Preliminary results with the nitric oxide donor linsidomine chlorhydrate in the treatment of human erectile dysfunction.

Recent experimental studies showed an important role of endothelium derived relaxing factor for cavernous smooth muscle relaxation. Since nitric oxide seems to account for the biological actions of endothelium derived relaxing factor, a study was done to examine a possible role of the nitric oxide donor linsidomine chlorhydrate (SIN-1) in the treatment of erectile dysfunction. To determine a therapeutically useful dose 0.1, 0.2, 0.5 and 1 mg. SIN-1 were injected intracavernously in patients with erectile dysfunction. Each dose was given to 2 patients. Then, 63 patients received 1 mg. SIN-1, including 7 who had prolonged erections to minimal doses of papaverine plus phentolamine and 4 who did not respond with a full erection to other pharmacological agents. Intracavernous injection of SIN-1 induced a dose-dependent erectile response by increasing the arterial inflow and relaxing cavernous smooth muscles. Of the patients 29 had a full, 21 an almost full and 13 a moderate erection to 1 mg. SIN-1. There were no systemic or local side effects. In the patients with prolonged erections to papaverine plus phentolamine the mean duration of a full erectile response to SIN-1 was 57 minutes. Compared to the responses to a papaverine (15 mg./ml.) and phentolamine (0.5 mg./ml.) mixture, the erection induced by SIN-1 was superior in 10, comparable in 47 and inferior in 6 patients. Our data suggest a possible role for SIN-1 in the treatment of erectile dysfunction. Possible advantages may be that erection is induced by a mechanism similar to that occurring physiologically, a decreased risk of inducing prolonged erections and low therapy costs.     

褪黑素抗氧化治疗糖尿病大鼠阴茎勃起功能障碍的研究

目的 观察褪黑素对糖尿病大鼠阴茎勃起功能的影响,探讨氧化应激在糖尿病性勃起功能障碍发病机制中的作用.方法 一次性腹腔注射STZ建立糖尿病大鼠模型,随机分为糖尿病组、褪黑素(MT)治疗组以及对照组.8周后通过电刺激各组大鼠勃起神经来检测海绵体内压,评价勃起功能;采用硫代芭比妥酸法检测阴茎海绵体组织中丙二醛(MDA)含量,黄嘌呤氧化酶法测超氧化物氧化酶(SOD)活性;免疫组化染色半定量分析各组大鼠阴茎海绵体中平滑肌及内皮的含量.结果 与正常对照组相比,阴茎海绵体组织中MDA含量显著增加(P＜0.01),SOD活性降低(P＜0.05),最大海绵体内压(ICP)亦显著降低(P＜0.05);与糖尿病组相比,MT组大鼠海绵体MDA含量明显降低(P＜0.05),其SOD活性和ICP显著升高(P＜0.05);且其海绵体平滑肌及海绵窦内皮细胞含量明显提高.结论 MT可通过改善组织中氧化应激水平,促进阴茎海绵体平滑肌和内皮组织修复,提高勃起功能;抗氧化治疗可能为糖尿病性勃起功能障碍的防治提供新的策略.     

Hemodynamics of penile erection

In the flaccid state, the smooth muscles of the cavernous arterioles and trabeculae are contracted, and minimal blood flow enters the sinusoids. Relaxation of these smooth muscles incites arterial dilation, venous compression, and sinusoidal relaxation and results in penile erection.     

Corpora cavernosa ultrastructure in vascular erectile dysfunction

Open biopsy of the corpus cavernosum was performed in 13 nondiabetic patients with erectile dysfunction. The history and physical examination, sleep rigidity and tumescence monitoring, hormonal assays, duplex ultrasonography with papaverine, and cavernosometry and cavernosography, formed the basis of categorizing each patient into 1 of 5 etiological groups. These groups included neurogenic, moderate arterial, severe arterial, venous and fibrotic causes for organic erectile dysfunction. The cavernous smooth muscle and endothelium in each patient appeared to be normal on light and electron microscopy. We conclude that cavernous biopsy is of limited value to determine therapeutic options in patients with erectile dysfunction.     

