Isolated Rat Vas Deferens Research Articles

A thin-layer chromatographic procedure for the assay of labelled noradrenaline and its metabolites in tissues and in incubation medium.

A method for the extraction, separation and quantitative determination of [3H]noradrenaline [3H-NA] and its five major metabolites has been devised using thin layer chromatography. This procedure was used to study the pattern of 3H-NA and its metabolites in the total radioactivity of the tissues and that released spontaneously from the rat isolated vas deferens. Whereas in tissues 3H-NA represented almost all of the total radioactivity (94-8+/-0.47%), in the samples of spontaneous outflow it represented only 16-8+/-2.1%. The rest was mostly accounted for by the five metabolites, primarily 3H-DOPEG and 3H-MOPEG. These findings show that in the rat vas deferens 3H-NA is preferentially metabolized via the two glycol derivatives, i.e. 3H-DOPEG and 3H-MOPEG.

Effect of meptazinol on evoked responses in rat vas deferens.

Responses of rat isolated vas deferens to electrical stimulation through field electrodes (400 mA, 1 ms duration, single shocks at 5 min intervals) were potentiated by meptazinol (10 to 300 microM) in whole tissues and also in the separated prostatic and epididymal portions. The effect was fast in onset, reproducible and easily reversed by washing. Prazosin (0.1 microM) practically abolished the response of the epididymal portion to electrical stimulation while the response of the prostatic portion was only slightly reduced (less than 20%). In the presence of prazosin, meptazinol still produced potentiation of the response of the prostatic portion. Nifedipine (2 microM) practically abolished the response of the prostatic portion to electrical stimulation while the response of the epididymal portion was only slightly reduced (less than 20%). In the presence of nifedipine, meptazinol no longer produced potentiation of the response of the epididymal portion. Exogenous ATP (5 microM to 1 mM) and phenylephrine (1 to 50 microM) produced a contractile response which was potentiated in the presence of meptazinol (100 microM) but in the presence of meptazinol (100 microM) and nifedipine (5 mM) together, potentiation of phenylephrine no longer occurred. It is suggested that potentiation by meptazinol of electrically induced responses in this tissue is due to a direct action on the smooth muscle.

Stereoselectivity of catecholamines: differential effects of cocaine and desipramine on catecholamine-induced contractions of the rat isolated vas deferens.

The effect of uptake inhibitors, cocaine and desipramine, on the contractile response of the rat isolated vas deferens to the enantiomers of noradrenaline and adrenaline and to the corresponding deoxy-derivatives, dopamine and epinephline, was investigated. Cocaine (10(-6)M) significantly potentiated all six agonists; the effect was most marked for the laevo-isomers (-)-noradrenaline and (-)-adrenaline. Desipramine (10(-7) M) also potentiated (-)-noradrenaline, (+)-noradrenaline, (-)-adrenaline, (+)-adrenaline and epinephline but, in contrast, antagonized dopamine. This selective antagonism of dopamine by desipramine was also observed for the separated epididymal and prostatic ends of the rat vas deferens.

Differential blockade of pre- and postsynaptic alpha-adrenoceptors by the 2-R and 2-S enantiomers of WB4101.

Agonists and antagonists of the alpha-adrenoceptor have been shown to possess different degrees of potency at the pre- and postsynaptic levels. The present investigation was undertaken to see whether the two optical isomers of WB4101 likewise exhibit differential blockade at the two receptor sites. This was achieved by measuring the potencies of 2-R and 2-S WB4101 against noradrenaline-induced contractions of the rat isolated vas deferens and against clonidine-induced inhibition of the twitch response in field stimulated rat vas deferens. Results showed that though the enantiomers exhibited widely differing potency, as indicated by calculations of pA2 values, at the postsynaptic level, they possessed almost identical potency presynaptically. In addition, 2-aminomethyl-1,4-benzodioxan itself both exhibited reasonable presynaptic alpha-adrenoceptor blocking activity, whilst being devoid of activity postsynaptically. The values for slope on the Schild plots for 2-R and 2-S WB4101 indicated that they produced classical competitive antagonism at the postsynaptic receptor but at the presynaptic level the values for slope were indicative of a non-competitive type of blockade. Results are discussed in terms of recent suggestions of that agonists and antagonists of the alpha-adrenoceptor may not share a common mechanism or site of action at the presynaptic level.

Presynaptic agonist effect of phentolamine in the rabbit vas deferens and rat cerebral cortex.

