A nitric oxide-like factor mediates nonadrenergic-noncholinergic neurogenic relaxation of penile corpus cavernosum smooth muscle.

This study was initiated to characterize nonadrenergic-noncholinergic (NANC) inhibitory neurotransmission in penile corpus cavernosum. Using organ baths, isometric tension measurements were made in strips of human and rabbit corpus cavernosum. In examining endothelium-mediated responses, cumulative additions of exogenous acetylcholine elicited dose-dependent relaxations which were significantly reduced or completely inhibited in tissues treated with NG-monomethyl L-arginine (L-NMMA; an inhibitor of nitric oxide synthesis), oxyhemoglobin (a nitric oxide scavenger), or methylene blue (a guanylate cyclase blocker). Tissues exposed to hypoxic conditions (PO2 = 5-10 mmHg) also did not respond to exogenous acetylcholine. Mechanical removal of the endothelium in human corporal strips or in situ treatment of rabbit corpora with detergent blocked the relaxation to acetylcholine. Transmural electrical stimulation of corporal tissue strips denuded of functional endothelium, in the presence of adrenergic blockade with bretylium and muscarinic receptor blockade with atropine, caused frequency-dependent relaxation. This neurogenic relaxation was reduced or prevented by L-NMMA, oxyhemoglobin, methylene blue, and hypoxia. The effects of L-NMMA were reversed by L-arginine and the effects of hypoxia were readily reversed by normoxic conditions. Authentic, exogenous nitric oxide relaxed corporal strips which were contracted with adrenergic agonists and this effect was significantly inhibited by oxyhemoglobin. It is concluded that (a) endothelium-mediated responses of corpus cavernosum smooth muscle are mediated by a diffusible nitric oxide-like substance; (b) NANC neurogenic inhibitory responses do not require functional endothelium, and (c) nitric oxide, or a closely related substance, may act as an inhibitory neurotransmitter in penile corpus cavernosum smooth muscle.

Oxygen tension regulates the nitric oxide pathway. Physiological role in penile erection.

Relaxation of the trabecular smooth muscle of the corpus cavernosum (the erectile tissue) of the penis is mediated by nitric oxide released by the nerves and endothelium. We have investigated the physiological role of oxygen tension in the regulation of trabecular smooth muscle tone. In human subjects, measurement of intracavernosal PO2 in blood drawn from corpus cavernosum in the flaccid state was comparable to that of venous blood (25-43 mmHg). Vasodilatation of the resistance arteries and trabecular smooth muscle relaxation by intracavernosal injection of papaverine and phentolamine caused oxygen tension to rise rapidly to arterial levels (PO2 approximately 100 mmHg). Isolated human and rabbit corpus cavernosum tissue strips in organ baths, exposed to arterial-like PO2 relaxed to the endothelium-dependent dilator acetylcholine and to electrical stimulation of the autonomic dilator nerves. These nitric oxide-mediated responses were progressively inhibited as a function of decreasing PO2 to levels measured in the flaccid penis. Reverting to normoxic conditions readily restored endothelium-dependent and neurogenic relaxation. Relaxation to exogenous nitric oxide was not impaired in low PO2. In rabbit corpus cavernosum, low PO2 reduced basal levels of cGMP and prevented cGMP accumulation induced by stimulation of dilator nerves. Furthermore, low PO2 inhibited nitric oxide synthase activity in corpus cavernosum cytosol. It is concluded that physiological concentrations of oxygen modulate penile erection by regulating nitric oxide synthesis in corpus cavernosum tissue.

Possible role of Na(+)-K(+)-ATPase in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide.

