Rabbit Corpus Cavernosum Tissue Research Articles

Effects of adenosine monophosphate used in combination with L-arginine on female rabbit corpus cavernosum tissue.

IntroductionSexual dysfunction is significantly more prevalent in women than in men. However, to date, no satisfactory oral treatment is yet available.AimThe aim of this study was to study the effects of adenosine monophosphate (AMP) alone or its combination with L-Arginine on the relaxation of the female rabbit corpus cavernosum.MethodsCylinder strips from the corporal body of the excised clitoris from female New Zealand White rabbits were incubated in Krebs solution. Phenylephrine (PE) precontraction was achieved, then the drugs AMP and L-Arginine were administered either independently or in sequential combinations to the strips under precontracted conditions.Main Outcome MeasuresContraction percentages were compared.ResultsWhen precontraction was induced by PE 8 μM or 20 μM, AMP was shown to induce relaxation up to 25% in a dose-dependent manner. The relaxation induced by L-Arginine reached 15.6% at 5.10−4 M vs. 16.5% at AMP 5.10−4 M under the same experimental conditions. Nitric oxide (NO) synthase inhibitor N-nitro-L-arginine strongly inhibited the relaxing effect provoked by AMP, suggesting that the action mechanism of this nucleotide is related to the NO pathway. The combination of L-Arginine at 5.10−4 M with AMP at different doses ranging from 5.10−4 M to 10−3 M significantly amplified the relaxing response up to 40.7% and 58%, respectively.ConclusionsOur results demonstrate that AMP induces a relaxing effect on the female rabbit corpora. They also show that L-Arginine and AMP can potentiate each other and that a synergistic effect can be obtained by their combined use. Because only slight differences exist between both sexes in response to NO donors and/or nucleotide purines or in their use together, it is very likely that close biochemical mechanisms, although not to the same degree and not quite similar, are involved in the engorgement of the penis and the clitoris of New Zealand White rabbits. Stücker O, Pons C, Neuzillet Y, Laemmel E, and Lebret T. Original research-sexual medicine: Effects of adenosine monophosphate used in combination with L-Arginine on female rabbit corpus cavernosum tissue. Sex Med 2014;2:1–7.

Saw Palmetto Extract Enhances Erectile Responses by Inhibition of Phosphodiesterase 5 Activity and Increase in Inducible Nitric Oxide Synthase Messenger Ribonucleic Acid Expression in Rat and Rabbit Corpus Cavernosum

To evaluate whether saw palmetto extract (SPE) relaxes corpus cavernosum and explore the underlying mechanisms. Forty Sprague-Dawley rats and 30 New Zealand rabbits were randomly allocated into 3 SPE-treated groups (low-, middle-, and high-dose) and 1 saline-treated control group. SPE was administered intragastrically for 7 consecutive days. Another 23 rats treated with sildenafil were used to appraise the erectile response to electrical stimulation of nerves in the corpus cavernosum. The erectile functions of rats and rabbits were evaluated 24 hours after the last SPE administration or 15 minutes after intragastric sildenafil. Outcome measures included corpus cavernosum electrical activity recording, phosphodiesterase 5 (PDE5) activity detected by the colorimetric quantitative method, and messenger ribonucleic acid (mRNA) expression level for PDE5 and inducible nitric oxide synthase (iNOS) determined using real-time polymerase chain reaction. In the SPE-treated animals, the relaxant response to electrical stimulation of nerves in the corpus cavernosum, reflected by the amplitude of the electrical activity within the cavernosum, was significantly and dose-dependently augmented. Similar effects were observed in the sildenafil-treated rats. PDE5 activity in rat and rabbit corpus cavernosum tissues was significantly and dose-dependently inhibited in SPE-treated animals, whereas the iNOS mRNA level increased compared with the saline group. PDE5 mRNA, however, was only significantly enhanced in the rats treated with the middle dose of SPE. The results suggest that SPE may have potential application value for the prevention or treatment of erectile dysfunction through an increase in iNOS mRNA expression and inhibition of PDE5 activity in corpus cavernosum smooth muscles.