Clonidine inhibited the electrically-induced twitch response of the rabbit and rat isolated vas deferens preparations and also the K+-evoked release of [3H]noradrenaline from rat cortical slices. This effect of clonidine was antagonized competitively by yohimbine. Phentolamine inhibited the electrically-induced twitch response of the rabbit, but not the rat, vas deferens and in low concentrations (less than 0.1 microM) also inhibited the K+-evoked release of [3H]NA from rat cortical slices. These inhibitory effects of phentolamine were antagonized by yohimbine in a competitive manner but were not antagonized by indoramin, an alpha 1-adrenoceptor antagonist. In the rabbit vas deferens, the effects of phentolamine were shown not to be due to the stimulation of beta-, H1-, H2-, 5-HT- or muscarinic receptors. These results are consistent with the view that phentolamine can act as an agonist at presynaptic alpha 2-adrenoceptors in the rabbit vas deferens and rat cortex but not in the rat vas deferens.

Some actions of 4,17a-dimethyl-4,17a-diaza-D-homo-5alpha-androstane dimethiodide (HS-342), a new neuromuscular blocking drug.

Abstract The effects of the newly-synthesized bisquaternary steroid 4,17a-dimethyl-4,17a-diaza-D-homo-5α-androstane dimethiodide (HS-342) have been investigated on the rat isolated phrenic nerve-hemidiaphragm, chick biventer cervicis and intact cat tibialis anterior muscle preparations, on the guinea-pig isolated ileum and on the rat isolated vas deferens preparations. The anticholinesterase activity of HS-342 was also measured. In the skeletal muscle preparations HS-342 exhibited properties of a post-junctionally active neuromuscular blocking agent of the non-depolarizing class. In the anaesthetized cat HS-342 exhibited approximately equal activity to that of tubocurarine, but its duration of action was about one-third of that of tubocurarine. HS-342 exhibited low anticholinesterase activity, low muscarinic blocking activity and apparently had no effect on the adrenergic neuroeffector junction studied.

Ca2+ channel-blocking effect of the yohimbine derivatives, 14 beta-benzoyloxyyohimbine and 14 beta-pho-nitrobenzoyloxyyohimbine.

Yohimbine possesses a relatively selective alpha 2-adrenoceptor antagonistic effect and a weak Ca2+ channel blocking activity, so two derivatives, 14 beta-benzoyloxyyohimbine and 14 beta-rho-nitrobenzoyloxyyohimbine were compared with yohimbine using those parameters. The two derivatives blocked Ca2+-induced contraction of the rat perfused mesenteric vascular bed at 3 X 10(-6) M, and developed dose-dependent shifts of the dose-response curve to the right in concentrations from 3 X 10(-6) to 10(-5) M. Yohimbine showed a weak Ca2+ channel-blocking effect only at a concentration of 10(-5) M. On the other hand, both derivatives at 3 X 10(-6) M did not affect the dose-response curve to noradrenaline-induced vasoconstriction. Furthermore, at 10(-8) M they had no effect on the dose-response curve to clonidine-induced inhibition of the twitch response of the rat isolated vas deferens evoked by electric stimulation, whereas yohimbine significantly attenuated clonidine-induced inhibition. These results indicate that introduction of bulky substituents into the 14-position of yohimbine intensely potentiated the Ca2+ channel-blocking effects and reduced alpha-adrenoceptor antagonistic effects compared with those of yohimbine, and suggest that chemical modifications of yohimbine may lead to structurally new types of Ca2+ channel-blockers.

Analysis of the effects of apomorphine and bulbocapnine in relation to the proposed dopamine receptor.

Abstract On rat isolated vas deferens, apomorphine was found to be l/5th as active as dopamine. Reserpine or cocaine pretreatment failed to reduce the response to apomorphine. Low concentrations of apomorphine which do not cause contraction of the tissue, antagonize the effects of dopamine. The effects of dopamine were antagonized equally by phentolamine or apomorphine. On rabbit aortic strips 4 × 10−4M apomorphine repeated at 45 min intervals induces pronounced tachyphylaxis. During the tachyphylactic period dopamine was not inhibited to a significantly greater extent than was phenylephrine. Bulbocapnine tested against dopamine and phenylephrine yielded identical pA2 values of 6. Only at 10−5M was bulbocapnine observed to produce a preferentially greater blockade of dopamine. Dopamine or isoprenaline-induced relaxations of aortic strips were not blocked by bulbocapnine. Dopamine and 3 times 10−6M bulbocapnine increased the chronotropic effects in atria. Apomorphine and higher doses of bulbocapnine produced rate decelerating effects. On atria low doses of apomorphine were equally effective in reducing the effects of dopamine or histamine. These results are discussed in light of the proposal that the effects of apomorphine and bulbocapnine involve dopamine receptor interactions. In all three tissues there was no clear cut evidence of specific dopamine receptors.

