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.     

Effects of partial bladder outlet obstruction on contraction and relaxation response of rabbit corpus cavernosum

It has been well established that erectile dysfunction (ED) is a common incident in patients with benign prostate hyperplasia. Animal models have been described to investigate the relationship between bladder obstruction and ED. In this study, we aimed to investigate whether partial bladder outlet obstruction (PBOO) induces changes in the contraction and relaxation response of corpus cavernosum smooth muscle (CCSM) of the penis in the rabbit model. Partial bladder obstruction was performed in rabbits as previously described. After 2 and 4 weeks of follow-up, control, sham-operated (2- and 4-week duration) and partial bladder outlet obstructed (obstruction of 2- and 4-week duration) rabbits were sacrificed and their bladder masses determined. Then CCSM tissue was obtained. Contraction responses induced by 124 mM KCl, phenylephrine (10(-6) to 10(-4)M) and relaxation responses induced by doxazosin (10(-7) to 10(-5)M) in CCSM of rabbits were determined. The obtained contraction and relaxation responses of all groups were compared. Bladder weight was significantly higher in PBOO groups than in control and sham-operated rabbits. Contraction responses induced by KCl and phenylephrine were statistically enhanced in the 4-week PBOO groups than controls. However, there was no statistically significant difference in any KCl, phenylephrine and doxazosin responses between 2- and 4-week sham-operated and PBOO groups. The rabbit model of PBOO described for the studies which examine bladder responses is useful for creating bladder outlet obstruction. However, this model is not suitable for the investigation of outlet obstruction-related ED.     

Increased contractility of diabetic rabbit corpora smooth muscle in response to endothelin is mediated via Rho-kinase beta

Corpus cavernosum smooth muscle (CCSM) from rabbits made diabetic for 6 months as a result of alloxan injection exhibited increased sensitivity (3vs 9 nM EC(50)) and generated 20-50% greater force to endothelin-1 (ET-1) compared to CCSM from normal rabbits. In contrast, the force produced by the CCSM in response to KCl and phenylephrine was not significantly altered in diabetic CCSM. The increased ET-1 sensitivity is associated with a two to three-fold upregulation of ET receptor A at both mRNA and protein levels in diabetic CCSM. ET-1-induced CCSM contraction is largely dependent upon Rho-kinase (ROK), since it is almost completely blocked by Y-27632 (a highly selective ROK inhibitor). Furthermore, expression of ROKbeta isoform is selectively upregulated in CCSM from diabetic rabbits. Thus, an increased CCSM tone, modulated by sensitization of the endothelin-mediated contractile pathway via ROK, may be a key component of the molecular mechanism of diabetes-induced erectile dysfunction.     

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.     

内源性一氧化碳对离体犬阴茎海绵体平滑肌的作用

目的:探讨内源性一氧化碳(CO)对离体犬阴茎海绵体平滑肌作用的影响。方法:利用水浴条件下阴茎海绵体肌条的张力测定技术,用CO合成的关键酶血红素氧合酶(HO)的诱导剂———氯高铁血红素诱导海绵体平滑肌生成内源性CO,观察CO对去氧肾上腺素(PE)诱导收缩的阴茎海绵体肌条作用的影响。结果:氯高铁血红素对10μmol/L PE诱导的肌条收缩具有浓度依赖性的松弛作用,10~100μmol/L氯高铁血红素对平滑肌肌条的松弛效应与空白对照相比明显升高(P<0.01)。用锌原卟啉-Ⅸ(ZnPP-Ⅸ)或亚甲蓝孵育处理后的肌条,氯高铁血红素的舒张作用明显减弱(P<0.01)。结论:内源性CO具有浓度依赖性松弛阴茎海绵体平滑肌的作用,其机制可能是通过CO环磷酸鸟苷途径作用所致。     

Role of rho-kinase activity in angiotensin II-induced contraction of rabbit clitoral cavernosum smooth muscle

