Central control of erection and its pharmacological modification

Non-pharmacological and drug treatment of autonomic dysfunction in multiple system atrophy: current status and future directions

Multiple system atrophy (MSA) is a sporadic, fatal, and rapidly progressive neurodegenerative disease of unknown etiology that is clinically characterized by autonomic failure, parkinsonism, cerebellar ataxia, and pyramidal signs in any combination. Early onset and extensive autonomic dysfunction, including cardiovascular dysfunction characterized by orthostatic hypotension (OH) and supine hypertension, urinary dysfunction characterized by overactive bladder and incomplete bladder emptying, sexual dysfunction characterized by sexual desire deficiency and erectile dysfunction, and gastrointestinal dysfunction characterized by delayed gastric emptying and constipation, are the main features of MSA. Autonomic dysfunction greatly reduces quality of life and increases mortality. Therefore, early diagnosis and intervention are urgently needed to benefit MSA patients. In this review, we aim to discuss the systematic treatment of autonomic dysfunction in MSA, and focus on the current methods, starting from non-pharmacological methods, such as patient education, psychotherapy, diet change, surgery, and neuromodulation, to various drug treatments targeting autonomic nerve and its projection fibers. In addition, we also draw attention to the interactions among various treatments, and introduce novel methods proposed in recent years, such as gene therapy, stem cell therapy, and neural prosthesis implantation. Furthermore, we elaborate on the specific targets and mechanisms of action of various drugs. We would like to call for large-scale research to determine the efficacy of these methods in the future. Finally, we point out that studies on the pathogenesis of MSA and pathophysiological mechanisms of various autonomic dysfunction would also contribute to the development of new promising treatments and concepts.

Topiramate-associated sexual dysfunction: A systematic review

INTRODUCTION

Sexual pharmacotoxicity renders patients with epilepsy at a risk for sexual dysfunction (SD). This study is aimed to analyze the relationship between sexual function and topiramate to avoid topiramate-associated SD.

METHODS

A systematic review following the PRISMA guidelines was performed to elucidate any SD occurrence in patients receiving topiramate.

RESULTS

A total of 17 publications were reviewed. Based on limited polytherapy observational studies, the frequency of self-reported topiramate-associated SD, libido disorder, and orgasmic disorder in patients with polytherapy was 9.0%, 9.0%, and 2.6%, respectively (grade C evidence). Female patients mainly had anorgasmia, whereas male patients principally had erectile dysfunction. The daily dose of topiramate in patients with SD was within the recommended dose. Sexual adversity usually occurred from 4weeks after topiramate use but favorably subsided without eventful complications after topiramate substitution or dose reduction in all patients.

CONCLUSIONS

Topiramate can elicit different patterns of SD, especially anorgasmia in women and erectile dysfunction in men, even with a therapeutic dose. Detailed drug education and careful monitoring are necessary to maximize sexual health, especially in persons undergoing polytherapy and with other risks for SD. Moreover, a rapid response, such as substitution or reduction of the dose, is suggested when SD occurs during its use.

The effects of dopamine receptor agonists on BK Ca channels and signal transduction mechanism in corpus cavernosal smooth muscle cells

In this study, we investigated the effect of dopamine receptor agonists on potassium channels' activity and their signal transduction pathway in corporal smooth muscle cells. We used cultured human corporal smooth muscle cells. The whole cell and cell-attached configuration of the patch-clamp technique were used for electrophysiological recordings, and enzyme immunoassay was used for measuring cyclic AMP (cAMP) and cyclic GMP levels. Extracellular application of 10 microM dopamine and apomorphine significantly increased whole-cell K(+) currents by 283.5+/-55.7% (at +60 mV; n=12, P<0.001), 292.4+/-58.8.0% (at +60 mV; n=9, P<0.005), respectively. We confirmed that the increase in whole-cell currents was mainly due to activation of the tetraethylammonium-sensitive large conductance Ca(2+)-activated K(+) channels (BK(Ca) channels). Enzyme immunoassay indicated that dopamine and apomorphine stimulates cAMP levels in corporal smooth muscle cells in a concentration-dependent fashion. The activation of BK(Ca) channels by dopamine receptor agonists in corporal smooth muscle cells might be one of the mechanisms in inducing penile erection.

