Prostanoid Production in Rabbit Corpus Cavernosum. II. Inhibition of Oxidative Stress

Course of transforming growth factor ß1 in the systemic and cavernous blood of healthy males through different penile conditions

Studies on erectile dysfunction (ED) have revealed a relationship between smooth muscle atrophy and the accumulation of collagen in the corpus cavernosum (CC). Transforming growth factor ß1 (TGF ß1) is a cytokine which has been proposed to be involved in the fibrotic process in the CC. We aimed to evaluate the course of TGF ß1 in the systemic and cavernous blood of 17 healthy males through different phases of the sexual arousal response (exemplified by the penile conditions flaccidity, tumescence, rigidity and detumescence). An enzyme-linked immunoassay was used to measure the concentration of TGF ß1 (ng/ml) in both the systemic and cavernous blood at the stages of flaccidity, tumescence and detumescence. TGF levels were significantly higher in the cavernous compartment than in the systemic blood. A linear decrease was evident in the cavernous blood when the flaccid penis became tumescent (24.3 ± 14.5 to 13.9 ± 6.5) and rigid (to 8.7 ± 3.1). At detumescence, TGF increased to 18.3 ± 10.4. In contrast, the levels in the systemic circulation remained unchanged. The results are in support of the hypothesis that the concentration of TGF ß1 in the CC is regulated by adequate blood flow and oxygenation.

Nicotine in high concentration causes contraction of isolated strips of rabbit corpus cavernosum

It is well known that cigarette smoke can cause erectile dysfunction by affecting the penile vascular system. However, the exact effects of nicotine on the corpus cavernosum remains poorly understood. Nicotine has been reported to cause relaxation of the corpus cavernosum; it has also been reported to cause both contraction and relaxation. Therefore, high concentrations of nicotine were studied in strips from the rabbit corpus cavernosum to better understand its effects. The proximal penile corpus cavernosal strips from male rabbits weighing approximately 4 kg were used in organ bath studies. Nicotine in high concentrations (10^-5~10^-4 M) produced dose-dependent contractions of the corpus cavernosal strips. The incubation with 10^-5 M hexamethonium (nicotinic receptor antagonist) significantly inhibited the magnitude of the nicotine associated contractions. The nicotine-induced contractions were not only significantly inhibited by pretreatment with 10^-5 M indomethacin (nonspecific cyclooxygenase inhibitor) and with 10^-6 M NS-398 (selective cyclooxygenase inhibitor), but also with 10^-6 M Y-27632 (Rho kinase inhibitor). Ozagrel (thromboxane A2 synthase inhibitor) and SQ-29548 (highly selective TP receptor antagonist) pretreatments significantly reduced the nicotine-induced contractile amplitude of the strips. High concentrations of nicotine caused contraction of isolated rabbit corpus cavernosal strips. This contraction appeared to be mediated by activation of nicotinic receptors. Rho-kinase and cyclooxygenase pathways, especially cyclooxygenase-2 and thromboxane A₂, might play a pivotal role in the mechanism associated with nicotine-induced contraction of the rabbit corpus cavernosum.

The effects of trimetazidine and sildenafil on bilateral cavernosal nerve injury induced oxidative damage and cavernosal fibrosis in rats

AIM

The aim of this study was to compare the effects of sildenafil and trimetazidine on bilateral cavernosal nerve injury-induced oxidative damage and fibrotic changes in cavernosal tissue in rat model.

MATERIAL AND METHODS

A total of 32 male Sprague-Dawley rats were randomly divided into 4 groups; each group consist 8 rats (control, BCI, BCI + TMZ, and BCI + sildenafil groups). Tissue superoxide dismutase (SOD), malondialdehyde (MDA), and protein carbonyl (PC) levels were determined biochemically and distribution of cavernosal fibrosis density among groups was performed histopathologically.

RESULTS

Tissue SOD levels in BCI group were significantly lower than the control group (P < 0.05). Tissue MDA and PC levels in BCI group were significantly higher than the control group (P < 0.05). TMZ and sildenafil administration significantly increased tissue SOD levels (P < 0.05) and reduced tissue MDA and PC levels (P < 0.05). Histologically, the degree of cavernosal fibrosis and collagen density was higher in BCI group in comparison to control, TMZ-treated, and sildenafil-treated groups.

