules, which have been suggested to play crucial roles in erectile physiology and CRF-related ED as well. Three groups of animals were utilized: (1) age-matched control rats, (2) CRF-induced rats, (3) CRF-induced rats treated with chronic administration of sildenafil (5 mg kg⁻¹ p.o. for 6 weeks [treatment started after 6 weeks of CRF induction]). At 3 months, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Penile tissue advanced glycation end products (AGE''s)/5-hydroxymethyl-2-furaldehyde, malondialdehyde (MDA), cGMP (ELISA), inducible nitric oxide synthase (iNOS) and neuronal NOS (nNOS) (Western blot) analyses were performed in all rat groups. CRF-induced rats had a significant decrease in erectile function when compared to control rats (P < 0.05). The increase in both intracavernosal pressure (ICP) and area under the curve of CRF-induced rats treated with sildenafil (Group 3) was greater than CRF-induced rats (Group 2). Additionally, sildenafil treatment decreased AGE, MDA and iNOS levels, while it preserved nNOS and cGMP contents in CRF-induced penile tissue. Decreased AGE, MDA, iNOS and increased nNOS, cGMP levels at the sildenafil-treated group increased both ICP and Total ICP to CNS, which led to improve erectile function in CRF-induced rats. The results of the present study revealed the therapeutic effect of chronic sildenafil administration on erectile function in CRF-induced rats.     

Long-term continuous sildenafil treatment ameliorates corporal veno-occlusive dysfunction (CVOD) induced by cavernosal nerve resection in rats

It was recently reported in the rat that vardenafil given in a continuous long-term manner was successful in preventing smooth muscle fibrosis in the penile corpora cavernosa and corporal veno-occlusive dysfunction (CVOD) that occur following bilateral cavernosal nerve resection (BCNR), a model for human erectile dysfunction after radical prostatectomy. To expand on this finding and to determine whether this effect was common to other PDE5 inhibitors, and occurred in part by stimulation of the spontaneous induction of inducible nitric oxide synthase (iNOS, also known as NOS2), male Fischer 344 rats (N=10/group) were subjected to either BCNR or unilateral cavernosal nerve resection (UCNR) and treated with sildenafil (20 mg kg(-1) day(-1)) in the drinking water daily for 45 days. Additional BCNR groups received L-NIL (6.7 mg kg(-1) day(-1)) as inhibitor of iNOS activity, with or without concurrent sildenafil administration. It was determined that sildenafil, like vardenafil, (1) prevented the 30% decrease in the smooth muscle cell/collagen ratio, and the 3-4-fold increase in apoptosis and reduction in cell proliferation, and partially counteracted the increase in collagen, seen with both UCNR and BCNR; and (2) normalized the CVOD, measured by dynamic infusion cavernosometry, induced by both BCNR and UCNR. The long-term inhibition of iNOS activity exacerbated corporal fibrosis and CVOD in the BCNR rats, but sildenafil functional effects were not affected by L-NIL. These data suggest that the salutary effects of continuous long-term PDE5 inhibitors on erectile function post-cavernosal nerve resection involve their ability to prevent the alterations in corporal histology induced by cavernosal nerve damage, in a process apparently independent from endogenous iNOS induction.     