Combined strategy of mesenchymal stem cell injection with vascular endothelial growth factor gene therapy for the treatment of diabetes-associated erectile dysfunction

This study was designed to investigate the effect of vascular endothelial growth factor 164 adenovirus (Ad-VEGF(164))-transfected mesenchymal stem cells (MSC) on improving erectile function in diabetic rats. Forty-five male Sprague-Dawley rats were injected with streptozotocin to develop type 1 diabetes, whereas 10 served as normal controls. Diabetic rats were randomly divided into 3 groups: rats that underwent intracavernous injection with phosphate-buffered saline (DM+PBS), unmodified MSCs (DM+MSC), and Ad-VEGF(164)-transfected MSCs (DM+VMSC). Normal controls received intracavernous injection of PBS. Four weeks after injection, erectile function was measured by cavernous nerve electrostimulation. Penile tissue was harvested for histology and enzyme-linked immunoassay. Prior to injection, high expression of VEGF was confirmed in Ad-VEGF(164)-transfected MSCs by enzyme-linked immunoassay. Four weeks after injection, the erectile function, as well as the content of smooth muscle and endothelium in corpus cavernosum increased significantly in the MSC-injected groups compared with the DM+PBS group. There was a significant improvement of erectile function, the content of smooth muscle and endothelium, and the VEGF concentration in the corpus cavernosum in the DM+VMSC group compared with the DM+MSC group. Our study validates the effect of intracavernous injection of MSCs for diabetes-associated erectile dysfunction in an animal model. The combined strategy of MSC injection with VEGF gene therapy-enhanced therapy of MSCs for the treatment of diabetes-associated erectile dysfunction.     

Effects of bacterial endotoxin on the contraction and relaxation responses of the rabbit cavernous smooth muscles

PURPOSE: We evaluated effects of bacterial endotoxin during septicemia on contraction and relaxation responses of cavernous smooth muscles in rabbits. MATERIALS AND METHODS: We performed isometric tension studies with norepinephrine (NE), endothelium-dependent and endothelium-independent vasodilators, and nonadrenergic noncholinergic (NANC)-selective electrical field stimulation on the muscle strips of control and endotoxin (lipopolysaccharide; LPS)-treated rabbits. To determine reversibility of the LPS effects on the cavernous smooth muscle, the contraction and relaxation studies were repeated after resting the strips for 1 day at 4C. We also investigated the effect of the nonspecific nitric oxide synthase (NOS) inhibitor (NW-nitro-L-arginine methyl ester; L-NAME) and the selective immunologic NOS inhibitor (aminoguanidine) on reactivity of the strips to NE and acetylcholine. RESULTS: Contractile response to NE was significantly (p <0.01) reduced in the cavernous smooth muscles from the systemically and locally LPS-treated rabbits, compared with control group. Both aminoguanidine and L-NAME markedly improved the diminished contraction of the strips. Relaxation response to endothelium-dependent agonists (acetylcholine and bradykinin) was significantly (p <0.05) decreased in the LPS-treated groups, compared with the control group but not to endothelium-independent vasodilators (papaverine and verapamil) and NANC-selective electrical field stimulation. L-NAME completely inhibited the relaxation response to acetylcholine in the control and LPS-treated groups but aminoguanidine did not. The impaired contraction and relaxation of the strips was completely restored after resting for 1 day. CONCLUSIONS: Bacterial endotoxin may cause non-endothelial overproduction of NO and inhibition of endothelium-derived NO production, which may contribute to impairment of contraction and relaxation of rabbit cavernous smooth muscles.     

Effect of basic fibroblast growth factor incorporating gelatin microspheres on erectile function in the diabetic rat

PURPOSE: We report the potential of basic fibroblast growth factor (bFGF) incorporating gelatin microspheres to preserve erectile function in a diabetic rat model. MATERIALS AND METHODS: A total of 48 adult male rats were divided into 3 groups, namely control (nondiabetic rats), diabetes mellitus (DM) (diabetic rats that received gelatin microspheres with saline) and bFGF (diabetic rats that received gelatin microspheres with bFGF). After 4 and 8 weeks we examined intracavernous pressure responses with electrical stimulation to the cavernous nerve. For histological examination of the penis we performed Azan-Mallory staining for smooth muscle and collagen, and immunohistochemistry for endothelial nitric oxide synthase (NOS) in endothelium and neuronal NOS in cavernous nerve fiber. RESULTS: Although the intracavernous pressure response was significantly lower in the DM group than in the control group, pressure in the bFGF group was maintained at the normal level found in controls. Azan-Mallory staining showed a mass decrease in smooth muscle in cavernous tissue in the DM group. However, that in the bFGF group was maintained. There was no significant difference in endothelial NOS positive areas and the distribution of the diameter of neuronal NOS positive nerve fibers in cavernous tissue among the 3 groups. CONCLUSIONS: We report the maintenance of erectile function with bFGF incorporating gelatin microspheres in diabetic rats. The rationale of this maneuver is smooth muscle preservation by the long-term release of bFGF. This is a novel therapeutic option that is clinically applicable for diabetes induced erectile dysfunction.     

