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Erectile dysfunction (ED) associated with type 2 diabetes mellitus (T2DM) involves dysfunctional nitric oxide (NO) signaling and increased oxidative stress in the penis. However, the mechanisms of endothelial NO synthase (eNOS) and neuronal NO synthase (nNOS) dysregulation, and the sources of oxidative stress, are not well defined, particularly at the human level. The objective of this study was to define whether uncoupled eNOS and nNOS, and NADPH oxidase upregulation, contribute to the pathogenesis of ED in T2DM men. Penile erectile tissue was obtained from 9 T2DM patients with ED who underwent penile prosthesis surgery for ED, and from six control patients without T2DM or ED who underwent penectomy for penile cancer. The dimer-to-monomer protein expression ratio, an indicator of uncoupling for both eNOS and nNOS, total protein expressions of eNOS and nNOS, as well as protein expressions of NADPH oxidase catalytic subunit gp91phox (an enzymatic source of oxidative stress) and 4-hydroxy-2-nonenal [4-HNE] and nitrotyrosine (markers of oxidative stress) were measured by western blot in this tissue. In the erectile tissue of T2DM men, eNOS and nNOS uncoupling and protein expressions of NADPH oxidase subunit gp91phox, 4-HNE- and nitrotyrosine-modified proteins were significantly (p < 0.05) increased compared to control values. Total eNOS and nNOS protein expressions were not significantly different between the groups. In conclusion, mechanisms of T2DM-associated ED in the human penis may involve uncoupled eNOS and nNOS and NADPH oxidase upregulation. Our description of molecular factors contributing to the pathogenesis of T2DM-associated ED at the human level is relevant to advancing clinically therapeutic approaches to restore erectile function in T2DM patients., (© 2017 American Society of Andrology and European Academy of Andrology.)

Introduction: Recent research suggests that priapism in sickle cell disease (SCD) is due to dysregulation of penile erection homeostasis including alteration of nitric oxide synthase (NOS) and phosphodiesterase type 5 (PDE5) activities by excessive levels of reactive oxygen species (ROS) released during hemolysis. It is unknown if subacute exposure to hemolysis is sufficient or if chronic reconditioning of erectile tissues is required for perturbation of homeostatic pathways and whether PDE5 inhibitor (PDE5I) treatment can restore erectile homeostasis in the subacute setting., Aims: The aim of this study was to investigate the effects of subacute hemolysis (3-month exposure) on priapism and NO pathway regulation., Methods: Mice underwent bone marrow transplantation with either SCD (BM-SS) or wild-type (WT) bone marrow. BM-SS mice were treated with sildenafil 100 mg/kg/day. We measured intracavernous pressure (ICP) measurements with or without cavernous nerve stimulation following bone marrow transplantation to assess for priapism., Main Outcome Measures: ICP and frequency of erections were assessed. Penile tissues were analyzed for NOS, protein kinase G (PKG), PDE5, and ROS activities., Results: BM-SS mice demonstrated a priapism phenotype. PDE5I treatment reduced the frequency of erections in BM-SS mice (1.7 ± 1.1 vs. 5.5 ± 2.8 erections per hour, P < 0.05). Penile tissues from BM-SS mice demonstrated decreased NOS, PKG, PDE5 and elevated ROS activities compared with that of control mice. PDE5I treatment increased NOS (11.6 ± 1.3% vs. 7.8 ± 2.3%, P < 0.05) and PDE5 (76.3 ± 9.8% vs. 52.3 ± 11.1%, P < 0.05) activities and decreased ROS activity (137.8 ± 12.1% vs. 199.1 ± 11.3%, P < 0.05) compared with non-PDE5I treated BM-SS mice. PKG activity was increased beyond control levels with PDE5I treatment (158.4 ± 10.3%, P < 0.05)., Conclusion: Short-term hemolysis is sufficient to establish a priapism phenotype and results in loss of erectile function. PDE5I treatment ameliorates priapism, in part, because of restored NO balance with decreased ROS generation and increased PDE5 activity., (© 2015 International Society for Sexual Medicine.)

