Nitric oxide-mediated corpus cavernosal smooth muscle relaxation is impaired in ageing and diabetes

OBJECTIVE: To examine nitric-oxide (NO)-mediated relaxation in cavernosal smooth muscle in a rat model of diabetes, as previous experiments showed that HbA1c (an isoform of glycosylated haemoglobin and a marker of long-term diabetic control) impaired NO-mediated relaxation of normal corpus cavernosal tissue through the generation of superoxide anions. MATERIALS AND METHODS: Eight weeks after the induction of diabetes, male Wistar rats were killed and cavernosal tissue obtained. Strips were contracted with 1 micromol/L noradrenaline before applying acetylcholine or electrical field stimulation (EFS) or sodium nitroprusside (SNP). Relaxation responses were repeated in the presence of L-arginine (100 micromol/L), indomethacin (10 micromol/L) or superoxide dismutase (SOD, 120 IU/mL). Young and age-matched control animals were examined in the same way. RESULTS: Eight weeks of uncontrolled diabetes caused a significant impairment in mean relaxation responses to acetylcholine (P < 0.05) and to EFS (P < 0.05), but not to SNP, compared with young and age-matched controls, respectively. L-arginine, indomethacin and SOD had no significant effect on this impairment. Ageing caused a lesser but significant impairment in EFS-mediated cavernosal smooth muscle relaxation (P < 0.05). CONCLUSION: Diabetes impairs endothelial and neuronal NO-mediated cavernosal smooth muscle relaxation in rats in vitro. This effect is not mediated by an alteration in the intracellular action of NO, the availability of NO, superoxide anion inactivation of NO or the generation of constrictor prostanoids. It is possible that cholesterol or advanced glycation end products are responsible for the effect of diabetes on penile smooth function.     

The effect of DA-8159 on corpus cavernosal smooth muscle relaxation and penile erection in diabetic rabbits

A previous study showed that DA-8159, a potent type 5 phosphodiesterase inhibitor, enhanced the relaxation of the smooth muscles in the normal rabbit corpus cavernosum. In this study, we investigated the in vitro effects of DA-8159 on cavernosal smooth muscle relaxation and the in vivo erectogenic potential in diabetic rabbits, since erectile dysfunction is a well-known sequela of diabetes mellitus. Diabetes mellitus was induced in male New Zealand White rabbits with alloxan monohydrate. Cavernosal strips from age-matched control and 8-week diabetic animals were mounted in organ baths. The relaxation responses to sodium nitroprusside (10^-910^-5 M), a nitric oxide donor, were assessed in the presence or absence of DA-8159 (10^-910^-6 M). For the penile erection test, DA-8159 was given orally (1~10 mg/kg) to diabetic rabbits and the length of the uncovered penile shaft was measured in a time-course manner in the presence or absence of intravenous sodium nitroprusside. The sodium nitroprusside-stimulated relaxations were significantly impaired in the corpus cavernosum from the diabetic group (IC₅₀=1.07×10^-6 M following 8 weeks of diabetes mellitus; compared with 0.48×10^-6 M for age-matched controls). DA-8159 significantly and dose-dependently enhanced the sodium nitroprusside-stimulated relaxation in the diabetic groups. In addition, DA-8159 induced a dose-dependent penile erection in diabetic rabbits, which was potentiated by intravenous sodium nitroprusside. These results suggest that DA-8159 is an effective treatment for diabetic erectile dysfunction but further evaluation of the efficacy on human needs to be performed.     

Advanced glycation end-products are responsible for the impairment of corpus cavernosal smooth muscle relaxation seen in diabetes

