Sexual bother and function after radical prostatectomy: predictors of sexual bother recovery in men despite persistent post-operative sexual dysfunction.

Changes in sexual bother (SB) following radical prostatectomy (RP) negatively affect health-related quality of life (HRQoL) of prostate cancer survivors. However, post-operative SB tends to be neglected whereas sexual function (SF) is thoroughly assessed in clinical practice and few studies have focused on and evaluated patients' SB. We retrospectively reviewed 2 345 consecutive patients who underwent RP between 2001 and 2009 at a single institution. SF and SB were assessed using Expanded Prostate Cancer Index Composite (EPIC) questionnaires. We stratified our cohort by SB recovery and post-operative SF status, including a subset of men who recovered SB despite persistent post-RP sexual dysfunction. Multivariable logistic regression analyses were conducted to identify factors for men who have SB recovery. Of 319 eligible patients, 133 (41.7%) recovered their SB at a mean of 20 months after RP. Among the 133 men who demonstrated SB recovery, 109 had post-operative sexual dysfunction. Patients with SB recovery despite post-RP sexual dysfunction were more likely to be old (p = 0.004), to have higher clinical T stage (p < 0.001), to have more non-nerve-sparing RP (p < 0.001), to have lower pre-operative EPIC-SF/SB scores (p < 0.001), to have more extracapsular extension (p = 0.031) and to be PDE5i non-users after surgery (p < 0.001). In multivariable analysis, predictors for this subset were lower comorbidity (OR 0.62, p = 0.043), higher clinical cancer stage (OR 2.35, p = 0.026), worse pre-operative SF (OR 0.98, p = 0.010), SB (OR 0.98, p < 0.010) and no PDE5i use (OR 0.37, p = 0.002); age was not related (OR 0.99, p = 0.555). As SB can influence patients' overall HRQoL, expectations of SB recovery should be provided to patients in the same way that SF recovery is presented. This study may help clinicians to discuss SB with patients and assess their potential for SB recovery following RP.

On-demand use of erectile aids in men with preoperative erectile dysfunction treated by whole gland prostate cryoablation.

Prostate cryoablation is an established minimally invasive treatment for localized prostate cancer (PCa). However, the impairment of erectile function (EF) is considered a serious complication of the procedure. To investigate the efficacy of erectile aids following cryotherapy, 93 patients who underwent whole gland prostate cryoablation with required complete medical records were analyzed. The changes in postoperative EF were evaluated using the International Index of Erectile Function (IIEF-5) questionnaire. Additionally, independent factors that could have a correlation to the postoperative IIEF-5 score or postoperative Expanded Prostate Cancer Index Composite (EPIC) score were assessed. In the entire cohort, the mean preoperative IIEF-5 score was 7.0 ± 6.2. A total of 72 (77.4%) patients had moderate-to-severe preoperative erectile dysfunction. In longitudinal investigation, the patients using erectile aids showed the ability to recover to baseline after 24 months from cryoablation compared with the patients not using erectile aids. There were significant differences of IIEF-5 scores between these groups at 24 months (7.5 vs 3.0; P = 0.025) and 36 months (8.5 vs 3.5; P = 0.010). In multivariate analysis, the use of erectile aids correlated with restoration of IIEF-5 scores (odds ratio, 5.11; confidence interval (CI), 1.87-13.96; P < 0.001) and lower EPIC sexual bother (coef, 19.61; CI, 0.32-38.89; P = 0.046). Our data indicate that on-demand use of erectile aids could help restore EF and reduce sexual bother after whole gland prostate cryoablation. Although, erectile aids could not play a role as an adequate treatment for ED after whole gland prostate cryoablation, these results may aid in the decision-making process for PCa patients with preoperative and postoperative ED who have concern about sexual health-related quality of life.

Concordance in the perception of couples recovering from primary surgical treatment of prostate cancer.