Introduction: Female sexual arousal disorder (FSAD) is a major component of female sexual dysfunctions, affecting 25-70% of women. The mechanisms of FSAD are poorly understood. Estrogen contributes to the control of genital blood flow during the sexual response. Vascular effects of estrogen are mostly attributed to its regulation of endothelial nitric oxide (NO) production. However, the role of endothelial NO synthase (eNOS) and the mechanisms that regulate eNOS in female genital tract structures are largely unknown., Aim: To review available evidence of the mechanisms of eNOS regulation in female genital tract structures., Methods: This article reviews the literature that relates to the role of NO and eNOS in female sexual arousal and its modulation by estrogen., Main Outcome Measures: Association between female sexual arousal, NO, and eNOS., Results: The NO/cyclic guanosine monophosphate pathway is believed to have a primary role in the regulation of clitoral and vaginal blood flow, and smooth muscle relaxation during sexual arousal. Estrogen is critical for maintaining vaginal and clitoral blood flow and vaginal transudate production. Estrogen regulates eNOS by genomic mechanisms, involving augmented mRNA transcription and protein synthesis, and by non-genomic mechanisms, which occur without alterations in gene expression. However, limited studies have evaluated the physiological role of endothelial NO and the molecular mechanisms of eNOS regulation in the female genital tract., Conclusions: The effects of estrogen on increasing genital blood flow and smooth muscle relaxation have been attributed mostly to regulation of eNOS. However, the exact mechanisms of eNOS regulation in female genital tract structures and the molecular basis for the eNOS defect with aging and vascular diseases warrant further investigation.

Purpose: We determined the effect of passive secondhand cigarette smoke on 1) erectile function in vivo, 2) molecular mechanisms involved in penile vascular function, and 3) erectile function and penile molecular signaling in the presence of phosphodiesterase type 5 inhibitor therapy., Materials and Methods: Four groups of mice were used, including group 1--controls, group 2--mice exposed to 3 weeks of secondhand smoke (5 hours per day for 5 days per week), group 3--control plus sildenafil (100 mg/kg per day) and group 4--smoke exposed plus sildenafil (100 mg/kg per day). Cavernous nerve electrical stimulation and intracavernous injection of acetylcholine were done to assess erectile function. Constitutive and inducible nitric oxide synthase activity, reactive oxygen species generation, nitrotyrosine formation and superoxide anion levels were assessed., Results: Decreased erectile responses to cavernous nerve electrical stimulation and impaired endothelium dependent erectile responses to ACh in mice exposed to secondhand smoke were observed. Superoxide anion was increased in endothelial and corporeal smooth muscle cells of smoking mouse penises. In mice exposed to secondhand smoke constitutive nitric oxide synthase activity was decreased, and inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation increased. Sildenafil therapy restored constitutive nitric oxide synthase activity in the penis of smoking mice, decreased inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation, and improved erectile responses to cavernous nerve electrical stimulation and acetylcholine., Conclusions: Short-term exposure to secondhand smoke impairs erectile function through excessive penile reactive oxygen species signaling and inducible nitric oxide synthase activity. Decreased penile constitutive nitric oxide synthase activity may be attributable to the decreased endothelial nitric oxide synthase activity resulting from increased oxidative stress. Sildenafil therapy restored nitric oxide synthase activity and decreased reactive oxygen species signaling, resulting in improved erectile function.