Androgens play a pivotal role in maintaining penile tissue architecture and erection: a review

Androgens are essential for development, growth, and maintenance of penile structure, and regulate erectile physiology by multiple mechanisms. Here we provide a concise overview of the basic research findings pertaining to androgen modulation of erectile tissue architecture and physiology. A significant body of evidence exists pointing to a critical role of androgens in erectile physiology. Studies in animal models have provided fundamental knowledge on the role of androgens in modulating tissue architecture and cellular, molecular, and physiological mechanisms. Based on data from our laboratory and those reported by others, we believe that androgens play a pivotal role in maintaining the structure and function of the peripheral penile nerve network, the structural integrity of the corpora cavernosa, the tunica albuginea, and the endothelium of the cavernous spaces. Further, androgens play an important role in regulating the differentiation of precursor cells into trabecular smooth muscle. In this review, we will focus our discussion on findings pertaining to the role of androgens in regulating penile tissue architectural elements in modulating penile function. This knowledge has a profound impact on the potential use of androgens in the clinical setting to treat patients with erectile dysfunction.     

Gene transfer of endothelial nitric oxide synthase partially restores nitric oxide synthesis and erectile function in streptozotocin diabetic rats

PURPOSE: We determined whether adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis of streptozotocin induced diabetic rats could improve the impaired erectile response. MATERIALS AND METHODS: Two experimental groups of animals were transfected with adenoviruses, including streptozotocin (Sigma Chemical Company, St. Louis, Missouri) diabetic rats with AdCMVbetagal and streptozotocin diabetic rats with AdCMVeNOS. At 1 to 2 days after transfection these study animals underwent cavernous nerve stimulation to assess erectile function and their responses were compared with those of age matched control rats. In control and transfected streptozotocin diabetic rats eNOS and neuronal NOS (nNOS) were examined by Western blot analysis. Constitutive and inducible NOS activities were evaluated in the presence and absence of calcium by L-arginine to L-citrulline conversion and nitrate plus nitrite levels were measured. In control and streptozotocin diabetic penes beta-galactosidase activity and localization were determined. RESULTS: After transfection with AdCMVbetagal beta-galactosidase was localized to the endothelium and smooth muscle cells of the streptozotocin diabetic rat penis. Streptozotocin diabetic rats had a significant decrease in erectile function, as determined by peak and total intracavernous pressure (area under the curve) after cavernous nerve stimulation compared with control rats. Streptozotocin diabetic rats transfected with AdCMVeNOS had peak intracavernous pressure and area under the curve similar to those in control animals. This change in erectile function was a result of eNOS over expression with an increase in eNOS protein expression and constitutive NOS activity as well as an increase in nitric oxide biosynthesis, as reflected by an increase in cavernous nitrate plus nitrite formation. There was no change in nNOS protein expression or calcium independent conversion of NOS (inducible NOS activity). CONCLUSIONS: Adenoviral gene transfer of eNOS significantly increased peak and total intracavernous pressure to cavernous nerve stimulation in streptozotocin diabetic rats to a value similar to the response observed in control rats. Our results suggest that eNOS contributes significantly to the physiology of penile erection. These data demonstrate that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the streptozotocin diabetic rat.     