Isometric tension measurement using a selective Rho-kinase inhibitor (+)- (R)-trans4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide (Y-27632) and a selective myosin light chain kinase (MLCK) inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML7) were used in rabbit clitoral cavernosum smooth muscle (CSM). N(G)-nitro-L-arginine methyl ester (L-NAME) was used to evaluate the relationship between NO release and Rho-kinase. Y-27632 significantly attenuated contractions induced by ANG II, dose-dependently. However, ML7 did not affect the contractile response to ANG II except in the high concentrations of ML7. Y-27632 inhibited contraction with phenylephrine (PhE), but ML7 did not inhibit contraction with PhE. Nitric oxide synthase inhibitor (NAME) did not affect the Y-27632-induced relaxation in the pre-contracted strip with PhE. The present study demonstrates that G-protein-coupled increase in myofilament Ca(2+) sensitivity mediated through the RhoA/Rho-kinase signal pathway is involved in the control by ANG II of the clitoral CSM tone. RhoA/Rho-kinase pathway acts in the ANG II-induced contraction independently of the NO pathway.     

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.     

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     

Involvement of alpha-receptors and potassium channels in the mechanism of action of sildenafil citrate

Modulation of the adrenergic activity and interfering with channels such as potassium channels may affect relaxation and contraction of the corpus cavernosum. Sildenafil is a selective phosphodiesterase-5 inhibitor, proven effective in treating erectile dysfunction.In this study, the effect of sildenafil citrate on alpha-receptors modulation and potassium channels was tested. The direct relaxant effect of sildenafil citrate was studied by measuring changes in isometric tension in isolated strips of rabbit corpus cavernosum and rat aortic ring precontracted with phenylephrine or KCl compared to that of diazoxide in the presence and absence of tetraethylammonium. The inhibitory effect of sildenafil on electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle was also studied compared to that of phentolamine. Muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M on phenylephrine-precontracted rabbit corpus cavernosum strips was not attenuated by N(G)-nitro-L-arginine (3 x 10(-5) M). Cumulative addition of sildenafil (1 x 10(-9)-1 x 10(-6) M) and phentolamine (1 x 10(-9)-1 x 10(-6) M) to the organ bath dose-dependently inhibited electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle, with almost similar EC(50) values. Sildenafil (1 x 10(-7) M) also inhibited phenylephrine-induced contraction of rat aortic rings by 39.83+/-3.01%. In addition, tetraethylammonium (1 x 10(-3) M) significantly attenuated the muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M) on phenylephrine-precontracted strips of rabbit corpus cavernosum.Sildenafil citrate is capable of producing cavernosal smooth muscle relaxation by an additional mechanism that may involve alpha-receptors and potassium channel opening.     

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.     

The evaluation of the effects of renal failure on erectile dysfunction in a rabbit model of chronic renal failure

OBJECTIVE: To determine whether chronic renal failure (CRF) reduces nitrergic relaxant responses in a rabbit model. MATERIALS AND METHODS: Ten rabbits underwent surgery to induce uraemia (CRF rabbits) and a further 10 a sham operation (controls). Corpus cavernosal tissue was prepared and used in organ-chamber experiments, with relaxation assessed against a background of pre-contraction with phenylephrine. At the plateau of contraction, relaxation responses to cumulative concentrations of carbachol or sodium nitroprusside (SNP), to test endothelium-dependent and -independent relaxations, respectively, were assessed. Before electrical-field stimulation (EFS), the tissue was treated with an adrenergic nerve blocker and a muscarinic receptor blocker to eliminate the adrenergic and cholinergic components, and to determine the relaxation responses to the stimulation of nonadrenergic, noncholinergic (NANC) nerves. The relaxation responses in corporal strips obtained from CRF rabbits were compared with those from controls. RESULTS: When tissues were contracted with KCl, tensions were similar in all groups. The impairment in concentration-dependent relaxation with carbachol was significant in CRF rabbits, but SNP- and papaverine-induced concentration-dependent relaxation responses were no different among the groups. EFS-induced frequency-dependent relaxations were significantly lower in CRF rabbits than in controls. CONCLUSION: CRF inhibits the NANC-mediated relaxation of rabbit corpus cavernosum smooth muscle. Changes in NANC-mediated and carbachol-induced (endothelium-dependent) relaxation of corporal smooth muscle in the rabbit are probably caused by uraemia and subsequently, hyperthyroidism, hyperparathyroidism or low testosterone levels in CRF. These results also suggest that if vasoactive agents are to be used for treating erectile dysfunction in uraemic patients, direct-acting vasodilators and phosphodiesterase inhibitors will be useful.     