Impaired endothelial nitric oxide synthase (eNOS) function is associated with erectile dysfunction in diabetes mellitus, but the exact molecular basis for the eNOS defect in the diabetic penis remains unclear. We investigated whether hyperglycemia increases O-GlcNAc modification of eNOS in the penis, preventing phosphorylation at the primary positive regulatory site on the enzyme and hampering mechanisms of the erectile response. Type I diabetes mellitus was induced in male rats by alloxan (140 mg/kg, i.p.). After 5 wk, the diabetic rat penis exhibited increased O-GlcNAc modification of eNOS and decreased eNOS phosphorylation at Ser-1177 at baseline compared with the control rat penis; eNOS phosphorylation at Thr-495, Ser-615, and Ser-633 was not affected. In addition, eNOS phosphorylation at Ser-1177 was impaired in the diabetic rat penis in response to penile blood flow (shear stress) elicited by electrical stimulation of the cavernous nerve (ES) and to recombinant human VEGF165. Phosphorylation of Akt, a mediator of shear stress-induced eNOS phosphorylation at Ser-1177, was decreased in the diabetic penis at baseline, but it was restored by ES. Erectile response to shear stress elicited by ES and to VEGF was decreased in diabetic compared with control rats. This work demonstrates that eNOS inactivation occurs in the diabetic penis by a glycosylation mechanism specifically at Ser-1177, by which the enzyme is rendered incapable of activation by fluid shear stress stimuli and VEGF signaling. In vivo penile erection paradigm supports the physiologic relevance of O-GlcNAc modification in vascular disorders associated with diabetes.

Despite demonstrated clinical efficacy of sildenafil for the temporary treatment of erectile dysfunction, the possibility that sildenafil used long-term durably augments erectile ability remains unclear. We investigated whether continuous long-term administration of sildenafil at clinically relevant levels to aged rats "primes" the penis for improved erectile ability and involves nitric oxide (NO) or RhoA/Rho-kinase signaling pathways. In aged, but not young rats, sildenafil prolonged erection and increased the protein expressions of phosphorylated endothelial NO synthase (eNOS) at serine-1177 and phosphorylated Akt at serine-473 in penes. Only in the young rat penis, protein expressions of phosphodiesterase-5 and phosphomyosin phosphatase target subunit 1, a marker of Rho-kinase activity, were increased by sildenafil. Sildenafil inhibited phosphodiesterase-5 activity in penes of young and aged rats coincident with assayed free plasma levels of the drug equivalent to clinically therapeutic measurements. We conclude that erectile ability can be enhanced under preconditions of erectile impairment by long-term inhibition of phosphodiesterase-5 and that the effect is mediated by Akt-dependent eNOS phosphorylation. The lack of erectile ability enhancement in young rats by long-term phosphodiesterase-5 inhibition may relate to restrained NO signaling by phosphodiesterase-5 up-regulation, lack of incremental Akt and eNOS phosphorylation, and heightened Rho-kinase signaling in the penis.

The objective of the present study was to evaluate whether vascular endothelial growth factor (VEGF)-induced penile erection is mediated by activation of endothelial nitric oxide synthase (eNOS) through its phosphorylation. We assessed the role of constitutively activated eNOS in VEGF-induced penile erection using wild-type (WT) and eNOS-knockout (eNOS(-/-)) mice with and without vasculogenic erectile dysfunction. Adult WT and eNOS(-/-) mice were subjected to sham operation or bilateral castration to induce vasculogenic erectile dysfunction. At the time of surgery, animals were injected intracavernosally with a replication-deficient adenovirus expressing human VEGF145 (10(9) particle units) or with empty virus (Ad.Null). After 7 days, erectile function was assessed in response to cavernous nerve electrical stimulation. Total and phosphorylated protein kinase B (Akt) as well as total and phosphorylated eNOS were quantitatively assessed in mice penes using Western immunoblot and immunohistochemistry. In intact WT mice, VEGF145 significantly increased erectile responses, and in WT mice after castration, it completely recovered penile erection. However, VEGF145 failed to increase erectile responses in intact eNOS(-/-) mice and only partially recovered erectile function in castrated eNOS(-/-) mice. In addition, VEGF145 significantly increased phosphorylation of eNOS at Serine 1177 by approximately 2-fold in penes of both intact and castrated WT mice. The data provide a molecular explanation for VEGF stimulatory effect on penile erection, which involves phosphorylated eNOS (Serine 1177) mediation.

