Responses Of Rat Vas Deferens Research Articles

Effects of cromakalim (BRL 34915) on mechanical responses of rat vas deferens to noradrenaline and naphazoline

The contractile responses produced by noradrenaline were compared to those produced by naphazoline in the rat isolated vas deferens, a preparation which is usually quiescent. The responses to noradrenaline were biphasic: prominent spontaneous contractile activity was superimposed on contractions produced by naphazoline. After removal of naphazoline the rat vas deferens displayed periodic spontaneous activity. The effects of cromakalim and verapamil were compared on contractions induced by noradrenaline and naphazoline and on spontaneous activity induced by exposure to naphazoline. Cromakalim (1–10 × 10 −7 M) shifted to the right the cumulative concentration-response curve of naphazoline but not that of noradrenaline; at the same range of concentrations, cromakalim inhibited naphazoline-induced periodic spontaneous activity. Verapamil (3–30 × 10 −8 M) flattened in a dose-dependent manner the concentration-response curves of noradrenaline and naphazoline; higher concentrations of verapamil (3–30 × 10 −6 M) were required to modify periodic spontaneous activity. It was concluded that naphazoline but not noradrenaline can block K + channel(s) and that this property can represent an important difference imidazolines and phenethylamines.

Effects of K<sup>+</sup>-Free Solution on Contractile Responses of Rat Vas deferens

The effect of K(+)-free solution as well as its modulatory effect on neurogenic and agonist-induced contractile responses in rat vas deferens were investigated in the present study. Isolated rat vas deferens, normally a quiescent smooth muscle, developed spontaneous contractions on exposure to K(+)-free solution which was not affected by tetrodotoxin (3 x 10(-7) mol/l) or prazosin (10(-6) mol/l) but was abolished in Ca(2+)-free medium. Transmural field stimulus (3-30 Hz; 0.5 ms duration; supramaximal voltage; 10 s) induced biphasic responses, consisting of fast and slow components, were markedly inhibited in K(+)-free medium and were restored on readdition of K+ to the medium. Similarly, the twitch responses at 0.1 Hz were also inhibited in K(+)-free solution. In the absence of K+, the sensitivity of the tissues to noradrenaline (10(-6) to 10(-4) mol/l) and ATP (10(-4) mol/l) was not significantly altered. The observations made in the present study suggest that spontaneous contractions induced by K(+)-free solution are myogenic in origin and are dependent on extracellular Ca2+. Selective inhibition of neurogenic responses in K(+)-free medium without any significant effect on exogenous noradrenaline and ATP is suggestive of the involvement of prejunctional inhibition of neurotransmitter release.

Relationship between α-adrenoceptor occupancy and contractile response in rat vas deferens. Experimental and theoretical analysis

The rat vas deferens has been considered to be the tissue of choice to study α-adrenergic drugs. However, some of these agonists have elicited complex responses in this organ. Therefore, detailed characterization of α-adrenoceptor-mediated responses of the rat vas deferens was the aim of this work. Experiments were designed to study the contractile response of this tissue to phenylethanolamine (noradrenaline) and to two imidazolines (oxymetazoline and naphazoline). These responses were related to receptor occupancy and to other parameters of drug action, i.e. dissociation constants, relative efficacies, ED 50 and maximal responses. A theoretical model was used to check the experimental data. There was a non-linear relationship between response and receptor occupancy with all three agonists. The dissociation constants for noradrenaline, oxymetazoline and naphazoline were 11.06, 0.15 and 0.10 μM, respectively. The rat vas deferens had 75–80% spare receptors for noradrenaline. Oxymetazoline and naphazoline were shown to be partial agonists with low relative efficacies as compared to noradrenaline (0.0063 and 0.0056 respectively). The dose-response curves generated by the model for partial agonists were similar to the curves obtained experimentally in vitro.

Specific [ 3H]propionyl-neuropeptide Y (NPY) binding in rabbit aortic membranes: Comparisons with binding in rat brain and biological responses in rat vas deferens

The binding of biologically active [3H]propionyl-NPY to rabbit aortic membranes was specific and saturable. Scatchard analysis indicated a single class of binding sites with a Kd of 1.1 nM. The rank order of potencies for displacement of [3H]propionyl-NPY binding by NPY analogs in the aorta correlated with their potencies in displacing binding in brain and their activity in inhibiting contractions of the field-stimulated rat vas deferens. However, differences were noted in the absolute or relative potencies of other related polypeptides both in regards to aorta compared to brain NPY binding and NPY binding compared to activity in the vas deferens. Collectively, the results support proposals for heterogeneity of NPY receptors.

