Effects of diabetes on nitric oxide-mediated relaxations in male rat corpus cavernosum smooth muscle

INTRODUCTION: We evaluated the effects of diabetes on nitric oxide-mediated relaxations and nitric oxide synthase activity in male rat corpus cavernosum smooth muscles. METHODS: Eight-week-old male rats were assigned to three groups: control (injected with the vehicle), DM (diabetes mellitus, induced by injection with 65 mg/kg streptozotocin), and TES (testosterone, testosterone supplemented after induction of diabetes). After 8 weeks, corpus cavernosum smooth muscle strips were mounted in an organ bath for isometric tension recordings. Electrical field stimulation (EFS, 2-ms pulse duration, 0.3-20 Hz and 3 s train) was applied to the strips precontracted with 30 microM phenylephrine. The microdialysis probe was inserted into the strip, and Krebs-Henseleit solution was perfused into the probe. The dialysate during EFS was collected, and the amount of NO(-)(2)/NO(-)(3) (NOx) released in the dialysate was measured by the Greiss method. Sodium nitroprusside (0.1 nM to 10 mM) and carbachol (1 nM to 10 mM) were cumulatively added to the strips precontracted with 30 microM phenylephrine. RESULTS: EFS caused frequency-dependent relaxations and NOx releases of the strips. Pretreatment with N(omega)-nitro-L-arginine (100 microM) and tetrodotoxin (1 microM) completely inhibited the relaxations and NOx releases. The maximum relaxation was significantly greater in the DM group than in the control or TES group. The release of NOx was significantly greater in the DM group than in the control or TES group. Sodium nitroprusside, the endothelium-independent vasodilator, relaxed the tissues in all three groups. There were no significant differences among control, DM and TES groups in the maximum relaxation to sodium nitroprusside. CONCLUSION: The present data suggest that diabetes enhances nitric oxide synthase activity and nitric oxide-mediated relaxations in the male rat corpus cavernosum by the reduced testosterone level in the diabetic animals.     

Effects of platelet-activating factor on nitrergic transmission in rabbit corpus cavernosum

AIM: The information currently available suggests that nonadrenergic noncholinergic (NANC) transmitters, particularly nitric oxide, are involved in the relaxation of penile erectile tissues. Platelet-activating factor (PAF) is a chemical mediator and is involved in many physiological and pathophysiological events. It is well known that several of the vascular actions of PAF are mediated by the generation of nitric oxide. We designed this study to test the hypothesis that PAF has an effect on NANC responses in rabbit corpus cavernosum strips. METHODS: Rabbit corpus cavernosum strips were precontracted with phenylephrine (10(-5) mol/L). Isometric tension changes produced by carbachol (10(-9)-10(-5) mol/L), sodium nitroprusside (10(-8)-10(-5) mol/L) and electrical field stimulation (for 10 s at sequential frequencies of 2, 4, 8, 16, and 32 Hz as square-wave pulses of 50 mV) were recorded with a pressure transducer. These relaxations were compared to those obtained in the presence of PAF. RESULTS: PAF had no effect on endothelium-dependent, endothelium-independent or electrical field stimulation-induced NANC relaxation responses in isolated rabbit corpus cavernosum strips. There was no statistically significant difference between the pD(2) and E(max) values for carbachol or sodium nitroprusside in the presence of PAF. CONCLUSIONS: Our results suggest that PAF does not modify the endothelium-dependent, endothelium-independent or electrical field stimulation-induced NANC relaxation responses in isolated rabbit corpus cavernosum strips.     