Deficiency of either neuronal nitric oxide synthase (NOS1) or endothelial nitric oxide synthase (NOS3) leads to cardiac hypertrophy in mice. Loss of both produces concentric left ventricular (LV) remodeling, in which increased wall thickness is accompanied by reduced cavity size. In humans, this phenotype develops in elderly hypertensive patients and independently predicts mortality. Accordingly, we tested the hypothesis that NOS1/3(-/-) mice have reduced longevity compared to either NOS1(-/-) or NOS3(-/-). Survival data on colonies of NOS1(-/-) (n = 295), NOS3(-/-) (n = 525), and NOS1/3(-/-) (n = 331) mice were collected for 2 years. NOS1(-/-) mice had increased mortality compared to NOS3(-/-) (relative risk, RR 2.5, P < 0.001), whereas NOS1/3(-/-) fared significantly worse (RR 7.3, P < 0.001 vs. NOS3(-/-)). Importantly, gender did not affect survival in NOS1(-/-) or NOS3(-/-), but male NOS1/3(-/-) mice had 2-fold increased mortality compared to females. NOS1/3(-/-) mice developed progressive myocyte hypertrophy and interstitial fibrosis with age. NOS1/3(-/-) mice underwent in vivo hemodynamic analysis with a combined pressure-volume catheter to assess age-related cardiovascular changes. Compared with control, NOS1/3(-/-) demonstrated hypertension and hypercontractility at all ages, and developed passive diastolic dysfunction with increasing age. Thus, combined deficiency of NOS1 and NOS3 causes increased mortality, myocyte hypertrophy, and an age-associated increase in ventricular stiffness. These findings suggest that cardiac NO signals may play an essential role in successful cardiac aging.

Nitrergic neurotransmission triggering penile erection is mediated by nitric oxide (NO) synthesized in the cavernosal nerves of the penis by penile neuronal NO synthase (PnNOS). In the central nervous system, nNOS is activated by the N-methyl-D-aspartate receptor (NMDAR) and, presumably, is inhibited by the protein inhibitor of NOS (PIN). The PnNOS and NMDAR are expressed in the penis, and PnNOS has been localized in penile nerves. Both proteins colocalize with PIN in the hypothalamus and the spinal cord involved in the control of erection. The present study aimed to elucidate the relationship between PnNOS, PIN, and NMDAR in the penis. It was found that in the rat, PIN was expressed in the pelvic ganglion and the cavernosal nerve, and penile PIN cDNA was cloned, sequenced, and expressed. Immunohistochemistry localized PIN to the cavernosal and dorsal nerve of the penis, whereas NMDAR was not detected in the latter. Dual-fluorescence labeling showed that PnNOS colocalized with PIN in both nerves but with NMDAR only in the cavernosal nerve. Aging did not affect the mRNA levels of PnNOS, nNOS, NMDAR, and PIN. Both PIN and NMDAR were detected in penile nerves of the wild-type and nNOS(-/-) mouse. The PIN protein did not inhibit or bind NOS in penile extracts, and in vivo, PIN cDNA reduced the erectile response to electrical field stimulation. In conclusion, PIN and NMDAR colocalize with PnNOS in penile nerves, but the functional significance of these protein interactions for penile erection remains to be elucidated.

Nitric oxide (NO*) is produced endogenously from NOS isoforms bound to sarcolemmal (SL) and sarcoplasmic reticulum (SR) membranes. To investigate whether locally generated NO* directly affects the activity of enzymes mediating ion active transport, we studied whether knockout of selected NOS isoforms would affect the functions of cardiac SL (Na+ + K+)-ATPase and SR Ca2+-ATPase. Cardiac SL and SR vesicles containing either SL (Na+ + K+)-ATPase or SR Ca2+-ATPase were isolated from mice lacking either nNOS or eNOS, or both, and tested for enzyme activities. Western blot analysis revealed that absence of single or double NOS isoforms did not interrupt the protein expression of SL (Na+ + K+)-ATPase and SR Ca2+-ATPase in cardiac muscle cells. However, lack of NOS isoforms in cardiac muscle significantly altered both (Na+ + K+)-ATPase activity and SR Ca2+-ATPase function. Our experimental results suggest that disrupted endogenous NO* production may change local redox conditions and lead to an unbalanced free radical homeostasis in cardiac muscle cells which, in turn, may affect key enzyme activities and membrane ion active transport systems in the heart.