Although prostate cancer affects men, research shows effects on both members of the couple. We analyzed concordance in couples recovering from primary surgical treatment of prostate cancer when surveyed on psychological domains including emotional status, relationship, self-image, partnership quality and support. Retrospective Sexual Surveys were utilized to survey physiological changes as well as psychological effects. In total, 28 heterosexual couples (56 people) were enrolled. Patients were treated between February 2002 and March 2007 with a median follow-up of 26 (range: 4-59) months. When polled on psychological aspects that may have been affected by treatment, overall concordance was 75.0%. Partnership had the highest concordance (92.2%) with treatment satisfaction questions following in second (90.7%). Subcategories focused on self-image (77.5%), relationship (67.3%), support (66.4%) and emotional status (55.6%), were less concordant. Although couples report relationships as strong and team-like, misconception between partners is widespread. Further research with regards to the effect of such disparities in couples might provide additional insight into improving recovery.

Timing and patterns of recurrences and deaths from prostate cancer following adjuvant pelvic radiotherapy for pathologic stage T3/4 adenocarcinoma of the prostate.

To determine the timing and patterns of late recurrence after radical prostatectomy (RP) alone or RP plus adjuvant radiotherapy (RT). Between 1970 and 1983, 159 patients underwent RP for newly diagnosed adenocarcinoma of the prostate and were found to have positive surgical margins, extracapsular extension and/or seminal vesicle invasion. Of these, 46 received adjuvant RT and 113 did not. The RT group generally received 45-50 Gy to the whole pelvis, then a boost to the prostate bed (total dose of 55-65 Gy). In the RP group, 62% received neoadjuvant/adjuvant androgen deprivation vs 17% in the RT group. Patients were analyzed with respect to timing and patterns of failure. Only one patient was lost to follow-up. The median follow-up for surviving patients was nearly 20 years. The median time to failure in the surgery group was 7.5 vs 14.7 years in the RT group (P=0.1). Late recurrences were less common in the surgery group than the RT group (9 and 1% at 10 and 15 years, respectively vs 17 and 9%). In contrast to recurrences, nearly half of deaths from prostate cancer occurred more than 10 years after treatment. Deaths from prostate cancer represented 55% of all deaths in these patients. Recurrences beyond 10 years after RP in this group of patients were relatively uncommon. Despite its long natural history, death from prostate cancer was the most common cause of mortality in this population with locally advanced tumors, reflecting the need for more effective therapy.

Bacterial biofilms and implantable prosthetic devices.

Erectile dysfunction afflicts millions of men. A group of patients with advanced degeneration of their erectile tissue do not respond to pharmacological therapy, and surgical prosthetic reconstruction represents an attractive and highly satisfying alternative. Yet many men are unwilling to take this step due to fear of infection. Implanted prosthetic devices are at risk for infection because they provide a platform for the development of a bacterial biofilm, an organized bacterial colony that grows on the surface of the implanted material. The biofilm is resistant to all efforts to eradicate it short of removal of the foreign material. Bacteria may attach to the surface of the foreign material by surface charge attraction, hydrophilic/hydrophobic interactions, and by specific attachment by fimbrae. Growth, colonization, and maturation follow bacterial attachment. A mature biofilm is composed of three layers: a linking film binding the biofilm to the surface; a base film made up of a compact layer of bacteria; and a surface film from which free-floating bacteria can arise and spread. The majority of the surface layer is made up of exopolysaccharide matrix. Bacteria deep within the biofilm matrix live in a protected environment; diffusion of antibiotics is difficult, low oxygen tension leads to a lower bacterial metabolic rate rendering the bacteria functionally resistant to high levels of antibiotics. Effective strategies to reduce prosthetic infection levels must rely on the prevention of biofilm formation through surface modification. Possible mechanisms include the addition of antimicrobials to the surface of the device, or chemical modifications, which reduces bacterial attachment.

Vasculogenic impotence. Arterial and venous surgery.