Effects of nucleotides adenosine monophosphate and adenosine triphosphate in combination with L‐arginine on male rabbit corpus cavernosum tissue

Purines and more specifically adenosine monophosphate (AMP) and adenosine triphosphate (ATP) have a strong relaxant effect on smooth muscle cells of the dog, rabbit and human corpus cavernosum, to approximately the same degree as nitric oxide (NO). However, purines are considered as modulators of erectile function rather than key mediators. This suggests that the use of purines combined with NO donors could be effective to treat some specific erectile disorders. The relaxation induced by the combination of l-arginine (Arg), a natural substrate for NO synthase, was assessed with a purine-nucleotide (AMP, ATP) on a rabbit corpus cavernosum model, to determine if these substances could potentiate each other's effect. When a pre-contraction was induced by phenylephrine, AMP alone induced a 43% CC relaxation rate and ATP alone a 26% rate. The relaxation rate induced by Arg was lower in comparison (8% at 5.10(-4) m vs. 25% at AMP 5.10(-4) m and 15% at ATP 5.10(-4) m). NO synthase inhibitor n-nitro-l-arginine did not modify the relaxing effect provoked by AMP suggesting that the mechanism of action of this nucleotide does not involve the NO pathway. The combination of Arg at 5.10(-4) m with either AMP or ATP at different doses ranging from 5.10(-4) to 10(-3) m significantly enhanced the relaxing response reaching rates of 62 and 80% respectively, leading to a synergistic effect. The present data indicate that a 'NO donor' combined with an 'adenosine donor' could be an effective therapeutic approach.

Effects of tetrandrine on cAMP and cGMP levels in rabbit corpus cavernosum in vitro

The aim of this study was to further investigate the relaxation mechanism of tetrandrine (Tet), a bis-benzylisoquinoline alkaloid isolated from the Chinese medicinal herb-root of Stephania tetrandra S Moore, on rabbit corpus cavernosum tissue in vitro. The effects of Tet on the concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in isolated and incubated rabbit corpus cavernosum tissue were recorded by means of 125I radioimmunoassay. The basal concentration of cAMP in corpus cavernosum tissue was 5.67 ± 0.97 pmol mg−1. Tet increased the cAMP concentration in a dose-dependent manner (p < 0.05), but this effect was not inhibited by an adenylate cyclase inhibitor (cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine, MDL-12, 330A) (p > 0.05). The accumulation of cAMP induced by prostaglandin E1 (PGE1, a stimulator of cAMP production) was also augmented by Tet in a dose-dependent manner (p < 0.05). The basal concentration of cGMP in corpus cavernosum tissue is 0.44 ± 0.09 pmol mg−1. Tet did not affect this concentration of cGMP, neither in the presence nor the absence of a guanyl cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) (p > 0.05). Further, sodium nitroprusside (SNP, a stimulator of cGMP production)-induced cGMP production was not enhanced by Tet (p > 0.05). Tet, with its relaxation mechanism, can enhance the concentration of cAMP in rabbit corpus cavernosum tissue, probably by inhibiting PDEs activity.

Effect of a methanol extract of Arctium lappa on penile erection in penile smooth muscle

The aim of the present study was to investigate whether a methanol extract of Arctium lappa (EAL) augments penile erection. In isolated endothelium‐intact rabbit corpus cavernosum preconstricted with phenylephrine, EAL relaxed penile smooth muscle in a dose‐dependent manner, which was inhibited by pretreatment with a nitric oxide synthase inhibitor, NG‐nitro‐L‐arginine methyl ester (L‐NAME), and a soluble guanylyl cyclase inhibitor, 1H‐[1,2,4]‐oxadiazole‐[4,3‐α]‐quinoxalin‐1‐one (ODQ), L‐type Ca2+ channel blockers, verapamil, and diltiazem, respectively. On the other hand, penile smooth muscle relaxation induced by EAL was not blocked by several inhibitors including indomethacin, atropine, propranolol, tetraethylammonium (TEA), and glibenclamide, respectively. In addition, incubation of endothelium intact rabbit corpus cavernosum tissues with EAL increased cGMP production in a dose‐dependent manner. Taken together, these results suggest that EAL may be induce penile erection through the activation of penile tissue NO/cGMP system and/or Ca2+channels in rat corpus cavernosum.