Effects of long‐term treatment with fluoxetine and venlafaxine on rat isolated vas deferens

Antidepressant therapy is considered as one of the factors leading to male infertility. In this study, the effects of long-term treatment with fluoxetine or venlafaxine were investigated on electrical field stimulation (EFS, 1-64 Hz), noradrenaline (10(-8) to 10(-4) M), serotonin (10(-8) to 10(-4) M), adenosine 5'-triphosphate [ATP (10(-8) to 10(-4) M)] and 80 mM KCl-induced contractile responses in the epididymal and prostatic portions of rat isolated vas deferens strips. Serotonin-induced contractile responses were significantly increased in the epididymal portion of the vas deferens obtained from the fluoxetine-treatment group, whereas in the prostatic portion there was no change. However, venlafaxine treatment had no effect on serotonin responses in the either portion of the vas deferens. Both fluoxetine and venlafaxine treatment significantly inhibited ATP-evoked contractions of the prostatic and epididymal portions of the rat vas deferens, but had no effect on EFS, noradrenaline- and KCl-evoked contractions of the vas deferentia in both portions. In conclusion, these results suggest that chronic treatment with fluoxetine and venlafaxine affects vas deferens motility. Purinoceptors may, at least in part, responsible for the impaired motility in chronic treatment of venlafaxine and fluoxetine.

In Vitro Studies of the Activity of Newly Sinthesized Nociceptin / Orphanin FQ Receptor Ligand Analogues

Based on template hexapeptides Ac-Arg-Tyr-Tyr-Arg-Trp-Lys-NH(2) and Ac-Arg-Tyr-Tyr-Arg-Ile-Lys-NH(2) analogues and corresponding deacylated homologues were synthesized substituting ornithine, diaminobutanoic (Dab) and diaminopropanoic (Dap) acids for lysine at position 6. The aim was to investigate the effect of the newly synthesized compounds on the neurogenic contractions of isolated rat vas deferens. Ac-Arg-Tyr-Tyr-Arg-Trp-Lys-NH(2) and its analogues manifested a strong inhibitory effect on the neurogenic contractions without effect on the muscle tone, which is characteristic effect of NOP receptor agonists. In contrast, Ac-Arg-Tyr-Tyr-Arg-Ile-Lys-NH(2) and its analogs manifested a strong inhibitory effect on the muscle tone and negligible effect on the neurogenic contractions which is characteristic effect of NOP receptor antagonists. The most active were the peptides in which Dab or Dap is the substitute. The study reveals that substitution of Lys with shorter amino acids could increase agonist or antagonist activity of the peptide.

α1- and α2-Adrenoceptor hyporesponsiveness in isolated bisected vas deferens of bile duct-ligated rats

It has been suggested that cholestasis accompanied with changes in autonomic balance and hyporesponsiveness in muscarinic and adrenergic receptors of some organs, e.g. cardiovascular system. Increased plasma levels of epinephrine and norepinephrine has been shown during cholestasis suggesting augmented activity of sympathetic nervous system. In this study we evaluate both alpha(1) and alpha(2) responsiveness in isolated rat vas deferens, as a tissue with rich adrenergic innervations. Epididymal and prostatic halves of vas deferens responsiveness have been studied to phenylephrine and clonidine respectively in three groups of un-operated, sham-operated (sham), and bile duct-ligated (BDL) rats. Our results indicate that in vas deferens of BDL animals, the concentration-response curve of both phenylephrine and clonidine shifted to rightward compared to control group, while the position of concentration-response curve of sham group did not change significantly (P > 0.05). EC(50) of phenylephrine and IC(50) of clonidine were increased showing a decreased responsiveness of tissue to phenylephrine (P < 0.05) and clonidine (P < 0.001) in BDL rats. In this study, both subtype of alpha-adrenoceptors (alpha(1) and alpha(2)) has been studied in cholestatic rat vas deference. Our results showed that cholestasis induce hyporesponsiveness to phenylephrine and clonidine. These results are consistent with previous reports, suggesting the hyporesponsiveness of alpha(1)-adrenoceptors in pulmonary artery and papillary muscle and mesenteric beds. Our conclusion is that the cholestasis induces hyporesponsiveness to phenylephrine and clonidine in epididymal (alpha(1)-adrenoceptors) and prostatic (alpha(2)-adrenoceptors) halves of rat vas deferens respectively. Although the logical explanation to this hyporesponsiveness is the down regulation but it has been suggested that it is not because of down regulation.