Arterial revascularization and venous ligation procedures have been introduced within the past 2 decades. Each procedure has in common with the other the fact that initial applications of the operations were widespread among the population of men with vasculogenic erectile dysfunction. In each case, disappointing long-term results led to more limited use of surgery targeting specific groups that clearly would benefit from the procedures. The wider application of these procedures in vasculogenic erectile dysfunction is not supported by the available results. The Clinical Guidelines Panel of the American Urological Association supported this view in 1996 after a meta-analysis of literature reports and declared that venous and arterial surgery was not justified in routine use, especially in patients with arteriosclerosis. Further studies are likely to refine patient selection but are unlikely to expand the therapeutic use of these procedures.

Vascular endothelial growth factor restores corporeal smooth muscle function in vitro.

PURPOSE: The therapeutic use of vasculogenic growth factors has been successfully demonstrated in models of organ ischemia. We determined whether vascular endothelial growth factor (VEGF) would reverse corporeal smooth muscle dysfunction in the hypercholesterolemic rabbit model of erectile dysfunction. MATERIALS AND METHODS: A total of 36 New Zealand White rabbits were fed a normal (12) or 1% cholesterol (24) diet and treated after 6 weeks with 0.9 mg. VEGF or vehicle. At 6 weeks 24 rabbits received a single intracavernous dose and 12 received a single intravenous bolus of either drug. Ten days after injection corporeal smooth muscle function was analyzed after relaxation to acetylcholine and sodium nitroprusside using isometric tension studies. Corporeal sections were assessed for smooth muscle content with f-actin staining and VEGF expression by immunohistochemical study and enzyme-linked immunosorbent assay. RESULTS: Endothelium dependent (acetylcholine) and nitric oxide mediated (sodium nitroprusside) smooth muscle relaxation were impaired in cholesterol fed animals (p = 0.021 and 0.003, respectively). Intracavernous VEGF treatment restored sodium nitroprusside mediated relaxation to normal (p = 0.015) and intravenous VEGF restored acetylcholine and sodium nitroprusside mediated relaxation (p = 0.014 and 0.018, respectively). Decreased smooth muscle content was noted in cholesterol fed animals versus normal diet controls (p = 0.008), which was not affected by VEGF treatment (p = 0.450). Corporeal endothelial cell content was increased after intracavernous but not intravenous VEGF treatment (p = 0.001 and 0.385, respectively). VEGF expression was augmented after treatment with recombinant VEGF (p <0.001). CONCLUSIONS: VEGF administration variably mitigated the impairment of corporeal smooth muscle relaxation in the hypercholesterolemic rabbit model of erectile dysfunction.

Intracavernosal injections of vascular endothelial growth factor protects endothelial dependent corpora cavernosal smooth muscle relaxation in the hypercholesterolemic rabbit: a preliminary study.

Atherosclerosis is a major risk factor for erectile dysfunction, and loss of endothelium-dependent vasodilation appears early in the development of this disorder. Nitric oxide (NO) appears to be the principle mediator of erectile function and is generated in part by the sinusoidal endothelium. Vascular endothelial growth factor (VEGF) is an angiogenic growth factor and an endothelial cell-specific mitogen and the actions of VEGF are coupled to NO. In this preliminary study, we investigated whether VEGF could be used to protect endothelial dependent cavernosal relaxation from the atherosclerotic injury induced by a hypercholesterolemic diet.Two groups of New Zealand white adult male rabbits received a 1% cholesterol diet for four weeks, and two groups consumed normal rabbit chow. Half of the rabbits consuming the 1% cholesterol diet received weekly penile injections of 0.3 mg VEGF (n=8), and half injections of normal saline (n=8). Rabbits fed normal chow followed a similar protocol, half received weekly penile injections of 0.3 mg VEGF (n=6) and half were given weekly penile injections of normal saline (n=6). Isometric tension studies (with norepinephrine, acetylcholine, sodium nitroprusside and histamine) were performed on isolated strips of corpora cavernosa. The degree of corporal smooth muscle relaxation in response to ACH and SNP administration was recorded and compared. Significant elevation in serum total cholesterol levels occurred in rabbits receiving 4 weeks of the 1% cholesterol diet (727+/-75.6 mg/dl vs 38.7+/-5.53 mg/dl) P<0.01. There were no significant differences in cavernosal contraction in any group, while cavernosal smooth muscle from rabbits on normal chow retained the ability to relax in response to ACH and SNP in tissue bath. The hypercholesterolemic rabbits receiving VEGF had a significantly higher maximal per-cent relaxation to ACH (111+/-28.9) compared to the hypercholesterolemic rabbits that received NS (77+/-23.1, P<0.001). This difference in percent maximal relaxation to SNP was also present for hypercholesterolemic/VEGF rabbits (129.4+/-24) versus the hypercholesterolemic/NS rabbits (115.0+/-18, P=0.033). In conclusion, intracavernosal injections of VEGF appear to protect corporal endothelium from hypercholesterolemia induced injury, thus preserving endothelial dependent corporal smooth muscle relaxation in hypercholesterolemic rabbit.