1. This study was designed to determine the role of sodium-potassium adenosine triphosphatase (Na(+)-K(+)-ATPase) in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide (NO). In addition, we determined if the modulation of Na(+)-K(+)-ATPase activity by NO is dependent on the increase in intracellular cyclic GMP concentration. 2. The effect of NO donors, sodium-nitroprusside (SNP) and S-nitroso-glutathione (S-NO-Glu), and a permeable cyclic GMP analogue, 8-bromo-cyclic GMP, on Na(+)-K(+)-ATPase activity (measured as ouabain-sensitive 86Rb-uptake) was studied in human cultured corpus cavernosum smooth muscle cells (HCCSMC). In addition, the effect of the cyclic GMP lowering agent, methylene blue, on NO-induced increase in Na(+)-K(+)-ATPase activity was studied. 3. SNP (1 microM) caused time-dependent increases in ouabain-sensitive Rb-uptake (33-72%) over 2-20 min in HCCSMC. The stimulation of ouabain-sensitive Rb-uptake by SNP was concentration-dependent (30 and 102% with 0.1 and 1 microM SNP, respectively). Similarly, significant increases in ouabain-sensitive Rb-uptake were obtained with 1 and 10 microM S-NO-Glu. In contrast, incubation of HCCSMC with 8-bromo-cyclic GMP (100 microM) did not increase ouabain-sensitive Rb-uptake. 4. S-NO-Glu induced-increase in intracellular cyclic GMP synthesis, but not the increase in ouabain-sensitive Rb-uptake, was completely inhibited by methylene blue in HCCSMC. 5. The Na(+)-K(+)-ATPase inhibitor, ouabain, caused a concentration-dependent increase in tension (0.5 to 2 fold) in tissues contracted with 15 mM KCl. SNP and S-NO-Glu caused a concentration-dependent relaxation (concentration required to cause half maximal relaxation (ED50) = 0.04 and 0.2 microM, respectively) of HCC strips contracted with 15 mM K+. Ouabain (0.1 to 10 microM) inhibited the response to SNP and S-NO-Glu by shifting the concentration-response curves to the right and preventing full smooth muscle relaxation.6. These results indicate that the activity of Na+-K+-ATPase modulates the contractility of HCC smooth muscle, and that NO stimulates Na+-K+-ATPase activity in HCCSMC independently of its ability to increase the intracellular cyclic GMP concentration. They also suggest that stimulation of Na+-K+-ATPase activity plays an important role in NO-induced relaxation of HCC smooth muscle

Differential effects of serotonin reuptake inhibitors on erectile responses, NO-production, and neuronal NO synthase expression in rat corpus cavernosum tissue.

Increased incidence of impotence is associated with some selective serotonin-reuptake-inhibitors (SSRIs), but the pathophysiological mechanism is unknown. Paroxetine and citalopram are extensively used SSRIs, but only paroxetine has been shown to inhibit nitric oxide synthase (NOS) activity. NO is a key mediator of penile erection. Thus, the aim of this study was to determine the effects of paroxetine and citalopram on erectile function and NO production, in a rat model. Application of cavernosal nerve electrical stimulation produced frequency-related intracavernosal pressure (ICP) increases, which were inhibited by the NOS inhibitor, N(G)-nitro-L-arginine (0.3 mg x kg(-1)). Acute or chronic (2 weeks) paroxetine-treatment (10 mg x kg(-1)) reduced ICP-responses, while citalopram did not. Paroxetine, but not citalopram, significantly reduced nitrite+nitrate plasma levels by 61.4% and inhibited penile neuronal NOS (nNOS) protein expression by 31.2% after chronic treatment. The results show that paroxetine inhibits erectile responses in rats. We propose that this effect is due to reduced NO production and nNOS expression.

Functional and radiologic evidence of vascular communication between the spongiosal and cavernosal compartments of the penis.

OBJECTIVES: To investigate the possible communication of the glans penis and corpus spongiosum with the corpora cavernosa. METHODS: We performed a functional and anatomic study in men with erectile dysfunction. The functional study consisted of the injection of alprostadil (10 to 20 micrograms) into the glans in 17 men while recording intracavernosal pressure (ICP). Once the ICP response had stabilized, patients received a second injection of alprostadil by direct intracavernosal (IC) administration. For the anatomic study, a spongiogram was performed in 5 patients by the injection of radiologic contrast into the glans. RESULTS: Injection of alprostadil into the glans caused tumescence of the glans and corpus spongiosum, followed by tumescence of the corpora cavernosa with an increase in ICP from 9 +/- 2 mm Hg (mean +/- SD) at baseline to a peak response of 50 +/- 25 mm Hg. Subsequent IC injection of alprostadil, on average, increased ICP by only 5 mm Hg (a 15% increase) above the response to injection in the glans. The spongiogram demonstrated drainage of the glans into the deep dorsal vein, as well as drainage of the spongiosum into the circumflex veins, which in turn drained into the deep dorsal vein. Filling of the corpora was also visualized, suggesting that it occurred in a retrograde manner, through the draining venules. CONCLUSIONS: Our study demonstrates that injection of alprostadil into the spongy tissue of the glans can provoke erection of the corpora cavernosa, and that common channels for the drainage of the glans, corpus spongiosum, and corpora cavernosa are most likely the route for drug transfer from the spongiosal to the cavernosal compartment.

