Molecular Mechanisms of Vacuum Therapy in Penile Rehabilitation: A Novel Animal Study

EUROPEAN UROLOGY 58 (2010) 773 780 available at www.sciencedirect.com journal homepage: www.europeanurology.com Sexual Medicine Molecular Mechanisms of Vacuum Therapy in Penile Rehabilitation: A Novel Animal Study Jiuhong Yuan a,b, Haochen Lin c,b, Ping Li d, Rongzheng Zhang e, Annie Luo e, Francesco Berardinelli f, Yutian Dai c, Run Wang b,g, * a Department of Urology, West China Hospital, Sichuan University, Chengdu, China b Division of Urology, University of Texas Health Science Center, Houston, TX, USA c Department of Urology, Affiliated Drum Tower Hospital, Nanjing University School of Medicine, Nanjing, Jiangsu Province, China d Department of Leukemia, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA e Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston, TX, USA f Urology, Department of Medicine and Aging Science, G. D Annunzio University, Chieti, Italy g Department of Urology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA Article info Article history: Accepted July 7, 2010 Published online ahead of print on July 16, 2010 Keywords: Cavernous nerve injury Erectile dysfunction Penile rehabilitation Radical prostatectomy Vacuum erectile device Vacuum therapy Abstract Background: Penile rehabilitation (PR) is widely applied after radical prostatectomy. Vacuum erectile device (VED) therapy is the one of three PR methods used in the clinical setting that improve erectile function (EF) and is the only PR method which may preserve penile length. However, its unknown mechanism hampered doctors recommendations and patients compliance. Objectives: To assess the effects of VED therapy on erectile dysfunction (ED) in a rat model of bilateral cavernous nerve crush (BCNC) and to investigate the molecular mechanism of VED in postprostatectomy ED. Design, setting, and participants: This was an experimental study using Sprague-Dawley rats in three groups: sham, BCNC, and BCNC plus VED. Intervention: Intervention included BCNC, electrical stimulation of the cavernous nerve (CNS), and VED therapy. Measurements: At the end of a 4-wk period, CNS was used to assess EF by maximum intracavernosal pressure (ICP)/mean arterial pressure (MAP) ratio and duration (area under the curve [AUC]). For the structural analyses, whole rat penis was harvested. Terminal deoxynucleotidyl transferase biotin-dutp nick end labeling assay was used for the assessment of apoptotic indices (AI). Immunohistochemistry was performed for endothelial nitric oxide synthase (enos), a-smooth muscle actin (ASMA), transforming growth factor beta 1 (TGF-b1), and hypoxia inducible factor-1a (HIF-1a). Staining for Masson s trichrome was utilized to calculate the smooth muscle/collagen ratios. Results and limitations: EF was improved with VED therapy measured by ICP/MAP ratios and AUC. VED therapy reduced HIF-1a expression and AI significantly compared with control. Animals exposed to VED therapy had decreased TGF-b1 expression, increased smooth muscle/ collagen ratios, and preserved ASMA and enos expression. Conclusions: To our knowledge, this is the first scientific study to suggest that VED therapy in the BCNC rat model preserves EF through antihypoxic, antiapoptotic, and antifibrotic mechanisms. Published by Elsevier B.V. on behalf of European Association of Urology. * Corresponding author. Department of Urology, University of Texas Medical School, M.D. Anderson Cancer Center, 6431 Fannin Street, Ste. 6.018, Houston, TX 77030, USA. Tel. +1 713 500 7337; Fax: +1 713 500 0546. E-mail address: run.wang@uth.tmc.edu (R. Wang). 0302-2838/$ see back matter Published by Elsevier B.V. on behalf of European Association of Urology. doi:10.1016/j.eururo.2010.07.005

