Rabbit Vas Deferens Research Articles

Regulation of nerve-evoked contractions of rabbit vas deferens by acetylcholine.

Stimulation of intramural nerves in the vas deferens of many species yields a classical biphasic contraction comprised of an initial fast component, mediated by P2X receptors and a second slower component, mediated by α1-adrenoceptors. It is also recognized that sympathetic nerve-mediated contractions of the vas deferens can be modulated by acetylcholine (Ach), however there is considerable disagreement in the literature regarding the precise contribution of cholinergic nerves to contraction of the vas deferens. In this study we examined the effect of cholinergic modulators on electric field stimulation (EFS)-evoked contractions of rabbit vas deferens and on cytosolic Ca2+ levels in isolated vas deferens smooth muscle cells (VDSMC). The sustained component of EFS-evoked contractions was inhibited by atropine and by the selective M3R antagonist, 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP). EFS-evoked contractions were potentiated by Ach, carbachol (Cch), and neostigmine. The sustained phase of the EFS-evoked contraction was inhibited by prazosin, an α1-adrenoceptor antagonist and guanethidine, an inhibitor of noradrenaline release, even in the continued presence of Ach, Cch or neostigmine. The soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one enhanced the amplitude of EFS-evoked contractions and reduced the inhibitory effects of 4-DAMP. Isolated VDSMC displayed spontaneous Ca2+ oscillations, but did not respond to Cch. However, the α1-adrenoceptor agonist, phenylephrine, evoked a Ca2+ transient and contracted the cells. These data suggest that EFS-evoked contractions of the rabbit vas deferens are potentiated by activation of M3 receptors and reduced by activation of a sGC-dependent inhibitory pathway.

Determination of In Vivo Bmax and Kd for 11C-GR103545, an Agonist PET Tracer for κ-Opioid Receptors: A Study in Nonhuman Primates

The κ-opioid receptors (KOR) are involved in mood disorders and addictive conditions. In vivo imaging studies of this receptor in humans have not been reported because of the lack of a selective ligand. We used a recently developed selective KOR agonist tracer, (11)C-GR103545, and performed a study in rhesus monkeys to estimate the in vivo receptor concentration (Bmax) and dissociation equilibrium constant (Kd). Four rhesus monkeys underwent 12 scans with (11)C-GR103545 on a PET scanner under baseline and self-blocking conditions. The injected mass was 0.042 ± 0.014 μg/kg for the baseline scans and ranged from 0.16 to 0.3 μg/kg for the self-blocking scans. The radiotracer was administered in a bolus-plus-infusion protocol, and cerebellum was used as the reference region in kinetic analysis. Binding potential (BPND) values were computed as [(CROI/CREF) - 1], where CROI and CREF are the mean of the radioactivity concentrations from 90 to 120 min after tracer administration in a given region of interest (ROI) and in the cerebellum. In 6 scans, arterial input functions and free fraction in plasma (fp) were measured. In addition, a 2-tissue-compartment model was used to compute the volume of distribution in the cerebellum (VT_REF), which was then used to estimate the free-to-nondisplaceable concentration ratio (fND) as fp/VT_REF. A Scatchard plot was used to estimate Bmax, and Kd(ND) = Kd/fND, the Kd value with respect to the cerebellar concentration. Individual data were first analyzed separately and then pooled together. When Kd(ND) was allowed to vary among ROIs, results were variable; therefore, Kd(ND) was constrained to be constant across ROIs, whereas Bmax was allowed to be ROI-dependent and animal-dependent. A global estimate of 1.72 nM was obtained for Kd(ND). Estimated Bmax ranged from 0.3 to 6.1 nM across ROIs and animals. The Kd estimate of 0.048 nM, obtained by correcting Kd(ND) by the factor fND, was in good agreement with the half maximal inhibitory concentration (IC50) of 0.018 nM determined from functional assays in rabbit vas deferens and inhibition constant (Ki) of 0.02 nM measured in radioligand competition assays using cloned human receptors. On the basis of these data, a suitable tracer dose of 0.02 μg/kg was selected for use in humans. The use of a bolus-plus-infusion protocol with the KOR agonist tracer (11)C-GR103545 permitted the successful estimation of Bmax and Kd(ND) in vivo. On the basis of the estimated Kd value, a tracer dose of 1.4 μg (3.38 nmol) for an average body weight of 70 kg was chosen as the mass dose limit in human studies using this novel agonist radiotracer.