Molecular mechanisms for the regulation of penile smooth muscle contractility.

Relaxation of smooth muscle is viewed as a 'resetting' of contractile machinery and the resumption of a pre-contractile state is accomplished by lowering cytosolic Ca(2+) and/or by decreasing the sensitivity of the contractile machinery to Ca(2+). There are several mechanisms whereby cytosolic Ca(2+) can be reduced and relaxation achieved but, in general, all pathways depend upon the accumulation of cyclic nucleotides cAMP and cGMP or on the activation of K(+) channels resulting in hyperpolarization. Recently, activation of Na(+)/K(+) ATPase by nitric oxide has been shown to be involved in the relaxation of trabecular smooth muscle. Since Na(+)/K(+) ATPase is electrogenic, its stimulation would cause hyperpolarization and, in turn, would prevent the opening of voltage-dependent Ca(2+) channels. This manuscript briefly reviews the molecular mechanisms affected by muscle relaxants and vasodilators in the treatment of erectile dysfunction. International Journal of Impotence Research (2000) 12, Suppl 4, S34-S38.

Molecular mechanisms for the regulation of penile smooth muscle contractility.

Relaxation of penile smooth muscle (arterial and trabecular) initiates and maintains penile erection. Relaxation of smooth muscle is viewed as a 'resetting' of contractile machinery by resumption of a precontractile state accomplished by lowering cytosolic Ca(+2) and/or by a decrease in sensitivity of the contractile machinery to Ca(+2). There are various mechanisms whereby cytosolic Ca(+2) can be reduced and relaxation achieved, but in general, all pathways depend on the accumulation of the nucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) or activation of K channels with hyperpolarization. Another mechanism, activation of Na(+)/K(+) adenosine triphosphatase (ATPase) by nitric oxide, has been shown to be involved in relaxation of trabecular smooth muscle. Since Na(+)/K(+) ATPase is electrogenic, its stimulation would cause hyperpolarization. Hyperpolarization will prevent the opening of voltage-dependent calcium channels. Guanylate cyclase, which catalyzes the conversion of guanosine triphosphate to cGMP, is activated by nitric oxide. cGMP activates protein kinase G, which through multiple phosphorylations facilitates calcium sequestration and reduces the entry of calcium into the cell. Other muscle relaxants act by way of a cAMP-dependent mechanism such as prostaglandin E, vasoactive intestinal polypeptide, and catecholamines (via beta-receptors). These substances react with membrane receptors coupled to a GS-type protein that stimulates adenylate cyclase, which catalyzes the accumulation of cAMP. DOI: 10.1038/sj/ijir/3900790

Vardenafil reverses erectile dysfunction induced by paroxetine in rats.

Selective serotonin reuptake inhibitors (SSRIs) are associated with a high incidence of impotence. Paroxetine is an extensively used SSRI that has been shown to impair erectile function in patients, to induce erectile dysfunction and to inhibit nitric oxide synthase (NOS) activity and NO production in animal models. NO is a key mediator of penile erection. Vardenafil is a type 5 phosphodiesterase inhibitor that potentiates NO-mediated responses in isolated trabecular smooth muscle and penile erection in men in clinical trials. The aim of this study was to evaluate the effects of vardenafil on the impairment of erectile responses produced by paroxetine in the rat model. Application of cavernosal nerve electrical stimulation (CNES) produced frequency-related intracavernosal pressure (ICP) increases, which were inhibited by the NOS inhibitor N(G)-nitro-L-arginine (0.3 mg/kg) and potentiated by vardenafil (0.3 mg/kg). Acute paroxetine treatment (10 mg/kg) significantly reduced ICP-responses to CNES. This inhibition was completely reversed by vardenafil (0.3 mg/kg) administration. The results show that the erectile dysfunction induced by paroxetine in rats can be effectively treated with vardenafil, suggesting that the use of this compound could be a reasonable therapeutic approach to treating erectile dysfunction associated with SSRI administration.

