Effect of chronic renal failure on the purinergic responses of corpus cavernosal smooth muscle in rabbits

OBJECTIVE: To examine purinergic relaxation responses in chronic renal failure (CRF) in an experimental rabbit model, and thus evaluate the possible involvement of the purinergic system in erectile dysfunction with CRF. MATERIALS AND METHODS: The relaxant effects of ATP were measured in strips of corpus cavernosum smooth muscle taken from control and CRF rabbits. CRF was induced in New Zealand white rabbits as previously described. Penises were excised from CRF rabbits 4 weeks after inducing uraemia. In an organ bath the strips from controls and CRF rabbit corpus cavernosum were pre-contracted with phenylephrine and increasing doses of adenosine and ATP added. RESULTS: In the pre-contracted rabbit cavernosal tissue the relaxations induced by adenosine and ATP were unchanged in CRF. CONCLUSION: The lack of any relaxant effect of adenosine or ATP on the relaxation of cavernosal smooth muscle in rabbits with CRF might be because the relaxant effects of these agents are endothelium-independent and the endothelial purinergic receptor density was unchanged in CRF.     

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.     

The participation of adenosine receptors in the adenosine 5''-triphosphate-induced relaxation in the isolated rabbit corpus cavernosum penis

AIM: To investigate the participation of adenosine receptors in the adenosine 5'-triphosphate (ATP)-induced relaxation in the corpus cavernosum penis (CCP) of rabbits. METHODS: The ATP-induced relaxation was assessed on the noradrenaline precontracted CCP of rabbits in the presence and absence of 8-(3-chlorostyryl)caffeine (CSC); an adenosine A(2A) receptor antagonist; alloxazine and MRS1754; adenosine A(2B) receptor antagonists; and ARL67156, an inhibitor of ecto-nucleoside triphosphate diphosphohydrolases. RESULTS: Adenosine and ATP relaxed the noradrenaline precontracted CCP of rabbits in a concentration-dependent manner. The adenosine- and ATP-induced relaxations were suppressed by alloxazine and MRS1754, but not by 8-(3-chlorostyryl)caffeine. ARL67156 potentiated the ATP-induced relaxation but not the adenosine-induced one. MRS1754 suppressed the ATP-induced relaxation potentiated by ARL67156. CONCLUSIONS: The above results suggest that, in the CCP of rabbits, the adenosine receptor mediating adenosine-induced relaxation is of the A(2B) receptor and the ATP directly causes relaxation through the A(2B) receptor on the CCP.     

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     

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.     

Changes in the smooth muscle of the corpora cavernosum related to reversal of partial bladder outlet obstruction in rabbits

Previous studies have demonstrated that partial bladder outlet obstruction (PBOO) in the rabbit induces an increase in corpus cavernosum smooth muscle (CCSM) tone, which may make it difficult for the CCSM to relax. Thus, to determine whether the corpus cavernosum restores relaxation after reversal of PBOO, we investigated the physiologic, histologic, and cell biology in penises obtained from rabbits 4 weeks and 8 weeks after reversal of PBOO. CCSM from bladder outlet-obstructed and obstruction-reversed rabbits showed significant decreases in the contractile responses to phenylephrine. The relaxation responses to electrical field stimulation (EFS), ATP, acetylcholine, and sodium nitroprusside (SNP) were decreased in obstructed and reversed for 4 weeks groups. By 8 weeks of reversal, the relaxation of CCSM was increased gradually in response to EFS, SNP, and acetylcholine. However, the response to ATP did not result in the relaxation of CCSM to control levels. The ratio of SM to collagen decreased after obstruction and remained low after reversal. Expression of both isoforms of Rho kinase (ROK) was increased in obstruction groups. At 4 weeks of reversal, the expression of ROK alpha remained at obstruction level, whereas ROK beta expression decreased in comparison with the obstruction group. By 8 weeks of reversal, expression of both ROK alpha and beta significantly decreased when compared with the obstruction group. These results suggested that the poor relaxation response at reversal of 4 weeks was associated with incomplete decreased expression of both isoforms of ROK, whereas the incomplete recovery of the CCSM relaxation response at reversal of 8 weeks may be associated with structural alterations in the CC and irreversible damage from PBOO.     