CONCLUSION

BCI caused oxidative damage and increased cavernosal fibrosis in rat penis. TMZ and sildenafil treatment decreased oxidative damage and reduced the degree of fibrosis in penile tissue due to BCI.

Preclinical evidence for the benefits of penile rehabilitation therapy following nerve-sparing radical prostatectomy

Erectile dysfunction following radical prostatectomy remains a frequent problem despite the development of nerve-sparing techniques. This erectile dysfunction is believed to be neurogenic, enhanced by hypoxia-induced structural changes which result in additional veno-occlusive dysfunction. Recently, daily use of intracavernous vasoactive substances and oral use of PDE5-inhibitors have been clinically studied for treatment of postprostatectomy erectile dysfunction. Since these studies showed benefits of “penile rehabilitation therapy,” these effects have been studied in a preclinical setting. We reviewed experimental literature on erectile tissue preserving and neuroregenerative treatment strategies, and found that preservation of the erectile tissue by the use of intracavernous nitric oxide donors or vasoactive substances, oral PDE5-inhibitors, and hyperbaric oxygen therapy improved erectile function by antifibrotic effects and preservation of smooth muscle. Furthermore, neuroregenerative strategies using neuroimmunophilin ligands, neurotrophins, growth factors, and stem cell therapy show improved erectile function by preservation of NOS-containing nerve fibers.

Pharmacology of erectile dysfunction in man

Erectile dysfunction (ED) is defined as the consistent or recurrent inability of a man to attain and/or maintain a penile erection sufficient for sexual activity (2nd International Consultation on Sexual Dysfunction-Paris, June 28th-July 1st, 2003). Following the discovery and introduction of sildenafil, research on the mechanisms underlying penile erection has had an enormous boost and many preclinical and clinical papers have been published in the last 5 years. This review is structured in order to give the reader an overview of the clinical and preclinical data available on the peripheral regulation of and the mediators involved in human penile erection. The most widely accepted risk factors for ED are discussed. The article is focused on human data, and the safety and effectiveness of the 3 commercially available Phosphodiesterase-5 (PDE5) inhibitors used to treat ED are also discussed.

Nitric oxide/redox-based signalling as a therapeutic target for penile disorders

Oxidative and/or nitrosative stress is implicated in the pathogeneses of assorted penile disorders of clinical significance, notably erectile dysfunction, priapism and penile fibrosis. It is becoming increasingly recognised that the generation and activity of reactive oxygen and nitrogen species in the penis influence vascular homeostasis of this organ, with adverse effects exerted at cellular and molecular levels. Furthermore, these elements may interact with molecular signalling pathways operating in the penis, modulating their functional roles. This interaction in particular suggests that by accessing molecular targets associated with oxidative/nitrosative stress in the penis, new pharmacotherapeutic approaches may be developed to promote normal erectile ability and preserve erectile tissue health. This notion pertains to, but also extends beyond, interventions which predictably target components of the nitric oxide-based signal transduction pathway for the on-demand treatment of erectile dysfunction. The next line of pharmaceuticals for disorders of the penis, in general, may well spawn from an integrative understanding of the complex regulatory interactions influenced by, as well as influencing nitric oxide signalling in this organ.

Cyclic nucleotide signaling in cavernous smooth muscle

INTRODUCTION

Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. AIMS. To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed.

METHODS

Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation.

RESULTS

More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG).