Effects of acute and chronic apomorphine on sex behavior and copulation-induced neural activation in the male rat

Apomorphine is a non-selective dopaminergic receptor agonist. Because of its pro-erectile effects, apomorphine is clinically used for treatment of erectile dysfunction. We investigated the effects of subcutaneous apomorphine administration (0.4 mg/kg rat) on sexual behavior and mating-induced Fos-expression following acute (day 1) or chronic apomorphine treatment (days 8 and 15) in sexually experienced male rats. Consistent facilitatory effects of apomorphine were observed in the reduced numbers of mounts and intromissions over time and an increased ejaculation frequency on day 1. The first post-ejaculatory interval, however, was lengthened, while other behavioral parameters were unaffected. Fos-immunoreactivity induced by acute apomorphine administration (barrel cortex, paraventricular hypothalamic nucleus, central amygdala and locus coeruleus) was strongly reduced after chronic administration. After mating, induction of Fos-immunoreactivity was observed in well-known areas like medial preoptic nucleus and the posterodorsal medial amygdaloid area. Apomorphine, however, reduced mating-induced Fos-immunoreactivity in the nucleus accumbens shell and prevented its occurrence in its core area. This remarkable apomorphine effect was not observed in any other brain area. We conclude that the behavioral (pro-erectile) effects of apomorphine are consistent over time, and that the diminished accumbens-Fos-immunoreactivity and the elongated post-ejaculatory interval may reflect a decreased response to remote cues from the estrus female.

The role of nitric oxide in erectile dysfunction: implications for medical therapy

Erectile dysfunction is a common, multifactorial disorder that is associated with aging and a range of organic and psychogenic conditions, including hypertension, hypercholesterolemia, diabetes mellitus, cardiovascular disease, and depression. Penile erection is a complex process involving psychogenic and hormonal input, and a neurovascular nonadrenergic, noncholinergic mechanism. Nitric oxide (NO) is believed to be the main vasoactive nonadrenergic, noncholinergic neurotransmitter and chemical mediator of penile erection. Released by nerve and endothelial cells in the corpora cavernosa of the penis, NO activates soluble guanylyl cyclase, which increases 3',5'-cyclic guanosine monophosphate (cGMP) levels. Acting as a second messenger molecule, cGMP regulates the activity of calcium channels as well as intracellular contractile proteins that affect the relaxation of corpus cavernosum smooth muscle. Impaired NO bioactivity is a major pathogenic mechanism of erectile dysfunction. Treatment of erectile dysfunction often requires combinations of psychogenic and medical therapies, many of which have been only moderately successful in the past. The advent of oral phosphodiesterase type 5 (PDE-5) inhibitors, however, has greatly enhanced erectile dysfunction treatment; patients have demonstrated high tolerability and success rates for improved erectile function. The efficacy of the PDE-5 inhibitors also serves to illustrate the importance of the NO-cGMP pathway in erectile function since these agents counteract the degradation of NO-generated cGMP. Because not all patients respond to PDE-5 inhibitors, additional therapies are being investigated, such as soluble guanylyl cyclase activators and NO donors, which act on NO-independent and NO-dependent pathways, respectively.