774 EUROPEAN UROLOGY 58 (2010) 773 780 1. Introduction Prostate cancer is the most common solid-organ cancer in men and one of the leading causes of death [1]. With early detection and radical prostatectomy (RP), the 15-yr overall, actuarial, cancer-specific survival rate has reached 90% [2,3]. Unfortunately, RP is associated with at least transient erectile dysfunction (ED), with ED rates ranging from 20% to 90% depending upon the study reviewed [1 4]. It is postulated that the development of post-rp ED is due predominantly to a combination of temporary cavernous nerve (CN) injury and damage to the erectile tissue secondary to neuropraxia and potentially the absence of cavernosal oxygenation [5]. To improve the patients quality of life and the acceptance of the RP, penile rehabilitation (PR) after RP is now widely applied in clinical practice [3]. Currently, PR methods include the use of phosphodiesterase type 5 inhibitors, intracavernosal injection/intraurethral suppository, the vacuum erectile device (VED), or combination therapy [3]. Vacuum therapy utilizes negative pressure to distend the corporal sinusoids and to increase blood inflow to the penis. Clinical data indicated that vacuum therapy is the only PR method that may preserve penile length, improves patient and partner sexual satisfaction, and allows earlier return of spontaneous erection [3,6]. However, its unknown mechanism hampered doctors recommendation and patients compliance [3]. To explore the underlying mechanism of VED therapy after RP, we applied our newly designed rat-specific VED [7] to the bilateral cavernous nerve crush (BCNC) rat model. The BCNC rat model is believed to simulate the neural injury that occurs during RP and is designed to study the mechanisms of ED after RP as well as to explore EDminimizing strategies [8]. Fig. 1 Erectile function assessment by intracavernous pressure tracing under cavernous nerve stimulation. Representative intracavernous pressure (ICP) tracing in response to cavernous nerve stimulation (CNS) (7.5 V for 60 s) at week 4 after (A) sham operation, (B) bilateral cavernous nerve crush (BCNC), and (C) BCNC plus VED therapy; (D) the voltage dependent erectile response to CNS represented by the ratio of maximum ICP/mean arterial pressure (MAP); (E) area under the erectile curve (AUC, mmhgs). Significant differences were found in ICP/MAP and AUC only at 5.0 V and 7.5 V, between BCNC group and BCNC plus VED group (both p < 0.05).

EUROPEAN UROLOGY 58 (2010) 773 780 775 2. Methods 2.1. Animal grouping, bilateral cavernous nerve crush, and vacuum erectile device therapy Fifteen Sprague-Dawley rats (Harlan Laboratories, Houston, TX, USA), initially weighing 200 250 g, were randomly and equally divided into three groups: (1) sham (CN expose surgery only, no nerve crushing, no VED therapy); (2) control (BCNC procedure, no VED therapy); and (3) treatment group (BCNC procedure; VED therapy beginning at 2 wk after BCNC surgery, 5 min twice daily with a 1 min interval, Monday Friday, total VED treatment time: 4 wk). The BCNC procedure was reported previously [8]. The animals were cared for and housed under strict guidelines established by the University Texas Health Science Center at Houston Institutional Animal Care and Use Committee. 2.4. Statistical analysis The mean averages were built for maximum ICP/mean arterial pressure (MAP) ratios, area under the ICP curves (AUCs), smooth muscle/collagen ratios, and AIs for each group, and reported as the mean plus or minus standard error of the mean. Individual pairwise comparison between groups was analyzed with independent two-tailed t tests. Results were considered statistically significant if p < 0.05. 3. Results 3.1. Erectile function assessment EF was assessed by tracing the ICP under the CNS, and in the meantime [(Fig._2)TD$FIG] measuring the AP. The typical ICP tracings of 2.2. Functional analysis and tissue harvesting At the end of 4 wk of treatment, the animals were recorded for intracavernosal pressure (ICP) and the corresponding arterial pressure (AP) with CN stimulation (CNS) under pentobarbital anesthesia [9]. At the completion of functional analysis, the penis was excised for histopathology. 2.3. Histopathology Following routine dehydration and paraffin embedding, tissue samples were cut into 5-mm sections from the midshaft of the penis mounted on slides and dried. Then the tissue slides, showing the cross-section of the corpora cavernosa (CC), were deparaffinized and rehydrated for following studies. 2.3.1. Masson s trichrome To evaluate the smooth muscle/collagen ratio, slides were stained for Masson s trichrome (MT) according to standard protocol, which was reported previously [9]. Smooth muscle/collagen ratios were analyzed using ImageJ v.1.43n (US National Institutes of Health, Bethesda, MD, USA). One slide per animal (slides are from the midshaft of penis about the same level) was used to calculate the ratio of the red-staining smooth muscle to the blue-staining collagen content in the cross-section of the CC building the group average. The ratios were compared among the three groups. 