Effect of hypothyroidism on the purinergic responses of corpus cavernosal smooth muscle in rabbits

AIMS: Several studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. In the present study, we examined purinergic relaxation responses in hypothyroidism in an experimental rabbit model and compared them with controls to evaluate the possible involvement of the purinergic pathway. MATERIALS AND METHODS: The study comprised 20 male New Zealand white rabbits. The rabbits were divided into two equal groups. We tested the effects of ATP, alpha beta ATP, and adenosine precontracted with phenylephrine on the isolated corpus cavernosum preparations from control and hypothyroid rabbits. We also evaluated the effects of ATP, alpha beta ATP, and adenosine on the cGMP levels in the isolated corpus cavernosum preparations from control and hypothyroid rabbits. RESULTS: T(3), T(4), and testosterone levels were significantly lower in hypothyroid rabbits. ATP, alpha beta ATP, carbachol, and electrical field stimulation (EFS)-induced frequency-dependent relaxation responses in the isolated rabbit corpus cavernosum strips precontracted with phenylephrine reduced significantly (P < 0.05). Adenosine-induced relaxation responses did not change significantly in hypothyroid rabbits. CONCLUSION: Reduction of relaxation response in hypothyroid rabbits corpus cavernosum can depend on a decreased release of nitric oxide (NO) from nitrergic nerves and endothelium.     

Effect of the plant-extract osthole on the relaxation of rabbit corpus cavernosum tissue in vitro

PURPOSE: We investigated the cavernosal relaxant effect of osthole, a coumarin isolated from Cnidium monnier (L.) Cusson which has been long used in China as a herbal medicine to improve male sexual dysfunction. MATERIALS AND METHODS: Strips of rabbit corpus cavernosum were precontracted with phenylephrine. Corporal relaxation evoked by osthole was then determined in the absence and presence of nitric oxide synthase inhibitor (L-NAME), soluble guanylate cyclase inhibitor (ODQ), cyclooxygenase inhibitor (indomethacin), tetradotoxin, and after endothelium deprivation. RESULTS: Corpus cavernosal strips showed relaxation in response to osthole (0.1 approximately 30 microM) in a dose-dependent manner. These effects were reduced partially but significantly by pretreatment with L-NAME, ODQ and by endothelial disruption. However, they were not affected by indomethacin and tetradotoxin treatment. Osthole pretreatment (from 1 to 30 microM) enhanced the sodium nitroprusside (0.3 microM)-induced relaxation of corpus cavernosum in a dose-dependent manner to a maximum of 3 times the pretreatment level at 30 microM osthole. However, this effect was abolished in the presence of zaprinast. Additionally, a higher concentration of osthole (30 microM) also enhanced forskolin-induced relaxation. CONCLUSION: The data suggested that osthole possesses a relaxant effect on rabbit corpus cavernosal tissues which is attributable to the release of NO from sinusoidal endothelium and to the potentiation of the cGMP and/or cAMP signal mediating relaxation of cavernosal smooth muscle by inhibiting phosphodiesterase.     

Effect of hypothyroidism on the nitrergic relaxant responses of corpus cavernosal smooth muscle in rabbits

BACKGROUND: The incidence of hormonal dysfunction as a cause of impotence remains controversial. However, several recent studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. METHODS: In the present study, we examined nitrergic responses in hypothyroidism in rabbit corpus cavernosum and compared them with controls. RESULTS: Carbachol-induced relaxation responses and electrical field stimulation (EFS)-induced frequency-dependent relaxations decreased significantly in hypothyroid rabbits. Papaverine and sodium nitroprusside (SNP)-induced relaxation responses did not change significantly in hypothyroid rabbits. The contraction responses of phenylephrine and EFS-induced frequency-dependent contractions were significantly decreased in the hypothyroid group. CONCLUSIONS: We can speculate that the reduction of relaxant responses to EFS and carbachol in hypothyroid rabbits can depend on a decreased release of nitric oxide (NO) from nitrergic nerves and endothelium or a reduction of muscarinic receptor density. Also, decreases in contraction responses may depend on diminished adrenoceptor density.     