Lack of central nitric oxide triggers erectile dysfunction in diabetes

Erectile dysfunction is a serious and common complication of diabetes mellitus. The proposed mechanisms for erectile dysfunction in diabetes include central and autonomic neuropathy, endothelial dysfunction, and smooth muscle dysfunction. The paraventricular nucleus (PVN) of the hypothalamus is known to be involved in centrally mediated penile erection. This study was designed to examine the role of nitric oxide (NO) within the central nervous system component of the behavioral responses including erection in diabetic rats. N-methyl-d-aspartic acid (NMDA)-induced erection, yawning, and stretch through the PVN can be blocked by prior administration of NO synthase (NOS) blocker, l-NMMA, in freely moving, conscious male normal rats. Four weeks after streptozotocin (STZ) and vehicle injections, NMDA-induced erection, yawning, and stretch responses through the PVN are significantly blunted in diabetic rats compared with control rats. Examination of neuronal NOS (nNOS) protein by Western blot analysis indicated a reduced amount of nNOS protein in the PVN of rats with diabetes compared with control rats. Furthermore, restoring nNOS within the PVN by gene transfer using adenoviral transfection significantly restored the erectile and yawning responses to NMDA in diabetic rats. These data demonstrate that a blunted NO mechanism within the PVN may contribute to NMDA-induced erectile dysfunction observed in diabetes mellitus.

Botanical therapies in sexual dysfunction

Sexual dysfunction is a serious medical and social symptom that occurs in 10%-52% in men and 25%-63% in women. Numerous central and peripheral neural circuits control sexual activity. Impairment of one or more of these functional circuits may have a significant impact on personal, social and biological relationships. Although several aspects of sexual motivation and performance are known, a complete picture of the various factors that control human sexual activity is still unknown. The available drugs and treatments have limited efficacy, unpleasant side effects and contraindications in certain disease conditions. A variety of botanicals are known to have a potential effect on the sexual functions, supporting older claims and offering newer hopes. This review, while evaluating various factors that control sexual function, identifies a variety of botanicals that may be potentially useful in treating sexual dysfunction.

Pre- and postsynaptic localization of the 5-HT7 receptor in rat dorsal spinal cord: Immunocytochemical evidence

Several lines of evidence indicate that 5-HT7 receptors are involved in pain control at the level of the spinal cord, although their mechanism of action is poorly understood. To provide a morphological basis for understanding the action of 5-HT on this receptor, we performed an immunocytochemical study of 5-HT7 receptor distribution at the lumbar level. 5-HT7 immunolabelling is localized mainly in the two superficial laminae of the dorsal horn and in small and medium-sized dorsal root ganglion cells, which is consistent with a predominant role in nociception. In addition, moderate labelling is found in the lumbar dorsolateral nucleus (Onuf's nucleus), suggesting involvement in the control of pelvic floor muscles. Electron microscopic examination of the dorsal horn revealed three main localizations: 1) a postsynaptic localization on peptidergic cell bodies in laminae I-III and in numerous dendrites; 2) a presynaptic localization on unmyelinated and thin myelinated peptidergic fibers (two types of axon terminals are observed, large ones, presumably of primary afferent origin, and smaller ones partially from intrinsic cells; this presynaptic labelling represents 60% and 22% of total labelling in laminae I and II, respectively); and 3) 16.9% of labelling in lamina I and 19.8% in lamina II are observed in astrocytes. Labeled astrocytes are either intermingled with neuronal elements or make astrocytic "feet" on blood vessels. In dendrites, the labelling is localized on synaptic differentiations, suggesting that 5-HT may act synaptically on the 5-HT7 receptor. This localization is compared with other 5-HT receptor localizations, and their physiological consequences are discussed.

Peripheral relaxant activity of apomorphine and of a D1 selective receptor agonist on human corpus cavernosum strips