Voltage and time dependency of calcium mediated phasic and tonic responses in rat vas deferens smooth muscle—The effect of some calcium agonist and antagonist agents

1. Phasic and tonic components of the K+-induced contracture response were found to be expressed to different degrees in the prostatic and epididymal portions of the rat vas deferens. 2. With elevation of external potassium greater than 25 mM, the mechanisms underlying the phasic component operate only transiently before inactivation and replacement with tonic tension. 3. Both phasic and tonic components of the vas deferens response to potassium were markedly dependent upon external calcium ions. 4. Nifedipine and verapamil equally inhibited the phasic and tonic components of the K+ response in the prostatic vas deferens. However, inhibition by these agents was far more pronounced in the phasic components than in the tonic component of the epididymal vas deferens. 5. BAY K 8644 potentiated, in a dose-dependent manner, the phasic components of the K+ response, particularly in the prostatic vas deferens. 6. Abscisic acid also potentiated, in a dose-dependent manner the K+ response of rat vas deferens, but this action was far more pronounced in the tonic component of the epididymal portion. 7. Papaverine abolished the BAY K 8644 potentiated epididymal K+ response but did not affect the BAY K 8644 potentiated prostatic K+ response. 8. It is concluded that abscisic acid potentiated responses associated with the activation of voltage-dependent, non-inactivating slow calcium channels. 9. Papaverine, nifedipine and verapamil appear to be less selective than abscisic acid in that they equally inhibit phasic and tonic responses in prostatic vas deferens, but these may be interdependent, yet they more strongly inhibit phasic responses of epididymal vas deferens.

Voltage and time dependency of calcium mediated phasic and tonic responses in rat vas deferens smooth muscle—The effect of some calcium agonist and antagonist agents

Voltage and time dependency of calcium mediated phasic and tonic responses in rat vas deferens smooth muscle—The effect of some calcium agonist and antagonist agents

Capsaicin enhances the non‐adrenergic twitch response of rat vas deferens

1 Capsaicin (Cap) enhanced the twitch response of the epididymal and prostatic portions of rat vas deferens induced by field stimulation at 0.1 Hz. The effect of Cap was reproducible and showed no desensitization. 2 Prazosin, and pretreatment with reserpine or Cap did not affect the potentiating effect of Cap, whereas pretreatment with 6-hydroxydopamine abolished the action of Cap. 3 Cap tended to attenuate the contractions induced by noradrenaline, tyramine and ATP. 4 Like Cap, substance K and substance P augmented the twitch response without causing desensitization, but their effects differed somewhat from that of Cap. Calcitonin gene-related peptide inhibited the twitch response. 5 These results suggest that Cap enhances a stimulation-induced, prazosin-resistant non-adrenergic twitch response of rat vas deferens through an as yet undefined prejunctional mechanism. This mechanism is possibly mediated by some peptide released in response to Cap from sensory neurones, which in turn acts on sympathetic nerves and increases stimulation-induced release of a mediator or cotransmitter responsible for the non-adrenergic twitch response. However, the possibility that Cap has a direct action on sympathetic nerves cannot be ruled out.

Bradykinin receptor antagonists used to characterize the heterogeneity of bradykinin-induced responses in rat vas deferens

The application of bradykinin to the isolated, transmurally stimulated rat vas deferens caused two effects: increase of the basal tension of the tissue and potentiation of the magnitude of electrically driven twitches. These bradykinin responses were not evenly distributed along the ductus. The direct contractile action of bradykinin was found to be stronger in the epididymal half of the tissue while the potentiation of the muscle twitches was more pronounced in the prostatic half of the rat ductus. Bradykinin is more potent to potentiate the electrically driven twitches than to act as a postjunctional agonist. Tyr-bradykinin, [Tyr 5]bradykinin and [Tyr 8]bradykinin exhibited significant differences in the potency ratio to produce each of these responses. [Thi 5,8, D-Phe 7]bradykinin is a weak postjunctional agonist but was a full agonist to potentiate the electrically induced twitches. Furthermore, this compound antagonized the bradykinin-induced contractions. [Hyp 3, Thi 5,8, D-Phe 7] bradykinin was devoid of agonist activity at either pre- or postjunctional sites; it behaved as a pure antagonist and was more than potent its non-hydroxylated analog. the addition of a D-Arg residue at the amino terminal increased the antagonist potency significantly. The pA 2 of D-Arg-[Hyp 3, Thi 5,8, D-Phe 7bradykinin to antagonize the postjunctional effect of bradykinin was 6.35, a value that differed significantly from the value of 6.93 required to block the prejunctional effect of the peptide. The bradykinin receptor antagonists did not modify significantly the magnitude of the contractile responses caused by angiotensin II, norepinephrine or 5-hydroxytryptamine.