The relaxation mechanisms of tetrandrine on the rabbit corpus cavernosum tissue in vitro

The relaxation mechanisms of tetrandrine (Tet) on the rabbit corpus cavernosum tissue in vitro were investigated. Strips of rabbit corpus cavernosum were mounted in organ chambers. The effects of Tet were examined on isolated muscle strips pre-contracted with phenylephrine (PE) alone, in the presence of N W-nitro-L-arginine (LNNA, a nitric oxide synthase inhibitor), 1-H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one(ODQ, a guanylyl cyclase inhibitor), indomethacin (cyclooxygenase inhibitor), tetraethylammonium (TEA, Ca2+-activated K+ channel blocker), 4-aminopiridine (4-AP, voltage dependent K+ channel blocker) and glibenclamide (ATP sensitive K+channel blocker). The effects of Tet on KCl-induced contraction of isolated muscle strips were also investigated. The procedure of calcium absence–calcium addition was designed to observe the effect of Tet on the two components of the contractile responses to PE based on the source of Ca2+ (extracellular vs. intracellular). Corpus cavernosum strips showed relaxation in response to Tet (10−8 ∼ 10−3 mol L−1) in a concentration-dependent manner with an IC50 of 3.73 × 10−5 mol L−1. However, they were not affected by LNNA, ODQ, indomethacin and K+-channel blockers. Tet (10 μmol L−1, 30 μmol L−1) concentration dependently reduced the maximal contraction response of isolated strips induced by KCl to (73.0 ± 3.8) and (41.5 ± 3.4)%, respectively (p < 0.01). In the procedure of calcium absence–calcium addition, Tet 100 μmol L−1 inhibited both intracellular calcium-dependent and extracellular calcium-dependent contraction induced by PE (20 μmol L−1) (p < 0.05). The inhibition ratios were (23.8 ± 7.1) and (40.7 ± 11.2)%, respectively. The results of the present study suggest that Tet possesses a relaxant effect on rabbit corpus cavernosum tissues, which is attributable to the inhibition of extracellular Ca2+ influx and the inhibition of release of intracellular-stored Ca2+, but not mediated by the release of nitric oxide, prostaglandins or by the activation of potassium channels.

Role of Chloride Channels in the Regulation of Corpus Cavernosum Tone: A Potential Therapeutic Target for Erectile Dysfunction

Recent electrophysiological recordings have identified the existence of outward, excitatory chloride (Cl(-)) currents in rat, rabbit, and human corpus cavernosum (CC) muscle cells. The aim of this study was to investigate the physiological role of Cl(-) currents in the maintenance of cavernosal muscle tone in isolated rabbit CC tissues. CC strips (1 x 1 x 5 mm) were suspended in tissue bath chambers for isometric tension experiments. Spontaneous cavernosal tone and contractions elicited by field stimulation or administration of established smooth muscle constrictors were examined in the presence of chloride channel (ClC) blockers, niflumic acid (NFA), and anthracene-9-carboxylic acid (A9C). Both spontaneous myogenic activity and contractile responses to field stimulation, norepinephrine, histamine, and endothelin-1 were reduced by ClC blockers. Results. In CC strips exhibiting intrinsic myogenic tone, NFA (30 and 100 microM) and A9C (1 mM) caused a relaxation of the tone. In addition, spontaneous contractile activity in CC was abolished in the presence of either ClC blocker. In CC strips precontracted with norepinephrine, histamine, and endothelin-1, both ClC blockers significantly reversed the tone. The ability of NFA and A9C to reverse norepinephrine-induced tone was unaffected by N(omega)-nitro-L-arginine, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, and cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine. In addition, neither indomethacin nor tetraethylammonium affected the relaxant response of NFA. NFA and A9C inhibited the neurogenic and norepinephrine-induced contractions in a concentration-dependent manner. While NFA exerted persistent inhibition on neurogenic contraction, inhibition of neurogenic contractions by A9C was readily reversible. On K(+)-depolarized CC, NFA induced a concentration-related relaxation, whereas A9C was inert, suggesting an additional mechanism of NFA on voltage-gated calcium channels. These results underline the importance of Cl(-) currents as a mechanism in the maintenance of cavernosal tone produced by adrenergic and various endogenous constrictors. Thus, the modulation of Cl(-) current, as an attractive and effective approach to regulate penile erection, and specific ClC blockers, as potential erectogenic agents, merits further research.