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.

Effect of cleistanthin A and B on adrenergic and cholinergic receptors

Objective:The aim was to study the in vitro and in silico interactions of cleistanthin A and B on the adrenergic and cholinergic receptors using isolated animal tissues and bioinformatics tools.Materials and Methods:The alpha adrenergic receptor activities of cleistanthin A and B were studied in vitro using a guinea pig vas deferens preparation. The beta adrenergic receptor activities of cleistanthin A and B on an isolated rat heart were studied in vitro using a modified Langendorff apparatus. The effects of cleistanthin A and B on the nicotinic and muscarinic cholinergic receptors were studied in vitro using rabbit vas deferens and rabbit jejunum, respectively. All the drug responses were recorded using a data acquisition system through a variable force transducer. The receptor–ligand interactions of cleistanthin A and B with adrenergic and cholinergic receptor proteins were determined using the ArgusLab molecular modeling and drug docking program.Results:Cleistanthin A and B significantly inhibited the actions of the alpha adrenergic receptor and the nicotinic cholinergic receptor. Cleistanthin A and B shifted the dose–response curve to the right with an increased EC50 value of phenylephrine and acetylcholine. Both cleistanthin A and B did not have any significant effect on the beta adrenergic and muscarinic cholinergic receptors.Conclusion:Cleistanthin A and B block the alpha adrenergic and nicotinic cholinergic receptors, but these compounds do not interact at all with the beta adrenergic and muscarinic cholinergic receptors.

ChemInform Abstract: 4-((Alkylamino)methyl)furo(3,2-c)pyridines: A New Series of Selective . kappa.-Receptor Agonists.

The synthesis of 5-(arylacetyl)-4-[(alkylamino)methyl]furo[3,2-c]pyri- dines (16-23, 26, 27) and their activities as κ-opioid receptor agonists are described. κ-Agonist potency was particularly sensitive to the na- ture of the basic moiety. In particular, in the rabbit vas deferens (κ- specific tissue), the 3-pyrrolidinol analogue (17) (IC 50 =2.7 nM) was found to be approximately 5-fold more potent than the corresponding py- rrolidine analogue (16) (IC 50 =15 nM). In the rat and hamster vasa de- ferentia (μ-specific and δ-specific tissues, respectively), (17) showed only weak antagonist activity (pK B >5.5), underlining its selectivity for the κ-opioid receptor. The major activity for (17) is resident in the 4S,3'S-isomer (26) (rabbit vas deferens IC 50 = 1.1 nM). Compound (26) displays excellent antinociceptive activity, as determined in the mouse acetylcholine-induced abdominal constriction test (ED 50 = 0.001 mg/kg, sc)

ChemInform Abstract: Synthesis and Pharmacology of the Putative Novel Muscarinic Agonist (S)-4-F-MePyMcN [(S)-4-(Pyrrolidino)-1-methyl-2-butynyl-N-(4-fluorophenyl) Carbamate Oxalate

Abstract ( S )-4-F-MePyMcN [( S )-4-(pyrrolidino)-1-methyl-2-butynyl-N-(4-fluorophenyl) carbamate oxalate] has been suggested to be a selective agonist at the M 1 subtype of muscarinic receptor [Lambrecht G. et al., Life Sci. 56 (1995) 815–822]. We synthesized the compound and tested its selectivity for different muscarinic receptors with binding experiments using rat cerebral cortex synaptosomal membranes and cloned human m1 to m5 receptors and by functional experiments on rabbit vas deferens preparations. There was little difference in affinity for the compound at the different cloned muscarinic receptors (IC 50 s for displacement of 3 H- N -methylscopolamine were 0.7-1.0 μM). On rabbit vas deferens preparations, ( S )-4-F-MePyMcN did reduce twitch responses to electrical stimulation like the known M 1 agonist McN-A-343, but unlike McN-A-343 the compound reduced postsynaptic sensitivity to noradrenaline, ATP and KCl. Because of these additional actions, ( S )-4-F-MePyMcN may not be suitable as a tool to study M 1 muscarinic receptors selectively.

Inhibition of field stimulation-induced contractions of rabbit vas deferens by muscarinic receptor agonists: selectivity of McN-A-343 for M1 receptors.