OBJECTIVE: To determine if advanced glycation end-products (AGEs) are responsible for the lower neuronal and endothelial-derived nitric oxide (NO)-mediated relaxation of corpus cavernosum in tissue in diabetic rats than in control rats. MATERIALS AND METHODS: Diabetes was induced in male Wistar rats by an intraperitoneal injection with streptozotocin (60 mg/kg). One group of diabetic rats was given free access to water and standard diet. A second group was given standard diet and aminoguanidine with their water (50 mg/100 mL) from the initiation of diabetes. Two groups of rats that were not diabetic acted as age-matched controls. After 8 weeks animals were killed by cervical dislocation, corpus cavernosal tissue strips harvested and mounted in an organ bath to measure isometric tension. After 90 min of equilibration at optimal resting tension and contraction with 1 micromol/L noradrenaline, the response to either acetylcholine or electrical field stimulation (EFS) after adding guanethidine (5 micromol/L) and atropine (1 micromol/L) was determined for each group. RESULTS: There was no difference between the baseline characteristics of all the experimental groups. After 8 weeks the mean body mass and glycosylated haemoglobin (HbA1c) were significantly greater in the diabetic than in control animals. Aminoguanidine had no effect on the recorded body mass or HbA1c. The in vitro relaxation response to the application of acetylcholine or EFS of tissue strips from age-matched control animals fed a standard diet and those supplemented with aminoguanidine were the same. The administration of aminoguanidine to diabetic animals for 8 weeks reversed the expected impaired relaxation response to acetylcholine; the response to EFS was similar. CONCLUSION: AGEs are more prevalent in erectile tissue from diabetic than in control animals. Aminoguanidine reversed the impairment in neuronal and endothelial NO-mediated penile smooth muscle relaxation seen in diabetes. As aminoguanidine prevents AGE formation, erectile dysfunction in diabetes is probably caused partly by the generation of AGEs.     

Effects of Ginkgo biloba extracts with mirodenafil on the relaxation of corpus cavernosal smooth muscle and the potassium channel activity of corporal smooth muscle cells

In this study, we investigated the effects of a combination of Ginkgo biloba extracts (GBE) and phosphodiesterase type 5 (PDE-5) inhibitors on the muscular tone of the corpus cavernosum and potassium channel activity of corporal smooth muscle cells. Strips of corpus cavernosum from male New Zealand white rabbits were mounted in organ baths for isometric tension studies. After contraction with 1×10⁻⁵ mol l⁻¹ norepinephrine, GBE (0.01–1 mg ml⁻¹) and mirodenafil (0.01–100 nmol l⁻¹) were added together into the organ bath. In electrophysiological studies, whole-cell currents were recorded by the conventional patch-clamp technique in cultured smooth muscle cells of the human corpus cavernosum. The corpus cavernosum was relaxed in response to GBE in a dose-dependent manner (from 0.64%±8.35% at 0.01 mg ml⁻¹ to 52.28%±11.42% at 1 mg ml⁻¹). After pre-treatment with 0.03 mg ml⁻¹ of GBE, the relaxant effects of mirodenafil were increased at all concentrations. After tetraethylammonium (TEA) (1 mmol l⁻¹) administration, the increased effects were inhibited (P<0.01). Extracellular administration of GBE increased the whole-cell K⁺ outward currents in a dose-dependent fashion. The increase of the outward current was inhibited by 1 mmol l⁻¹ TEA. These results suggest that GBE could increase the relaxant potency of mirodenafil even at a minimally effective dose. The K⁺ flow through potassium channels might be one of the mechanisms involved in this synergistic relaxation.     

Dual mechanism of action of nicorandil on rabbit corpus cavernosal smooth muscle tone

The potential of ATP-sensitive potassium channel openers (KCOs) for the treatment of male erectile dysfunction has recently been suggested based on positive clinical outcomes following intra-cavernosal administration of pinacidil. Agents that increase the levels of cGMP via elevation of nitric oxide (NO) nitroglycerin, for example, are also effective in improving erectile function preclinically and clinically. The aim of the present study was to determine the effects and mechanism of the action of nicorandil on rabbit corpus cavernosum. The in vitro regulation of smooth muscle tone was assessed in isolated cavernosal tissues pre-contracted with phenylephrine. Nicorandil, but not its major metabolite, relaxed phenylephrine-precontracted cavernosum smooth muscle with an EC(50) of 15 microM. The effects of nicorandil were only partially reversed by the K(ATP) channel blocker glyburide (10 microM) or by a soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4] oxadiazole [4,3-a] quinoxalin-1-one (ODQ, 3 microM). However, a combination of ODQ and glyburide completely blocked the relaxant effects of nicorandil. The results of the present study indicate that nicorandil can relax rabbit cavernosal tissue in vitro via a mechanism that involves activation of K(ATP) channels and stimulation of soluble guanylate cyclase.     