Apomorphine is used in the erectile dysfunction therapy and its action has been ascribed to the stimulation of central dopamine receptor. At the present stage, very little is known about the peripheral action of apomorphine on human corpus cavernosum (HCC). We have investigated the peripheral action of apomorphine and the role of dopamine receptors in HCC. We here demonstrate that both D1 and D2 receptors were expressed in the HCC, D1 receptors were two-fold more abundant than D2 and that both receptors were mainly localized on the smooth muscle cell component. Apomorphine in vitro exerted an anti-alpha1 adrenergic activity in human cavernosal strips since it prevented contraction induced by phenylephrine (PE), but not by U46619 or endothelin. Apomorphine elicited endothelium-independent and concentration-dependent relaxation of the strips contracted by PE, U46619 or endothelin. The EC50 values (microM) for apomorphine, in the presence and absence of endothelium, were 51.0+/-16 and 16.0+/-14, 120+/-19 and 150+/-18, 59.0+/-15 and 140+/-50 on PE-, U46619- or endothelin-induced contraction, respectively. Selective dopamine receptor agonist A-68930 (D1-like), but not quinpirole (D2-like), caused concentration-dependent relaxation of the cavernosal strips, which was partially prevented by endothelium removal or by treatment with an inhibitor of nitric oxide (NO) synthase. In conclusion, we show that (1) apomorphine has a peripheral relaxant direct effect as well as an antiadrenergic activity, (2) HCC possesses more D1-like (D1 and D5) than D2-like (D2, D3 and D4) receptors, (3) both D1- and D2-like receptors are mainly localized on smooth muscle cells and (4) the relaxant activity is most probably mediated by D1-like receptor partially through NO release from endothelium.

Blockade of neuronal nitric oxide synthase abolishes the toxic effects of Tx2-5, a lethal Phoneutria nigriventer spider toxin

The primary goal of this study was to determine whether Tx2-5, a sodium channel selective toxin obtained from the venom of the spider Phoneutria nigriventer, produced penile erection by means of nitric oxide mechanism. Toxin identity was analyzed by MALDI-TOF, ES-MS and N-terminal amino acid sequencing. Pretreating mice with the non-selective nitric oxide synthase (NOS) inhibitor N(omega)-Nitro-L-arginine methyl ester hydrochloride (L-NAME) and the selective neuronal-NOS inhibitor 7-Nitroindazole (7-NI) prior to Tx2-5 i.p. (10 microg/25 g mouse) injection challenged the hypothesis above. Controls were injected with the D-isomer or DMSO or saline. Results demonstrated that L-NAME inhibited penile erections in about half the animals treated, while 7-NI completely abolished this effect. Interestingly 7-NI also abolished all the other symptoms of intoxication induced by Tx2-5, including salivation, respiratory distress and death. Tx2-5 killed all the animals of the control group and no one in the 7-NI-treated group. We conclude that (1) intraperitoneal injections of Tx2-5 induce a toxic syndrome that include penile erection, hypersalivation and death by respiratory distress or pulmonary edema; (2) pretreatment with the non-selective NOS inhibitor L-NAME reduces the penile erection and partially protects from the lethal effects of Tx2-5; (3) pretreatment with the nNOS-selective inhibitor 7-NI completely abolishes all the toxic effects of Tx2-5, including penile erection and death suggesting that nNOS is the major player in this intoxication; (4) toxins from other animals that affect sodium channels in the same way as Tx2-5 and induce similar toxic syndromes may have as a major common target, the activation of nitric oxide synthases.

Update on oral treatments for male erectile dysfunction

Impairment of erectile function compromises quality of life in millions of men and their partners, many of whom prefer to suffer in silence. It is important to maintain an elevated index of clinical suspicion in patients with erectile dysfunction (ED) risk factors (e.g. hypertension, diabetes, coronary heart disease). There remains a high rate of voluntary discontinuation of therapy associated with most treatment modalities. Since the introduction of sildenafil, a greater awareness and openness regarding the epidemiology and treatment of male erectile dysfunction has emerged. The development of newer and potentially more efficacious phosphodiesterase type 5 (PDE5) inhibitors will serve to treat an even greater number of patients, allowing once daily and more convenient dosing. An increased understanding of the physiological principles of penile erection has allowed the development of novel oral pharmacological therapies. The new agents offer a potential benefit in a broader range of patients and clinical situations. They may provide a more acceptable alternative than other more invasive options (intracavernosal/urethral injection, implant surgery). The dopamine agonist apomorphine acts on the central control of penile erection to allow a sublingual preparation to produce a prompt response. It is not contraindicated in patients on nitrate medication for coronary artery disease, or in patients with depression or on antidepressants. As with any other treatment, the clinician's responsibility in the care of ED patients does not end with the writing of a prescription. Adequate education and follow-up are needed to optimize the efficacy and safety of oral ED therapy. Furthermore, patients and their partners need to be advised that the agents are not effective in the absence of sexual stimulation. Communicating with both the patient and his partner in a discreet, non-judgmental manner that fosters the physician-patient alliance can facilitate the recognition and treatment of ED.