Pro-erectile effect of vardenafil: in vitro experiments in rabbits and in vivo comparison with sildenafil in rats

OBJECTIVES: To assess pro-erectile responses to vardenafil, a new selective PDE5 inhibitor, in vitro in isolated rabbit corpora cavernosa, and in vivo in anaesthetized rats. METHODS: Rabbit cavernosal strips were precontracted with 10 microM phenylephrine. Dose-response relaxation curves to cumulative dosings of vardenafil (1 nM-10 microM) were constructed alone and in the presence of 10 mM L-NAME. Relaxation responses to electrical field stimulation (EFS) (2 Hz, 2 ms, 10 V) were compared in control preparations and in the presence of vardenafil (1-10 nM). Male Sprague-Dawley rats were anaesthetized with urethane and prepared for measurement of blood pressure and intracavernous pressure. Erectile responses (ICPmax/dBP x 100) to cavernous nerve submaximal stimulation (10 Hz, 1 ms, 0.45-1.6 V) were determined before, and 3, 10 and 23 min after i.v. administration of saline, vardenafil or sildenafil (0.1, 1 mg/kg). RESULTS: Vardenafil was effective in relaxing precontracted rabbit cavernosal strips (IC50 54 +/- 18 nM). This relaxing activity was partially antagonized with 10 mM L-NAME, increasing the IC50 to 620 +/- 81 nM. Vardenafil significantly increased (more than 4 times) relaxation of precontracted rabbit cavernosal strips to EFS at 10 nM. In anaesthetized rats, erectile responses were significantly facilitated 3 and 13 min after 0.1 and 1 mg/kg vardenafil was administered. In contrast, 1 mg/kg sildenafil only significantly increased erectile responses at 3 min post-injection. CONCLUSIONS: Vardenafil relaxes rabbit corpus cavernosum in vitro and is effective at a lower dose than sildenafil in facilitating erectile responses to cavernous nerve stimulation in anaesthetized rats.     

安雄对去势大鼠离体阴茎海绵体平滑肌舒张性的影响

目的 :探讨口服雄激素类药安雄对大鼠阴茎海绵体平滑肌舒张性的调节作用。　方法 :去势大鼠分别给予高、低剂量的安雄 ,与假手术组、去势组大鼠进行对照观察。治疗 4周后分别切取其阴茎海绵体 ,制成海绵体肌条 ,应用去甲肾上腺素对海绵体肌条进行预收缩 ,继予硝普钠 (SNP)、电刺激 (EFS)观测海绵体平滑肌的舒张性 ,比较各组的舒张百分率。　结果 :高剂量安雄 (2 0mg/kg)组其离体平滑肌条 ,对 10 -3 mol/LSNP和EFS的舒张百分率高于去势组 ;低剂量组 (10mg/kg)对 10 -3 mol/LSNP诱导的舒张百分率也高于去势组。统计学处理差异有显著性 (P <0 .0 1) ,　结论 :去势大鼠应用安雄可提高离体大鼠海绵体平滑肌的舒张百分率 ,可增强其海绵体平滑肌的舒张性     

Effect of chronic lithium administration on endothelium-dependent relaxation of rat corpus cavernosum: the role of nitric oxide and cyclooxygenase pathways

OBJECTIVE: To verify the effect of chronic lithium administration on the endothelium-dependent relaxation of rat corpus cavernosum, as lithium is a major drug for treating bipolar disorder and some studies showed that lithium might cause erectile dysfunction in such patients, by a mechanism as yet unknown. MATERIALS AND METHODS: LiCl (600 mg/L) was dissolved in drinking water and Sprague-Dawley rats received the solution for 30 days; control rats received tap water. After 30 days corporeal strips were prepared from both groups, mounted under tension in oxygenated organ baths, and pre-contracted with phenylephrine (7.5 microm). After equilibration, the strips were relaxed by acetylcholine (10 nm to 1 mm) in the presence or absence of indomethacin (a cyclooxygenase inhibitor; 20 microm). Furthermore, the relaxant responses to sodium nitroprusside (1 nm to 1 mm), a nitric oxide (NO) donor, were investigated in both groups. NADPH-diaphorase histochemistry was used to identify NO synthase within cavernosal tissue strips of both groups. RESULTS: The acetylcholine-dependent relaxation was significantly lower in lithium-treated rats than in controls. Although indomethacin decreased significantly the relaxant responses to acetylcholine in controls, it increased the relaxant responses in lithium-treated rats. NADPH-diaphorase staining was greater in the chronic lithium-treated than in control preparations. Sodium nitroprusside produced similar relaxation in both groups. CONCLUSION: Chronic lithium administration can impair the endothelium-dependent relaxation of rat corpus cavernosum; NO availability might decrease after lithium administration and the cyclooxygenase pathways might have a role in this effect.     