2.3.2. Immunohistochemistry The corporal tissue of the rat penis was immunohistochemically stained for endothelial nitric oxide synthase (enos), alpha smooth muscle actin (ASMA), hypoxia-inducible factor 1a (HIF-1a), and transforming growth factor beta 1 (TGF-b1) following the manufacturer s instructions. The antibodies of enos and ASMA were from Abcam Inc. (Cambridge, MA, USA); the antibodies of HIF-1a and TGF-b1 are from R&D Systems (Minneapolis, MN, USA). The results of the tissue sample staining were compared among the three groups: sham, control, and treatment. 2.3.3. Apoptosis assessment Terminal deoxynucleotidyl transferase biotin-dutp nick end labeling (TUNEL) assay was performed following the manufacturer s instructions (Roche Applied Science, Mannheim, Germany) to assess apoptosis. Two slides from two different animals per group were randomly selected. Each slide was analyzed by counting cells in five nonoverlapping zones of the entire mounted CC section at 400 magnification. The ratio of the percentage of cells stained with the TUNEL method to the total number of cells stained with 4 0,6 diamidino-2-phenylindole was recorded and reported as the apoptotic index (AI). Fig. 2 Vacuum erectile device (VED) therapy partially reversed bilateral cavernous nerve crush (BCNC)-induced HIF-1a expression. Compared with the sham operation group (A), immunohistochemistry demonstrated that BCNC (B) dramatically increased HIF-1a expression in penile sinusoid. VED treatment (C) partially reversed HIF-1a expression in penile sinusoid compared to nerve crush only (B).

776 EUROPEAN UROLOGY 58 (2010) 773 780 sham, BCNC, and BCNC with daily VED therapy are shown in Fig. 1A C. The analysis is presented in ICP/MAP ratios and AUCs (Fig. 1D and E). The ICP/MAP ratios in the sham group were 0.61 0.02 at 5.0 V and 0.71 0.03 at 7.5 V, which were significantly higher compared with all other groups ( p < 0.01). BCNC dramatically decreased the ICP/MAP ratios: 0.25 0.02 at 5 V and 0.32 0.03 at 7.5 V. The daily VED therapy in BCNC rats preserved the ICP/MAP ratios: 0.53 0.06 at 5 V and 0.65 0.03 at 7.5 V, which is significant compared with the BCNC control ( p < 0.01). The AUCs demonstrated the same trend as the ICP/MAP ratios in the three groups. 3.3. Apoptosis analysis At 6 wk after BCNC, the BCNC plus VED group demonstrated a significant reduction in apoptosis within the corporal tissue (Fig. 3C) with a mean AI of 21 4%, compared with an AI of 61 5% in the BCNC group ( p < 0.001) (Fig. 3B and D). For comparison, the AI value in the sham group was 10 6% (Fig. 3A and D), which was significantly lower compared with BCNC ( p < 0.001) or BCNC plus VED ( p < 0.05) (Fig. 3B, C and D). 3.4. Penile structure molecular analysis 3.2. Hypoxia assessment On IHC, the staining intensity of HIF-1a in the BCNC group (Fig. 2B) was dramatically higher than the sham group (Fig. 2A). In the BCNC plus VED group, the HIF-1a staining (Fig. 2C) was significantly reduced compared with the BCNC group, although still higher than the sham group. [(Fig._3)TD$FIG] 3.4.1. Endothelial nitric oxide synthase and alpha smooth muscle actin immunohistochemistry Immunohistochemical staining of enos in the BCNC group (Fig. 4B) was dramatically reduced compared with the sham group (Fig. 4A). The enos staining in the BCNC plus VED group (Fig. 4C) was significantly improved compared with BCNC group; however, it was still lower than sham group. ASMA expression showed the same trend (Fig. 4D F). Fig. 3 Vacuum erectile device (VED) therapy decreased apoptosis. Compared with the sham operation group (A), bilateral cavernous nerve crush (BCNC) (B) dramatically increased apoptosis in penile sinusoid (brown-stained nuclei; magnified T400), VED treatment (C) significantly reduced BCNC-induced apoptosis in penile sinusoid compared with nerve crush only (B). Apoptotic indices (AI) is presented as ratio of apoptotic nuclei (brown-stained nuclei) to total number of nuclei counted. A significantly reduced AI percentage for VED therapy was found (D) compared to BCNC only ( p < 0.01), although still higher than the sham group ( p < 0.05).