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     

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.     

In vitro evaluation of nebivolol effects on nonadrenergic noncholinergic responses in rabbit corpus cavernosum

The purpose of this study was to compare the effects of nebivolol on nonadrenergic noncholinergic (NANC) relaxation functions that are mediated by electric field stimulation (EFS) in rabbit corpus cavernosum smooth muscle by comparison with other beta‐adrenergic receptor blockers and show the level on which its effects through nitric oxide take place. After the effects of nebivolol on the isolated corpus cavernosum tissues that were contracted through the alpha‐adrenergic pathway and application of L‐NAME’ (N^G‐nitro‐L‐arginine methyl ester) which is a competitive inhibitor of nitric oxide synthase (NOS), the changes that occurred were recorded. Following the effect on the tissue that was contracted with phenylephrine in the presence of atropine and guanethidine that was created by EFS, nebivolol and other beta‐blockers were added and the changes were recorded. After receiving relaxation responses with EFS‐mediated NANC, no difference was observed between the relaxation responses due to addition of nebivolol and other beta‐adrenergic blockers (p > 0.05). The finding that nebivolol which has a NO‐mediated relaxation effect did not have an effect on EFS‐mediated NANC relaxation but created relaxation on the tissue that was contracted by phenylephrine and the effect was reversed by L‐NAME, shows that its effects are on a postsynaptic level.     

Does potassium induce the release of nitric oxide in the rabbit corpus cavernosum?

We investigated the effects of increases in the extracellular potassium concentration on the function of the rabbit corpus cavernosum. The resting tissue tension increased as the potassium concentration was increased from 4.7 mM to 20 mM or 30 mM. The maximum contraction induced by 200 μM phenylephrine was significantly decreased in the presence of 30 mM potassium compared with 4.7 mM potassium. After precontraction was induced with 200 μM phenylephrine, the magnitude of field-stimulated relaxation increased significantly as the potassium concentration was increased from 4.7 mM to 10 or 20 mM, but was almost completely abolished at 30 mM potassium. There was no difference in the suppressive effect of l-NAME on field-stimulated relaxation between specimens treated with 4.7 mM or 20 mM potassium. ATP- and bethanechol-induced relaxation was not affected by increases in the extracellular potassium concentration. A high-dose potassium solution (124 mM) induced contraction of the corpus cavernosum. In tissue precontracted with phenylephrine, a high-dose potassium solution that contained phenylephrine induced relaxation of corpus cavernosum; this relaxation was completely suppressed by l-NAME. These findings suggest that small increases in the extracellular potassium concentration increase field-stimulated relaxation of the corpus cavernosum and that this relaxation is not related to the effects of nitric oxide. Relaxation induced by high-dose potassium in tissue precontracted with phenylephrine is probably the result of release of nitric oxide. Received: 6 March 1997 / Accepted: 27 October 1997     

Effect of doxazosin with and without rho-kinase inhibitor on human corpus cavernosum smooth muscle in the presence of bladder outlet obstruction

PURPOSE: We investigated the relationship of adrenergic responses in corpus cavernosum tissues in the presence of BOO using the alpha1-adrenergic receptor antagonist doxazosin (Pfizer, New York, New York) and the rho-kinase inhibitor Y-27632 (Calbiochem, San Diego, California). MATERIALS AND METHODS: CCSM tissue was obtained from patients who underwent penile prosthesis implantation. Patients were divided into 2 groups according to the presence of BOO. The submaximal (EC80) concentration of phenylephrine (Sigma Chemical Co., St. Louis, Missouri) was calculated by evaluating adrenergic activity responses with cumulatively applied phenylephrine. After achieving a stable contraction plateau test compounds were put in an organ bath. The relaxant potencies of doxazosin and Y-27632 were expressed as the percent of inhibition of the contraction plateau induced EC80 concentration of phenylephrine. Relaxation responses in the 2 groups were compared. RESULTS: At the highest dose of increasing concentrations phenylephrine generated 70% more contraction response in the BOO positive group than in the BOO negative group. Doxazosin and Y-27632 caused concentration dependent relaxation in CCSM precontracted by phenylephrine. With doxazosin significantly higher relaxation responses were attained in the BOO positive group in terms of log IC50 and the maximal relaxation response (p = 0.0353 and 0.0003, respectively). Maximum relaxation responses following Y-27632 administration were significantly higher in the BOO positive group. CONCLUSIONS: The contractility of human corpus cavernosum is increased in the presence of BOO. Doxazosin and Y-27632 generate effective CCSM relaxation in the presence of BOO. Doxazosin and Y-27632 may be the alternatives for the treatment of erectile dysfunction associated with BPH.     