THE EFFECTS OF COLCHICINE ON A PEYRONIE'S-LIKE CONDITION IN AN ANIMAL MODEL

PURPOSE: We have developed an animal model of Peyronie's disease by injecting transforming growth factor beta (TGF-beta) into the rat penis. Our objective is to study the effects of colchicine on the Peyronie's condition in an animal model. MATERIALS AND METHODS: Thirty-six adult male Sprague-Dawley rats received TGF-beta injections into the tunica albuginea and were divided into two groups (n = 18 each). Rats in the first group were divided into three subgroups (n = 6 each). Each rat in the three subgroups received the following: Subgroup 1 received colchicine, subgroup 2 received ibuprofen, and subgroup 3 received regular water. The rats were euthanized after 6 weeks. Rats in the second group were also divided into three subgroups. These rats received the same treatments as the rats in the first group, but treatments began 6 weeks after TGF-beta injection. These rats were euthanized after 12 weeks. Tunical tissue samples were collected and examined using Hart and trichrome stains, electron microscopy (EM), and western blot analysis for TGF-beta detection. RESULTS: In the first group, the colchicine-treated rats exhibited less collagen deposition and less elastic fiber fragmentation than the untreated or ibuprofen-treated rats. EM confirmed the results and showed normal distribution and shape of both collagen and elastic fibers in the colchicine-treated group. In the second group, the colchicine-treated rats exhibited less crowding of the collagen fibers. However, the elastic fibers remained fragmented and scarce. Western blot analysis showed significant down-regulation of TGF-beta expression (5/6) in the colchicine-treated group after 6 weeks. Down-regulation was observed in only 1/6 in both ibuprofen and non-treated groups. After 12 weeks 2/6, 1/6, and 1/6 rats displayed down regulation in the colchicine treated, ibuprofen treated, and non-treated groups, respectively. CONCLUSION: Early colchicine treatment may suppress a Peyronie's like condition in the rat animal model.     

Effect of chronic ischemia on constitutive and inducible nitric oxide synthase expression in erectile tissue

Arterial occlusive disease is one of the leading causes of organic erectile dysfunction (ED). Recent studies have shown that the incidence of cardiovascular disease closely correlates with the prevalence of ED. Also, ED is thought to be an early signal of impending cardiovascular problems. We previously found that the atherosclerosis of iliohypogastric arteries in the rabbit causes ED, down-regulates cavernosal neuronal nitric oxide synthase (nNOS) gene expression, and impairs NO synthesis. The goal of this study was to determine the effect of atherosclerosis-induced ischemia on cavernosal nNOS, endothelial NOS (eNOS), and inducible NOS (iNOS) expression and NO-mediated smooth muscle relaxation in the rabbit. Our study showed that iliac artery blood flow, intracavernosal blood flow, and intracavernosal oxygen tension were unchanged 4 weeks after the induction of arterial atherosclerosis, whereas they were significantly diminished at weeks 8 and 16. Erectile responses to nerve stimulation and cavernosal smooth muscle relaxation were unchanged at week 4 and were significantly diminished at weeks 8 and 16 after the induction of atherosclerosis. Western blotting showed that cavernosal nNOS and eNOS protein levels were unaffected at week 4 but were significantly decreased at weeks 8 and 16 after the induction of atherosclerosis. iNOS protein, however, markedly increased during the course of the induced arterial disease. Immunohistochemical staining showed no change in cavernosal eNOS or nNOS expression at week 4. A dramatic decrease in both was evident at 8 and 16 weeks. iNOS expression progressively increased between 4 and 16 weeks of atherosclerosis. Down-regulation of nNOS and eNOS, along with up-regulation of iNOS, may explain ischemic cavernosal smooth muscle relaxation impairment in the rabbit. Ischemically altered NOS expression may be of great pathophysiologic importance in atherosclerosis-induced ED. These data may provide further insight into the mechanism of arteriogenic ED.     

Prospective analysis of 16S rDNA as a highly sensitive marker for bacterial presence in Peyronie's disease plaques

PURPOSE: Previous studies have implicated an infectious agent induced pathogenesis in Peyronie's disease. To our knowledge an association with venereal diseases or other infectious diseases has not been demonstrated to date, although Peyronie's disease is an inflammatory disorder. In case of an infectious origin of the disorder bacteria or at least their fragments should occur in the plaque. We investigated prospectively the occurrence of 16S rDNA as a highly sensitive marker for the presence of bacteria in inflammatory processes. MATERIALS AND METHODS: In 19 patients with idiopathic Peyronie's disease biopsy of the tunica albuginea was sampled. A total of 16 men with no evidence of Peyronie's disease served as the control group. In these men tissue from the tunica albuginea was obtained during penile prosthesis implantation for erectile dysfunction or during a Nesbit procedure for congenital penile curvature. Screening for bacterial DNA was performed prospectively using a polymerase chain reaction targeting bacterial 16S rDNA. RESULTS: In the tunica albuginea specimen 16S rDNA was not detectable in patients with Peyronie's disease or in the control group. CONCLUSIONS: The results of this study do not indicate an association between Peyronie's disease and bacterial infection.     