Vardenafil enhances clitoral and vaginal blood flow responses to pelvic nerve stimulation in female dogs.

The relaxation of the smooth muscle in the vagina and clitoris and the increase of blood flow into these organs is thought to be essential in the female sexual response. Vardenafil is a type 5 phosphodiesterase (PDE5) inhibitor that potentiates the nitric oxide (NO)/cGMP pathway facilitating penile smooth muscle relaxation and improving penile erection in men. Although the potentiation of the NO/cGMP pathway through PDE5 inhibitors can clearly enhance blood flow into the penis and is used in the therapy of male sexual dysfunction, there is controversy about the efficacy of these agents in improving female sexual function. The aim of this work was to evaluate the effects of vardenafil on the increase of blood flow into the vagina and clitoris induced by pelvic nerve electrical stimulation (PNES) in a female dog model. Application of PNES produced consistent and frequency-related increased blood flow into the vagina and clitoris of anesthetized female dogs. The magnitude and duration of the blood flow responses to PNES were variable among the different animals but remained stable over time within the same animal. The intravenous administration of vardenafil (1 mg/kg) significantly potentiated the increases in blood flow produced by PNES into the vagina (381.4 and 206.2% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) and clitoris (379.4 and 238.5% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) 20 min after administration. The significant enhancement of PNES-induced responses was maintained 50 min (224.5 and 181.0%, P<0.01 in vagina; 294.8 and 258.9%, P<0.05 in clitoris) and 80 min after vardenafil administration (209.5 and 156.9%, P<0.05 in vagina; 268.9 and 194.9%, P<0.05 in clitoris). Here we present a feasible model for research into female sexual function. Our results show that vardenafil effectively potentiates the blood flow responses to PNES in the genitalia of female dogs. These results emphasize the role of the NO/cGMP pathway in the local vasodilatory response in female sexual organs and provide a rationale for testing PDE5 inhibitors, such as vardenafil, as a treatment for certain forms of female sexual dysfunction.

Enhanced contractility of rabbit corpus cavernosum smooth muscle by oxidized low density lipoproteins.

We have investigated the effect of oxidatively-modified low density lipoproteins (ox-LDL) on the contractility of rabbit trabecular smooth muscle. Low density lipoproteins (LDL) were isolated from fresh human plasma pooled from multiple donors and oxidized by exposure to copper. Corpus cavernosum strips from New Zealand White rabbits were studied in organ chambers for isometric tension measurement. Corporeal strips in which moderate tone was induced by phenylephrine, contracted when exposed to ox-LDL, but not when exposed to either native LDL (nLDL) or LDL protected from oxidation by butylated hydroxytoleune (BHT-LDL). Removal of the endothelium, or treatment of the corporeal strips with N(omega)-nitro-L-arginine (nitric oxide synthase inhibitor), methylene blue of LY83583 (guanylate cyclase inhibitors/superoxide producing agents), did not prevent ox-LDL-induced contraction. ox-LDL, dose-dependently, enhanced the contractile response of corporeal strips to low and moderate concentrations by phenylephrine. nLDL had no significant effect on phenylephrine-induced contraction of corporeal strips. ox-LDL, nLDL or BHT-LDL had no effect on relaxation induced by the endothelium-dependent dilator, acetylcholine, or the nitric oxide donor, nitroprusside. In conclusion, this present study demonstrates significant pro-contractile effects of ox-LDL on corporeal smooth muscle, this effect is independent of the endothelium or the nitric oxide/cGMP pathway. The pro-contractile effect of ox-LDL may interfere with penile smooth muscle relaxation, necessary for the initiation and maintenance of penile erection.

Regulation of pre-synaptic alpha adrenergic activity in the corpus cavernosum.