Effects of the specific phosphodiesterase inhibitors on alloxan-induced diabetic rabbit cavernous tissue in vitro

An experimental study was done to examine a potential role of phosphodiesterase (PDE) inhibitors in the treatment of diabetic erectile dysfunction. Relaxant effect of specific PDE inhibitors were measured in strips of corpus cavernosum smooth muscle taken from control and diabetic groups. Diabetes mellitus was induced in New Zealand white rabbits using alloxan. Penises excised from diabetic rabbits 8 weeks after the induction of diabetes mellitus. In the organ bath strips from control and diabetic rabbit corpus cavernosum were precontracted and increasing doses of several PDE inhibitors were added. In the precontracted rabbit cavernous tissue, sulmazole and zaprinast specific PDE V inhibitors were equally potent and efficacious in vitro but amrinone, a specific PDE III inhibitor, exhibits low relaxant effects. All PDE inhibitors tested showed a similar relaxation effect on corpus cavernosum smooth muscle from control and 8-week diabetic rabbits. The present study provides the possibility of using selective PDE III and V inhibitors in the treatment of diabetic impotence.     

Relaxation effects of adrenomedullin in isolated rabbit corpus cavernosum smooth muscle

OBJECTIVES: To clarify the pharmacological effects of adrenomedullin, a potent vasodilator and hypotensive peptide isolated from human phaeochromocytoma cells, on corpus cavernosal smooth muscle in vitro, as the intracavernosal injection of adrenomedullin induces penile erection in the anaesthetized cat. MATERIALS AND METHODS: The effects of adrenomedullin were investigated in isolated muscle strips from New Zealand rabbit corpus cavernosum smooth muscle pre-contracted with phenylephrine alone, in the presence of indomethacin (cyclooxygenase inhibitor), Nomega-nitro l-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), and K+-channel blockers. RESULTS: Adrenomedullin caused relaxation of isolated pre-contracted rabbit corpus cavernosum strips in a concentration-dependent manner. The response of corpus cavernosum was unaffected L-NAME, indomethacin and K+-channel blockers. CONCLUSION: The relaxation exerted by adrenomedullin in rabbit corporal tissue may arise from the effect of the drug on its specific receptors and/or calcitonin gene-related peptide-1 receptors. The relaxant effect of adrenomedullin might lead to novel clinical applications for erectile dysfunction.     

Effects of vasoactive drugs on isolated rabbit corpus cavernosum penis

Recently, intracavernous injection of some vasoactive drugs has been performed for the diagnosis and treatment of impotence. Despite extensive studies the mechanism of erection is still obscure. Therefore, the author studied the effects of some vasoactive drugs on isolated rabbit corpus cavernosum penis. Norepinephrine, phenylephrine or clonidine caused contraction of isolated rabbit corpus cavernosum strips in a concentration-dependent manner. This contractile effect was more potent with norepinephrine and phenylephrine than with clonidine. Prazosin was more effective than yohimbine in inhibiting norepinephrine-induced contractions. Papaverine and verapamil strongly relaxed the strips contracted by norepinephrine. Prostaglandin E1 also showed a relaxant effect. Low concentrations of isoproterenol caused relaxation, but in high concentrations it caused contraction. Acetylcholine relaxed norepinephrine-contracted strips in a concentration-dependent manner. Although the relaxant effect of acetylcholine was weaker than that of papaverine at high concentrations, acetylcholine and papaverine were almost equally effective at low concentrations. Vasoactive intestinal polypeptide relaxed the strips, and it was significantly more potent than papaverine. These findings suggest that both postsynaptic alpha 1-adrenoceptors and alpha 2-adrenoceptors are present in rabbit corpus cavernosum penis, and that alpha 1-adrenoceptors are predominant. The flaccid state of the rabbit penis seems to be maintained mainly by alpha 1-adrenoceptors. Verapamil seems to be useful for the diagnosis and treatment of impotence as papaverine. Acetylcholine and vasoactive intestinal polypeptide may be neurotransmitters involved in erection.     