Evaluation of the role of corpus cavernosum electromyography as a noninvasive diagnostic tool in male erectile dysfunction

Corpus cavernosum electromyography (EMG) and its evolution: single potential analysis of cavernous electrical activity (SPACE) seem to be promising diagnostic methods in the evaluation of erectile dysfunction and smooth muscle integrity [4]. Our study concentrates on the role of EMG in the evaluation of corpus cavernosum smooth muscles, using it as a noninvasive technique for demonstrating autonomic erectile dysfunction through their influence on recording SPACE and consequent proper selection of patients for different therapeutic modalities. A total of 80 male patients were examined for the feasibility of transcutaneous registration of cavernous electrical activity with a 2-channel electrophysiological unit (Evamatic 2000, Dantec) with two surface electrodes bilaterally placed on the penile shaft. Ten patients had normal erectile function, but complained of other urological symptoms. They served as the controls for normal electrical activity. Fifty patients with organic impotence of nonvascular (neurogenic) or vascular (venogenic, arteriogenic) aetiologies were subjected to EMG in both the flaccid and the erect state. On the basis of the EMG patterns the patients were divided into the following groups: 34 patients having normal tracing in both the flaccid and the erect state, and 21 patients showing abnormal patterns of waves with evidence of autonomic neurogenic dysfunction and incomplete smooth muscle relaxation. Of the latter 4 had long-standing diabetes mellitus and 4 had spinal injuries.     

Possible role for acetylcholine as a neurotransmitter in canine penile erection

In 15 adult dogs, the possible role of acetylcholine as a parasympathetic neurotransmitter in canine penile erection was investigated. Intracavernous injection of increasing dosages of acetylcholine (0.1-100 micrograms) induced a dose-dependent erectile response with increased arterial flow, cavernous smooth muscle relaxation, and venous occlusion. This erectile response was completely abolished after muscarinic blockade by intracavernous injection of 0.1 mg atropine. After cavernous nerve stimulation, atropine injection significantly reduced the pudendal arterial flow (by 25%) and likewise caused a significant reduction in cavernous outflow restriction. Histologic staining showed acetylcholinesterase-positive fibers around the cavernous arteries and within the cavernous erectile tissue.     

THE EFFECT OF THE SPECIFIC PHOSPHODIESTERASE (PDE) INHIBITORS ON HUMAN AND RABBIT CAVERNOUS TISSUE IN VITRO AND IN VIVO

Purpose

Phosphodiesterases (PDE) are key enzymes in the regulation of the smooth muscle tone. Experimental studies showed PDE III and V-isoenzymes to play an important role in the smooth muscle tone regulation of corpus cavernosum. Recently, a specific PDE III-inhibitor (milrinone) and a PDE V-inhibitor (sildenafil) were introduced in clinical studies. An experimental study was done to examine a potential role of PDE-inhibitors in the treatment of erectile dysfunction.

Materials and Methods

In the organ bath, strips from human and rabbit corpus cavernosum were precontracted and increasing doses of PDE inhibitors were added. In patients with erectile dysfunction as well as in rabbits, intracavernous injections of milrinone were done.

Results

PDE-inhibitors dose-dependently relaxed human and rabbit corpus cavernosum strips. In the precontracted human cavernous tissue, milrinone and sildenafil were equally potent and efficacious in vitro. In the rabbit, milrinone induced slight tumescence but dramatic circulatory side effects. In patients, penile tumescences as well as full erections were observed.

Conclusions

Milrinone strongly relaxes human cavernous smooth muscle cells but it exhibits low relaxant effects in the rabbit cavernous tissue. In human tissue, sildenafil was equieffective with milrinone in vitro. In vivo, milrinone induced a good erectile response in humans but a poor erectile effect in rabbits. Our results support a possible potential for selective PDE-III and -V inhibitors in the treatment of impotence and give further evidence that the rabbit is an animal model of limited value to study the effects of drugs on cavernous smooth muscle tone regulation in vivo.     

Characterization of corpus cavernosum smooth muscle cell phenotype in diabetic rats with erectile dysfunction