Inhibition of rat vas deferens contractions by flavonoids in-vitro

Flavonoids are a large heterogeneous group of benzo-gamma-pyrone derivatives, which are abundantly present in our diet. In this study we investigated the effect of ten flavonoids (quercetin, kaempferol, morin, galangin, rutin, apigenin, flavone, naringenin, hesperitin and silybin) on the contractile response elicited by electrical field stimulation in the rat isolated vas deferens. All flavonoids tested inhibited vas deferens contractions. The relative order of potency of the tested flavonoids was naringenin > hesperitin > morin > kaempferol > apigenin > silybin > flavone > rutin > quercetin > galangin. Analysis of the chemical structures showed that the saturation of C-2-C-3 double bond and the presence of hydroxyl groups on the flavonoidic scaffold play an important role in the activity of flavonoids.

Structure−Activity Relationships in 1,4-Benzodioxan-Related Compounds. 9. From 1,4-Benzodioxane to 1,4-Dioxane Ring as a Promising Template of Novel α1D-Adrenoreceptor Antagonists, 5-HT1A Full Agonists, and Cytotoxic Agents

Novel 1,4-dioxane compounds structurally related to WB 4101 (1) were prepared in order to investigate the possibility that the quite planar 1,4-benzodioxane template of 1 might be replaced by the less conformationally constrained 1,4-dioxane ring. The biological profiles of the new compounds were assessed using binding assays at human cloned alpha 1-adrenoreceptor (alpha 1-AR) subtypes and 5-HT 1A receptors, expressed in Chinese hamster ovary and HeLa cell membranes, respectively, and by functional experiments in isolated rat vas deferens (alpha 1A), spleen (alpha 1B), and aorta (alpha 1D). Moreover, the cytotoxic effects of the novel compounds were determined in PC-3 prostate cancer cells. The results showed that the properly substituted 1,4-dioxane nucleus proved to be a suitable scaffold for selective alpha 1D-AR antagonists (compound 14), potential anticancer agents (compound 13), and full 5-HT 1A receptor agonists (compound 15). In particular, compound 15 may represent a novel lead in the development of highly potent 5-HT 1A receptor full agonists useful as antidepressant and neuroprotective agents.

The synthesis of N-phenoxyethyl-1-substituted-1,2,3,4-tetrahydroisoquinolines and their α 1-adrenoceptor blocking activity

A series of phenoxyisoquinolines, N-phenoxyethyl-1-(2-nitrophenyl)-1,2,3,4-THIQs 3a– 3d, N-phenoxyethyl-1-benzyl-1,2,3,4-THIQ 3e, N-phenoxyethyl-1-(2-aminophenyl)-1,2,3,4-THIQs 5f– 5i, N-phenoxyethyl-1-(2-phenoxyethylaminophenyl)-1,2,3,4-THIQs 5f′– 5i′, have been synthesized and tested in isolated rat vas deferens α-adrenoreceptors. Comparison of pA2 values for these compounds in the presence of phenylephrine confirms that α 1-adrenoceptor blocking activity of 3a– 3d (–NO 2 series) is more active than 6a– 6c (–NH 2 series) in the aortic rings isolated from SD rats. On the other hand, the electron-donating group at the 6-position of isoquinoline ring either increases or decreases the α 1-adrenoceptor blocking activity.