EUROPEAN UROLOGY 58 (2010) 773 780 777 3.4.2. TGF-b1 immunohistochemistry Immunohistochemical staining of TGF-b1 in the BCNC group (Fig. 4H) was dramatically increased compared with the sham group (Fig. 4G). The BCNC plus VED treatment was partially reversed (Fig. 4I), although it was still higher than sham group. 3.4.3. Smooth muscle/collagen ratios The staining with MT in the sham group revealed smooth muscle/collagen ratios of 63.8 1.7%, the highest smooth muscle/collagen ratio of all animal groups (Fig. 5D). This result was significantly higher compared with 20.0 1.6% for the BCNC group (Fig. 5A, B and D) (p < 0.05) and remained superior to the BCNC plus VED group as well (Fig. 5C and D) (p < 0.05). The BCNC plus VED group reached 40.4 1.4%, which was significantly greater than the BCNC group (p < 0.05), and displayed a clear trend toward improvement compared with the BCNC group (20.0 1.6%; p < 0.05), but not the sham group. 4. Discussion The rat BCNC as an RP-induced ED model has been widely accepted in PR research. It was first reported by Quinlan et al in 1989 and documented in prior experiments using this animal model in the assessment of functional and structural changes of erectile tissue under various interventions [8]. Our study showed a dramatic reduction in ICP/ MAP ratios and AUC in animals after BCNC when compared with the sham group. The reduced ICP/MAP ratios and AUC were associated with significantly reduced smooth muscle/ collagen ratios and highly increased apoptosis rates and TGF-b1 expression in the control group compared with sham animals. Previous reports in rat CN transection models have demonstrated increased apoptosis within the corpora. Klein et al reported that apoptosis of penile erectile tissue occurs after denervation of the rat penis [10]. User et al similarly confirmed increased apoptosis, especially subjacent to the tunica albuginea involving smooth [(Fig._4)TD$FIG] Fig. 4 Vacuum erectile device (VED) therapy preserves penile endothelial nitric oxide synthase (enos) and alpha smooth muscle action (ASMA) expression, and ameliorated transforming growth factor beta 1 (TGF-b1) expression. Penile tissue was harvested and processed after functional measurement. Immunohistochemistry was used for the expression of enos, ASMA, and TGF-b1 in penile sinusoid. Bilateral cavernous nerve crush (BCNC) dramatically reduced the expression of enos (B) and ASMA (E) compared to the sham group (A and D), respectively. VED therapy significantly preserved the expression of (C) enos ((BCNC plus VED therapy) and (F) ASMA (BCNC plus VED therapy) compared to (B) and (E), respectively. Compared to sham operation (G), BCNC (H) dramatically increased TGF-b1 expression in penile sinusoid. VED treatment (I) partially reversed TGF-b1 expression in penile sinusoid compared to nerve crush only (H).