川芎嗪舒张离体兔阴茎海绵体平滑肌的作用及其机制的初步研究

目的 :探讨川芎嗪 (Chuanxiongzine ,Ligustrazine)对离体兔阴茎海绵体平滑肌条的舒张效应及其作用机制。　方法 :采用离体家兔阴茎海绵体肌条张力记录法 ,观察川芎嗪对去氧肾上腺素 (phenylephrine,PE)诱导收缩的阴茎海绵体肌条的舒张作用 ;应用亚硝基左旋精氨酸甲酯 (L NAME)、ODQ预处理和去除内皮 ,分别记录川芎嗪对阴茎海绵体肌的舒张作用。采用放射免疫法测定川芎嗪对阴茎海绵体平滑肌肌条中cGMP和cAMP含量的影响。　结果 :川芎嗪对阴茎海绵体平滑肌具有浓度依赖性舒张作用 ,其EC50 为 1 .5 8× 1 0 -4mol/L ,ODQ可部分抑制川芎嗪对肌条的舒张效应 (P <0 .0 5 ) ,而L NAME预处理和去除内皮对川芎嗪舒张肌条的效应没有影响 (P >0 .0 5 )。川芎嗪处理组阴茎海绵体平滑肌肌条中的cGMP和cAMP含量分别是对照组的 1 .5和 2 .3倍 ,差异有显著性 (P <0 .0 5 )。　结论 :川芎嗪对阴茎海绵体平滑肌具有浓度依赖性的舒张效应 ,其舒张作用机制与增加cGMP、cAMP浓度有关     

PACAP 38 is involved in the non-adrenergic non-cholinergic inhibitory neurotransmission in the pig urinary bladder neck

AIMS: To investigate the role played by pituitary adenylate cyclase activating polypeptide 38 (PACAP 38) in the non-adrenergic non-cholinergic (NANC) neurotransmission of the pig urinary bladder neck. METHODS: Urothelium-denuded bladder neck strips were dissected and mounted in organ baths containing a physiological saline solution (PSS) at 37 degrees C and gassed with 5% CO(2) and 95% O(2), for isometric force recording. The relaxations to transmural nerve stimulation (EFS) or PACAP 38 were performed on strips precontracted with 1 microM phenylephrine (PhE). EFS experiments were carried out in the absence and the presence of guanethidine (10 microM), atropine (0.1 microM), and N(G)-nitro-L-arginine (L-NOARG, 100 microM), to block noradrenergic neurotransmission, muscarinic receptors, and nitric oxide (NO) synthase, respectively. RESULTS: EFS (2-16 Hz, 1 ms duration, 20 sec trains, 75 mA current output) evoked frequency-dependent relaxations which were reduced by the VIP/PACAP receptor antagonist PACAP (6-38) (3 microM), and by the neurotoxin of the capsaicin-sensitive primary afferents capsaicin (10 microM), and abolished by the neuronal voltage-activated Na(+) channel blocker tetrodotoxin (TTX, 1 microM). The vasoactive intestinal peptide (VIP) receptor antagonist [Lys(1), Pro(2,5), Arg(3,4), Tyr(6)]-VIP (3 microM) failed to modify the EFS-induced relaxations. PACAP 38 (1 nM-1 microM) induced concentration-dependent relaxations which were reduced by PACAP (6-38), TTX and by the neuronal voltage-gated Ca(2+) channel inhibitor omega-conotoxin GVIA (omega-CgTX, 1 microM). CONCLUSIONS: The results suggest that PACAP 38, mainly released from capsaicin-sensitive primary afferents, is involved in the NANC inhibitory neurotransmission of the pig urinary bladder neck, producing relaxation through neuronal and muscle VIP/PACAP receptor activation.     