Alternative methods for management of prostatic outflow obstruction.

During the past year no new therapies for prostatic outflow obstruction were introduced. Instead, research focused on refinement of treatments previously available. Further reports on the efficacy and safety of alpha 1-adrenergic receptor subtype selective agents have appeared. The long-term effects of finasteride on the natural history bladder outflow obstruction have become clearer. The clinical efficacy of device therapy has evolved, and information regarding intermediate-term outcomes is now available.

Alpha1-adrenergic receptor subtypes in human detrusor.

PURPOSE: To identify and quantitate alpha1-adrenergic receptor (alpha1AR) subtype expression in human detrusor. MATERIALS AND METHODS: Initial studies to determine alpha1AR expression in human detrusor were performed using saturation binding with [125I]HEAT. Once the presence of alpha1ARs was documented, subtype (alpha1a, alpha1b, alpha1d) expression at the mRNA level (and comparison with rat) was determined with RNase protection assays (human detrusor) and RT-PCR (human detrusor, rat whole bladder). Competition binding analysis with the alpha1dAR-selective ligand BMY7378 was used to measure alpha1AR subtype expression at a protein level in human detrusor. RESULTS: Alpha1AR expression in human detrusor was low but reproducible (6.3 +/- 1.0 fmol./mg. total protein). RNase protection assays performed on total RNA extracted from human detrusor revealed the following alpha1AR subtype expression: alpha1d (66%) > alpha1a (34%), and no alpha1b. RT-PCR confirmed alpha1AR subtype mRNA distribution in human detrusor with alpha1d (approximately 60-70%) > alpha1a (approximately 30-40%), and a lack of alpha1b mRNA. Rat whole bladder expressed different alpha1AR subtype mRNA than human detrusor, with alpha1a approximately alpha1b approximately alpha1d. The presence of alpha1d > alpha1a expression in human detrusor was confirmed at a protein level by competition analysis utilizing BMY7378 which revealed a two-site fit, with Ki and high affinity binding (66%) consistent with the alpha1dAR subtype. CONCLUSIONS: Human detrusor contained two alpha1AR subtypes (alpha1d > alpha1a), a finding that is different from rat, another commonly used animal model. Since non-subtype selective alpha1AR antagonists ameliorate irritative bladder symptoms (in men and women with/without outlet obstruction), and Rec 15/2739 (alpha1a selective antagonist) does not improve symptom scores in BPH, our findings suggest bladder alpha1dARs may provide a potentially novel mechanism underlying these therapeutic benefits.

Management of the buried penis in adults.