Nitric oxide mediates relaxation in rabbit and human corpus cavernosum smooth muscle

Summary We investigated in vitro the relaxant effect of exogenous acetylcholine (ACh) and electric-field stimulation (EFS) on rabbit and human corpus cavernosum smooth muscle strips (CC) precontracted with phenylephrine. The effects of EFS and ACh were monitored alone, after muscarinic receptor blockade and after inhibition of nitric oxide (NO) formation with l-N-nitroarginine (l-NOARG). In rabbit und human CC, both atropine and l-NOARG abolished the relaxant effects of ACh. The relaxant effects of EFS, however, were only slightly reduced by atropine to 97.5±17.5% in human CC and to 89.0±6.1% in rabbit CC. l-NOARG further reduced the EFS effects to 0.8±1.7% in human CC and to 16.2±8.7% in rabbit CC. In strips obtained from impotent patients with diabetes mellitus, the relaxant effects appeared to be significantly less than in strips from nondiabetic impotent men. Tetrodotoxin blocked the relaxant EFS effects in human and rabbit strips completely. The data indicate the important role of NO in cholinergically induced relaxation of cavernous smooth muscle in rabbits and humans. Our findings support the idea of NO as the nonadrenergic noncholinergic neurotransmitter in penile erection in both species. Rabbit erectile tissue might serve as an in vitro animal model for further investigation.     

Effect of hypothyroidism on the purinergic responses of corpus cavernosal smooth muscle in rabbits

AIMS: Several studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. In the present study, we examined purinergic relaxation responses in hypothyroidism in an experimental rabbit model and compared them with controls to evaluate the possible involvement of the purinergic pathway. MATERIALS AND METHODS: The study comprised 20 male New Zealand white rabbits. The rabbits were divided into two equal groups. We tested the effects of ATP, alpha beta ATP, and adenosine precontracted with phenylephrine on the isolated corpus cavernosum preparations from control and hypothyroid rabbits. We also evaluated the effects of ATP, alpha beta ATP, and adenosine on the cGMP levels in the isolated corpus cavernosum preparations from control and hypothyroid rabbits. RESULTS: T(3), T(4), and testosterone levels were significantly lower in hypothyroid rabbits. ATP, alpha beta ATP, carbachol, and electrical field stimulation (EFS)-induced frequency-dependent relaxation responses in the isolated rabbit corpus cavernosum strips precontracted with phenylephrine reduced significantly (P < 0.05). Adenosine-induced relaxation responses did not change significantly in hypothyroid rabbits. CONCLUSION: Reduction of relaxation response in hypothyroid rabbits corpus cavernosum can depend on a decreased release of nitric oxide (NO) from nitrergic nerves and endothelium.     

The effect of nitric oxide and peroxynitrite on rabbit cavernosal smooth muscle relaxation

 Nitric oxide (NO) mediates penile erection by inducing cavernosal smooth muscle relaxation. Superoxide anion (O₂ ⁻) can influence the activity of NO by reacting with it to produce peroxynitrite (PN). This is a highly reactive species that is known to attack a variety of biological targets. It is far more reactive and damaging than its precursors. We therefore, investigated the effect of PN on rabbit cavernosal smooth muscle relaxation and compared it to NO. Cavernosal strips from nine adult New Zealand White rabbits were excised (n=12 strips for each arm of the study) and mounted in organ baths. After pre-contraction with phenylephrine (PE) (100 μM) the strips were exposed to either NO or PN (1–100 μM) and subsequent smooth muscle relaxations monitored. Some tissues were incubated with oxadiazoloquinoxalin-1-one (ODQ; 10 μM), an inhibitor of guanylyl cyclase, before the addition of NO or PN. NO and PN induced concentration-dependent relaxations in all strips. However, PN (IC₅₀: 26 ± 3.6 μM) was significantly less potent than NO (IC₅₀: 11 ± 0.7 μM) [P < 0.01]. Relaxation induced by NO was immediate and short-lived, with the tension returning to its original level. In contrast, PN-initiated relaxations were of a slower onset and more prolonged, with the tissues unable to recover tension. However, after several washouts the tissues were fully responsive to PE. Both NO- and PN-mediated relaxations were inhibited by ODQ, suggesting the involvement of cGMP in this process. Although PN mediates cavernosal smooth muscle relaxation, it is much less potent than NO. As PN is thought to play a role in a variety of pathologies where erectile dysfunction is prominent, it may also contribute to the pathogenesis of erectile dysfunction.     