778 [(Fig._5)TD$FIG] EUROPEAN UROLOGY 58 (2010) 773 780 Fig. 5 Vacuum erectile device (VED) therapy partially preserves penile smooth muscle/collagen ratios. Masson s trichrome staining was used for penile smooth muscle/collagen ratios. Compared with sham operation (A), bilateral cavernous nerve crush (BCNC) (B) dramatically decreased penile smooth muscle/collagen ratio. VED treatment (C) significantly increased penile smooth muscle/collagen ratio compared to nerve crush only (D). muscle cells [11]. They hypothesized that damage to the subtunical smooth muscle cells prevents compression of the perforating subtunical veins, resulting in veno-occlusive dysfunction and subsequent failure of recovery of EF. The daily use of VED therapy commencing 2 wk after BCNC improved ICP/MAP ratios and AUCs compared with the control group at 4 wk. The 4-wk time point was chosen as this is generally believed to represent the 2-yr time point in the human [9]. After RP, the period of neuropraxia may last as long as 24 mo [12] and we generally expect EF recovery by this time point if ideal nerve-sparing RP was performed. The regimen we use is exactly what is used in the VED protocol in a clinical setting [13]. VED regimen in men after RP has been documented in preserving EF and penile length and size. Raina reported 109 patients with nerve-sparing RP who were placed into early VED daily usage (group 1, n = 74) versus no erectogenic aid (group 2, n = 35) with 9-mo follow-up, and showed early use of VED facilitates early sexual intercourse and early patient/spousal sexual satisfaction [14]. Kohler et al randomized 28 patients into early VED therapy or control (control group accepted VED therapy 6 mo later) with 1-yr observation and concluded that early VED use after RP improves sexual function [15]. Our experimental findings confirmed the clinical outcome of VED application. EF becomes impaired immediately following RP secondary to damage to CN during surgery, resulting in neuropraxia [16]. A reduction in arterial inflow has also been reported due to ligation of the accessory internal pudendal arteries during RP [17,18]. The combination of nerve damage with decreased arterial inflow may cause penile tissue hypoxia, leading to apoptosis and collagen deposition, which ultimately results in venous leak. This, in turn, has been linked to the pathophysiology of ED after RP [10,19 27]. As our data demonstrated, BCNC induced HIF-1a expression. With VED therapy, the HIF-1a expression was partially reversed. Although we did not have data on oxygen level in the rat penis after VED application due to technique limitation, we do see rat penis engorgement with pink color [7], and we see similar pressure with our device compared with the human one [7]. The latter demonstrated that mean O 2 saturation of corporal blood

EUROPEAN UROLOGY 58 (2010) 773 780 779 immediately after VED-induced erection was 79.2%, which translates to 58% arterial and 42% venous flows, respectively [28]. Therefore, we believe there is increased oxygenation of the penis when VED is applied. Daily VED-induced tissue oxygenation overcomes RP-induced hypoxia in a consistently flaccid penis, which is lack of spontaneous erection and nocturnal tumescence. Nocturnal erections have been implicated in preserving normal erectile function by providing regular tissue oxygenation [29]. The partial oxygenation of VED imitates the nocturnal erection and provides the penis with regular partial oxygenation. Our data showed that with regular partial oxygenation, the apoptosis of penile tissue was partially reversed. With intermittent interruption of penile hypoxia with VED application, progressive cavernosal fibrosis produced by persistent penile hypoxia was halted. It has been shown that the progressive cavernosal fibrosis induces venoocclusive dysfunction [30]. Our data also showed that VED therapy decreased TGF-b1 expression, and increased enos and ASMA, and smooth muscle/collagen ratios. Therefore, the VED regimen preserved penile EF via antihypoxic, antiapoptotic, and antifibrotic mechanisms to preserve the veno-occlusive mechanism. The oxygen level of the VED-applied penis is a key issue; however, it could not be measured in our experiments because of the technique challenge. In addition to the tissue oxygenation mechanism, the beneficial effects of VED therapy after RP may be mediated by stretch forces, other nutrient factors, and neuroregeneration, although we did not address it in our experiments. We also did not optimize the VED regimen, such as applying optimal vacuum pressure (highest oxygen level in the penis without intolerable side effects), application duration and frequency, and follow-up time. Ongoing experiments are needed to explore these issues. 