Subcellular localization of nitric oxide (NO) synthases with effector molecules is an important regulatory mechanism for NO signalling. In the heart, NO inhibits L-type Ca2+ channels but stimulates sarcoplasmic reticulum (SR) Ca2+ release, leading to variable effects on myocardial contractility. Here we show that spatial confinement of specific NO synthase isoforms regulates this process. Endothelial NO synthase (NOS3) localizes to caveolae, where compartmentalization with beta-adrenergic receptors and L-type Ca2+ channels allows NO to inhibit beta-adrenergic-induced inotropy. Neuronal NO synthase (NOS1), however, is targeted to cardiac SR. NO stimulation of SR Ca2+ release via the ryanodine receptor (RyR) in vitro, suggests that NOS1 has an opposite, facilitative effect on contractility. We demonstrate that NOS1-deficient mice have suppressed inotropic response, whereas NOS3-deficient mice have enhanced contractility, owing to corresponding changes in SR Ca2+ release. Both NOS1-/- and NOS3-/- mice develop age-related hypertrophy, although only NOS3-/- mice are hypertensive. NOS1/3-/- double knockout mice have suppressed beta-adrenergic responses and an additive phenotype of marked ventricular remodelling. Thus, NOS1 and NOS3 mediate independent, and in some cases opposite, effects on cardiac structure and function.

In the penis, nitric oxide (NO) can be formed by both neuronal NO synthase and endothelial NOS (eNOS). eNOS is activated by viscous drag/shear stress in blood vessels to produce NO continuously, a process mediated by the phosphatidylinositol 3-kinase (PI3kinase)/Akt pathway. Here we show that PI3-kinase/Akt physiologically mediates erection. Both electrical stimulation of the cavernous nerve and direct intracavernosal injection of the vasorelaxant drug papaverine cause rapid increases in phosphorylated (activated) Akt and eNOS. Phosphorylation is diminished by wortmannin and LY294002, inhibitors of PI3-kinase, the upstream activator of Akt. The two drugs also reduce erection. Penile erection elicited by papaverine is reduced profoundly in mice with targeted deletion of eNOS. Our findings support a model in which rapid, brief activation of neuronal NOS initiates the erectile process, whereas PI3-kinase/Akt-dependent phosphorylation and activation of eNOS leads to sustained NO production and maximal erection.

With the current understanding that nitric oxide (NO) mediates penile erection, the endothelial isoform of NO synthase (eNOS) has been implicated in this function. We undertook this study applying transgenic mice with targeted deletion of the eNOS gene (eNOS-/- mice) as an experimental approach to evaluate the importance of eNOS in cholinergically stimulated erectile function in vivo. Combined pharmacostimulation with intracavernosal carbachol (3 ng) administration and submaximal cavernous nerve (CN) electrical stimulation (16 Hz, 5 millisecond, 1 V) simultaneous with intracavernosal pressure (ICP) monitoring, and both biochemical assay of NO synthase activity and Western blot analysis of eNOS protein content in penile tissue, were performed on eNOS-/- mice and wild-type controls. Combined intracavernosal carbachol administration and submaximal CN electrical stimulation raised the recorded ICP, elicited by CN electrical stimulation alone in wild-type mice (from 35.7 +/- 2.7 to 48.1 +/- 5.5 mm Hg, P < .05) but not in eNOS-/ - mice (from 54.9 +/- 6.3 to 51.0 +/- 9.5 mm Hg, not significant [NS]). Pretreatment with the nonselective nitric oxide synthase inhibitor nitro-L-arginine methyl ester (L-NAME; 100 mg intracavernosally) blocked electrically stimulated ICP responses in eNOS-/- mice to baseline levels (37.8 +/- 4.4 vs 12.7 +/- 4.0 mm Hg, P < .05). In penes of eNOS-/- mice, approximately 60% NO synthase activity of wild-type penis levels was retained (NS), and eNOS protein was absent. We concluded that eNOS-/- mice preserve erectile function on the basis of a noncholinergic but NO-dependent mechanism and that eNOS physiologically mediates penile erection under cholinergic stimulation.