Induratio penis plastica—A factor of erectile dysfunction?

There are still diverse management options in Peyronie's disease and diverse opinions about the coincidence of Peyronie's disease and erectile dysfunction as well. The connection between Peyronie's disease and ED has been proved by some papers but on the other hand authors have refused to accept this claim. We have found erectile dysfunction in about 30% of our patients. We investigated 61 patients with Peyronie's disease. As diagnostic criteria assessment of angulation and erectile dysfunction are proposed. The tunica albuginea plication technique was used in 35 patients with good results. In our investigation we did not find any coincidence of Peyronie's disease with erectile dysfunction.     

Fibrin as an inducer of fibrosis in the tunica albuginea of the rat: a new animal model of Peyronie's disease

OBJECTIVES: To investigate the role of fibrin in inducing fibrosis in the tunica albuginea (TA) of the rat penis, to develop a new animal model for Peyronie's disease (PD). MATERIALS AND METHODS: The TA of rats (five per group per period) were injected with either saline, fibrin, transforming growth factor-beta1 (TGF-beta1) or TGF-beta1 plus fibrin; the rats were killed at 1, 3, and 6 weeks after injection. Images were analysed quantitatively from tissue sections stained for collagen (Masson trichrome), fibrin (Verhoeff's stain) and elastin (Hart's stain), and immunostained for TGF-beta1, inducible nitric oxide synthase (iNOS), heme oxygenase 1 (HO1), alpha-smooth muscle actin (ASMA), apoptosis (TUNEL) and plasminogen activator inhibitor (PAI). Collagen fibre organization was characterized by electron microscopy. Human PD plaque tissue and normal human TA were assayed for fibrin by immunohistochemistry in nine samples. RESULTS: At 1 week after injection of fibrin into the rat TA, only oedema was present; at 3 weeks, the oedema developed into a characteristic fibrotic PD-like plaque. The injection of TGF-beta1 into the TA also induced oedema in the TA at 1 and 3 weeks but there was very little evidence of a recognisable plaque at either time. Injection with TGF-beta1 plus fibrin resulted in oedema at 1 week but at 3 weeks there was a smaller plaque than with fibrin only. At 6 weeks the induced plaques in the fibrin-only and fibrin + TGF-beta1 groups persisted, and were comparable with those elicited at this time by TGF-beta1 alone. The control animals showed no pathology at any of the sample times. At 3 weeks the PD plaque induced by injection with fibrin alone had not only greater expression of TGF-beta1 than the TA of the animals receiving TGF-beta1 alone, but also greater levels of other markers of fibrosis, e.g. HO1 (reactive oxygen species), ASMA (presence of myofibroblasts), apoptosis, and PAI (inhibitor of fibrinolysis). iNOS, a known antifibrotic agent, was also increased. In human PD plaque tissue, fibrin was detected by immunohistochemistry in all nine specimens. CONCLUSIONS: These results suggest that fibrin, when introduced into the TA of the rat penis, acts as a potential profibrotic protein, possibly via the local release of TGF-beta1, and induces a plaque not only histologically similar to that induced by TGF-beta1 but to that of the human condition. Because fibrin can extravasate from the blood into the human TA after an injury to the TA, and because fibrin persists in the plaque tissue, we hypothesise that fibrin may play a key role in the pathogenesis of human PD.     

The protective effect of aminoguanidine on erectile function in diabetic rats is not related to the timing of treatment