5. Conclusions We have demonstrated that VED therapy in the BCNC model preserves EF and acts by preserving smooth muscle content and endothelial integrity via antihypoxia, antiapoptosis, and antifibrosis mechanisms. The daily VED therapy effect on EF recovery is consistent with patients results and without significant side effects. This scientific evidence, although from an animal model, may motivate physicians recommendations and improve patients compliance in the clinical setting. Author contributions: Run Wang had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Yuan, Lin, Wang. Acquisition of data: Yuan, Lin, Li, Zhang, Luo, Berardinelli. Analysis and interpretation of data: Yuan, Lin, Wang. Drafting of the manuscript: Yuan. Critical revision of the manuscript for important intellectual content: Dai, Wang. Statistical analysis: Yuan, Lin, Wang. Obtaining funding: Yuan, Wang. Administrative, technical, or material support: Yuan, Lin, Li, Zhang, Luo, Dai, Wang. Supervision: Wang. Other (specify): None. Financial disclosures: I certify that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/ affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None. Funding/Support and role of the sponsor: This study was funded in part by unlimited education/research grants from Augusta Medical System and Timm Medical Technologies, Inc. (Yuan, Wang). Acknowledgements: The authors would like to thank Ms. Dorothy Stradinger for her editorial assistance. References [1] Jemal A, Siegel R, Ward E, Hao Y, Xu J, Thun MJ. Cancer Statistics, 2009. CA Cancer J Clin 2009; 59:225 49. [2] Han M, Partin AW, Pound CR, Epstein JI, Walsh PC. Long-term biochemical disease-free and cancer-specific survival following anatomic radical retropubic prostatectomy. The 15-year Johns Hopkins experience. Urol Clin North Am 2001;28:555 65. [3] Wang R. Penile rehabilitation after radical prostatectomy: where do we stand and where are we going? J Sex Med 2007;4:1085 97. [4] Litwin MS, Hays RD, Fink A, et al. Quality-of-life outcomes in men treated for localized prostate cancer. JAMA 1995;273:129 35. [5] Levine LA. Erectile dysfunction following treatment of prostate cancer: new insights and therapeutic options. J Mens Health Gen 2004; 1:328 33. [6] Hinh P, Wang R. Overview of contemporary penile rehabilitation therapies. Adv Urol 2008;481218. [7] Yuan JH, Westney OL, Wang R. Design and application of a new ratspecific vacuum erectile device for penile rehabilitation research. J Sex Med 2009;6:3247 53. [8] Mullerad M, Donohue JF, Li PS, Scardino PT, Mulhall JP. Functional sequelae of cavernous nerve injury in the rat: is there model dependency. J Sex Med 2006;3:77 83. [9] Mulhall JP, Müller A, Donohue JF, et al. The functional and structural consequences of cavernous nerve injury are ameliorated by sildenafil citrate. J Sex Med 2008;5:1126 36. [10] Klein LT, Miller MI, Buttyan R, et al. Apoptosis in the rat penis after penile denervation. J Urol 1997;158:626 30. [11] User HM, Hairston JH, Zelner DJ, McKenna KE, McVary KT. Penile weight and cell subtype specific changes in post-radical prostatectomy model of erectile dysfunction. J Urol 2003;169:1175 9. [12] McCullough AR. Prevention and management of erectile dysfunction following radical prostatectomy. Urol Clin North Am 2001; 28:613 27. [13] Dalkin BL, Christopher BA. Preservation of penile length after radical prostatectomy: early intervention with a vacuum erection device. Int J Impot Res 2007;19:501 4. [14] Raina R, Agarwal A, Ausmundson S, et al. Early use of vacuum constriction device following radical prostatectomy facilitates early sexual activity and potentially earlier return of erectile function. Int J Impot Res 2006;18:77 81. [15] Köhler TS, Pedro R, Hendlin K, et al. A pilot study on the early use of the vacuum erection device after radical retropubic prostatectomy. BJU Int 2007;100:858 62.