Effect of hypothyroidism on the nitrergic relaxant responses of corpus cavernosal smooth muscle in rabbits

BACKGROUND: The incidence of hormonal dysfunction as a cause of impotence remains controversial. However, several recent studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. METHODS: In the present study, we examined nitrergic responses in hypothyroidism in rabbit corpus cavernosum and compared them with controls. RESULTS: Carbachol-induced relaxation responses and electrical field stimulation (EFS)-induced frequency-dependent relaxations decreased significantly in hypothyroid rabbits. Papaverine and sodium nitroprusside (SNP)-induced relaxation responses did not change significantly in hypothyroid rabbits. The contraction responses of phenylephrine and EFS-induced frequency-dependent contractions were significantly decreased in the hypothyroid group. CONCLUSIONS: We can speculate that the reduction of relaxant responses to EFS and carbachol in hypothyroid rabbits can depend on a decreased release of nitric oxide (NO) from nitrergic nerves and endothelium or a reduction of muscarinic receptor density. Also, decreases in contraction responses may depend on diminished adrenoceptor density.     

Hypercholesterolemia impairs endothelium-dependent relaxation of rabbit corpus cavernosum smooth muscle

The majority of cases of impotence are associated with vascular risk factors such as diabetes, hypercholesterolemia, hypertension and smoking. These factors induce impairment of endothelium-dependent relaxation of blood vessels in man and in experimental animals. In this study the effects of hypercholesterolemia on the reactivity of rabbit corpus cavernosum smooth muscle strips to endothelium-dependent and endothelium-independent agents were investigated. New Zealand White rabbits (n = 14) were randomly divided into control and treatment groups. The control group (n = 7) received a regular diet while the treatment group (n = 7) was fed a diet of 0.5% cholesterol and 4% peanut oil for 10 weeks. Animals were then sacrificed and the corporal tissue studied in organ chambers for isometric tension measurement. Tissue was contracted with phenylephrine and concentration-dependent relaxation to acetylcholine, in the presence and absence of indomethacin, and to nitroprusside were examined. Blood level of cholesterol in the cholesterol-fed group was significantly higher compared to the control group. Contractions to phenylephrine were similar in both groups. Hypercholesterolemia, however, inhibited relaxation to acetylcholine but did not alter relaxation to nitroprusside, a cyclic guanosine monophosphate (cGMP)-dependent, direct smooth muscle dilator. Indomethacin enhanced the relaxations to acetylcholine in both control and cholesterol-fed groups but did not correct the difference in the relaxation to acetylcholine between both groups. It is concluded that hypercholesterolemia impairs endothelium-mediated relaxation of rabbit corpus cavernosum smooth muscle. The mechanism for the endothelial dysfunction does not appear to involve alteration in cyclooxygenase products of arachidonate or the cGMP-dependent relaxation of corporal smooth muscle. Impairment of endothelium-dependent relaxation of corporal smooth muscle may contribute to the pathophysiology of impotence associated with hypercholesterolemia in man.     

Potassium channels and human corporeal smooth muscle cell tone: diabetes and relaxation of human corpus cavernosum smooth muscle by adenosine triphosphate sensitive potassium channel openers