OBJECTIVE: To assess the accumulation of advanced glycation end products (AGEs) in streptozotocin (STZ)-induced diabetic rat cavernosal tissue, and to determine whether the protective effect of aminoguanidine (AG) on erectile function is related to the timing of treatment, as the accumulation of AGEs in the penis may be important in the pathogenesis of diabetes mellitus-induced erectile dysfunction, and prolonged treatment with AG (a selective AGE inhibitor), prevents erectile dysfunction in this situation. MATERIALS AND METHODS: Harlan Sprague-Dawley rats were divided into groups 1-4, i.e. age-matched controls; STZ diabetic rats (60 mg/kg intraperitoneal) given free access to water; STZ diabetic rats treated with AG (1 g/L per day in the drinking water) immediately after inducing diabetes; and STZ-diabetic rats treated with AG 1 month after inducing diabetes, respectively. Two months after inducing diabetes the intracavernosal pressure was measured after cavernosal nerve stimulation, and cavernosal AGE (5-hydroxy methyl furfural, 5-HMF) levels assessed. RESULTS: Cavernosal tissue 5-HMF levels from groups 2 and 4 were significantly higher than in group 1 (control). The expression of 5-HMF in group 3 was similar to that in group 1. Diabetic rats had significantly lower erectile function than controls, while groups 3 and 4 (treated with AG) had normal erectile function, as measured by cavernosal nerve stimulation. CONCLUSIONS: The effect of AG on AGE levels seems to be time-dependent; that the 1-month treatment with AG improved erectile function with no change in AGEs suggests that AG has protective effects on the penile vasculature through alternative pathways.     

Effects of long-term vardenafil treatment on the development of fibrotic plaques in a rat model of Peyronie's disease

OBJECTIVES: To determine whether the phosphodiesterase-5 (PDE5) inhibitor, vardenafil, given orally and in different regimens, has a similar effect to that of the PDE5 inhibitor sildenafil, which prevented the development of a Peyronie's disease (PD)-like plaque formation induced by injecting transforming growth factor beta1 (TGF-beta1) into the tunica albuginea of the rat. MATERIALS AND METHODS: Vardenafil was given to male rats (eight per group) either in the drinking water or as an oral instillation once daily, at approximately 1 and approximately 3 mg/kg/day for 45 days after one injection with TGF-beta1 into the tunica albuginea, as an 'early preventive' treatment for TGF-beta1-induced formation of a PD-like plaque. Other groups received the two doses of vardenafil only in the drinking water, starting with a well-formed plaque, for 42 days ('late, therapeutic' administration). Sections of penile tissue were stained histochemically or immunohistochemically, followed by quantitative image analysis for collagen/smooth muscle and collagen III/I ratios, myofibroblast content (alpha-smooth muscle actin), TGF-beta1 expression, and apoptotic index. RESULTS: Preventative treatment with vardenafil at the higher dose (both continuous and once-daily treatments) reduced the collagen/smooth muscle and collagen III/I ratios, and the numbers of myofibroblasts and TGF-beta1-positive cells, and selectively increased the apoptotic index in the PD-like plaque. The lower dose was less effective, When vardenafil was given continuously in the drinking water for 41 days after the PD-like plaque was formed, there was only a partial reduction of the plaque. CONCLUSIONS: Long-term oral treatment with vardenafil slows and reverses the early stages of an experimental PD-like plaque in the rat, and might ameliorate a more advanced plaque.     

Application of pericardial graft in the surgical management of Peyronie's disease

PURPOSE: We investigated the use of Tutoplast cadaveric pericardium as an alternative material for grafting the tunica albuginea defect after Peyronie's plaque excision. MATERIALS AND METHODS: A total of 11 patients with significant penile curvature interfering with sexual intercourse were evaluated after at least 12 months of conservative therapy. Preoperative evaluation in all cases included penile duplex Doppler ultrasound studies. Chemically processed and gamma irradiated pericardium was used to graft the cavernosal defect after surgical excision of the penile plaque. In 3 patients a penile prosthesis was simultaneously placed secondary to documented erectile dysfunction at duplex Doppler ultrasound evaluation. RESULTS: Penile curvature resolved in all patients, allowing for normal sexual function after a mean followup of 14 months (range 9 to 19). No postoperative evidence of tissue rejection or infection was noted. In 1 patient urethro-corporal communication developed and a single penile cylinder was explanted. Another patient had a mild dorsal bulge at the site of graft placement when the prosthesis was fully inflated. CONCLUSIONS: Polymeric silicone material used to provide satisfactory results in the surgical treatment of Peyronie's disease but it is no longer available for biomedical use. We demonstrate the effective use of cadaveric pericardium as a graft material for cavernosal defects after Peyronie's plaque excision. Overall patient satisfaction, absence of a second surgical incision, relative low risk and ease of surgical placement make this material ideal for the surgical treatment of this disease process.     

Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.