780 EUROPEAN UROLOGY 58 (2010) 773 780 [16] Burnett AL. Rationale for cavernous nerve restorative therapy to preserve erectile function after radical prostatectomy: results from CaPSURE. J Urol 2004;171:703 8. [17] Mulhall JP, Graydon RJ. The hemodynamics of erectile dysfunction following nerve-sparing radical retropubic prostatectomy. Int J Impot Res 1996;8:91 4. [18] Mulhall JP, Slovick R, Hotaling J, et al. Erectile dysfunction after radical prostatectomy: hemodynamic profiles and their correlation with the recovery of erectile function. J Urol 2002;167:1371 5. [19] Saenz de Tejada I, Morouluan P, Tessier J, Kim JJ, Goldstein I, Frohrib D. Trabecular smooth muscle modulates the capacitor function of the penis. Studies on a rabbit model. Am J Physiol 1991;260: H1590 5. [20] Moreland RB, Traish A, McMillin MA, Smith B, Goldstein I, Saenz de Tejada I. PGE1 suppresses the induction of collagen synthesis by transforming growth factor-beta 1 in human corpus cavernosum smooth muscle. J Urol 1995;153:826 34. [21] Moreland RB, Watkins MT, Nehra A, et al. Oxygen tension modulates transforming growth factor-b1 expression and PGE production in human corpus cavernosum smooth muscle cells. Mol Urol 1998;2:41 7. [22] Moreland RB, Gupta S, Goldstein I, Traish A. Cyclic AMP modulates TGF-beta-1 induced fibrillar collagen synthesis in cultured human corpus cavernosum smooth muscle cells. Int J Impot Res 1998;10: 159 63. [23] Moreland RB. Is there a role of hypoxemia in penile fibrosis: a viewpoint presented to the Society for the Study of Impotence. Int J Impot Res 1998;10:113 20. [24] Moreland RB, Albadawi H, Bratton C, et al. O 2 -dependent prostanoid synthesis activates functional PGE receptors on corpus cavernosum smooth muscle. Am J Physiol Heart Circ Physiol 2001;281:H552 8. [25] Leungwattanakij S, Bivalacqua TJ, Usta MF, et al. Cavernous neurotomy causes hypoxia and fibrosis in rat corpus cavernosum. J Androl 2003;24:239 45. [26] Gontero P, Kirby R. Proerectile pharmacological prophylaxis following nerve-sparing radical prostatectomy. Prostate Cancer Prostatic Dis 2004;7:223 6. [27] McVary KT, Podlasek CA, Wood D, McKenna KE. Apoptotic pathways are employed in neuropathic and diabetic models of erectile dysfunction. J Urol 2006; 175(Suppl):387. Abstract 1203. [28] Bosshardt RJ, Farwerk R, Sikora R, Sohn M, Jakse G. Objective measurement of the effectiveness, therapeutic success and dynamic mechanisms of the vacuum device. Br J Urol 1995;75:786 91. [29] Kim N, Vardi Y, Padma-Nathan H, Daley J, Goldstein I, Saenz de Tejada I. Oxygentensionregulates the nitric oxidepathway. Physiological role in penile erection. J Clin Invest 1993;91:437 42. [30] Ferrini MG, Kovanecz I, Sanchez S, et al. Fibrosis and loss of smooth muscle in the corpora cavernosa precede corporal veno-occlusive dysfunction (CVOD) induced by experimental cavernosal nerve damage in the rat. J Sex Med 2009;6:415 28.