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     

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.     

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     

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.     

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.     

SILDENAFIL, A TYPE-5 CGMP PHOSPHODIESTERASE INHIBITOR, SPECIFICALLY AMPLIFIES ENDOGENOUS cGMP-DEPENDENT RELAXATION IN RABBIT CORPUS CAVERNOSUM SMOOTH MUSCLE IN VITRO

Purpose

The primary mechanism for relaxation of corpus cavernosum smooth muscle (CCSM) and penile erection depends upon nitric oxide (NO)-induced elevation of myoplasmic cyclic guanosine monophosphate (cGMP). Agents that enhance the NO-cGMP signal transduction pathway may prove beneficial in treating erectile dysfunction. Sildenafil, a selective type-5 cGMP phosphodiesterase inhibitor, was investigated to determine the specific mechanism(s) involved in the therapeutic use of this compound to treat impotence.

Materials and Methods

Isolated strips of rabbit corpus cavernosum were stimulated isometrically with phenylephrine. Graded relaxations were induced using various concentrations of sodium nitroprusside (SNP) alone and in combination with sildenafil. At fixed times, the tissues were rapidly frozen and processed for myosin light chain (MLC) phosphorylation using isoelectric focusing with Western blot analysis, and cGMP content using radioimmunoassay techniques.

Results

Sildenafil alone reduced spontaneous tone in unstimulated CCSM, but had little effect on phenylephrine-induced isometric tension in the absence of a NO donor (SNP). Sildenafil sensitized the tissue to SNP for relaxation, but the relationship between relaxation and [cGMP] was unchanged by sildenafil. Relaxation from peak isometric force was correlated with [cGMP] but not MLC phosphorylation.

Conclusions

Sildenafil relaxes CCSM by amplifying the effects of the normal, endogenous cGMP dependent relaxation mechanisms.     

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     

Does tourniquet application alter the nitrergic responses of rabbit corpus cavernosum penis?

Objective To investigate the effects of short and long periods of tourniquet application on corporal nerves, endothelium and smooth muscle responses. Methods After the rabbits were anesthetized with xylazine (5 mg/kg) and ketamine hydrochloride (35 mg/kg), a standard rubber circular band was applied to the base of the penis. After waiting for 20, 40 and 60 min, the tourniquets were removed and the penil tissue was reperfused for 5 min. In all groups, relaxation [carbachol, sodium nitroprusside (SNP) and electrical field stimulation (EFS) and contraction (phenylephrine and EFS)] responses were examined. In another set of experiments, the rabbits were killed 24 h after the tourniquet period of 60 min and carbachol-induced relaxation responses were obtained. Results SNP- and EFS-induced relaxation responses were similar in all groups. Carbachol-induced relaxation responses were not altered in tissues from 20 min tourniquet group, but they were significantly reduced in tissues from 40 and 60 min tourniquet group compared to that from control group. The impaired endothelium-mediated relaxation responses did not return to control levels after 24 h of reperfusion period. Neither phenylephrine nor EFS-mediated contraction responses were altered with tourniquet application. Conclusions The results suggest that long period of tourniquet application altered endothelium-dependent muscarinic receptor-mediated relaxation responses. This is the first functional study that examined the effects of tourniquet application on corpus cavernosum tissue. In conclusion, it can be suggested that if tourniquet is necessary in penile surgery the application time of up to 20 min is more appropriate instead of prolonged usage.     

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.