A European multicentre study to evaluate the tolerability of apomorphine sublingual administered in a forced dose-escalation regimen in patients with erectile dysfunction

OBJECTIVE

To determine the risk-benefit ratio of a forced dose-escalation regimen (2 to 3 to 4 mg) in a European clinical study evaluating apomorphine sublingual (SL) in treating erectile dysfunction (ED), by evaluating the overall tolerability and efficacy of the regimen compared with placebo in patients with ED, and evaluating efficacy by assessing the proportion of successful attempts resulting in sexual intercourse.

PATIENTS AND METHODS

This randomized, double-blind, two-arm, parallel-group study was conducted in 507 patients enrolled at 34 European sites. After a 1-2 week screening period, patients were treated for 8 weeks with either placebo or apomorphine SL administered as a forced dose-escalation regimen. Heterosexual men (aged 18-70 years) were eligible for participation in the study if they were in stable health, a stable relationship of > or = 6 months duration, had a history of erectile inability, and were diagnosed with ED (successful in fewer than half of attempts to attain and maintain an erection firm enough for intercourse during the 30 days before screening). Patients provided information (recorded on diary cards and reviewed at each study visit) about the frequency and success in achieving erections and of sexual intercourse attempts during both the screening and treatment periods. The dosing regimen required patients to take one tablet of apomorphine SL (2 mg for 2 weeks, then 3 mg for 2 weeks and finally 4 mg for the remaining 4 weeks) or placebo 15-25 min before intercourse, and intercourse was to be attempted at least twice a week. Safety data were collected throughout the 8-week study period, and included recording adverse events, vital signs and changes in laboratory test values for standard haematology and biochemistry variables. The primary efficacy variable was the proportion of successful attempts, defined as an erection rigid enough for sexual intercourse, occurring after dosing (successful intercourse rate). The proportion of erections achieved was a secondary efficacy variable.

RESULTS

Of the 507 patients, 254 received apomorphine SL and 253 received placebo; 87% of patients in both groups completed the 8-week treatment period. Of the patients receiving apomorphine SL, 24% had hypertension, 11% had coronary artery disease, 10% had diabetes, and 5.5% had benign prostatic hypertrophy; 62.6% of treated patients received concomitant medications for these maladies. The treatment groups were balanced for demographic and baseline variables, including comorbidity factors. Treatment-emergent adverse events, reported by > 5% of patients in the treated group, were nausea (9.8%), dizziness (7.1%) and headache (6.7%), compared with 0.4%, 2.4% and 4.0%, respectively, in the placebo group. Sixty-six patients withdrew from the study, 16 because of study drug-related adverse events (12 from the apomorphine and four from the placebo group). Six patients (three in each group) reported a total of nine serious treatment-emergent adverse events, all of which resolved by the end of the study. In the intention-to-treat population, the proportion of successful attempts at sexual intercourse and of erections were statistically greater in the apomorphine than in the placebo group (P = 0.001 and 0.021, respectively); analysis of the per-protocol population results confirmed this significant difference.

CONCLUSION

This European study supports the safety and tolerability of apomorphine SL despite the forced escalation to a 4-mg dose (exceeding the approved 2-3 mg dose). Adverse effects were not treatment-limiting. These results further support the clinically significant efficacy of apomorphine SL for treating ED at all doses used. The risk/benefit ratio supports apomorphine SL as a safe and effective alternative in managing ED.