Verapamil enhances the non-adrenergic twitch response of rat vas deferens

Verapamil (3 × 10 −6−3 × 10 −5 M) enhanced the twitch contractions of the epididymal and prostatic portions of vas deferens stimulated at 0.1 Hz. This verapamil effect was essentially similar to those of diltiazem, D-600 and Bay K 8644. However, when stimulation at 2 Hz was used verapamil (3 × 10 −5 M) attenuated the contractions of the epididymal portion by half but still augmented those of the prostatic portion. Verapamil enchanced the reserpine- and prazosin-resistant component of the stimulation-induced contractions of both portions of the vas deferens. Yohimbine augmented the twitch response but attenuated the verapamil-augmented response. Verapamil did not augment norepinephrine- or tyramine-induced contractions whereas it augmented ATP-induced contractions of the prostatic portion but not of the epididymal portion. Verapamil increased the stimulation-evoked 3H-efflux from the vas deferens labelled with [ 3H]norepinephrine. It is suggested that verapamil augments non-adrenergic responses of both portions of the vas deferens by acting as a Ca agonist on the prejunctional site to increase the release of co-transmitter, or by acting on the postjunctional site to enhance the action of the substance released. Its effect in augmenting norepinephrine release is concluded not to contribute to the potentiating action.

L-methionine enhances the contractile response to norepinephrine of rat vas deferens.

Under Ca-depleted conditions, the contractile responses of rat vas deferens in the presence of norepinephrine were not elicited until the addition of CaCl2. L-Methionine enhanced the contractile response of vas deferens in the presence of methylation blockers under these conditions. The enhancing effect of L-methionine on some other smooth muscles could not be determined because under Ca-depleted conditions, these muscles showed 60-80% of the maximal contractile response on addition of CaCl2 alone. These findings suggested that L-methionine has an enhancing effect on contraction of the rat vas deferens as it does on rat uterine muscle.

P-195 - Capsaicin augments the non-adrenergic response of rat vas deferens

P-195 - Capsaicin augments the non-adrenergic response of rat vas deferens

Effects of α,β-methylene ATP on biphasic responses of rat vas deferens

The epididymal region of isolated vas deferens of the rat was stimulated locally with field electrodes. Continuous perfusion with alpha,beta-methylene-adenosine-5'-triphosphate (mATP, 10(-5) M) desensitized the P2-purinoceptors and the effect of this on the two components of tetanic responses and the 'non-adrenergic' and adrenergic phases of single shock responses were examined. Exposure to mATP selectively prevented the contractions to adenosine-5'-triphosphate (ATP, 10(-4)-5 X 10(-4) M) but not noradrenaline (NA, 10(-5) M) and preferentially blocked the secondary but not the primary tetanic component. It also depressed markedly the non-adrenergic phase of single shocks and either reduced or abolished the adrenergic phase. Thus the secondary tension development depends in the rat vas deferens on both the activation of alpha 1-adrenoceptors and the non-adrenergic twitch mechanism. The action of mATP involves more processes than the desensitization of the P2-purinoceptors so does not positively identify purinergic transmission. Direct NA-induced contraction contributes more to the primary than to the secondary tetanic component.

Responsiveness of rat vas deferens and stomach smooth muscles after treatment with indomethacin.