The effects of melatonin on ischemia-reperfusion induced changes in rat corpus cavernosum

PURPOSES: We determined the change in contractile activity and oxidant damage after ischemia-reperfusion of rat corpus cavernosum and investigated the effects of melatonin (Sigma Chemical Co., St. Louis, Missouri) on these parameters. MATERIALS AND METHODS: The abdominal aorta of male Wistar albino rats was occluded to induce ischemia-reperfusion. Melatonin (10 mg./kg.) or vehicle (1% alcohol in saline per kg.) was administered subcutaneously before ischemia-reperfusion. In the sham operated control group the abdominal aorta was left intact and the rats were treated with melatonin or vehicle. After decapitation corporeal tissues were placed in organ baths or stored for biochemical measurements. RESULTS: In sham operated rats phenylephrine added cumulatively caused a concentration dependent contraction in corpus cavernosum strips precontracted with KCl and acetylcholine added cumulatively to strips precontracted with phenylephrine caused a dose dependent relaxation response. In the ischemia-reperfusion group contraction and relaxation responses decreased significantly compared within controls. Melatonin treatment in the ischemia-reperfusion group reversed these responses. Myeloperoxidase activity and the lipid peroxidation level of the corporeal tissues in the ischemia-reperfusion group were significantly higher than in the sham operated control group. Melatonin treatment in the ischemia-reperfusion group decreased myeloperoxidase activity and the lipid peroxidation level compared with ischemia-reperfusion alone, whereas melatonin treatment alone had no significant effect on these parameters. CONCLUSIONS: In this study the corporeal tissues of rats exposed to ischemia-reperfusion had lower responses to contractile and relaxant agents than those of sham operated rats. Treatment with melatonin before ischemia-reperfusion almost completely reversed smooth muscle responses and prevented the increased myeloperoxidase activity and lipid peroxidation of corporeal tissues.     

Nitric oxide mediates relaxation in rabbit and human corpus cavernosum smooth muscle

Summary We investigated in vitro the relaxant effect of exogenous acetylcholine (ACh) and electric-field stimulation (EFS) on rabbit and human corpus cavernosum smooth muscle strips (CC) precontracted with phenylephrine. The effects of EFS and ACh were monitored alone, after muscarinic receptor blockade and after inhibition of nitric oxide (NO) formation with l-N-nitroarginine (l-NOARG). In rabbit und human CC, both atropine and l-NOARG abolished the relaxant effects of ACh. The relaxant effects of EFS, however, were only slightly reduced by atropine to 97.5±17.5% in human CC and to 89.0±6.1% in rabbit CC. l-NOARG further reduced the EFS effects to 0.8±1.7% in human CC and to 16.2±8.7% in rabbit CC. In strips obtained from impotent patients with diabetes mellitus, the relaxant effects appeared to be significantly less than in strips from nondiabetic impotent men. Tetrodotoxin blocked the relaxant EFS effects in human and rabbit strips completely. The data indicate the important role of NO in cholinergically induced relaxation of cavernous smooth muscle in rabbits and humans. Our findings support the idea of NO as the nonadrenergic noncholinergic neurotransmitter in penile erection in both species. Rabbit erectile tissue might serve as an in vitro animal model for further investigation.     

Nitric oxide is a potent relaxant of human and rabbit corpus cavernosum.

Nitric oxide (NO) caused a potent, marked, and transient relaxation of precontracted strips of corpus cavernosum isolated from humans and rabbits. The relaxation response elicited by NO was very similar to the relaxation evoked by electrical field stimulation via the nonadrenergic-noncholinergic pathway. Sodium nitroprusside, nitroglycerin, and S-nitroso-N-acetylpenicillamine, which are nitrovasodilators known to generate NO, also caused marked concentration-dependent relaxation of corpus cavernosum. Relaxant responses to NO were enhanced by the cyclic GMP phosphodiesterase inhibitor M&B 22,948 and inhibited by oxyhemoglobin. Similarly, relaxation of corpus cavernosum in response to electrical field stimulation or acetylcholine was enhanced by M&B 22,948 and inhibited by oxyhemoglobin. NO stimulated cyclic GMP formation in corpus cavernosum and a close positive correlation was found between the magnitudes of relaxation and cyclic GMP formation. The data suggest that NO-elicited activation of guanylate cyclase and cyclic GMP formation represents the signal transduction mechanism responsible for relaxation and nonadrenergic-noncholinergic-mediated penile erection. These observations indicate that NO is a potent relaxant of human and rabbit corpus cavernosum and support our hypothesis that endogenous NO is the principal mediator of penile erection caused by nonadrenergic-noncholinergic stimulation.     