Inhibition of the field stimulation-induced twitch responses of the rabbit vas deferens by the muscarinic receptor agonist, McN-A-343, has been attributed to presynaptic muscarinic receptors of the M1 subtype located on noradrenergic nerve terminals. Stimulation of these receptors causes inhibition of transmitter release and inhibition of the contractile response. However, the selectivity of McN-A-343 for M1 receptors has been questioned and this throws doubt on whether the prejunctional receptors of the rabbit vas deferens are of the M1 subtype. In this study we have undertaken a comprehensive re-evaluation of the inhibition of prostatic and epididymal portions of the rabbit isolated field-stimulated vas deferens by several agonists, including McN-A-343, and quantified the antagonism by M1-selective antagonists, pirenzepine and telenzepine. Prostatic and epididymal portions of vasa deferentia from New Zealand White rabbits were immersed in a low Ca2+ Krebs solution at 32+/-0.5 degrees C gassed with 5% CO2 in oxygen. Yohimbine (1.0mM) was present throughout to block prejunctional alpha2-adrenoceptors. Field stimulation was applied by repeated application of single pulses (30 V, 0.05 Hz, 0.5 ms) and isometric contractions recorded. Carbachol and oxotremorine initially potentiated the epididymal contractions but at higher concentrations there was inhibition. In the prostatic portion, oxotremorine only inhibited. McN-A-343 produced inhibitory responses only in both epididymal and prostatic portions. Pirenzepine shifted the concentration-response curves forthe inhibitory responses to oxotremorine to the right. However, the potentiation of the twitches also became more apparent with the lower concentrations of oxotremorine. Schild plots for the antagonism by pirenzepine yielded pA2 values of 7.96+/-0.004 and 7.7+/-0.02 for the epididymal and prostatic portions, respectively. The concentration-response curves for the inhibition of twitches by McN-A-343 were displaced to the right in a parallel manner by pirenzepine in both prostatic and epididymal portions with no potentiation of the twitches. The Schild plot for this antagonism generated pA2 values of 7.68+/-0.01 and 8.07+/-0.01, respectively. Telenzepine caused parallel shifts of the McN-A-343 concentration-response curves to the right in prostatic portions, the pA2 value being 8.70+/-0.13. Telenzepine (10(-7) M) abolished the inhibitory effect of carbachol to reveal only concentration-dependent potentiation of the contractions. The Schild plot for antagonism of this contractile effect yielded a pA2 value (7.07+/-0.09) that was significantly less by almost two orders of magnitude (1.70) than the value for the antagonism by telenzepine of the McN-A-343-induced inhibitory response. The pA2 values of pirenzepine and telenzepine against the inhibitory responses of the rabbit vas deferens are consistent with the involvement of M1 receptors. This leads to the conclusion that McN-A-343 causes inhibition through this receptor type. The doubts concerning the selectivity of McN-A-343 for M1 receptors are therefore unfounded. The fact that McN-A-343 does not display a selective binding profile suggests that its selectivity does not arise from affinity differences but probably resides in its intrinsic efficacy.

Synthesis, Affinity Profile and Functional Activity of Potent Chiral Muscarinic Antagonists with a Pyrrolidinylfuran Structure

Starting from the structure of previously studied muscarinic agonists, characterized by a pyrrolidinylfuran scaffold, a new series of muscarinic antagonists was synthesized by substituting the 5-position of the furane cycle with bulky hydrophobic groups. Both tertiary amines and the corresponding iodomethyl derivatives were obtained and studied. All the new compounds show high affinity toward cloned human muscarinic M(1)-M(5) receptors expressed in Chinese hamster ovary (CHO) cells and behave as competitive antagonists on classical models of muscarinic receptors. The diastereoisomeric mixture of the highest affinity compound of the series was resolved into the four optical isomers by chiral HPLC. The relative and absolute configuration of the obtained compounds was established by means of a combined strategy based on X-ray crystallography and chiroptical techniques. Although generally fairly potent, the compounds showed only modest subtype selectivity, with the exception of 2a and 6a, which in functional assays presented clear-cut selectivity for the muscarinic receptors present in rabbit vas deferens.