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.     

6种中药提取物对离体新西兰白兔阴茎海绵体的松弛作用

目的:比较6种中药提取物(甲基莲心碱、粉防己碱、葛根素、灯盏花乙素、人参皂苷Rg1和人参皂苷Rb1)松弛离体新西兰白兔阴茎海绵体的作用。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6种中药提取物对去氧肾上腺素(PE)诱导收缩的阴茎海绵体肌条的松弛作用。结果:在(10-8~10-3)mol/L,甲基莲心碱、粉防己碱、葛根素和灯盏花乙素对PE诱导收缩的肌条具有浓度依赖性松弛作用,其IC50分别为4.60×10-6、3.73×10-5、8.03×10-4和3.33×10-3mol/L。而人参皂苷Rg1和人参皂苷Rb1对PE诱导收缩的肌条松弛作用较弱,终浓度为10-3mol/L时,仅分别松弛(16.32±13.36)%和(11.21±7.59)%。结论:6种中药提取物对离体新西兰白兔阴茎海绵体的松弛作用,甲基莲心碱最强。     

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.     

Relaxant effects of some benzothiazolinone derivatives on isolated rabbit corpus cavernosum

 In the present study, two 6-(fluorobenzoyl)-3-piperazinomethyl-2-benzothiazolinone derivatives were synthesized and their relaxant effects on isolated rabbit corpus cavernosum investigated. Compounds Y-16 and Y-21 can alter the ability of corpus cavernosum smooth muscle to contract. Strips of rabbit corpus cavernosum smooth muscle were mounted in isolated tissue baths for measurement of isometric contractile force. Compounds (10⁻⁶–10⁻³ M) did not cause contraction but induced relaxation in precontracted corpus cavernosum smooth muscle. Neither N-nitro-l-arginine methylester (L-NAME) nor indomethacin affected the relaxant effect of these compounds. Glibenclamide and tetraethylammonium chloride (TEA) also did not influence the relaxation induced by the compounds. In conclusion, in isolated rabbit corpus cavenosum, Y16 and Y21 have a relaxant potency equal or superior to known vasoactive agents. Further investigations are needed to show the importance of these effects for the diagnosis and treatment of erectile dysfunction. Received: 5 December 2000 / Accepted: 5 March 2001     

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

Aim： To investigate the relaxation mechanisms of neferine （Nef） on the rabbit corpus cavemosum tissue in vitro. Methods： Strips of rabbit corpus cavemosum were mounted in organ chambers. The effects of Nef were examined on isolated muscle strips precontracted with phenylephrine （PE） alone, in the presence of NW-nitro-L-arginine （LNNA, a nitric oxide synthase inhibitor）, 1-H-[ 1,2,4]oxadiazolo[4,3-tx]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 absencecalcium 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）. Results： Corpus cavemosum strips relaxed in response to Nef （10-9-10-4 mol/L） in a concentration-dependent manner with an IC50 of 4.60 × 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 KC1 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 × 10^5 mol/L） （P 〈 0.05）. The inhibition ratios were 26.2% ± 5.4% and 48.3% ±7.6%, respectively. Conclusion： The results of the present study suggest that Nef possesses a relaxant effect on rabbit corpus cavemosum tissues, which is attributable to the inhibition of extracellular Ca^2＋ influx and the inhibition of release of intracellular stored Ca^2＋, but not mediated by the