An aqueous extract of Coptis chinensis (ACC) augments rat penile tissue erection

The aim of the present study was to investigate whether an aqueous extract of Coptis chinensis (ACC) augments penile erection in vivo and in ex vivo. In isolated endothelium‐intact rabbit corpus cavernosum preconstricted with phenylephrine, ACC (10−7−10−4 g/ml) relaxed penile smooth muscle in a dose‐dependent manner, which was inhibited by pretreatment with a nitric oxide synthase inhibitor, and a soluble guanylyl cyclase (sGC) inhibitor, respectively. In addition, incubation of endothelium intact rabbit corpus cavernosum tissues with ACC increased cGMP production in a dose‐dependent manner. ACC‐induced cGMP production was not blocked by pretreatment with L‐NAME or ODQ. Moreover, IBMX, a non‐selective phosphodiesterase (PDE) inhibitor, or zaprinast, a type 4, 5‐selective PDE inhibitor caused more increase in cGMP production than ACC alone. On the other hand, there are no significant difference between increases in penile tissue cGMP production induced ACC and co‐treated with ACC and IBMX or zaprinast, respectively. ACC (100, 500 mg/kg) also caused increase in intracavernous pressure and area under the curve in rats in a dose dependent manner. These results suggest that ACC maybe induce penile erection through the activation of penile tissue NO/cGMP system and/or inhibition of PDE in rat corpus cavernosum.

Effects of plant extract neferine on cyclic adenosine monophosphate and cyclic guanosine monophosphate levels in rabbit corpus cavernosum in vitro

To further investigate the relaxation mechanism of neferine (Nef), a bis-benzylisoquinoline alkaloid extracted (isolated) from the green seed embryo of Nelumbo nucifera Gaertn in China, on rabbit corpus cavernosum tissue in vitro. The effects of Nef on the concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in isolated and incubated rabbit corpus cavernosum tissue were recorded using 125I radioimmunoassay. The basal concentration of cAMP in corpus cavernosum tissue was 5.67 +/- 0.97 pmol/mg. Nef increased the cAMP concentration in a dose-dependent manner (P < 0.05), but this effect was not inhibited by an adenylate cyclase inhibitor (cis-N-[2-phenylcyclopentyl]azacyclotridec-1-en-2-amine, MDL-12, 330A) (P > 0.05). The accumulation of cAMP induced by prostaglandin E1 (PGE1, a stimulator of cAMP production) was also augmented by Nef in a dose-dependent manner (P < 0.05). The basal concentration of cGMP in corpus cavernosum tissue is 0.44 +/- 0.09 pmol/mg. Nef did not affect this concentration of cGMP, either in the presence or in the absence of a guanyl cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) (P > 0.05). Also, sodium nitroprusside (SNP, a stimulator of cGMP production)-induced cGMP production was not enhanced by Nef (P > 0.05). Nef, with its relaxation mechanism, can enhance the concentration of cAMP in rabbit corpus cavernosum tissue, probably by inhibiting phosphodiesterase activity.