PURPOSE: Buried penis, most commonly seen in children, is particularly debilitating in adults, resulting in the inability to void standing and it affects vaginal penetration. The pathophysiology, including scar contracture of the distal soft tissue and skin envelope with concurrent descent of the abdominal fat pad, represents a surgical challenge. We developed a management algorithm to evaluate and treat adults with buried penis. MATERIALS AND METHODS: From January 1, 1994 to May 1, 1996, 7 patients 23 to 66 years old presented with buried penis. Diabetes mellitus, a common co-morbid condition, was present in 5 patients, and 5 of 7 were morbidly obese. RESULTS: Surgical correction was performed in 5 patients with excellent results in 3. Resection of scar contracture was sufficient to provide adequate length and none required release of the suspensory ligament. Panniculectomy was performed in 1 patient. One man requiring a graft to achieve adequate penile coverage required reoperation. This patient had undergone a previous attempted repair with extensive contracture. All patients regained potency postoperatively. CONCLUSIONS: With appropriate planning and adherence to basic reconstructive surgical principles, correction of the buried penis can yield a high success rate.

Pharmacology of tamsulosin: saturation-binding isotherms and competition analysis using cloned alpha 1-adrenergic receptor subtypes.

BACKGROUND: alpha 1-adrenergic receptors (alpha 1 ARs) are important in the dynamic component of benign prostatic hyperplasia (BPH). Currently, several alpha 1AR antagonists are being used in the treatment of BPH. METHODS: In order to more fully characterize the pharmacology of the alpha 1AR antagonist tamsulosin, we utilized saturation-binding isotherms with [3H] tamsulosin to determine the Kd of this compound at all three cloned alpha 1AR subtypes stably expressed in rat-1 fibroblasts. To confirm these results, we performed competition binding experiments, displacing [125I]HEAT with increasing concentrations of alfuzosin, doxazosin, 5-methyl-urapidil, prazosin, tamsulosin, terazosin, and (+)YM617 (stereoisomer of tamsulosin) in the same clonal cell lines. RESULTS: [3H]tamsulosin binds to cloned alpha 1AR subtypes with a rank order of affinity of alpha 1a = alpha 1d > alpha 1b. Competition experiments confirmed the relative nonselectivity of alfuzosin, doxazosin, and prazosin, but revealed slight alpha 1b = alpha 1d > alpha 1a selectivity for terazosin, and clear alpha 1a = alpha 1d > alpha 1b for (+)YM617 and tamsulosin([-]YM617); alpha 1a > alpha 1d > alpha 1b selectivity for 5-methyl-urapidil was confirmed. CONCLUSIONS: We conclude that tamsulosin displays selectivity for alpha 1a and alpha 1d ARs. This selectivity may contribute to the tamsulosin efficacy reported in several recent clinical studies in patients with BPH.

Effects of androgen deprivation on prostate alpha 1-adrenergic receptors.

OBJECTIVES: Benign prostatic hyperplasia (BPH), the most common benign tumor in men, consists of two components-static (enlargement regulated by androgens) and dynamic (smooth muscle contraction through alpha 1-adrenergic receptors [alpha 1-ARs]). Because medical therapy of BPH involves tissue androgen deprivation, we studied the influence of androgen deprivation and replacement on regulation of rat ventral prostate alpha 1-ARs. METHODS: Prostate weight, alpha 1-AR density, autoradiographic images, histologic features, and cell-specific protein were examined before and after castration and androgen replacement. RESULTS: Castration decreases ventral prostate wet weight, a process reversed by testosterone administration. In contrast, there is an apparent increase in alpha 1-AR density (29 +/- 4 versus 65 +/- 6 fmol/mg total protein, mean +/- SEM) after castration, returning to baseline with testosterone replacement; alpha 1-AR density remains constant in control liver membranes. Alpha 1-ARs predominate in stroma throughout androgen deprivation therapy. Epithelially derived cells decrease (83% to 67%) after castration, resulting in a relative doubling in stroma (17% to 33%); the protein content of epithelial and stromal cells remains identical. Therefore, prostate-specific increases in alpha 1-ARs appear to result from relative increases in the ratio of smooth muscle to epithelium after castration rather than from direct upregulation of alpha 1-AR protein. CONCLUSIONS: Because alpha 1-AR density does not decrease with androgen deprivation, these studies suggest that alpha 1-AR antagonists remain an important component in BPH therapy, even when 5-alpha-reductase inhibitors are utilized.