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.

Penile erection is mediated by nitric oxide (NO) synthesized by the neuronal nitric oxide synthase (nNOS). In the rat penis, the main nNOS mRNA variant, PnNOS, differs from cerebellar nNOS (CnNOS) by a 102 base pair insert encoding a 34-amino acid sequence. In the mouse, two nNOS mRNAs have been identified: nNOSalpha, encoding a 155-kDa protein, and an exon 2-deletion variant, nNOSbeta, encoding a 135-kDa protein that lacks a domain where a protein inhibitor of nNOS (PIN) binds. We wished to determine whether PnNOSalpha and beta are expressed in the rat penis and are located in the nerves and whether the beta form persists in the potent nNOS knock-out mouse (nNOS( big up tri, open big up tri, open)). A PnNOS antibody against the insert common to both PnNOSalpha and beta detected the expected 155-kDa protein in PnNOSalpha-transfected cells. This antibody, and the one common to PnNOS/CnNOS, showed (on Western blots) the 155- and 135-kDa nNOS variants in rat penile tissue during development and aging. PnNOSalpha mRNA and its subvariants were found as the main nNOS in the penile corpora, the cavernosal nerve, and the pelvic ganglia, with lower levels of PnNOSbeta mRNA. In tissue sections, PnNOS protein was immunodetected in the penile nerve endings in the rat and in the nNOS wild-type and nNOS( big up tri, open big up tri, open) mice. An antibody against the sequence encoded by exon 2 did not react (on Western blots) with the 135-kDa band, which confirms that this protein is the beta form. In conclusion, both PnNOSalpha and beta are expressed in the rat penis at all ages and are located in the nerves. The beta form may allow nitric oxide synthesis during erection to be partially insensitive to PIN. The residual expression of PnNOS, and possibly CnNOS, in the penis of the nNOS( big up tri, open big up tri, open) mouse occurs through transcription of the beta mRNA, and this may explain the retention of erectile function when the expression of nNOSalpha is disrupted.

Nitric oxide (NO) acts as a neuronal messenger in both the central and peripheral nervous systems and has been implicated in reproductive physiology and behavior. Pharmacological inhibition of nitric oxide synthase (NOS) with the nonspecific NOS inhibitor, l-N(G)-nitro-Arg-methyl ester (l-NAME), induced deficits in both the number of ovarian rupture sites and the number of oocytes recovered in the oviducts of mice. Female neuronal NOS knockout (nNOS-/-) mice have normal numbers of rupture sites, but reduced numbers of oocytes recovered following systemic injections of gonadotropins, suggesting that NO produced by nNOS accounts, in part, for deficits in ovulatory efficiency observed after l-NAME administration. Additionally, endothelial NOS knockout (eNOS-/-) mice have reduced numbers of ovulated oocytes after superovulation. Because endothelial NOS has been identified in ovarian follicles, and because of the noted reduced breeding efficiency of eNOS-/- mice, the present study sought to determine the role of NO from eNOS in mediating the number of rupture sites present after ovulation. Estrous cycle length and variability were consistently reduced in eNOS-/- females. The number of rupture sites was normal in eNOS-/- mice under natural conditions and after administration of exogenous GnRH. After exogenous gonadotropin administration, eNOS-/- females displayed a significant reduction in the number of ovarian rupture sites. Female eNOS-/- mice also produced fewer pups/litter compared to WT mice. These data suggest that NO from endothelial sources might play a role in mediating rodent ovulation and may be involved in regulation of the timing of the estrous cycle., (Copyright 1999 Academic Press.)