Relaxation mechanisms of neferine on the rabbit corpus cavernosum tissue in vitro

To investigate the relaxation mechanisms of neferine (Nef) on the rabbit corpus cavernosum tissue in vitro. Strips of rabbit corpus cavernosum were mounted in organ chambers. The effects of Nef were examined on isolated muscle strips precontracted with phenylephrine (PE) alone, in the presence of N(W)-nitro-L-arginine (LNNA, a nitric oxide synthase inhibitor), 1-H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, a guanylyl cyclase inhibitor), indomethacin (cyclooxygenase inhibitor), tetraethylammonium (Ca(2+)-activated K(+) channel blocker), 4-aminopiridine (4-AP, voltage dependent K(+) channel blocker) and glibenclamide (ATP sensitive K(+) channel blocker). The effects of Nef on KCl-induced contraction of isolated muscle strips were also investigated. The procedure of calcium absence-calcium addition was designed to observe the effect of Nef on two components of the contractile responses to PE based on the source of Ca(2+) (extracellular vs. intracellular). Corpus cavernosum strips relaxed in response to Nef (10(-9)-10(-4) mol/L) in a concentration-dependent manner with an IC(50) of 4.60 X 10(-6) mol/L. However, they were not affected by LNNA, ODQ, indomethacin or K(+)-channel blockers. Nef (10(-6) mol/L, 10(-5) mol/L) concentration dependently reduced the maximal contraction response of isolated strips induced by KCl to 79.3%+/-5.5% and 61.5%+/-3.2%, respectively (P < 0.01). In the calcium absence-calcium addition procedure, Nef 10(-5) mol/L inhibited both intracellular calcium-dependent and extracellular calcium-dependent contraction induced by PE (2 X 10(-5) mol/L) (P < 0.05). The inhibition ratios were 26.2%+/-5.4% and 48.3%+/-7.6%, respectively. The results of the present study suggest that Nef possesses a relaxant effect on rabbit corpus cavernosum tissues, which is attributable to the inhibition of extracellular Ca2+ influx and the inhibition of release of intracellular stored Ca(2+), but not mediated by the release of nitric oxide, prostaglandins or by the activation of potassium channels.

Nicotine potentiates the nitrergic relaxation responses of rabbit corpus cavernosum tissue via nicotinic acetylcholine receptors

The presence of neuronal nicotinic acetylcholine receptors in rabbit corpus cavernosum tissue and possible mechanisms underlying the potentiation of electrical field stimulation induced relaxation by nicotine were analyzed. In corpus cavernosum tissue strips nicotine (3 × 10 − 5 M) and acetylcholine (10 − 3 M) produced potentiation on electrical field stimulation (amplitude 50 V; frequency 4 Hz; width 0.8 ms) induced relaxation responses. This nicotine-induced potentiation was not altered by atropine (10 − 6 M), guanethidine (5 × 10 − 6 M) and indomethacin (10 − 5 M), but abolished by hexamethonium chloride (10 − 5 M) and l-nitro arginine methyl ester (10 − 5 M). Nicotine did not cause any alteration on a single dose of carbachol (3 × 10 − 5 M) and sodium nitroprusside (10 − 5 M) induced relaxation responses. The results suggest that, nicotine-induced potentiation is NO and nicotinic acetylcholine receptor dependent but independent from prostaglandin synthesis, activation of muscarinic receptors and does not require intact adrenergic neurons. Nicotine did not affect smooth muscle and endothelium directly. In conclusion, in this study we showed for the first time that, nicotine acts on the nicotinic acetylcholine receptors located on the nitrergic nerves, thereby evoking the release of NO from these nerve terminals inducing relaxation response in rabbit corpus cavernosum tissue.

Epimedium brevicornum Maxim extract relaxes rabbit corpus cavernosum through multitargets on nitric oxide/cyclic guanosine monophosphate signaling pathway