Effect of magnesium on the function of the rabbit corpus cavernosum

Contraction and relaxation of the smooth muscle, including the corpus cavernosum, are mediated by changes in the intracellular concentration of calcium. Since magnesium modulates the movement of calcium it can modify the function of the erectile tissue. We designed this study to investigate the effects of magnesium in doses ranging from 5 to 30 mM on the function of the rabbit corpus cavernosum in vitro. The resting tension of tissue strips was significantly reduced by exposure to a solution high in magnesium (5–30 mM). The contractile response to field stimulation under resting conditions, and the contraction to phenylephrine, were significantly decreased by magnesium (5–30 mM). There were no differences in the contractile strength of the corpus cavernosum to KCl. Although the relaxation induced by field stimulation under preincubation with 200 M phenylephrine was abolished in the presence of 30 mM magnesium, there were no differences at a concentration of 5 mM or of 10 mM magnesium. The relaxation induced by sodium nitroprusside under precontraction with 200 M phenylephrine was further increased by magnesium dose dependently. A high concentration of magnesium (30 mM) enhanced both bethanechol-induced and ATP-induced relaxations under precontraction with phenylephrine. Our study demonstrated that magnesium reduced the receptor-mediated contraction of the rabbit corpus cavernosum and enhanced the relaxation of this tissue induced by sodium nitroprusside, bethanechol, and ATP.     

Modulation of Ca2+ sensitivity regulates contractility of rabbit corpus cavernosum smooth muscle

PURPOSE: We examined the role of the modulation of Ca2+ sensitivity for regulating the contractility of corpus cavernosum smooth muscle. MATERIALS AND METHODS: We applied simultaneous measurements of intracellular Ca2+ concentration and tension in fura-PE3 loaded intact strips and receptor coupled permeabilization by alpha-toxin. RESULTS: In intact fura-PE3 loaded strips the tension induced by 10 microM. phenylephrine was significantly greater than that produced by depolarization with 118 mM. K+, although the extent of intracellular Ca2+ concentration elevations was similar. During sustained contraction induced by 10 microM. phenylephrine the application of 10 microM. Y-27632 (a Rho kinase inhibitor) induced relaxation with a slight decrease in intracellular Ca2+ concentration, while the application of 3 microM. GF109203X (a protein kinase C inhibitor) induced relaxation without changing intracellular Ca2+ concentration. In alpha-toxin permeabilized strips 10 microM. phenylephrine induced a larger increase in force at a constant intracellular Ca2+ concentration and produced a leftward shift in the intracellular Ca2+ concentration-tension relationship, a response that was partially inhibited by pretreatment with Y-27632 or GF109203X. CONCLUSIONS: These results indicate that in rabbit corpus cavernosum smooth muscle phenylephrine induces contraction not only by increasing intracellular Ca2+ concentration, but also by increasing Ca2+ sensitivity of the contractile apparatus in a Rho kinase and protein kinase C dependent manner. Antagonism of Ca2+ sensitization pathways in the corpus cavernosum smooth muscle represents an alternate target for the treatment of erectile dysfunction.     

