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

Association of nNOS and Rho-kinase with age-associated erectile dysfunction in Sprague-Dawley rats

The present study aimed to investigate the changes of Rho-associated kinase (Rho-kinase) and neuronal nitric oxide synthase (nNOS) expression in age-associated erectile dysfunction (ED) in Sprague-Dawley (SD) rats. A total of 100 intact male SD rats were divided into 20 groups according to their age (5-24 months; rats that were the same age in months were in the same group). Erectile response measurements were performed and the functional index intracavernosal pressure/mean arterial pressure (ICP/MAP) was tested, followed by detection of Rho-kinase and nNOS protein by western blot analysis. Finally, correlation analyses of the association between ICP/MAP and Rho-kinase, nNOS, or nNOS/Rho-kinase, as well as between age and nNOS or Rho-kinase, were performed. The functional index ICP/MAP decreased with age in SD rats. Moreover, the expression of nNOS protein decreased, while Rho-kinase expression increased, indicating that the nNOS/Rho-kinase ratio decreased with age. The Pearson's correlation coefficients for the association between ICP/MAP and Rho-kinase, nNOS and nNOS/Rho-kinase ratio were -0.917, 0.853 and 0.937, respectively (P<0.01). Furthermore, nNOS was found to be significantly negatively correlated with age (r=-0.855; P<0.01), whereas Rho-kinase was positively correlated with age (r=0.943; P<0.01). Age-associated ED was therefore correlated with decreased nNOS and increased Rho-kinase, indicating that the nNOS/Rho-kinase ratio may be used as a candidate indicator of age-associated ED.

Beneficial Effects of Scutellaria baicalensis on Penile Erection in Streptozotocin-Induced Diabetic Rats

We have reported that ethanol extracts of the root from Scutellaria baicalensis Georgi (ESB) relax cavernous smooth muscles via the NO/cGMP system and Ca[Formula: see text]-sensitive K[Formula: see text] channels in the rabbit corpus cavernosum. In the present study, erectile function was assessed by intracavernous pressure (ICP) and mean arterial pressure (MAP) during electrical stimulation of the cavernous nerve. The ICP/MAP ratio was dose-dependently increased by the treatment of ESB in normal SD rats ([Formula: see text]). To investigate the beneficial effect of ESB on erectile dysfunction in a diabetic animal model, male SD rats were injected with streptozotocin (60[Formula: see text]mg/kg) and then 300[Formula: see text]mg/kg/day ESB was administered daily for eight weeks. In our in vivo study, administration of ESB in STZ rats significantly increased the ICP, ICP/MAP ratio, area under the curve (AUC), as well as the cavernous cGMP levels. Morphometric analyses showed that ESB administration increased both smooth muscle volume and the regular arrangement of collagen fibers compared to the STZ group. The protein expression levels of endothelial nitric oxide synthase (eNOS) and SM [Formula: see text]-actin from penile tissues were also significantly increased in the ESB-treated rats. Taken together, these results suggest that ESB ameliorates penile erectile dysfunction via the activation of the NO/cGMP pathways of the penile corpus cavernosum in a streptozotocin-induced diabetic rat model.

Parasympathomimetic Effect of Shilajit Accounts for Relaxation of Rat Corpus Cavernosum

Previous studies have reported an enhancement of central cholinergic signal cascade by shilajit. For the present study, it was hypothesized that parasympathomimetic effect of shilajit accounting for relaxation of rat corpus cavernosum may be one of the major mechanisms attributing to its traditional role as an aphrodisiac. To test this hypothesis, the acute peripheral effect of standard acetylcholine (ACh), shilajit, and their combination was evaluated on cardiorespiratory parameters such as mean arterial blood pressure (MABP), heart rate (HR), respiratory rate (RR), and neuromuscular transmission (NMT). Furthermore, in vitro effect of standard ACh, shilajit, and their combination was tested on the rat corpus cavernosum. Six groups were used for the in vivo study ( N = 5): Group I (control-saline), Group II (ACh), Group III (Sh), Group IV (Sh followed by ACh), Group V (Atropine followed by ACh), and Group VI (Atropine followed by Sh). The in vitro study included four groups: Group I (control-saline), Group II (ACh), Group III (Sh), and Group IV (Sh followed by ACh). The results of the in vivo study confirmed the peripheral parasympathomimetic effect of shilajit (400 µg/mL). The in vitro results revealed that shilajit (400 and 800 µg/mL) relaxed cavernous strips’ concentration dependently and enhanced ACh-mediated relaxations. The peripheral parasympathomimetic effects of shilajit were confirmed by blockade of shilajit-induced relaxations (in vitro) and shilajit-induced lowering of MABP and HR (in vivo) by atropine.