CONTRACTILE RESPONSES OF PROSTATIC AND EPIDIDYMAL PORTIONS OF ISOLATED RABBIT VAS DEFERENS TO ELECTRICAL FIELD STIMULATION

The prostatic and epididymal portions of rabbit vas deferens were different in the reactivity to electrical field stimulation (EFS), adenosine triphosphate (ATP) and noradrenaline (NA). The EFS produced biphasic contractile response; VIZ. the first rapid twitch like (phasic) and the second slow sustained (tonic) contraction. The ratio of the amplitude of the phasic contraction to that of the tonic contraction in response to the EFS was higher in the prostatic portion than that in the epididymal portion. The increase of stimulation frequency from 5 to 10 and 20 Hz more markedly augmented the tonic contractile response than the phasic contractile response. Then, the ratio of the amplitude of the phasic contraction to that of the tonic contraction decreased according to the increase of the stimulation frequency. The tension development of the phasic and the tonic contractile responses to the EFS in the prostatic portion was significantly larger than those in the epididymal portion. The administration of 1 mM ATP produced phasic contraction. The contractile response to 1 mM ATP was more remarkably appeared in the prostatic portion than in the epididymal portion. The administration of 10 microM NA produced slow sustained tonic contraction, which also more markedly appeared in the prostatic portion than in the epididymal portion. The findings may indicate that the prostatic portion of rabbit vas deferens was more strongly innervated by purinergic nerves, and had higher reactivity to EFS, ATP and NA than the epididymal portion.

Synthesis, Affinity Profile, and Functional Activity of Muscarinic Antagonists with a 1-Methyl-2-(2,2-alkylaryl-1,3-oxathiolan-5-yl)pyrrolidine Structure

Starting from a previously studied muscarinic ligand, characterized by a 1,3-oxathiolane nucleus, a new series of muscarinic antagonists were designed by increasing the stereochemical complexity of the molecules. A small library of enantiomeric and diastereomeric 2,2-diphenyl- and 2-cyclohexyl-2-phenyl substituted compounds was thus obtained. All the tested compounds show a high affinity toward cloned human muscarinic hm1-hm5 receptors expressed in CHO cells and a good antagonistic activity on functional assays, with a modest selectivity on rabbit vas deferens.

EFFECTS OF CANNABINOID RECEPTOR ACTIVATION ON RABBIT BISECTED VAS DEFERENS STRIPS

1. In the present study, the effects of anandamide and WIN 55,212-2, cannabinoid receptor agonists, were investigated on electrical field stimulation (EFS)-induced biphasic twitch responses obtained from the epididymal and prostatic portions of rabbit vas deferens strips. 2. Anandamide and WIN 55,212-2 dose-dependently inhibited both the first and second phases of the EFS-induced twitch responses recorded from epididymal and prostatic portions of the vas deferens over the concentration range 10(-9) to 3 x 10(-6) mol/L. 3. The cannabinoid CB1 receptor antagonist AM 251 (10(-6) mol/L) and the cannabinoid CB2 receptor antagonist AM 630 (10(-6) mol/L) had no effect on the inhibitory action of anandamide on the biphasic twitch responses in the prostatic and epididymal portions of the rabbit vas deferens. 4. In both the prostatic and epididymal portions of the rabbit vas deferens, AM 251 significantly, but not completely, reversed the inhibitory effect of WIN 55,212-2 on the first phase of the twitch response. In contrast, AM 630 did not have any effect on the inhibitory action of WIN 55,212-2 in the rabbit vas deferens strips. 5. The inhibitory effects of anandamide or WIN 55,212-2 on EFS-induced twitch responses of both the prostatic and epididymal portions of the rabbit vas deferens were not altered in the presence of 10(-5) mol/L naloxone. 6. These results suggest that cannabinoid receptors may have a modulatory role in the regulation of sympathetic transmission in the rabbit vas deferens. However, further investigation is required to characterize the receptors involved.

Expression and Functional Activity of Phosphodiesterase Type 5 in Human and Rabbit Vas Deferens

Expression and Functional Activity of Phosphodiesterase Type 5 in Human and Rabbit Vas Deferens

Expression and functional activity of phosphodiesterase type 5 in human and rabbit vas deferens