DAMGO and 6β-glycine substituted 14-O-methyloxymorphone but not morphine show peripheral, preemptive antinociception after systemic administration in a mouse visceral pain model and high intrinsic efficacy in the isolated rat vas deferens

Peripheral μ-opioid receptors (MOR) have emerged as important components of inhibitory nociceptive pathways. Here, the antinociceptive effects of MOR agonists, the 6β-glycine derivative of 14-O-methyloxymorphone (HS-731), DAMGO and morphine were evaluated in a mouse model of visceral pain. The abdominal acetic acid-induced writhing test was used to examine the peripheral, preemptive antinociceptive opioid action on visceral nociception. HS-731 administered subcutaneously (s.c.) or intracerebroventricularly (i.c.v.) dose-dependently and completely inhibited writhing, being 24–598-fold more potent, depending on the administration route, than two selective MOR agonists, the enkephalin analogue [d-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO) and morphine. A longer duration of action (2–3h) was induced by HS-731 given before acetic acid, while shorter effect was produced by morphine (30–60min) and DAMGO (30–45min). The antinociceptive effects of systemic opioids were reversed by the s.c. opioid antagonist, naloxone. Blocking of central MOR by the selective MOR antagonist d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP, i.c.v.) resulted in a significant reduction of antinociception of s.c. morphine, whereas it completely failed to antagonize the effects of systemic HS-731 or DAMGO. In in vitro studies, HS-731 and DAMGO, but not morphine showed high intrinsic efficacy, naltrexone-sensitive agonist effect at MOR of the rat vas deferens. These data demonstrate that selective activation of peripheral MOR by systemic s.c. HS-731 or DAMGO produces potent peripheral, preemptive visceral antinociception, while morphine's effects are mediated primarily through central mechanisms. Our findings support the role of peripheral MOR in the pathology of pain states involving sensitization of peripheral nociceptors.

Specific H +/K +-ATPase inhibitors decreased contractile responses of isolated rat vas deferens

The effect of H +/K +-ATPase inhibitors on rat vas deferens contractility was investigated in vitro. Omeprazole (100–300 μM), lansoprazole (100–300 μM) and SCH 28080 (10–100 μM) (2-methyl-8-(phenylmethoxy)-imidazo[1,2-a]pyridine-3-acetonitrile) decreased contractile responses of vas deferens to electrical field stimulation, high K + (80 mM) and phenylephrine in a reversible, reproducible and concentration-dependent manner. The inhibitory potency of lansoprazole on vas deferens contractility was increased in relatively acidic solution (pH 6.9), suggesting that the site of action may be related to H +/K +-ATPase. However, lansoprazole-induced inhibition on contractility was unaltered in K + free solution, indicating that the mechanism of action is independent from H +/K +-ATPase. Reversible nature of omeprazole and lansoprazole-induced inhibition on contractility also suggests that the effects are not due to inhibition of H +/K +-ATPase, since both compounds are irreversible inhibitors of the enzyme. Presence of ouabain (5 μM) did not decrease lansoprazole-induced inhibition on contractility but potentiated the inhibitory effect of lansoprazole, suggesting that lansoprazole-induced inhibition is not mediated by the inhibition of Na +/K +-ATPase. Calcium-induced contractions in high K +–Ca 2+ free medium were completely antagonized by lansoprazole, implying that lansoprazole inhibits Ca 2+ entry through voltage-gated channels. In conclusion, three H +/K +-ATPase inhibitors decreased contractile responses of rat vas deferens to various stimulants in vitro. They may act on a common mechanism, which plays a crucial role in regulating rat vas deferens contractility and this mechanism is probably involved in the regulation of intracellular Ca 2+.

L-NAME pre-treatment partially inhibits the agmatine-evoked depression of the electrically induced twitch contraction of isolated rat vas deferens

The effect of the putative endogenous ligand for α 2-adrenoceptors and imidazoline receptors agmatine was studied in sympathetic neurotransmission in the rat epididymal vas deferens. Tissues were obtained from N ϖ-nitro- l-arginine methyl ester ( l-NAME)-treated or normal animals and were contracted by electrical stimulation or by exogenous adenosine 5′-triphosphate (ATP). In the electrically stimulated epididymal end, agmatine produced an inhibitory effect on twitch contraction that was partially reversed in l-NAME-treated animals, whereas the inhibition produced by clonidine was not affected by l-NAME treatment. The nitric oxide (NO)-donor S-nitroso- N-acetyl-penicillamine (SNAP) also inhibited twitch contraction. Neither agmatine nor SNAP interfered with the responses induced by exogenous ATP in the epididymal end. Removal of the epithelium of the preparation did not modify the agmatine response. We conclude that a nitrergic pathway activated by agmatine plays a role in its inhibitory effect in rat vas deferens, but it remains to be investigated whether it results from a direct action on the enzyme NO-synthase or a receptor-mediated mechanism.