Epimedium brevicornum Maxim (EbM) has been reputed to have sexual stimulation effects on males. The study is aimed to test the hypothesis that EbM extracts relaxed the corpus cavernosum (CC) smooth muscle through activation of multitargets on nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway. Water extract of EbM and its subfraction (EP-20) were prepared and standardized by high-performance liquid chromatography. Isolated rabbit CC strips were mounted in organ baths and isometric tension was recorded in the presence or absence of specific inhibitors related to NO/cGMP signaling such as L-N(G)-nitro-arginine methyl ester (L-NAME), 1H-[1,2,4]oxadiazolo-[4,3-a] quinoxalin-1-one (ODQ, a guanylyl cyclase inhibitor) or phosphodiesterase 5 (PDE 5) inhibitors. cGMP level was determined in EP-20-treated CC strips. The results showed that EP-20 enriched the content of L-arginine in the process of purification and relaxed the CC smooth muscle precontracted with phenylephrine (PE, 1 microM) in a concentration-dependent manner. Besides, EP-20 increased the amount of cGMP production in rabbit CC tissues. Coincubation with EP-20 and L-NAME or ODQ significantly decreased EP-20-induced relaxation whereas EP-20 increased sodium nitroprusside-induced relaxation in PE-precontracted CC strips. Besides, EP-20 increased the potency and the duration of the relaxation effects caused by electrical field stimulation. Finally, EP-20 could potentiate PDE 5 inhibitors in relaxation of PE-precontracted CC strips. We concluded that extract of EbM relax the CC smooth muscle through multitargets in NO/cGMP/PDE 5 pathway and might bring into perspective the treatment strategy for those patients with erectile dysfunction.

Effects of ligustrazine on the contraction of isolated rabbit corpus cavernosum strips

To investigate the role of ligustrazine on relaxation of the isolated rabbit corpus cavernosum tissue in vitro, the effects of ligustrazine on the corpus cavernosum were observed by using experimental method of smooth muscle strips. Concentration-responses to phenylephine (PE) and KCl were recorded. The results showed that ligustrazine concentration-dependently depressed the contraction response of smooth muscle strips induced by PE. The maximum percentage relaxation of cavernosal strips by ligustrazine was 74.1% +/- 6.2% (compared with control: 21.9% +/- 5.6%, P < 0.01). Ligustrazine concentration-dependently reduced the amplitude of the contraction induced by cumulative doses of PE or KCl, shifted the cumulative concentration response curves of PE and KCI to the right and depressed their maximal responses. It was concluded that ligustrazine could significantly relax the cavernosal muscle contraction induced by PE in vitro. The results suggested that ligustrazine inhibited calcium ion influx.

3-Thio-quinolinone maxi-K openers for the treatment of erectile dysfunction

A series of Maxi-K openers for the treatment of erectile dysfunction based on the 3-thio-quinolinone core is described. Significant levels of channel opening (up to 550% of control) are seen in transfected oocytes. Functional activity in rabbit corpus cavernosum tissue strips confirms the potential to effect therapy for ED, the effect being maximal for the 3-amino-2-hydroxy thiol side chain.

Modulation of Intrinsic Cavernous Tone and Nitric Oxide Production by Arginase in Rabbit Corpus Cavernosum

Arginase shares the common substrate L-arginine with nitric oxide synthase (NOS). We investigated the roles of NOS and arginase for modulating intrinsic and vasoconstrictor tone in rabbit corpus cavernosum (RCC). Isolated RCC tissues were used for isometric tension experiments, and NOS and arginase activities. The endothelium lining RCC lacunar spaces was disrupted and/or removed by saponin treatment. Following stretch of approximately 1gm NG-nitro-L-arginine methyl ester (L-NAME) as a NOS inhibitor caused endothelium dependent contraction, while the potent and specific arginase inhibitor N omega-hydroxy-nor-L-arginine (nor-NOHA) caused endothelium dependent relaxation. Relaxation with nor-NOHA was reversed by L-NAME. In the presence of 10 mM L-arginine 0.1 mM nor-NOHA was ineffective. Pretreatment with 0.1 mM L-NAME and 0.1 mM nor-NOHA did not significantly affect the vasoconstrictor response to phenylephrine. The magnitude of contraction with 0.1 mM L-NAME and relaxation with 0.1 mM nor-NOHA during contraction induced by phenylephrine were not significantly different from changes with L-NAME and nor-NOHA under intrinsic basal tone. In the enzymatic study NOS and arginase were detectable in cavernous homogenates. Nor-NOHA inhibited arginase but not NOS activity. Results indicate that basal nitric oxide production from the endothelium regulates intrinsic cavernous tone and endogenous arginase activity in the endothelium modulates tone by inhibiting nitric oxide production, presumably through competition with constitutive NOS for the common substrate L-arginine.