Effect of an Ethanol Extract of Scutellaria baicalensis on Relaxation in Corpus Cavernosum Smooth Muscle

Aims of study. The aim of the present study was to investigate whether an ethanol extract of Scutellaria baicalensis (ESB) relaxes penile corpus cavernosum muscle in organ bath experiments. Materials and methods. Changes in tension of cavernous smooth muscle strips were determined by penile strip chamber model and in penile perfusion model. Isolated endothelium-intact rabbit corpus cavernosum was precontracted with phenylephrine (PE) and then treated with ESB. Results. ESB relaxed penile smooth muscle in a dose-dependent manner, and this was inhibited by pre-treatment with N^G-nitro-l-arginine methyl ester (l-NAME), a nitric oxide (NO) synthase inhibitor, and 1H-[1, 2, 4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ), a soluble guanylyl cyclase (sGC) inhibitor. ESB-induced relaxation was significantly attenuated by pretreatment with tetraethylammonium (TEA), a nonselective K⁺ channel blocker, and charybdotoxin, a selective Ca²⁺-dependent K⁺ channel inhibitor. ESB increased the cGMP levels of rabbit corpus cavernosum in a concentration-dependent manner without changes in cAMP levels. In a perfusion model of penile tissue, ESB also relaxed penile corpus cavernosum smooth muscle in a dose-dependent manner. Conclusion. Taken together, these results suggest that ESB relaxed rabbit cavernous smooth muscle via the NO/cGMP system and Ca²⁺-sensitive K⁺ channels in the corpus cavernosum.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Vasoactivity, antioxidant and aphrodisiac properties of Caesalpinia benthamiana roots

AIMS OF THE STUDY

Caesalpinia benthamiana (=Mezoneuron benthamianum) (Fabaceae) is an African tropical plant whose roots are used in traditional medicine as an aqueous decoction for many purposes, especially for erection impairment but its action mechanism is unknown. The action of Caesalpinia benthamiana on sexual behaviour and some assays on potential modes of action were performed.

MATERIALS AND METHODS

The aqueous extract of Caesalpinia benthamiana (AECB) was tested for vasorelaxing properties using isolated rat aortic rings precontracted by phenylephrine. Influence of AECB in the production of endothelial isoform of nitric oxide synthase (eNOS) was measured by quantitative polymerase chain reaction (QPCR) analysis. Scavenging activities versus reactive oxygen species (ROS), such as superoxide anion (O(2).(-)), hydrogen peroxide (H(2)O(2)), and hypochlorous acid (HOCl) were assessed. Action of AECB on the cellular generation of O(2).(-) was also tested in a physiopathology model of oxidative burst using human polymorphonuclear neutrophils stimulated by phorbol myristate acetate. The aphrodisiac properties of AECB administered orally by gavage (50 mg/kg body weight) to male rats were evaluated by observing the sexual behaviour of animals. Finally, a short-term toxicity study was undertaken to establish the therapeutic index of AECB administered orally to rats at high dose (2 g/kg body weight).

RESULTS

C. benthamiana roots are rich in phenolic compounds (gallic acid, resveratrol and tannins). The results showed that AECB had significant vasorelaxing properties. The extract also had a strong radical activity against ROS in cell-free and cellular systems and stimulated eNOS mRNA expression. As for the aphrodisiac activity of AECB in male rats, results have shown that sexual parameters are stimulated. Furthermore, after oral administration at high dose, AECB causes no mortality or changes in rats' behaviour.

CONCLUSION

AECB enhanced the sexual activity of male rats. This could be partly explained by its vasorelaxant properties, which may be caused by an increase in NO production in vascular bed and a decrease in its destruction.

The effects of age and streptozotocin diabetes on the sympathetic innervation in the rat penis