Nitric oxide (NO) has been established as a neurotransmitter in both the central and peripheral nervous systems. Three isoforms of its synthetic enzyme, NO synthase (NOS), have been identified: 1) in the endothelial lining of blood vessels (eNOS), 2) an inducible form found in macrophages (iNOS), and 3) in neurons (nNOS). Previous studies using pharmacological agents that block all three isoforms of NOS have revealed that NO mediates several aspects of reproductive physiology and behavior, including anomalies in male sexual behavior and erectile function. To determine the specific contribution of the endothelial isoform of NOS in male reproductive behavior, we studied mice missing the gene for only eNOS (eNOS-/-). Wild-type (WT) and eNOS-/- animals were placed with an estrous WT female and observed for 45 min. Both WT and eNOS-/- mice displayed equivalent motivation to mount the stimulus female. However, eNOS-/- mice exhibited striking anomalies in ejaculatory function. A higher percentage of eNOS-/- than WT mice ejaculated during the testing period (p < 0.001). This increased propensity to ejaculate was apparently due to reduced stimulation required to elicit ejaculation; eNOS-/- mice required significantly fewer mounts (p < 0.003) and intromissions (p < 0.001) to ejaculate compared to WT mice. Taken together, these results suggest that NO synthesized by eNOS may be involved in ejaculatory physiology, but not sexual motivation.

Background: Nitric oxide (NO) plays an important role in numerous reproductive processes. To date, most studies have assessed the role of NO by using nonspecific pharmacological inhibitors of the precursor to NO, nitric oxide synthase (NOS). These pharmacological NOS inhibitors suppress all isoforms of NOS; thus, the precise contribution of each isoform to female reproductive physiology is unknown. The purpose of this study was to determine the specific role of neuronal NOS (nNOS) in the regulation of ovulation in female mice lacking the gene that encodes for nNOS (nNOS-/-)., Materials and Methods: Ovulation was assessed in wild-type (WT) and nNOS-/- female mice by examining the number of ovarian rupture sites and number of oocytes recovered from the oviducts following mating or exposure to exogenous gonadotropins (i.e., 5 IU pregnant mares serum gonadotropin [PMSG] and 5 IU human chorionic gonadotropin [hCG]). Ovulatory efficiency was determined as the number of ovulated oocytes per number of ovarian rupture sites. To examine whether ovulatory deficits in nNOS-/- mice were due to alternations in central mechanisms, plasma luteinizing hormone (LH) concentrations were assessed in WT and nNOS-/- mice that were challenged with 25 ng of gonadotropin-releasing hormone (GnRH). To determine whether ovulatory deficits in nNOS-/- mice were due to local ovulation processes, nerves innervating the reproductive tract of WT and nNOS-/- females were examined for the presence of nNOS protein., Results: There were substantial fertility deficits in nNOS-/- female mice; the nNOS-/- mice had fewer oocytes in their oviducts following spontaneous and gonadotropin-stimulated ovulation. Pituitary responsiveness to exogenous GnRH challenge was intact in nNOS-/- mice. Dense nNOS protein staining was observed in nerves innervating the reproductive tracts of WT mice., Conclusions: The reproductive deficits in nNOS-/- females are most likely due to alternations in the transfer of oocytes from the ovaries to the oviducts during ovulation. These results suggest that defects in neuronally derived NO production may contribute to female infertility.