粉防己碱松弛离体新西兰白兔阴茎海绵体作用的研究

目的 :探讨粉防己碱 (Tet)对离体新西兰白兔阴茎海绵体的松弛作用。　方法 :采用离体新西兰白兔阴茎海绵体肌条张力记录法 ,观察Tet对氯化钾 (KCl)和去氧肾上腺素 (PE)诱导收缩的阴茎海绵体肌条的松弛作用 ;L 硝基精氨酸 (L NNA)和亚甲蓝处理后 ,Tet对PE诱导收缩的阴茎海绵体肌条松弛的作用。　结果 :10 μmol/L及3 0 μmol/L的Tet使KCl诱导的最大收缩反应分别降低为 ( 73 .0± 3 .8) %和 ( 41.5± 3 .4) % ,降低程度与Tet的浓度呈正比 (P <0 .0 1)。Tet对 10 μmol/LPE诱导的肌条收缩具有浓度依赖性松弛作用 ,1、10、3 0、10 0 μmol/L的Tet对PE诱导的阴茎海绵体肌条收缩的松弛效应分别为 ( 6.0± 1.4) %、( 2 1.3± 2 .2 ) %、( 47.4± 3 .3 ) %和 ( 68.1±3 .6) % (P <0 .0 1) ;而L NNA及亚甲蓝对Tet的松弛作用没有影响 (P >0 .0 5 )。　结论 :Tet能浓度依耐性地松弛离体新西兰白兔阴茎海绵体 ,其作用机制可能是通过阻滞钙通道 ,而与一氧化氮 环鸟苷酸 (NO cGMP)通路无关     

An in vitro study of nonadrenergic-noncholinergic activity on the cavernous tissue of mouse

The relaxant effects of electrical field stimulation (EFS) and exogenously applied acetylcholine (ACh) or acidified NaNO₂ (a-NaNO₂) were investigated in the isolated mouse corpus cavernosum precontracted with phenylephrine hydrochloride (PE). Tetrodotoxin (TTX) blocked the relaxant effects of EFS completely, whereas it had no effect on the responses to ACh or a-NaNO₂. Guanethidine and indomethacin failed to affect the electrically or ACh-induced relaxations. Atropine completely blocked the effect of ACh; however, it caused a slight reduction in the relaxation evoked by EFS.N ^G- Nitro-l-arginine (l-NOARG) reduced the effects of EFS and ACh significantly, but it was ineffective on the relaxations induced by a-NaNO₂. The inhibitory action ofl-NOARG was partly restored byl-arginine, but not byd-arginine. Methylene blue (MB) and hydroxocobalamin (HC) exhibited significant inhibition on the relaxations evoked by EFS, ACh and a-NaNO₂. Hydroquinone (HQ) reduced relaxation due to a-NaNO₂, but did not affect that of EFS and ACh. Our findings suggest that EFS-induced relaxations of mouse cavernosal tissue are mediated by a transmitter which probably resembles an organic nitrate.     

Pre-junctional alpha2-adrenoceptors modulation of the nitrergic transmission in the pig urinary bladder neck

AIMS: To investigate the nitric oxide (NO)-mediated nerve relaxation and its possible modulation by pre-junctional alpha2-adrenoceptors in the pig urinary bladder neck. METHODS: Urothelium-denuded bladder neck strips were dissected, and mounted in isolated organ baths containing a physiological saline solution (PSS) at 37 degrees C and continuously gassed with 5% CO2 and 95% O2, for isometric force recording. The relaxations to transmural nerve stimulation (electrical field stimulation [EFS]) or exogenously applied NO were carried out on strips pre-contracted with 1 microM phenylephrine (PhE) and treated with guanethidine (10 microM) and atropine (0.1 microM), to block noradrenergic neurotransmission and muscarinic receptors, respectively. RESULTS: EFS (0.2-1 Hz, 1 msec duration, 20 sec trains, current output adjusted to 75 mA) evoked frequency-dependent relaxations which were abolished by the neuronal voltage-activated Na+ channel blocker tetrodotoxin (TTX, 1 microM). These responses were potently reduced by the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine (L-NOARG, 30 microM) and further reversed by the NO synthesis substrate L-arginine (L-ARG, 3 mM). The alpha2-adrenoceptor agonist BHT-920 (2 microM) reduced the electrically evoked relaxations, its effectiveness being higher on the responses induced by low frequency stimulation. BHT-920-elicited reductions were fully reversed by the alpha2-adrenoceptor antagonist rauwolscine (RAW, 1 microM). Exogenous NO (1 microM-1 mM) induced concentration-dependent relaxations which were not modified by BHT-920, thus eliminating a possible post-junctional modulation. CONCLUSIONS: These results indicate that NO is involved in the non-adrenergic non-cholinergic (NANC) inhibitory neurotransmission in the pig urinary bladder neck, the release of NO from intramural nerves being modulated by pre-junctional alpha2-adrenoceptor stimulation.     