The contractile responses of rat vas deferens and longitudinal stomach fundus strips to stimulants and relaxants were studied after treatment with indomethacin (Ind) injected i.p. at doses of 15 mg/kg for 24 hr and 25 mg/kg for 48 hr. The treatment with Ind reduced the amount of both spontaneously and electrically-evoked release of a prostaglandin (PG)-like substance from the isolated n. hypogastricus-vas deferens preparations. A considerable decrease of the responsiveness to exogeneous noradrenaline occurred in vas deferens isolated from Ind-pretreated rats. The EC50 values of noradrenaline increased as compared to the control value. The contractile responses of the isolated longitudinal stomach fundus strips to acetylcholine, serotonin, PGE2, PGF2 and arachidonic acid were reduced while the relaxant action of noradrenaline and papaverine was potentiated after Ind treatment. It is assumed that endogeneous PGs participate in the regulation of smooth muscle activity through potentiation of the postjunctional excitatory action of noradrenaline in vas deferens and through interaction with the transmembrane ion transport in stomach fundus smooth muscles.

An endogenous brain substance, CDS (clonidine-displacing-substance), inhibits the twitch response of rat vas deferens

The effect of CDS, an endogenous brain substance that specifically displaces bound [ 3H]clonidine and [ 3H]rauwolscine in rat brain membranes and human platelets, has been tested in isolated, field-stimulated rat vas deferens. CDS, obtained after an extensive purification procedure as a single peak from an HPLC sizing column, inhibited the electrically stimulated rat vas deferens similarly to the inhibitory action of clonidine, an α 2-agonist. The effective dose of CDS as an inhibitor of the vas deferens is equivalent to its effective dose in displacing specifically bound [ 3H]clonidine in rat brain membranes. Furthermore, the CDS inhibition of the twitch response is reversed by two α 2-adrenergic antagonists, yohimbine and phentolamine. From these results, it is suggested that CDS extracted from brain, with affinity for clonidine sites, may be involved in the non-adrenergic fast response of the sympathetic transmission of the vas deferens.

Activation of α 1-adrenoceptors increases [ 3H]inositol metabolism in rat vas deferens and caudal artery

Rings of rat vas deferens and caudal artery were incubated with [ 3H]inositol in Krebs-Ringer bicarbonate buffer containing 10 mM lithium chloride, and the production of water-soluble [ 3H]inositol phosphates was monitored. Norepinephrine increased [ 3H]inositol phosphate accumulation 7-fold in rings from vas deferens and 3-fold in rings from caudal artery. Epinephrine, phenylephrine and methoxamine were as effective as norepinephrine, suggesting that these drugs are full agonists in causing this response. Prazosin, phentolamine and yohimbine completelu blocked the stimulation by norepinephrine in both tissues with potencies typical of blockade of α 1-adrenoceptors. Despite a substantial receptor reserve for α 1-adrenoceptor mediated contractile responses, clonidine, p-amino-clonidine, phenyl-propanolamine and ephedrine can only cause a partial contractile response in rat vas deferens. However, all of these partial agonists were either as effective or more effective in increasing [ 3H]inositol phosphate accumulation in rat vas deferens as they were in activating a contractile response. These data suggest that α 1-adrenoceptors increase phosphatidylinositol turnover in rat vas deferens and caudal artery, and that there may be a receptor reserve for α 1-adrenoceptor mediated increases in [ 3H]inositol phosphate accumulation in these smooth muscles.

Effect of strychnine on the contractile response of rat vas deferens

Strychnine at concentrations of 0.1 ∼ 1.0 μM induced supersensitivity of rat vas deferens to α-agonists but not to other stimulants. Strychnine-treatment resulted in an increase in the number of α-adrenoceptors, determined by measuring the binding of [ 3H]prazosin. Glycine did not have any significant effect on the contracture and did not antagonize the action of strychnine. Thus, specific supersensitivity of α-adrenergic system was induced by treatment with low concentrations of strychnine.

Relationship between alpha 1-adrenoceptor density and functional response of rat vas deferens. Studies with phenoxybenzamine.

The relationship between the density of alpha 1-adrenoceptors and the longitudinal contractile response of rat vas deferens was examined by using phenoxybenzamine to irreversibly decrease alpha 1-adrenoceptor density. Receptor density was measured by Scatchard plots of saturation analysis of specific 125I-BE 2254 (125IBE) binding and compared to the potency of alpha-adrenoceptor agonists in causing contraction and the maximum contraction elicited by these agonists. Treatment of isolated vasa deferentia in organ baths with phenoxybenzamine caused a dose-dependent decrease in the density of 125IBE binding sites, the potency of the full agonist phenylephrine in activating contraction, and the maximum contractile response. The percentage of functional receptors remaining after phenoxybenzamine treatment (q value) was calculated from the contraction data and compared to the percentage of 125IBE binding sites remaining. The reduction in the number of functional receptors was much greater than the reduction in the number of 125IBE binding sites at all doses of phenoxybenzamine. Since the magnitude of the contractile response caused by a weak partial agonist should be approximately proportional to the density of functional receptors in the tissue, partial agonists were used as an independent measure of the degree of functional receptor inactivation. Bath application of two different doses of phenoxybenzamine caused a decrease in the maximal contraction caused by the partial agonists clonidine and ephedrine which was similar to the calculated decrease in the q value, but not to the observed decrease in the density of 125IBE binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of tris buffer on the contractile responses of rat vas deferens