The objective was to describe the changes in catecholamine levels, noradrenaline (NA) release and the ultrastructural and immunohistochemical changes in the sympathetic nerves in the penis of STZ-diabetic rats. Amines were measured using HPLC. Nerves were studied using immunocytochemistry for tyrosine hydroxylase, and electron microscopy. Diabetic animals were compared with age-matched controls. The concentration of penile NA increases at least 2.5-fold after about 10 weeks of hyperglycaemia, is maintained for over 40 weeks. The rate of release of NA in the diabetics also increases approximately by fourfold. Immunohistochemical staining for tyrosine hydroxylase showed either no change or an increase in the levels of the enzyme around the central arteries and the outer coverings of the corpus cavernosum. Cavernosal nerves show increased intensity of staining for tyrosine hydroxylase, and the presence of dilated nerve fibres and engorged endings. The axons of the dorsal nerve of the diabetic penis have a smaller cross-sectional area that is most marked in unmyelinated axons. In the diabetic penis, the nerve endings appear to contain significantly more NA than the controls, and the turnover of noradrenaline is increased substantially. There is immunocytochemical evidence of an increase in staining for tyrosine hydroxylase, suggesting an increase in synthetic activity. These results are discussed in relation to the existing literature on the role of amines in normal and disordered erectile function. In particular, the increased concentration and turnover of NA in the diabetic rat contrasts with the fall in NA in cavernosal blood described during normal erection in humans.

Vasoactivity and antioxidant properties of Microdesmis keayana roots

Endothelial isoform of nitric oxide synthase (eNOS) mRNA expression increases in the corpora cavernosum, penile arteries and arterioles during erection. But eNOS expression and nitric oxide (NO), the product of its catalytic action, are inactivated by reactive oxygen species (ROS), especially by superoxide anion. ROS are involved in the impairment of endothelium-dependent relaxation and are responsible for some of the pathologies linked to erectile dysfunction (i.e. hypertension, atherosclerosis, etc.). While investigating Microdesmis keayana J. Léonard (Pandaceae) (syn. Microdesmis puberula Hook.f. ex. Planch.), used in African traditional medicine for erectile dysfunction, the hypotensive and the vasorelaxing properties of the aqueous extract of Microdesmis keayana (AEMK) were, respectively, tested using normotensive rabbits and aorta strips of guinea pigs in an organ bath experience. Interaction of AEMK in endothelial production of eNOS was measured by the quantitative polymerase chain reaction (QPCR) analysis. The scavenging activities versus ROS, such as superoxide anion (O(2)(.-)), hydrogen peroxide (H(2)O(2)), hypochlorous acid (HOCl) and hydroxyl radical (HO.) were evaluated. Action of AEMK on cellular generation of superoxide anion was also tested in a physiopathology model of oxidative burst using human polymorphonuclear neutrophils (PMNs) stimulated by phorbol myristate acetate. The results showed that Microdesmis keayana roots had significant hypotensive and vasorelaxing properties. These properties are due to both antioxidant activities and stimulation of eNOS mRNA expression. Therefore, AEMK stimulated indirectly NO production in the vascular bed.

Testing Endothelial Function of Brachial and Cavernous Arteries in Patients with Erectile Dysfunction

INTRODUCTION

There is considerable clinical and scientific evidence that endothelial dysfunction may be an important clinical link connecting erectile dysfunction (ED) with cardiovascular diseases.

AIMS

To modify the method of assessment of endothelial function of cavernosal arteries, to develop a new algorithm for evaluating its results, and to investigate the relationship between postocclusive changes in the diameter of brachial and cavernous arteries.

METHODS

The study participants were 212 patients presenting to our department complaining of ED and 40 healthy volunteers without sexual problems, which formed the control group. All patients with ED underwent complex evaluation and ultrasound assessment of postocclusive changes in the diameter of cavernosal arteries modified by us and standard ultrasound assessment of endothelium-dependent flow-mediated dilation of the brachial artery.

MAIN OUTCOME MEASURES

As the main outcome measure, the percent of increase of the cavernosal arteries diameter (PICAD) was recorded.

RESULTS

In the patients with arteriogenic ED, PICAD values were significantly less than in other groups (P < 0.001 for pairs of comparison). At the same time there were no differences between the control group and groups of patients with psychogenic and organic nonarterial ED. The sensitivity and specificity of a PICAD value of 50% in diagnosis of arteriogenic ED were 100% and 98.2%, respectively. In all groups and in the entire sample of patients studied we did not find a correlation between PICAD and postocclusive changes in the diameter of brachial arteries.

CONCLUSION

The method of ultrasound assessment of postocclusive changes in the diameter of cavernosal arteries is reliable and a highly informative tool for diagnosis of arteriogenic ED. It cannot be substituted by technically simpler method of ultrasound examination of brachial arteries, while results of the latter could help to define the necessity of performing an examination of cavernous arteries.