Phenotypic modulation from a contractile to a proliferative state within vascular smooth muscle cells has a critical role in the pathogenesis of a variety of cardiovascular diseases. To investigate the characterization of corpus cavernosum smooth muscle cell phenotype in diabetic rats with erectile dysfunction, a group of Sprague-Dawley rats (n=30) were induced by intraperitoneal injection of streptozotocin (60?mg?kg(-1)) and screened by subcutaneous injection of apomorphine (100?μg?kg(-1)) for the measurement and comparison of the penile erections, and then three different groups were defined. Primary corpus cavernosum smooth muscle cells were cultured and passaged. The cavernous tissue segments were subjected to quantitative real-time polymerase chain reaction to determine the expressions of smooth muscle α-actin (SMA), SM myosin heavy chain (SMMHC), smoothelin, calponin and myocardin. Cell contractility in vitro and western blot analysis of SMA and SMMHC in the cavernous tissues and cells were determined. Compared with the control group (n=8) and the diabetes mellitus group (n=5), the expressions of SMA, calponin, SMMHC, smoothelin and myocardin mRNA were decreased in the cavernous tissues in rats of the diabetic erectile dysfunction group (n=15; P=0.001 and 0.02, P=0.014 and 0.012, both P<0.001, P=0.005 and <0.001, P=0.003 and 0.035, respectively). The levels of SMA and SMMHC proteins showed a significant decrease in cavernous tissues and cultured cells in rats of the diabetic erectile dysfunction group. Cells of the diabetic erectile dysfunction group exhibited significantly less contractility compared with those of other groups (P<0.001). Corpus cavernosum SM cell possesses the ability to modulate the phenotype under hyperglycemic conditions, which could have a key role in the pathogenesis of diabetic erectile dysfunction.     

高血压大鼠海绵体平滑肌细胞间连接的变化

目的:比较自发性高血压大鼠(SHR)和正常血压大鼠阴茎海绵体平滑肌细胞间连接改变及与阴茎勃起功能的关系。方法:注射阿朴吗啡(APO)观察14周龄SHR(SHR组,n=5)、W istar-Kyoto大鼠(WKY组,n=5)阴茎勃起情况,用透射电镜观察其阴茎海绵体平滑肌细胞间连接超微结构,RT-PCR测定海绵体平滑肌细胞Connexin 43的mRNA表达,免疫组化观察Connexin 43蛋白表达。结果:SHR组大鼠阴茎勃起次数明显低于WKY组(P<0.05),电镜发现SHR组大鼠阴茎海绵体平滑肌细胞间大量胶原纤维增生,Connexin 43蛋白及其mRNA表达较WKY组显著降低(P<0.05)。结论:高血压影响阴茎勃起功能,阴茎海绵体平滑肌细胞间连接的病理改变可能是高血压性勃起功能障碍的发病机制之一。     

Acetylcholine as a possible neurotransmitter in penile erection

We investigated the erectile response to intracavernous injection of increasing doses of acetylcholine (0.5 to 500 micrograms.) in 10 monkeys. To differentiate between nicotinic (ganglionic) and muscarinic (parasympathetic postganglionic) effects, acetylcholine was likewise administered after 1.6 mg. trimethaphan camsylate and 0.1 mg. atropine, alone or sequentially. Erections were induced by cavernous nerve stimulation before and after atropine. Acetylcholine induced a dose-dependent, triphasic erectile response: a first tumescence phase followed by contraction and a subsequent second phase of tumescence. Atropine reduced but did not abolish the erectile response to acetylcholine: attainment of maximal intracavernous pressure after neurostimulation was both delayed and reduced (mean 25 cm. H2O). Only after combined nicotinic and muscarinic blockade was the erectile response to acetylcholine completely abolished. Histologic staining for acetylcholinesterase in five additional monkeys that had not received acetylcholine showed dense staining within the cavernous erectile tissue and around the cavernous arteries. Our data suggest that acetylcholine is a possible neurotransmitter for penile erection in monkeys.     

Oxidative stress in arteriogenic erectile dysfunction: prophylactic role of antioxidants

PURPOSE: We searched for markers of oxidative stress in cavernous ischemia and examined the effect of long-term antioxidant intake on arteriogenic erectile dysfunction (ED) in the rabbit. MATERIALS AND METHODS: Antioxidant activity of known antioxidant beverages, such as pomegranate juice (PJ), red wine, blueberry juice, cranberry juice, orange juice and green tea, was examined spectrophotometrically. PJ demonstrated the highest free radical scavenging capacity. The effect of long-term PJ intake on intracavernous blood flow and penile erection was then examined in the rabbit model. Erectile tissues were processed to assess oxidative stress and smooth muscle relaxation, immunohistochemical staining of nitric oxide synthase (NOS) and histomorphometry. RESULTS: On spectrophotometric analysis PJ showed the highest capacity to decrease low density lipoprotein oxidation and inhibit cellular oxidative stress in macrophages. The rabbit model of arteriogenic ED demonstrated decreased intracavernous blood flow, erectile dysfunction, loss of smooth muscle relaxation, decreased endothelial NOS and neuronal NOS, increased inducible NOS expression, diffused cavernous fibrosis and increased cavernous levels of the oxidative product isoprostane 8-epi-prostaglandin F2alpha. Long-term PJ intake increased intracavernous blood flow, improved erectile response and smooth muscle relaxation in ED and control groups while having no significant effect on NOS expression. PJ intake prevented erectile tissue fibrosis in the ED group. CONCLUSIONS: Arteriogenic ED accumulates oxidative products in erectile tissue, possibly via an intrinsic mechanism. Oxidative stress may be of great importance in the pathophysiology of arteriogenic ED. Antioxidant therapy may be a useful prophylactic tool for preventing smooth muscle dysfunction and fibrosis in ED.     