CONCLUSIONS

The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

Time-dependent reduction of acetylcholine-induced relaxation in corpus cavernosum of cholestatic rats: role of nitric oxide and cyclooxygenase pathway

The endothelium-dependent relaxation of corpus cavernosum smooth muscle and the roles of nitric oxide (NO) and arachidonic acid products of cyclooxygenase were investigated in non-operated, SHAM-operated, and bile duct-ligated rats. We further investigated the time-dependent alterations of corpus cavernosum relaxation in 2-, 7-, and 14-day bile duct-ligated animals. Acetylcholine produced concentration-dependent relaxation in phenylephrine-precontracted strips of corpus cavernosum. A significant reduction in the acetylcholine-induced relaxation was observed 2 days after bile duct ligation, and a greater reduction was observed on subsequent days. Incubation with 20 microM indomethacin reduced the acetylcholine-induced relaxation of the corpus cavernosum of unoperated rats while it had no effect in the corpus cavernosum of bile duct-ligated rats. Chronic treatment with Nomega-Nitro-L-Arginine Methyl Ester (L-NAME, 3 mg/kg/day, intraperitoneally) reduced the relaxation responses in the unoperated group while it had no effect in the bile duct-ligated group. These results show that acetylcholine-induced corporal relaxation is impaired in cholestatic rats, and this may be related to deficient nitric oxide production by the endothelium. The involvement of prostaglandins in this impairment seems unlikely.

Reperfusion of ischemic corporal tissue: physiologic and biochemical changes in an animal model of ischemic priapism

OBJECTIVES

To assess the physiologic and biochemical changes resulting from ischemia and reperfusion. Effective therapy for ischemic priapism reestablishes corporal venous outflow and arterial inflow and results in increased corporal partial pressure of oxygen. Data are limited concerning reperfusion injury of ischemic erectile tissue associated with reactive oxygen species (ROS) and the potential role of ROS scavengers in the clinical therapy of ischemic priapism.

METHODS

Anesthetized adult New Zealand white male rabbits (n = 7) were exposed to a low oxygen tension breathing gas to achieve hypoxia within the corpora cavernosa. This resulted in a mean systemic oxygen saturation of 60%. The pelvic nerve was electrically stimulated to induce penile erection, and the base of the erect penis was clamped. After varying durations of ischemia, the clamp was removed to allow reperfusion. We determined the intracavernosal oxygen tension, histologic changes, myeloperoxidase activity, and lipid peroxidation.

RESULTS

Corporal partial pressure of oxygen progressively decreased as the duration of priapism increased. A statistically significant increase was noted in myeloperoxidase activity and lipid peroxidation with corporal reperfusion. Polymorphonuclear leukocyte infiltration was documented in the ischemic reperfused tissue.

CONCLUSIONS

In the management of ischemic priapism, reperfusion causes erectile tissue injury owing to the presence of ROS. There is a need to investigate the utility of ROS scavengers and antioxidants in the management of ischemic priapism.

Cavernous neurotomy causes hypoxia and fibrosis in rat corpus cavernosum

The etiologies of erectile dysfunction (ED) after nerve-sparing radical prostatectomy have not been clearly elucidated. The aim of this study was to evaluate the effects of cavernous nerve injury on cavernous fibrosis, and to consider measures to prevent irreversible damage to the cavernous tissues. Twenty male Sprague-Dawley rats constituted the study population. The animals were divided into 2 groups; group 1 consisted of sham-operated rats (n = 10), and group 2 consisted of rats that underwent incision of both cavernous nerves (n = 10). Three months later, all rats underwent intracavernous papaverine injection (300 and 600 mg), and intracorporal pressures were recorded. Transforming growth factor-beta(1) (TGF-beta(1)) messenger RNA (mRNA) expression from rat penile tissue was measured using reverse transcriptase-polymerase chain reaction. Hypoxia-inducible factor-1alpha (HIF-1alpha), TGF-beta(1), and collagen I and III protein expressions were determined by Western blot analysis and immunohistochemical staining. Erectile function as studied with intracavernosal papaverine injection and histological analysis of penile cross-sections at 3 months was similar in both groups. TGF-beta(1) mRNA expression, HIF-1alpha, TGF-beta(1), and collagen I and III protein expressions were significantly greater in the neurotomy group. Immunohistochemical staining for TGF-beta(1), HIF-1alpha, and collagen III were qualitatively more positive in the neurotomy group, whereas collagen I staining was similar. This study demonstrates an increase in TGF-beta(1), HIF-1alpha, and collagen III synthesis in rat cavernosal smooth musculature after cavernous neurotomies. In theory, cavernous fibrosis may be reduced by employing various vasoactive agents or interventions that increase oxygenation to the corporal tissues during the postoperative period.