Hypercholesterolemia impairs endothelium-dependent relaxation of rabbit corpus cavernosum smooth muscle

The majority of cases of impotence are associated with vascular risk factors such as diabetes, hypercholesterolemia, hypertension and smoking. These factors induce impairment of endothelium-dependent relaxation of blood vessels in man and in experimental animals. In this study the effects of hypercholesterolemia on the reactivity of rabbit corpus cavernosum smooth muscle strips to endothelium-dependent and endothelium-independent agents were investigated. New Zealand White rabbits (n = 14) were randomly divided into control and treatment groups. The control group (n = 7) received a regular diet while the treatment group (n = 7) was fed a diet of 0.5% cholesterol and 4% peanut oil for 10 weeks. Animals were then sacrificed and the corporal tissue studied in organ chambers for isometric tension measurement. Tissue was contracted with phenylephrine and concentration-dependent relaxation to acetylcholine, in the presence and absence of indomethacin, and to nitroprusside were examined. Blood level of cholesterol in the cholesterol-fed group was significantly higher compared to the control group. Contractions to phenylephrine were similar in both groups. Hypercholesterolemia, however, inhibited relaxation to acetylcholine but did not alter relaxation to nitroprusside, a cyclic guanosine monophosphate (cGMP)-dependent, direct smooth muscle dilator. Indomethacin enhanced the relaxations to acetylcholine in both control and cholesterol-fed groups but did not correct the difference in the relaxation to acetylcholine between both groups. It is concluded that hypercholesterolemia impairs endothelium-mediated relaxation of rabbit corpus cavernosum smooth muscle. The mechanism for the endothelial dysfunction does not appear to involve alteration in cyclooxygenase products of arachidonate or the cGMP-dependent relaxation of corporal smooth muscle. Impairment of endothelium-dependent relaxation of corporal smooth muscle may contribute to the pathophysiology of impotence associated with hypercholesterolemia in man.     

The effects of long-term oral administration of L-arginine on the erectile response of rabbits with alloxan-induced diabetes

OBJECTIVE: To investigate the effects of the long-term oral administration of L-arginine on the impaired neurogenic and endothelium-dependent relaxation responses of corpus cavernosum smooth muscle from alloxan-induced diabetic rabbits. MATERIALS AND METHODS: Thirty-two New Zealand white rabbits were used in four groups of eight each. In group 1, the rabbits received no treatment after the induction of diabetes with alloxan hydrochloride given intravenously; in group 2, L-arginine (1 mg/mL) was administered orally after the induction of diabetes; in group 3, 6 U/day of insulin was injected subcutaneously; group 4 was maintained with no treatment (as litter-mate controls) for 8 weeks. Thereafter, the rabbits were killed by exsanguination and the penis removed en bloc. The reactivity of corpus cavernosum strips from the penis was then assessed in organ chambers. RESULTS: Relaxation and contraction responses of corpus cavernosum strips to sodium nitroprusside and potassium chloride, respectively, were similar in all groups. Relaxation responses of corpus cavernosum strips elicited by electrical field stimulation and carbachol from rabbits in group 1 were less than in controls; the responses to carbachol were not significantly impaired in group 2 and 3, whereas responses to electrical field stimulation were impaired in both groups when compared with the control group. CONCLUSION: The impairment of endothelium-dependent and nerve-mediated relaxation by diabetes appears to involve an alteration in nitric oxide/cyclic GMP pathway. Administration of oral L-arginine increased endothelium-dependent relaxation, probably through activating nitric oxide synthase. Additionally, decreasing elevated blood glucose concentration and advanced glycosylation products by insulin treatment protected endothelium-dependent relaxation, whereas neither L-arginine nor insulin treatment restored impaired neurogenic relaxation.