The molecular mechanisms underlying the regulation of vas deferens (VD) motility and semen emission are still poorly understood. We now report evidence on VD expression of phosphodiesterase type 5 (PDE5), which regulates nitric oxide (NO)-induced relaxation and cGMP breakdown in smooth muscle cells. In human VD, the PDE5 abundance was relatively high (>3 x 10(6) molecules/microg total RNA), although 10-fold lower than in corpora cavernosa (CC). Also cGMP metabolising activity was higher in CC than in VD. However, both tissues share the same sensitivity to a broad panel of cGMP-related PDE inhibitors: sildenafil, tadalafil, dipyridamole, zaprinast, vinpocetine, EHNA and cilostamide. Based on the rank order of potency of these PDE inhibitors, we found that the cGMP metabolizing activity in human VD mostly corresponds to PDE5. PDE5 was immunolocalized in all the muscular layers of human and rabbit VD and was found to be negatively involved in regulating NO-induced relaxation. In addition, by using a rabbit model of hypogonadotropic hypogonadism, we found that PDE5 gene expression and activity are androgen-dependent in VD, as previously demonstrated in CC. In fact, the sensitivity to a NO-donor (NCX4040), its enhancement by PDE5 inhibitors and the PDE5-related cGMP breakdown were all affected by androgen manipulation. Our results provide a hypothesis explaining the beneficial effects of PDE inhibitors in patients with rapid ejaculation.

A COMPARATIVE STUDY ON CONTRACTILE RESPONSES OF RABBIT AND GUINEA PIG VASA DEFERENTIA TO ELECTRICAL FIELD STIMULATION

Contractile responses of rabbit and guinea pig vasa deferentia to electrical field stimulation (EFS) are compared. A muscarinic receptor blocking agent, 1 microM atropine markedly reduced phasic and tonic contraction induced by EFS (20 Hz, 0.5 msec, 30 V, for 30 sec) in rabbit vas deferens, while it only slightly depressed those in guinea pig vas deferens. Further addition of an adrenergic alpha1 receptor blocking agent, 1 microM prazosin markedly depressed the second tonic contraction in both rabbit and guinea pig vasa deferentia. In the presence of atropine and prazosin, further addition of a P2X purinoceptor desensitizing agent, 10 microM alpha,beta-methylene ATP (alpha, beta-MeATP) abolished the residual phasic contractile response in guinea pig vas deferens, while it partially depressed that in rabbit vas deferens. The administration of 10 microM alpha,beta-MeATP in the absence of atropine and prazosin markedly potentiated the phasic contractile response of rabbit vas deferens to EFS, while it depressed that of guinea pig vas deferens. Contractile response of rabbit vas deferens to alpha,beta-MeATP was more potent than those of ATP and 2-methyl-thioATP (2-Me-thioATP), while these nucleotides had almost same potency in guinea pig vas deferens. These findings may indicate that contribution of cholinergic, adrenergic and purinergic neurotransmission to the contractile response of rabbit vas deferens to EFS is different from that of guinea pig vas deferens.

Synthesis and Antagonistic Activity at Muscarinic Receptor Subtypes of Some Derivatives of Diphenidol

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effects of structural modifications of N-CPM-normorphine derivatives on agonist and antagonist activities in isolated organs.

The agonistic and antagonistic properties of N-cyclopropylmethyl (N-CPM) morphine derivatives were observed in mouse vas deferens (MVD), longitudinal muscle of guinea pig ileum (GPI) and rabbit vas deferens (LVD). In MVD the K(e) values of the titled compounds (N-CPM-morphine, N-CPM-isomorphine, N-CPM-dihydromorphine, N-CPM-dihydroisomorpPhine, N-CPM-dihydromorphone and naltrexone) were measured for mu-, kappa- and delta-receptors using normorphine, ethylketocyclazocine (EKC) and D-Pen2-D-Pen5-enkephaline (DPDPE) as selective agonists on the receptors, respectively. For mu-receptors of MVD the tested compounds showed similar affinity. For kappa-receptors the non-iso-6-OH derivatives possessed much less affinity than the iso-derivatives. Similar difference could be observed for delta-receptors. The agonistic activities of these compounds in MVD were observed to be between 0-20% of the inhibition of muscle contractions. In GPI the compounds except naltrexone possessed strong agonistic activities effectively antagonized by nor-binaltorphimine (nor-BNI) (K(e) of nor-BNI was 0.23 nM) suggesting that they were strong kappa-receptor agonists. We investigated these agents in LVD too, which contains kappa-receptors, but they did not produce any agonist potencies. It raises the possibility that the kappa-receptor subtypes of LVD and MVD are different from the kappa-receptor subtype of GPI or the vasa deferentia contain much fewer kappa-receptors than GPI and the intrinsic activities of these compounds are too small to reach the 50% inhibition of the contractions.