PURPOSE: Sustained contraction of human corporeal smooth muscle depends on continuous transmembrane calcium flux through voltage gated calcium channels. K channels modulate corporeal smooth muscle membrane potential and, thus, ultimately affect transmembrane calcium flux. Therefore, we characterized relaxation responses elicited by the K channel modulators pinacidil and levcromakalim on isolated human corporeal tissue strips. We also evaluated the possibility that there may be alterations in adenosine triphosphate sensitive K channel pharmacology/function related to the presence of diabetes mellitus. MATERIALS AND METHODS: A total of 215 isolated human corporeal tissue strips obtained from 57 male patients with organic erectile dysfunction were investigated. Cumulative concentration-response curves were constructed at half log increments for steady state relaxation responses elicited by pinacidil and levcromakalim on equivalently phenylephrine pre-contracted (to approximately 75% of maximum) isolated corporeal tissue strips. Potassium currents were measured using the cell attached whole cell patch clamp technique on freshly isolated corporeal smooth muscle cells. RESULTS: A concentration dependent, glibenclamide sensitive relaxation response of phenylephrine pre-contracted corporeal tissue strips was observed for pinacidil and levcromakalim. Consistent with such observations, electrophysiological recordings on freshly isolated myocytes revealed that pinacidil (10 microM.) and levcromakalim (10 microM.) induced whole cell potassium currents that were blocked by glibenclamide (10 microM.). In addition, statistical analysis revealed that phenylephrine pre-contracted corporeal tissue strips from patients without diabetes were more sensitive to relaxation by both compounds than corporeal tissue strips excised from those with diabetes. Furthermore, relaxation responses elicited by pinacidil and levcromakalim were not affected by charybdotoxin or 4-aminopyridine but were completely reversed by KCl or tetraethylammonium chloride. CONCLUSIONS: These data indicate that the adenosine triphosphate sensitive K channel subtype is likely to have an important role in the relaxation of isolated corporeal tissue strips and, moreover, they are the molecular target for the K channel modulators/openers levcromakalim and pinacidil. Such observations are consistent with the supposition that alterations in the structure/function/activity of these potassium channels may underlie at least some aspects of observed diabetes related differences in tissue sensitivity to K channel modulators.     

Endothelial and neuronal-derived nitric oxide mediated relaxation of corpus cavernosal smooth muscle in a rat, in vitro, model of erectile function

We set out to establish a simple, reproducible, rat in vitro model of erectile function and to use this to demonstrate the functional importance of both neuronal- and endothelial-derived nitric oxide within this animal. Two corpora cavernosal smooth muscle strips were harvested from sexually mature male Wistar rats and mounted in an organ bath for measurement of isometric tension. Following contraction with noradrenaline the strips were relaxed by the addition of either acetylcholine or sodium nitroprusside. Electrical field stimulation was performed in the presence of atropine and guanethidine. Relaxation responses were repeated in the presence of methylene blue, L-arginine, L-NNA and haemoglobin +/- L-arginine. Methylene blue abolishes the relaxation to acetylcholine and EFS; L-NNA and haemoglobin cause a significant impairment in the relaxation response. L-arginine reverses the effect of haemoglobin. In conclusion, the inhibitory, relaxant stimulus of rat corpora cavernosa is due to both neuronal nitric oxide and endothelial-derived nitric oxide released in response to cholinergic stimulation.     

Misoprostol induces relaxation of human corpus cavernosum smooth muscle: comparison to prostaglandin E1

Prostaglandin E1 (PGE1) relaxes trabecular smooth muscle by interacting with specific G-protein coupled receptors on human corpus cavernosum smooth muscle and increasing intracellular synthesis of cAMP. Misoprostol (Cytotec), is an oral prostaglandin E analogue. The purpose of this study was to compare the functional activity of misoprostol with PGE1 in human corpus cavernosum and cultured human corpus cavernosum smooth muscle cells. Misoprostol, misoprostol free acid or PGE1 induced dose-dependent relaxations in strips of human corpus cavernosum. At concentrations greater than 10(-6) M, tissue recontraction was observed with all three agents. This was abrogated by pretreatment with the thromboxane A2 receptor antagonist SQ29,548. From these observations, we conclude that misoprostol is activated by human corpus cavernosum in situ and relaxes phenylephrine-precontrated tissue strips in vitro. This relaxation response is mediated by the increased cAMP synthesis by these agents.     