Nitric oxide-cyclic GMP pathway with some emphasis on cavernosal contractility

Nitric oxide (NO) is formed from the conversion of L-arginine by nitric oxide synthase (NOS), which exists in three isoforms: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). nNOS is expressed in penile neurons innervating the corpus cavernosum, and eNOS protein expression has been identified primarily in both cavernosal smooth muscle and endothelium. NO is released from nerve endings and endothelial cells and stimulates the activity of soluble guanylate cyclase (sGC), leading to an increase in cyclic guanosine-3',5'-monophosphate (cGMP) and, finally, to calcium depletion from the cytosolic space and cavernous smooth muscle relaxation. The effects of cGMP are mediated by cGMP dependent protein kinases, cGMP-gated ion channels, and cGMP-regulated phosphodiesterases (PDE). Thus, cGMP effect depends on the expression of a cell-specific cGMP-receptor protein in a given cell type. Numerous systemic vasculature diseases that cause erectile dysfunction (ED) are highly associated with endothelial dysfunction, which has been shown to contribute to decreased erectile function in men and a number of animal models of penile erection. Based on the increasing knowledge of intracellular signal propagation in cavernous smooth muscle tone regulation, selective PDE inhibitors have recently been introduced in the treatment of ED. Phosphodiesterase 5 (PDE5) inactivates cGMP, which terminates NO-cGMP-mediated smooth muscle relaxation. Inhibition of PDE5 is expected to enhance penile erection by preventing cGMP degradation. Development of pharmacologic agents with this effect has closely paralleled the emerging science.     

Calcitonin-gene-related peptide: a possible role in human penile erection and its therapeutic application in impotent patients

A functional study was done to examine a possible role of calcitonin-gene-related peptide in human penile erection and its possible therapeutic applications for patients with erectile dysfunction. In the determination of an effective dosage, 5 ng. (2 patients), 50 ng. (2 patients), 500 ng. (4 patients), 5 micrograms (4 patients) and 25 micrograms (7 patients) were injected intracavernously, and pulse and blood pressure were monitored. Arterial inflow was measured by Doppler sonography, smooth muscle relaxation was determined by the analysis of cavernous electrical activity and cavernous outflow occlusion was recorded by cavernosometry. In 12 patients the erectile response of prostaglandin E1 was compared to the response of an equal (6 patients) or decreased dose of prostaglandin E1 combined with an equal weight of calcitonin-gene-related peptide. In 14 patients the erectile response to the combination of calcitonin-gene-related peptide and prostaglandin E1 was compared to the response of prostaglandin E1 alone, and with a combination of 15 mg./ml. papaverine and 0.5 mg./ml. phentolamine. Calcitonin-gene-related peptide induced an increase in the penile arterial inflow, cavernous smooth muscle relaxation and cavernous outflow occlusion. Histochemical results indicated nerve fibers positive for calcitonin-gene-related peptide within the cavernous bodies. A dose-dependent erectile response to calcitonin-gene-related peptide was observed at doses of 500 ng. to 25 micrograms. Systemic side effects were first observed at a dose of 25 micrograms in 2 of 7 patients. The combination of calcitonin-gene-related peptide and prostaglandin E1 was more effective in inducing a full erection than either prostaglandin E1 alone or the combination of papaverine and phentolamine. Pain was reported in 4% of the patients who received the combination of calcitonin-gene-related peptide and prostaglandin E1, whereas 42% of those who received prostaglandin E1 alone reported pain. Our results suggest that calcitonin-gene-related peptide may be a possible neurotransmitter for penile erection. A combination of calcitonin-gene-related peptide and prostaglandin E1 seems to be an effective alternative combination in the treatment of impotence.