Nitric oxide synthase (NOS) is expressed in the prostate of various species, including humans. NOS catalyzes the production of nitric oxide (NO), which may function in prostatic smooth-muscle relaxation. To investigate further the role of NO in the prostate, we examined neuronal NOS expression in the aging canine prostate, after hormonal perturbation, and correlated these results with histopathologic findings. The study comprised the following treatment groups: intact dogs (treatment group 1, n = 6); dogs who were castrated at 7 days of age and received testosterone and estrogen replacement at 2 years of age (treatment group 2, n = 10); and dogs who were castrated at 2 years of age and received testosterone and estrogen replacement at 2 years of age (treatment group 3, n = 9). Studies were done on prostates removed from dogs after euthanasia at 6 years of age. In treatment group 1, complex benign prostatic hyperplasia (BPH) was observed in all specimens. In treatment group 2, atrophy was observed in 70%, normal prostate with small areas of hyperplasia in 20%, and BPH in 10% of specimens. In treatment group 3, atrophy was observed in 78%, normal histology with small areas of hyperplasia in 11%, and BPH in 11% of specimens. Neuronal NOS localizations were confirmed by western blot analysis and by immunohistochemistry in 0% and 17%, respectively, of specimens in treatment group 1, in 60% and 70%, respectively, of specimens in treatment group 2, and in 67% and 71%, respectively, of specimens in treatment group 3. Neuronal NOS immunoreactivity was localized in histologically normal prostates of four intact, young-adult control dogs (2 years of age). For all treatment groups, neuronal NOS immunoreactivity was confirmed by western blot in 86% of atrophic prostates but in no prostates with BPH (P < 0.001), and it was confirmed by immunohistochemistry in 75% of atrophic prostates but in only 13% of prostates with BPH (P < 0.02). These data suggest that, in the canine prostate, NO release relates to growth and pathology. Low levels of neuronal NOS expression in BPH tissue, compared with higher levels in atrophic tissue, suggest that neuronal NOS expression is down-regulated in the prostate with benign cellular proliferation whereas it is maintained or possibly up-regulated in the prostate with prostatic involution. Whether altered neuronal NOS expression contributes to the pathogeneses of BPH and prostatic involution or whether it occurs as a consequence of these processes requires further investigation.

Purpose: Our aim was to identify and localize nitric oxide synthase isoforms in the human clitoris in support of the hypothesis that nitric oxide mediates erectile function in this organ., Materials and Methods: Nitric oxide synthase immunohistochemistry studies specific for neuronal, inducible and endothelial isoforms of the enzyme were performed on human clitoral tissue obtained from 4 patients (3 with female pseudohermaphroditism and 1 with true hermaphroditism) at feminizing genitoplasty and from 1 phenotypically normal woman at autopsy., Results: Neuronal nitric oxide synthase immunoreactivity was detected in nerve bundles and fibers coursing within the glans clitoris and corpora cavernosa of the clitoris, predominating in the latter tissue. Specific inducible nitric oxide synthase immunoreactivity was not identified. Endothelial nitric oxide synthase immunoreactivity was detected in vascular and sinusoidal endothelium of these tissues with a predominance in the glans clitoris., Conclusions: The presence and anatomical localizations of nitric oxide synthase isoforms in the human clitoris indicate that nitric oxide is generated in this organ. These data suggest that nitric oxide may be involved in the erectile physiology of the clitoris as a modulator of clitoral smooth muscle activity. Functional studies are required to support this hypothesis.

Idiopathic voiding disorders affect up to 10-15% of men and women. We describe bladder abnormalities in mice with targeted deletion of the gene for neuronal nitric oxide synthase which model the clinical disorders. The mice possess hypertrophic dilated bladders and dysfunctional urinary outlets which do not relax in response to electrical field stimulation or L-arginine. The mice also display increased urinary frequency.

Background: Nitric oxide (NO) has been implicated as a mediator of penile erection, because the neuronal isoform of NO synthase (NOS) is localized to the penile innervation and NOS inhibitors selectively block erections. NO can also be formed by two other NOS isoforms derived from distinct genes, inducible NOS (iNOS) and endothelial NOS (eNOS). To clarify the source of NO in penile function, we have examined mice with targeted deletion of the nNOS gene (nNOS- mice)., Materials and Methods: Mating behavior, electrophysiologically induced penile erection, isolated erectile tissue isometric tension, and eNOS localization by immunohistochemistry and Western blot were performed on nNOS- mice and wild-type controls., Results: Both intact animal penile erections and isolated erectile tissue function are maintained in nNOS mice, in agreement with demonstrated normal sexual behaviors, but is stereospecifically blocked by the NOS inhibitor, L-nitroarginine methyl ester (L-NAME). eNOS is abundantly present in endothelium of penile vasculature and sinusoidal endothelium within the corpora cavemosa, with levels that are significantly higher in nNOS- mice than in wild-type controls., Conclusions: eNOS mediates NO-dependent penile erection in nNOS- animals and normal penile erection. These data clarify the role of nitric oxide in penile erection and may have implications for therapeutic agents with selective effects on NOS isoforms.