Effect of chronic renal failure on the purinergic responses of corpus cavernosal smooth muscle in rabbits

OBJECTIVE: To examine purinergic relaxation responses in chronic renal failure (CRF) in an experimental rabbit model, and thus evaluate the possible involvement of the purinergic system in erectile dysfunction with CRF. MATERIALS AND METHODS: The relaxant effects of ATP were measured in strips of corpus cavernosum smooth muscle taken from control and CRF rabbits. CRF was induced in New Zealand white rabbits as previously described. Penises were excised from CRF rabbits 4 weeks after inducing uraemia. In an organ bath the strips from controls and CRF rabbit corpus cavernosum were pre-contracted with phenylephrine and increasing doses of adenosine and ATP added. RESULTS: In the pre-contracted rabbit cavernosal tissue the relaxations induced by adenosine and ATP were unchanged in CRF. CONCLUSION: The lack of any relaxant effect of adenosine or ATP on the relaxation of cavernosal smooth muscle in rabbits with CRF might be because the relaxant effects of these agents are endothelium-independent and the endothelial purinergic receptor density was unchanged in CRF.     

中药益坎胶囊对动脉性勃起功能障碍大鼠阴茎海绵体平滑肌细胞表型转化的影响

目的:探讨中药益坎胶囊对动脉性勃起功能障碍(ED)大鼠阴茎海绵体平滑肌细胞表型转化的影响,以揭示益坎胶囊治疗ED的机制。方法:选取SD大鼠50只,其中10只设为正常组,另40只通过结扎双髂内动脉造成动脉性ED模型。造模后将其中10只设为模型对照组,其余30只灌胃给予ED治疗中药益坎胶囊,浓度分别为1.88、0.94、0.47 g/kg。给药1个月后,经腹腔注射阿朴吗啡,观察大鼠呵欠次数和阴茎勃起次数;切取大鼠的阴茎组织标本,通过免疫组化法观测海绵体平滑肌细胞收缩型性标志物碱性调宁蛋白(calponin 1)和合成型标志物骨桥蛋白(OPN)的表达,实验组结果与正常组和对照组进行比较。结果:注射阿朴吗啡后,正常组大鼠勃起次数为(4.48±1.25)次,模型对照组为(1.63±0.22)次,两组比较,差异有统计学意义(P0.01);给药后,中药益坎胶囊高、中、低剂量组大鼠勃起次数有明显改善[高剂量:(3.05±1.37)次;中剂量:(2.98±0.16)次;低剂量:(1.75±0.40)次]。免疫组化结果显示,模型对照组大鼠海绵体平滑肌细胞calponin 1表达减少,而OPN表达增多,与正常组相比差异有统计学意义(P0.05);与模型对照组相比,给药后,中药益坎胶囊高、中、低剂量组大鼠海绵体平滑肌细胞calponin 1表达增多,OPN表达减少。结论:中药益坎胶囊能改善动脉性ED大鼠的勃起功能,抑制海绵体平滑肌细胞表型由收缩型向合成型转化。     

Audiovisual sexual stimulation by virtual glasses is effective in inducing complete cavernosal smooth muscle relaxation: a pharmacocavernosometric study

Audiovisual sexual stimulation (AVSS) is frequently employed to promote cavernosal smooth muscle relaxation (SMR) in hemodynamic diagnostic settings for erectile dysfunction. Our aim has been to adapt conventional AVSS to the particular test conditions of pharmacocavernosometry and pharmacocavernosography (DICC), by the use of virtual glasses. Thirty-seven consecutive patients undergoing DICC were randomized in two groups: no-AVSS and AVSS through commercially available virtual glasses (VG-AVSS) with tri-dimensional capabilities and stereophonic headphones. Such device partially excludes the patient from the surrounding environment. In both groups a standard dose of vasoactive agents was intracavernosally administered, and possibly repeated (re-dosing), until complete SMR was obtained (3 doses/patient maximum). Psychometric tests (State Trait Anxiety Inventory and ad hoc visual analogue scales for embarrassment, stress and pain) were administered before and after DICC. The no-AVSS group consisted of 18 patients, the AVSS group of 19. Number of needed vasoactive agent doses: in the no-AVSS group 6 patients needed 1 dose, 3 patients 2, 9 patients 3 (mean dose number: 2.17); in the AVSS group 15 patients needed 1 dose, 1 patient 2, 3 patients 3 (mean dose number: 1.37). The difference in the number of doses used in the two groups was statistically significant (Student's t-test P = 0.007). Complete SMR, regardless of the number of used doses: in the no-AVSS group 9 patients (50%) achieved complete SMR, in the AVSS group 16 patients (84.2%). The difference in the two groups was statistically significant (chi-square P = 0.026). From evaluated psychometric measures no statistically significant difference between the two groups was detected. VG-AVSS significantly promotes complete SMR without increasing test related stress or anxiety. Its induced arousal suggests the possibility of performing dynamic evaluations of the erectile function with the oral agent sildenafil in place of intracavernosally administered vasoactive agents. VG-AVSS furthermore constitutes a promising tool for the investigation of normal physiology and pathophysiology of female sexual function.     