The neurotransmitters and vasoactive substances regulating tone in the smooth muscle of the penile arteries/arterioles and the trabeculae of the corpora cavernosa are critical mediators of the state of penile erection. Contemporary research reveals a coordinated, intricate interplay between the pathways of vasorelaxation and vasoconstriction representing a most efficient physiological mechanism to initiate and maintain penile erection. This paper will focus on the role of the adrenergic constrictor pathways in penile erection and, more specifically, on the pre-junctional adrenergic mechanisms that regulate smooth muscle constriction. All neurogenic constrictor responses are related to the release of norepinephrine from adrenergic nerves that act on post-junctional alpha-1 and pre-junctional and post-junctional alpha-2 receptor subtypes. Based on the current state of knowledge, there are at least three pre-junctional mechanisms regulating penile smooth muscle tone. First, norepinephrine release from the adrenergic nerves binds to the pre-junctional alpha-2 adrenoceptor on the adrenergic nerves and negatively regulates norepinephrine release. Blockade of this reaction by selective alpha-2 receptor antagonists (e.g. yohimbine or delequamine) will enhance norepinephrine release. Second, norepinephrine release from the adrenergic nerves binds to the pre-junctional alpha-2 adrenoceptor on the non-adrenergic, non-cholinergic (NANC) nerves and inhibits nitric oxide synthesis and release. Blockade of this reaction by selective alpha-2 receptor antagonists (e.g. yohimbine or delequamine) will enhance nitric oxide release, facilitating erection. Finally, cholinergic nerves pre-junctionally inhibit norepinephrine release from the adrenergic nerve and stimulate the NANC nerve to increase nitric oxide synthesis and release. These observations indicate that different neurotransmitters regulate the adrenergic neurotransmission pathway. Based on the above concepts for pre-junctional and post-junctional regulation of smooth muscle tone, the most efficacious strategy to reduce adrenergic activity and facilitate penile erection is to combine alpha-1 and alpha-2 adrenergic receptor antagonists. In this case, any enhancement of norepinephrine release is of little importance because the alpha-1 receptor antagonist will impede this vasoconstrictor response. This will also enhance the release of nitric oxide, which increases smooth muscle relaxation and decreases contraction resulting in penile erection.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part III--Clinical considerations of penile hemodynamic and rigidity erectile responses.

PURPOSE: The extent to which hemodynamic erectile responses predict penile buckling forces has not previously been analytically investigated. An engineering study was performed to compare hemodynamic data with penile buckling force values. METHODS: Dynamic infusion pharmacocavernosometry studies in 21 impotent patients (age 43, range 24-62 y) were accomplished to obtain information during penile erection concerning hemodynamic values, penile buckling forces and their determinants: intracavernosal pressure, erectile tissue mechanical properties and penile geometry. RESULTS: In the 21 patients, discrepancies existed in several patients who demonstrated normal hemodynamic values (low flow-to-maintain and high equilibrium intracavernosal pressures) but elevated cavernosal compliance values and diminished penile buckling forces. There was poor correlation between cavernosal compliance and equilibrium intracavernosal pressure (r = -0.36); better correlation between compliance and expandability (r = -0.72) and best correlation between dimensionless compliance and the dimensionless product of expandability with equilibrium pressure (r = -0.88). These data implied that cavernosal compliance was dependent on multiple factors, not only equilibrium intracavernosal pressure. CONCLUSIONS: Hemodynamic indices which correlate with intracavernosal pressure alone do not predict penile buckling forces since the latter are dependent not only on intracavernosal pressure but also on penile geometry and erectile tissue properties. The most relevant tissue property in predicting adequate penile buckling forces is cavernosal expandability. A new impotence classification system and diagnostic algorithm based on the determinants of penile rigidity and not exclusively on hemodynamic responses in proposed.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part I--Clinical implications of penile tissue mechanical properties.

PURPOSE: The least investigated physical determinant of penile rigidity has been penile tissue material properties. The goals in this study (Part I) were to define two penile mechanical parameters, cavernosal expandability X and tunical distensibility VE/VF, determine their magnitudes in humans and develop an analytical expression for penile volume as a function of these two tissue characteristics and intracavernosal pressure. METHODS: Dynamic infusion pharmacocavernosometry was performed in 21 impotent patients (age 43 +/- 19 y) to provide human geometric, hemodynamic and structural data. A mathematically derived model of hemodynamic and structural-dynamic characteristics of penile erection was developed (Parts I, II, III) incorporating penile tissue mechanical qualities. RESULTS: Cavernosal expandability X provided a measure of the ability to approach maximum volume at relatively low intracavernosal pressures. Tunical distensibility VE/VF denoted the maximal erect to flaccid penile volume ratio. The magnitudes of X and VE/VF in the study population were 0.04-0.17 mmHg-1 and 1.7-5.0 respectively. CONCLUSIONS: Enabling penile volume to be derived as a function of tissue mechanical characteristics and pressure, allows for penile rigidity to be expressed (in Part II) as a function of pressure, geometry and tissue qualities.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part II--Clinical implications of penile buckling.