Minimally invasive therapies in the treatment of erectile dysfunction in anticoagulated cases: a study of satisfaction and safety.

PURPOSE: We evaluated patient satisfaction with and the safety of vacuum therapy and self-injection during warfarin treatment of impotent men. MATERIALS AND METHODS: In a 24-week prospective study 33 patients were assigned to vacuum therapy or intracavernous injections with crossover at 12 weeks. Patients maintained diaries, and were followed with physical examinations, coagulation studies and questionnaires. RESULTS: Of the 33 patients 26 completed the study with 706 vacuum applications (mean 1.9 weekly) and 605 injections (mean 1.6 weekly). There are 11 acute minor complications with vacuum therapy (petechiae that resolved spontaneously) and no chronic complications. Only quality of climax was diminished with vacuum therapy. Self-injection resulted in acute minor complications (3 ecchymoses and 1 prolonged erection requiring intervention) and 1 chronic complication (corporeal fibrosis with mild curvature). CONCLUSIONS: The adverse effects of vacuum therapy and intracavernous self-injection in patients on warfarin do not exceed the rate in the general urological population. These therapies appear to be safe in patients receiving warfarin.

The effect of intracavernous injection of potassium channel openers in monkeys and dogs.

Cavernous smooth muscle relaxation is effected through a complex biochemical pathway; therefore, a defect in any step of this pathway may result in erectile dysfunction. Administration of pharmacologic agents which cause relaxation of the cavernous smooth muscle through a different mechanism may serve as an effective therapeutic alternative for impotent patients. To test this hypothesis two potassium channel openers, pinacidil and cromakalim, were used to initiate and maintain cavernous smooth muscle relaxation. The drugs were given as intracavernous injections in two animal models. In 10 dogs pinacidil and cromakalim produced full erection. With pinacidil (10(-2) M), the mean intracavernous pressure increased from a baseline pressure of 32.6 +/- 3.43 cm H2O to a peak intracavernous pressure of 131.8 +/- 12.01 cm H2O, and remained elevated for a period of 17.8 +/- 9.4 min. With cromakalim (10(-2) M) intracavernous pressure rose from a baseline pressure of 32 +/- 2.55 cm H2O to a peak intracavernous pressure of 140 +/- 3.39 cm H2O, for a period of 19.4 +/- 0.89 min. Additionally, in 5 primates injected with cromakalim (10(-2) M) intracavernous pressure rose from 24 +/- 3.81 to 131.2 +/- 7.56 cm H2O, for 27.0 +/- 4.79 min. It is concluded that both pinacidil and cromakalim can initiate and maintain erection in dogs and that cromakalim produces a similar erectile response in monkeys. Further study of the local and systemic effects of chronic injection is needed to determine whether this class of pharmacologic agents can provide therapy for impotent patients.

Sodium nitroprusside: physiologic effects as a nitric oxide donor in three species.

Recent in vitro and in vivo studies have suggested that nitric oxide may be the neurotransmitter responsible for cavernous smooth muscle relaxation and penile erection. Sodium nitroprusside, after combining with different kinds of thiols in the cellular cytoplasm, can effect nitric oxide release. We undertook this study to determine the physiologic response to sodium nitroprusside injection when used to induce and maintain penile erection in three species. Sodium nitroprusside was injected in increasing concentrations into the cavernous tissue of rats, dogs and monkeys. Dosages injected were 10(-4) M, 10(-3) M and 10(-2) M in 10 rats; 10(-4) and 10(-3) M in five dogs and five monkeys. The volume of drug injected was 0.05 ml for the rats and 0.5 ml for dogs and monkeys. The results show a dose-dependent erectile response to sodium nitroprusside injection (mean intracavernous pressure increase of 102.4 cm H2O in dogs, and 98.4 cm H2O in monkeys after injection of 10(-3) M nitroprusside). However, only a slight increase in intracavernous pressure (mean increase 28.4 cm H2O after injection of 10(-2) M of sodium nitroprusside) was noted in rats. The drop in blood pressure was > 15 mmHg in dogs and monkeys, while in rats it varied according to the dose studied. Sodium nitroprusside induced excellent erections in dogs and monkeys with minimal alteration in blood pressure. However, administration in rats resulted in hypotension. Nitroprusside may not be an acceptable nitric oxide donor for the treatment of male erectile dysfunction.