The effect of superoxide dismutase on nitric oxide-mediated and electrical field-stimulated diabetic rabbit cavernosal smooth muscle relaxation

OBJECTIVE: To investigate the effect of superoxide dismutase (SOD, the enzyme that accelerates the breakdown of the superoxide anion, O2- to H2O) on nitric oxide (NO)-mediated and electrical field stimulated (EFS) relaxation in diabetic rabbit cavernosal smooth muscle. Materials and methods Diabetes was induced with alloxan (65 mg/kg) in six adult New Zealand White rabbits. After 6 months, cavernosal smooth muscle strips from age-matched controls and diabetic animals were mounted in organ baths. After precontraction with phenylephrine (10 micromol/L) in the presence of atropine (1 micromol/L), guanethidine (5 micromol/L) and indomethacin (10 micromol/L), relaxation responses to EFS (1-20 Hz), carbachol (10(-8)-10(-4) mol/L) and sodium nitroprusside (SNP, 10(-9)-10(-4) mol/L) were assessed in the presence and absence of SOD (100 IU/mL). RESULTS: SNP- and carbachol-mediated (endothelium-independent and -dependent, respectively) relaxations were impaired in the diabetic cavernosal smooth muscle strips compared with controls (concentration required for 50% inhibition, 1.4 micromol/L for diabetic and 0.75 micromol/L for control with SNP, and 44 micromol/L for diabetic and 0.4 micromol/L for control with carbachol). SOD significantly enhanced both SNP- and carbachol-mediated diabetic cavernosal smooth muscle relaxations (both P < 0.05). EFS-mediated relaxations were also significantly (P < 0.05) impaired in the diabetic cavernosal smooth muscle strips; these relaxations were also significantly (P < 0.05) enhanced by SOD. CONCLUSION: NO- and EFS-mediated cavernosal smooth muscle relaxation is impaired in a rabbit model of diabetes but SOD significantly reversed the impaired relaxation. Therefore, in diabetes, the generation of reactive oxygen species may play an important role in the development of erectile dysfunction.     

A stretch-sensitive Cl- channel in human corpus cavernosal myocytes

With the patch clamp method we demonstrate a stretch-sensitive Cl- currents as well as stretch-sensitive Cl- channels in a small group (5%,n 117) of cultured human corpus cavernosal muscle cells. The current and the channel activities had the following characteristics: (1) Their equilibrium potentials changed with extracellular Cl- concentration close to that predicted by Nernst equation provided that the relevant channels had high permeability to Cl- but low permeability to acetate ions; (2) They were blocked by mM concentrations of Zn2+; (3) The i-v relation of single channel current was almost linear for holding potentials varied from -70 to +60 mV; and (4) The channels had unitary conductances of approximately 140-170 pS.     

Human and rabbit cavernosal smooth muscle cells express Rho-kinase

Rho-kinase is an enzyme involved in the Ca2+-sensitizing pathway in smooth muscle cells. Inhibition of this enzyme has been recently demonstrated to elicit penile erection by relaxing cavernosal smooth muscle. We aimed to investigate the presence and activity of Rho-kinase in human cavernosal smooth muscle. Primary culture of smooth muscle cells from human and rabbit penile corpus cavernosum was developed, and cells showed characteristic myocyte morphology and alpha-actin immunoreactivity. The presence of Rho-kinase was demonstrated by indirect immunofluorescence and Western blotting. A specific inhibitor of Rho-kinase, Y-27632, inhibited in a concentration-dependent manner the kinase activity of the protein immunoprecipitated with anti-Rho-kinase antibody. These results demonstrate for the first time expression and activity of Rho-kinase in human penile cavernosal smooth muscle cells and suggest that these cells can provide a cellular model for the study of enzymes involved in Ca2+-sensitizing pathways.