The effects of melatonin on ischemia-reperfusion induced changes in rat corpus cavernosum

PURPOSES

We determined the change in contractile activity and oxidant damage after ischemia-reperfusion of rat corpus cavernosum and investigated the effects of melatonin (Sigma Chemical Co., St. Louis, Missouri) on these parameters.

MATERIALS AND METHODS

The abdominal aorta of male Wistar albino rats was occluded to induce ischemia-reperfusion. Melatonin (10 mg./kg.) or vehicle (1% alcohol in saline per kg.) was administered subcutaneously before ischemia-reperfusion. In the sham operated control group the abdominal aorta was left intact and the rats were treated with melatonin or vehicle. After decapitation corporeal tissues were placed in organ baths or stored for biochemical measurements.

RESULTS

In sham operated rats phenylephrine added cumulatively caused a concentration dependent contraction in corpus cavernosum strips precontracted with KCl and acetylcholine added cumulatively to strips precontracted with phenylephrine caused a dose dependent relaxation response. In the ischemia-reperfusion group contraction and relaxation responses decreased significantly compared within controls. Melatonin treatment in the ischemia-reperfusion group reversed these responses. Myeloperoxidase activity and the lipid peroxidation level of the corporeal tissues in the ischemia-reperfusion group were significantly higher than in the sham operated control group. Melatonin treatment in the ischemia-reperfusion group decreased myeloperoxidase activity and the lipid peroxidation level compared with ischemia-reperfusion alone, whereas melatonin treatment alone had no significant effect on these parameters.

CONCLUSIONS

In this study the corporeal tissues of rats exposed to ischemia-reperfusion had lower responses to contractile and relaxant agents than those of sham operated rats. Treatment with melatonin before ischemia-reperfusion almost completely reversed smooth muscle responses and prevented the increased myeloperoxidase activity and lipid peroxidation of corporeal tissues.

The role of prostaglandins in penile erection

The balance of penile smooth muscle tone is finely controlled, with contractile factors acting in opposition to relaxant factors. The principal agents in this process are undoubtedly noradrenaline and nitric oxide. Prostaglandins probably have a crucial role in the 'fine tuning' of corporal smooth muscle tone. Their effects on control mechanisms in the healthy penis are more likely to be modulatory rather than direct.

Neurotransmission and the contraction and relaxation of penile erectile tissues

The balance between contractant and relaxant factors controls the smooth muscle of the corpus cavernosum and determines the functional state of the penis (detumescence and flaccidity versus tumescence and erection). Noradrenaline contracts both the corpus cavernosum and penile vessels, mainly via stimulation of alpha(1)-adrenoceptors. Recent investigations have demonstrated the presence of several subtypes of alpha 1-adrenoceptors (alpha(1A), alpha(1B), and alpha(1D)) in the human corpus cavernosum and also that the noradrenaline-induced contraction in this tissue is probably mediated by two or, possibly, three receptor subtypes. Even if much of the available in vitro information suggests that endothelins (ETs) may be of importance for mechanisms of detumescence and flaccidity, the role of the peptides in the control of penile smooth-muscle tone in vivo is unclear, as is the question as to whether they can contribute to erectile dysfunction. For further evaluation of the clinical importance of ETs in penile physiology and pathophysiology, clinical studies on ET-receptor antagonists would be of interest. Neurogenic nitric oxide (NO) has been considered the most important factor for relaxation of penile vessels and the corpus cavernosum, but recent studies in mice lacking neurogenic NO synthase (NOS) have shown these animals to have normal erections. This focuses interest on the role of endothelial NOS and on other agents released from nerves or endothelium. For the time being the most effective means of inducing penile erection in men involves the intracavernous administration of prostaglandin E1 (PGE1). PGE1 may act partly by increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP). Recent results obtained with the adenylate cyclase stimulator forskolin suggest that penile smooth-muscle relaxation leading to penile erection can be achieved through the cAMP pathway. Thus, transmitters and agents acting through this second-messenger system may significantly contribute to relaxation of penile smooth muscle and to erection.