The influences of Tris-(hydroxymethyl)aminomethane (Tris) on the contractile responses of rat vas deferens to norepinephrine (NE), potassium chloride (KCl) and field stimulation were investigated. Equilibration of rat vas deferens muscle strips in Tris containing Tyrode medium caused a significant increase in sensitivity to KCl, but had no effect on the maximum tension induced by NE or KCl. The biphasic responses to 10 −4 M Ne and 100 mM KCl, characterized by an initial fast (F) component followed by a slow (S) component, were differentially affected by Tris. The F components of NE- or KCl-induced contractions were significantly potentiated by Tris, whereas the S components of NE- or KCl-induced contractions were depressed. When the muscle strips were washed after NE- or KCl-induced contraction, the rate of relaxation reflecting the rate of loss of the sustained S-component was significantly slower in Tris-Tyrode than in Tyrode medium. In Ca 2+ free medium, the F component of NE-induced contraction but not the S component was markedly potentiated by Tris. Verapamil (10 −5 M) eliminated the potentiation by Tris of the F component and further reduced the S component of the NE-induced contraction in the Tris-Tyrode medium. Both F and S components of KCl-induced contractions of rat vas deferens were sensitive to verapamil and these depressant effects were further enhanced in the presence of Tris. The contraction elicited by field stimulation was also biphasic. However, only the S component was significantly depressed by Tris and this inhibitory effect was irreversible. We conclude that Tris can exert adverse effects on the contractile properties of rat vas deferens, probably via the disturbance of Ca 2+-handling by the smooth muscle membrane and possibly by affecting release of norepinephrine.

Acetylcholine potentiation of field stimulated rat vas deferens: A pre-synaptic muscarinic mechanism?

Acetylcholine (ACh) was found to markedly enhance the nerve stimulation induced twitch response of isolated, field-stimulated rat vas deferens (RVD). The ED 200 (concentration which enhances the twitch response to 200% of control) for this potentiation was 6 × 10 −6M with the maximum twitch response being increased by more than 3 fold (325 ± 30%). Carbachol (ED 200 = 8.5 × 10 −7M) showed identical results. With each drug the potentiation was competitively antagonized by atropine (10 −7−10 −5M). Physostigmine 10 −8−10 −6M) both enhanced the basal twitch response (215 ± 8% of control at 10 −5M) and the sensitivity of the RVD to ACh (ED 200 = 3.3 × 10 −7M) but not to carbachol. Atropine, on the other hand reduced the basal twitch response by 18 ± 3% at 10 −5M. Hemicholinium (10 −4M) also reduced the basal twitch responses by 23 ± 5%. ACh (10 −7M−10 −5M) did not modify the responses of unstimulated RVD to norepinephrine or KCl suggesting a pre-synaptic site of action. Taken together these results are compatible with the presence of a pre-junctional, excitatory muscarinic mechanism in the field stimulated RVD. That this cholinergic system may be of physiological significance is supported by the observations that atropine and hemicholinium depress while physostigmine enhances the twitch response in the absence of exogenous ACh.

Effect of islet-activating protein (IAP) on contractile responses of rat vas deferens: Evidence for participation of Ni(inhibitory GTP binding regulating protein) in the α2-adrenoceptor-mediated response

The effects of islet-activating protein (IAP) on the contractile responses of vas deferens to exogenous norepinephrine (NE) and electric stimulation (ES) were investigated. IAP treatment had no effect on the contractile response to NE. Pretreatment of the vas deferens with IAP (2.0 μg/ml) for 2 h however significantly attenuated the inhibitory effect of clonidine on ES-induced contractile responses, suggesting that feedback inhibition of presynaptic α 2-adrenoceptors is mediated by the Ni subunit of presynaptic adenylate cyclase.