PURPOSE: Penile buckling force was analytically described in terms of its constituents. In addition, theoretically-derived buckling force data were compared to clinically measured data and the influence of each constituent on penile buckling force data was assessed. METHODS: Using engineering buckling theory for a column, a mathematically-derived penile buckling model was developed which incorporated geometric and hemodynamic data obtained by dynamic infusion pharmacocavernosometry studies in 21 impotent patients (age 43, range 24-62 y) as well as penile tissue mechanical characteristics previously developed (Part I). RESULTS: In 17 of 21 patients the mean difference between theoretically derived and clinically measured buckling force data was 0.33 +/- 0.25 kg (r = 0.96). Factors which increased penile buckling forces were: (1) high intracavernosal pressure values (rigidity was related to pressure in an exponential-like fashion); (2) high penile aspect ratio (D/L) values (relatively large diameter/short length penile geometry) and high flaccid diameter; and (3) high cavernosal expandability values (a measure of the ability of the corpora to approach its erect volume with relatively low intracavernosal pressures). CONCLUSIONS: Pressure-volume data (pressure, geometry and tissue characteristics) obtained during erectile function testing have been shown, for the first time, to theoretically predict the magnitude of clinically-measured penile buckling forces.

The phosphodiesterase inhibitory selectivity and the in vitro and in vivo potency of the new PDE5 inhibitor vardenafil.

We investigated the potency and the selectivity profile of vardenafil on phosphodiesterase (PDEs) enzymes, its ability to modify cGMP metabolism and cause relaxation of penile smooth muscle and its effect on erections in vivo under conditions of exogenous nitric oxide (NO) stimulation. PDE isozymes were extracted and purified from human platelets (PDE5) or bovine sources (PDEs 1, 2, 3, 4 and 6). The inhibition of these PDEs and of human recombinant PDEs by vardenafil was determined. The ability to potentiate NO-mediated relaxation and influence cGMP levels in human corpus cavernosum strips was measured in vitro, and erection-inducing activity was demonstrated in conscious rabbits after oral administration together with intravenous doses of sodium nitroprusside (SNP). The effects of vardenafil were compared with those of the well-recognized PDE5 inhibitor, sildenafil (values for sildenafil in brackets). Vardenafil specifically inhibited the hydrolysis of cGMP by PDE5 with an IC50 of 0.7 nM (6.6 nM). In contrast, the IC50 of vardenafil for PDE1 was 180 nM; for PDE6, 11 nM; for PDE2, PDE3 and PDE4, more than 1000 nM. Relative to PDE5, the ratios of the IC50 for PDE1 were 257 (60), for PDE6 16 (7.4). Vardenafil significantly enhanced the SNP-induced relaxation of human trabecular smooth muscle at 3 nM (10 nM). Vardenafil also significantly potentiated both ACh-induced and transmural electrical stimulation-induced relaxation of trabecular smooth muscle. The minimum concentration of vardenafil that significantly potentiated SNP-induced cGMP accumulation was 3 nM (30 nM). In vivo studies in rabbits showed that orally administered vardenafil dose-dependently potentiated erectile responses to intravenously administered SNP. The minimal effective dose that significantly potentiated erection was 0.1 mg/kg (1 mg/kg). The selectivity for PDE5, the potentiation of NO-induced relaxation and cGMP accumulation in human trabecular smooth muscle and the ability to enhance NO-induced erection in vivo indicate that vardenafil has the appropriate properties to be a potential compound for the treatment of erectile dysfunction. Vardenafil was more potent and selective than sildenafil on its inhibitory activity on PDE5.

Analgesic effects of fibroblast growth factor in the rat.