Effects of Mondia whitei extracts on the contractile responses of isolated rat vas deferens to potassium chloride and adrenaline

Objective: To investigate the effects of the methylene chloride:methanol (CH2Cl2:MeOH, 1:1) extract of the dried roots of Mondia whitei Linn and its hexane and methanol fractions on potassium chloride (KCl) and adrenaline (Adr)-induced contractions of rat vas deferens. Materials and Methods: Isolated strips of normal adult rat vas deferens were mounted in a Ugo Basile single-organ bath containing Krebs solution. Cumulative concentration-response curves of KCl (1-7 x 10-2 M ) and adrenaline (1.21-8.45 x 10-7 M ) were established in the absence and presence of M. whitei (50-400 µg/ml). In separate experiments, after obtaining a stable plateau of contractions with KCl (60 m M ), M. whitei samples (50-400 µg/ml) were added cumulatively to relax the preparation. In KCl (60 m M ), containing depolarizing medium, cumulative concentration-contraction curve to CaCl2 (2-14 x 10-2 M ) was elicited in the absence and presence of the hexane fraction of M. whitei (50-400 µg/ml). Results: All the M. whitei samples produced rightward shift of the concentration-response curves to KCl and Adr. At high concentration of the plant extracts (400 µg/ml), a decrease of the maximal response to the contractile agents was observed compared with that obtained with the control. All the three extracts produced concentration-dependent relaxation of the plateau of contraction induced by KCl and the hexane fraction appeared to be the more potent. In calcium-free physiological salt solution, the hexane fraction of M. whitei produced rightward shift to the concentration-response curve to CaCl2 and completely abolished the contractile effect of calcium at high concentration (400 µg/ml). Conclusion: It is concluded that M. whitei extracts antagonized the contractile responses to KCl and Adr in isolated rat vas deferens, which could be due to the blockade of voltage-operated calcium channels.

Calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens: a relative potency measurement study.

We evaluated the calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens and determined their relative order of potency. Cumulative control concentration-response curves to calcium chloride were obtained in isolated rat vas deferens incubated in depolarizing calcium-free Krebs-Henseleit solution. Tissues were washed to baseline length and equilibrated with a given concentration of test drugs. After a 30-minute period a calcium concentration-response curve was repeated. The resulting rightward displacement of the concentration-response curve to calcium provided a dose ratio. The dose ratio was used in the Schild equation and the antagonism of calcium induced contractions was quantified by Schild analysis. The calcium channel blocking activity of thioridazine, clomipramine and fluoxetine was compared with nifedipine. All 4 drugs produced parallel rightward displacement of concentration-response curves to calcium. The potency of this effect was quantified by Schild analysis showing pA estimates, namely nifedipine 7, thioridazine 6.2, clomipramine 5.65 and fluoxetine 5. A characteristic profile of calcium channel blocking activity on the vas deferens was obtained for all test drugs. The relative order of potency was determined as thioridazine greater than clomipramine greater than fluoxetine. Differences in the potency of calcium entry blockade at peripheral end organs may contribute to differential effects of these drugs on delaying ejaculatory latency in patients with premature ejaculation.

Possible role of sildenafil in inhibiting rat vas deferens contractions by influencing the purinergic system

To evaluate the effect of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-selective type 5 phosphodiesterase, on isolated rat vas deferens and its connections with the purinergic system. Epididymal and prostatic portions of isolated vas deferens were placed in organ baths containing Krebs' solution. Contractions were induced by noradrenaline (NA), adenosine triphosphate (ATP), alpha,beta-methylene ATP and electrical field stimulation (EFS). The effect of sildenafil on the contractions was compared with suramin and Evans blue (EB). NA, ATP, alpha,beta-methylene ATP and EFS caused contractions in both portions of vas deferens. NA-induced contractions were unaffected by sildenafil and suramin but potentiated by EB. ATP-induced contractions were non-competitively inhibited in both portions by sildenafil and suramin but potentiated by EB. alpha,beta-methylene ATP-induced contractions were unaffected by sildenafil but were inhibited in both portions by suramin and EB. EFS-induced contractions were inhibited by sildenafil and suramin while potentiated by EB. Sildenafil inhibited the contractions in both portions of vas deferens, as did suramin. We have suggested that purinergic system has a role in this antagonism and it seems to be mediated by an ATP-dependent mechanism instead of a receptor interaction.