Effect of terfenadine on urination.

Anticholinergic side effects of commonly used antihistamines are known to aggravate voiding difficulties in older men with benign prostatic hypertrophy. Newer antihistamines, such as terfenadine (Seldane), with less anticholinergic side effects may not have such an effect on voiding. We performed a randomized, double-blind, placebo-controlled, crossover study in eight normal male volunteers (phase I) and in 11 patients with documented benign prostatic hypertrophy (phase II) to study the effect of terfenadine on voiding. Subjects received either 60 mg of terfenadine or an identical placebo twice daily for 1 week each. After a 1-week washout period, they were crossed over to receive the other drug. Evaluation took place on days 0, 7, 14, and 21. Prick skin testing was performed with serial threefold dilutions of histamine to assess efficacy and degree of compliance. Uroflowmetry and urinary symptom assessment were also done. In phase I, after 1 week of terfenadine, mean skin test suppression was 83.8% compared with -0.5% with placebo (P < .01). Urinary peak flow increased 10.4% on terfenadine and 9.7% on placebo (P = NS). In phase II, the mean prick skin test suppression was 87.8% compared with 12.0% for placebo (P < .002). Urinary peak flow was decreased 0.1% from baseline on terfenadine and increased by 18.7% for placebo (P = NS). None of the subjects noted alterations in voiding symptom scores. We conclude that the commonly recommended dose of terfenadine does not significantly alter voiding characteristics in normal men or in patients with documented benign prostatic hypertrophy.

Intracellular mechanism of penile erection in monkeys.

To elucidate the sequence of events between the release of neurotransmitters and cavernous smooth muscle relaxation in erection, we studied the role of the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) systems. In a well-established simian model, the effects of specific agonists and antagonists of the intracellular sequence for smooth muscle relaxation and potassium channel openers on the intracavernous pressure were examined. Sodium nitroprusside (10(-3) M), a nitric oxide releaser and thus a stimulant of the cGMP system, caused an increase in the intracavernous pressure from 82 to 115 cm H2O for 7 to 19 min and penile diameter from 24.8 +/- 2.28 to 43 +/- 4.87 mm. When nitroprusside was injected after methylene blue (10(-3) M), a specific antagonist of the enzyme guanylate cyclase, intracavernous pressure rise decreased significantly, but cromakalin, a potassium channel opener, provoked excellent increases after the block. A smaller dose of sodium nitroprusside (10(-4) M) caused an increase in intracavernous pressure from 35 to 85 cm H2O for 7 to 11.5 min. When nitroprusside was injected after zaprinast, a phosphodiesterase inhibitor, the increase in pressure ranged from 80 to 116 cm H2O for 15 to 30 min. Prostaglandin E1, an activator of the cAMP system, caused an increase in the intracavernous pressure of 20-80 cm H2O for 5 to 10 min, and an increase in penile diameter from 25 +/- 2.22 to 35 +/- 3.48 mm. The erectile response to PGE1, but not to cromakalin, was nearly abolished by ethylmaleimide, an adenylate cyclase blocker. The response to nitroprusside was significantly greater (P < 0.05) than to PGE1. Both systems, cAMP and cGMP, may be involved in cavernous smooth muscle relaxation, and cGMP is probably the predominant intracellular second messenger in penile erection in monkeys. Stimulants of the cGMP system, such as nitric oxide releasers, could represent a more physiological and effective approach in the treatment of erectile dysfunction.