Intraperitoneal (i.p.) injection of acidic fibroblast growth factor (aFGF) to Sprague-Dawley rats induced short-lasting analgesia as measured by tail-flick latency (TFL) test. The maximum effect, a 26% increase in tail-flick latency, was obtained 15 min following 1 microgram i.p. aFGF. By 30 min the effect was considerably reduced, and was no longer present by 45 min after treatment. Administration of heat-inactivated aFGF or a hybrid form of aFGF (CLYT/aFGF) that, although active, is unable to cross the blood-brain barrier (BBB), caused no analgesia. Furthermore, the analgesic effects of aFGF were prevented by pretreatment with the nitric oxide synthase inhibitor, L-NG-nitroarginine methyl ester (L-NAME). Our findings demonstrate an analgesic effect of FGF, which requires crossing of BBB and implicates the nitric oxide pathway.

Diabetic penile neuropathy.

In vitro studies strongly suggest the presence of autonomic neuropathy in impotent patients with diabetes mellitus. Morphologic studies reveal structural damage to the penile autonomic nerves. Biochemical, histochemical, and immunohistochemical evidence suggests a general depletion of the adrenergic, cholinergic, and NANC neurotransmitter systems that control penile erection. These in vitro studies on human tissue are, however, not performed with appropriate control tissue from potent patients with diabetes mellitus. For this reason, it is important to study diabetic penile neuropathy by developing animal models. The investigative work by Crowe and Fani in streptozocin-induced diabetes mellitus is encouraging, but more research efforts should be directed toward this objective. Clinical testing is needed to assess the functionality of the autonomic corporal nerves objectively. At present, the patient's erectile response to an intracavernosal injection of vasoactive agents is being studied. If there is an isolated autonomic neuropathy, as commonly exists in young patients with spinal cord injury, the erectile response to the intracavernosal injection is immediate and complete. This intracavernosal injection test for autonomic neuropathy records hemodynamic and not neurophysiologic responses. In patients with an accompanying hemodynamic impairment, such as cavernosal artery insufficiency or corporal veno-occlusive dysfunction, as commonly exists in patients with diabetes mellitus, the hemodynamic erectile response to the intracavernosal injection is impaired, and the presence or absence of autonomic neuropathy is subsequently masked.

Local control of penile erection. Nerves, smooth muscle, and endothelium.

This article reviews the state of knowledge on the neurologic and non-neurologic mechanisms that control the tone of the corpus cavernosum trabecular smooth muscle and the smooth muscles of penile arteries and veins. It includes discussion of the role of the adrenergic, the cholinergic, and the nonadrenergic noncholinergic neuroeffector systems as well as the potential role of the vascular endothelium and prostaglandins in the control of penile erection.

Acidic fibroblast growth factor rescues gerbil hippocampal neurons from ischemic apoptotic death.

Neurotrophic factors have been shown to support the survival of injured neurons and promote their recovery. Here, we investigated whether acidic fibroblast growth factor (aFGF) could modify programmed cell death caused by transient forebrain ischemia in the gerbil. The data show that systemic administration of 2.6 microg aFGF after 5 min ischemia followed by 7 days of brain reperfusion significantly (p < 0.05) reduced the occurrence of apoptotic cell death in CA1 neurons. These data suggest that aFGF would contribute to brain protection after acute stroke.

Fibroblast growth factor-1 prevents myocardial apoptosis triggered by ischemia reperfusion injury.

BACKGROUND: Apoptosis is a constant feature of reperfusion injury in ischemic cardiac myocytes, leading to late cell death. Since fibroblast growth factors (FGFs) inhibit apoptosis in differentiated cells, we hypothesized that FGF-1 (acidic FGF), in its native form, and a non-mitogenic isoform would attenuate myocardial ischemia-reperfusion- induced apoptosis. METHODS AND RESULTS: The effect of native and non-mitogenic fibroblast growth factor-1 mutein (FGF-1 and m-FGF-1) on apoptosis assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method was tested in a rat model of 20 min regional myocardial ischemia and 24h reperfusion. Myocardial ischemia followed by reperfusion resulted in a high myocardial apoptosis rate in the area at risk. When given as a systemic bolus inmediately after myocardial ischemia, both FGF-1 and m-FGF-1 significantly reduced apoptosis (by 60 and 61.2, respectively; p<0.0001). CONCLUSIONS: The programed myocyte cell death triggered by ischemia-reperfusion injury is attenuated by FGF-1 in its native or non mitogenic isoforms, suggesting that this effect does not depend on the mitogenic properties of this protein. FGF-1 would contribute to the functional preservation of the myocardium after acute myocardial infarction.