Muscarinic subtypes profile modulation within a series of new antagonists, bridged bicyclic derivatives of 2,2-Diphenyl-[1,3]-dioxolan-4-ylmethyl-dimethylamine

A set of new muscarinic antagonists, bridged bicyclic derivatives of 2,2-diphenyl-[1,3]-dioxolan-4-ylmethyl-dimethylamine ( 1), was synthesized and tested to evaluate their affinity and selectivity for M 1, M 2, M 3 and M 4 receptor subtypes. The conformational constraint of 1 in a bicyclic structure, and the variation in distance and stereochemistry of the active functions allowed us to modulate the selectivity of interaction with the M 1–M 3 receptor subtypes. The most interesting compound was ( cis, trans)-2-(2,2-diphenylethyl)-5-methyl-tetrahydro-[1,3]dioxolo[4,5- c]pyrrole oxalate ( 6), which is equipotent with Pirenzepine on rabbit vas deferens (M 1-putative) but shows a better selectivity profile.

Synthesis and antagonistic activity at muscarinic receptor subtypes of some derivatives of diphenidol

A series of new derivatives, related to diphenidol and to its 2-carbonyl analogue, were designed as antimuscarinic agents. The synthesized compounds were evaluated both as hydrochlorides and as methiodides by functional tests at guinea-pig heart (M 2), guinea-pig ileum (M 3) and rabbit vas deferens (putative M 4). Two derivatives ( 3a and 5a) showed an M 3-selective profile similar to that of the reference compounds, though they resulted less potent.

Opioid activity of C8813, a novel and potent opioid analgesic

Compound trans-4-( p-bromophenyl)-4-(dimethylamino)-1-(2-thiophen-2-yl-ethyl)-cyclohexanol (C8813), structurally unrelated to morphine, is a novel analgesic. The present study examined the antinociception, opioid receptor selectivity and in vitro activity of C8813. The antinociceptive activity was evaluated using mouse hot plate and acetic acid writhing tests. In mouse hot plate test, the antinociceptive ED 50 of C8813 was 11.5 μg/kg, being 591 times and 3.4 times more potent than morphine and fentanyl respectively. In mouse writhing test, the antinociceptive ED 50 of C8813 was 16.9 μg/kg, being 55 times and 2.3 times more active than morphine and fentanyl respectively. In the opioid receptor binding assay, C8813 showed high affinity for μ-opioid receptor (K i = 1.37 nM) and δ-opioid receptor (K i = 3.24 nM) but almost no affinity for κ-opioid receptor (at 1 μM). In the bioassay, the inhibitory effect of C8813 in the guinea-pig ileum (GPI) was 16.5 times more potent than in the mouse vas deferens (MVD). The inhibitory effects of C8813 in the GPI and MVD could be antagonized by μ-opioid receptor antagonist naloxone and δ-opioid receptor antagonist ICI174,864 respectively. However, the inhibitory effect of C8813 in the rabbit vas deferens was very weak. These results indicated that C8813 was a potent analgesic and a high affinity agonist for the μ- and δ-opioid receptors.

Synthesis and opioid activity of new fentanyl analogs

Three new fentanyl analogs (compounds 3- 4- 5) have been synthesized and evaluated for antinociceptive properties using the writhing test. The analgesic property of the active compound, N-[1-phenylpyrazol-3-yl]- N-[1-(2-phenethyl)-4-piperidyl)] propenamide (compound 4), was tested using the hot plate test in mice. Its opioid agonistic activity was characterized using three isolated tissues: guinea pig ileum, mouse vas deferens, and rabbit vas deferens. Compound 4 was as effective as fentanyl or morphine and it showed less antinociceptive potency than fentanyl but it was more potent than morphine. The duration of the antinociception was similar to that of fentanyl. This compound inhibited the electrically evoked contractions of myenteric plexus-longitudinal muscle strips of guinea pig ileum and of mouse vas deferens but not those of rabbit vas deferens. These effects could be reversed by μ selective antagonists (naloxone and/or CTOP) but not by the δ selective antagonist naltrindole, thus indicating that the compound acted as a μ opioid agonist. Finally, the binding data confirmed that compound 4 had high affinity and selectivity for the μ-receptor.