Combination of phentolamine and l-arginine or sildenafil synergistically improves neurogenic relaxation of rabbit corpus cavernosum smooth muscle

Objectives. To analyze the effects of combining an alpha-adrenergic receptor antagonist, phentolamine, with an enhancer of the nitric oxide/cyclic guanosine monophosphate pathway ( l-arginine or sildenafil) on neurogenic relaxations of rabbit corpus cavernosum (RCC). Methods. Studies were performed on isolated RCC tissue in organ chambers. Transmural electrical stimulation (TES) was applied at increasing frequencies (0.5 to 6 Hz) on endothelin-contracted RCC strips, and the responses were evaluated. Results. The activation of alpha 2-adrenergic receptors with UK 14304 (0.3 μM) significantly inhibited the relaxation induced by TES in RCC strips in which adrenergic neurotransmission was blocked with guanethidine (10 μM). The relaxant responses produced by TES application on RCC strips without guanethidine were not significantly affected by the treatment with l-arginine or sildenafil but were significantly augmented by phentolamine (2.7-fold increase in maximum relaxation). Furthermore, the combinations of phentolamine with l-arginine or sildenafil markedly increased the relaxations evoked by the application of TES in RCC tissue, significantly more than those obtained in the presence of phentolamine alone (4.5 or 4.7-fold increase of maximum relaxation, respectively). Conclusions. Our results demonstrated a synergistic interaction between the alpha-adrenergic blockade and the potentiation of the nitric oxide/cyclic guanosine monophosphate pathway to increase neurogenic relaxation of trabecular smooth muscle relaxation. This fact suggests that the combination of alpha-adrenergic receptor blockade with l-arginine or sildenafil could represent a therapeutic advantage in the treatment of erectile dysfunction.

An Experimental Study of the Effect of Ginkgo Biloba Extract on the Human and Rabbit Corpus Cavernosum Tissue

Purpose To investigate the effect of subfractions of extract from the ginkgo on human and rabbit corpus cavernosal tissue and their possible use for the treatment of impotence. Materials and Methods Among the fractions of ginkgo biloba extract (GBE), nonginkgolide nonflavonoid fraction (NGF) has the most potent relaxing effect on vascular smooth muscle. We subfractionated NGF and speculated that some of the subfractions might have a very potent relaxing effect on corpus cavernosal tissue. Thereafter we have studied their effect on human and rabbit corpus cavernosum using organ bath and electrical field stimulation experiments. Results In the tissue precontracted by norepinephrine (10 sup -5 M.), corpus cavernosal tissue of human and rabbit showed relaxation in response to subfractions of NGF in a dose-dependent manner. 304U-1 showed the most potent relaxing effect (ED 50 = 0.74 mg./ml. in human, ED 50 = 0.66 mg./ml. in rabbit). 304U-1 elicits pharmacological actions on corus cavernosum smooth muscle via the signal transduction pathway whereby relaxation induced by 304U-1 is mediated by intracellular cAMP and perhaps partially by antagonizing of the adrenergic nervous system. A hyperpolarizing effect via potassium channel opening might also be related to this relaxing effect. Conclusion The subfractions of NGF, especially 304U-1, have a relaxing effect on corpus cavernosum tissue. 304U-1, which showed the most potent relaxing effect, can possibly be used as a drug for intracavernosal injection therapy. Considering the fact that the value of ED 50 is too high, further fractionation and in vivo study are needed before clinical use in an oral form.

An Experimental Study of the Effect of Ginkgo Biloba Extract on the Human and Rabbit Corpus Cavernosum Tissue

An Experimental Study of the Effect of Ginkgo Biloba Extract on the Human and Rabbit Corpus Cavernosum Tissue

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.