A novel compound JPM8: in vivo penile activity promotion in rats, effect on the relaxation and cGMP/cAMP accumulation in isolated rabbit corpora cavernosa

JPM8 is a novel sildenafil-like PDE5 inhibitor. Its efficacy was tested in vivo by the oral administration of drugs to a rat model and recording penile activity changes. Effect on the relaxation of the rabbit cavernosa was tested in vitro using an organ bath were drugs are added to the tissue media and relaxation was recorded using a transducer connected to a chart recorder. The accumulation of cGMP and cAMP was measured by incubation of cavernosa strips and then extracting the produced cGMP and cAMP in the incubation mixture, then quantitating it using ELISA. JPM8 showed increased and promoted sexual and penile activity in rats in a similar but slightly higher trend than the positive control sildenafil. JPM8 was more efficient in relaxing the rabbit corpora cavernosa than sildenafil. The cGMP and cAMP accumulation showed a similar trend for both drugs. We concluded that JPM8 was very effective in promoting sexual activity in rats, relaxing the corpora cavernosa and promoting cGMP accumulation in rabbits.

Pharmacological profile of evodiamine in isolated rabbit corpus cavernosum

This study was designed to examine the pharmacological properties of evodiamine in isolated rabbit corpus cavernosum. In phenylephrine-precontracted cavernosal strips, evodiamine (0.01-10 microM) induced a concentration-dependent relaxation. Endothelium removal, N(G)-nitro-L-arginine methyl ester (L-NAME), or 1-H-[1,2,4]oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ) treatment did not affect this effect. In endothelium-denuded preparations, evodiamine-evoked response was significantly reduced in 60 mM KCl-precontracted strips and by charybdotoxin treatment, but not by glibenclamide. Higher-concentration evodiamine (> or =10 microM)-induced relaxation was also accompanied by an increase in cAMP and cGMP levels, but this effect was not affected by cis-N-(2-phenylcyclopentyl)-azacyclotridec-1-en-2-amine mono-hydrochloride (MDL-12,330A, an adenylyl cyclase inhibitor) or ODQ (a guanylyl cyclase inhibitor), respectively. Evodiamine significantly augmented both the corporal relaxation and the accumulation of cyclic nucleotides to sodium nitroprusside and forskolin, respectively. Evodiamine also enhanced electrical field stimulation-evoked relaxation, and this additive effect was significantly counteracted by zaprinast. In preparations obtained from aged rabbits, evodiamine still elicited complete relaxation; in contrast, acetylcholine- and sodium nitroprusside-evoked maximal response was significantly blunted. In summary, evodiamine possesses a potent corporal relaxing effect which is attributable to endothelium-independent properties probably linked to charybdotoxin-sensitive K(+) channel activation in the cavernosal vasculature and by nonselective interfering phosphodiesterase to prevent cyclic nucleotide degradation. Furthermore, the physiological effects of evodiamine on the aged animals may implicate a potential for the treatment of erectile dysfunction.

Endothelial nitric oxide synthase protein expression, localization, and activity in the penis of the alloxan-induced diabetic rat

PURPOSE

To explore the possible relevance of endothelial nitric oxide synthase (eNOS) in the pathophysiology of erectile dysfunction (ED) associated with diabetes mellitus, we compared the catalytic activity, protein expression, and cellular localization of eNOS with those of neuronal nitric oxide synthase (nNOS) in the penis of rats with alloxan-induced diabetes.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were given alloxan or vehicle only and monitored weekly by Dextrostix for confirmation of glucosuria. Tail-flick immersion and penile reflex testing were used to evaluate sensory neuropathy and ED, respectively. At 4 to 5 weeks (early) and 10 to 11 weeks (late), animals were sacrificed, and their penes were subjected to nNOS and eNOS catalytic activity assay, Western immunoblotting, and immunohistochemistry examination. Masson's trichrome staining of penile tissue and serum testosterone measurements were performed for light microscopy and sex steroidogenic analysis, respectively.

RESULTS

Confirmed diabetic rats showed significant reductions in penile nNOS expression and eNOS activity and expression early, prior to observed ED, and nNOS and eNOS activities and expressions late, synchronous with ED. Decreased intensities of both nNOS staining, localized to the dorsal and cavernosal nerves distributing to the penis, and eNOS staining, localized to penile vascular and sinusoidal endothelium, were assessed in diabetic animals. Penile vascular and cavernosal tissue appeared intact in diabetic rats. Testosterone levels were equivalent in nondiabetic and diabetic rats.

CONCLUSIONS

In the penis of the alloxan-induced diabetic rat, eNOS protein expression and synthetic activity were reduced compared with the normal rat penis, independent of testosterone influence and in the absence of significant erectile tissue degenerative changes. These eNOS effects apparently preceded nNOS effects. Full elucidation of the possible mechanisms affecting eNOS function in the diabetic rat penis requires further investigation.

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.

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.