Neurotransmission In Rat Vas Deferens Research Articles

Effects of in vitro, acute and chronic treatment with fluoxetine on the sympathetic neurotransmission of rat vas deferens.

It is described that fluoxetine treatment is able to induce ejaculatory disorders. However, the exact mechanism is still not fully understood. Therefore, this study was carried out to further evaluate the anti-ejaculatory effects of fluoxetine, using different approaches (in vitro or in vivo treatments), on the sympathetic neurotransmission of the rat vas deferens. Vas deferens from male Wistar rats were used to check the in vitro effects of fluoxetine 10-6M, 3.10-6M or 10-5M. Animals were also acutely (20mg/kg, i.p. 4h or 24h) or chronically (10mg/kg, i.p., 30days) treated with fluoxetine or drug-free vehicle. The vas deferens from non-treated and treated animals were isolated and mounted in an isolated organ bath for the study of the contractions induced by adrenergic agonists, tyramine, 5-HT, Ca2+ or electrical field stimulation. In vitro or acute treatment with fluoxetine decreased the contraction induced by agonists, Ca2+ or electrical field stimulation. The chronic treatment with fluoxetine decreased the contractions induced agonists, tyramine or Ca2+, but did not modify the contractions induced by electrical field stimulation. We have shown that in vitro or in vivo fluoxetine treatment is able to alter the sympathetic neurotransmission of the rat vas deferens which could be related to alterations in the calcium signalling.

Prazosin-induced blockade of extraneuronal uptake facilitates dopaminergic modulation of muscle twitches in rat vas deferens.

Preliminary findings in our laboratory have shown that prazosin augmented the inhibitory effects of dopamine on the electrically-evoked muscle twitches in rat vas deferens. In this study, we opted to investigate the underlying mechanism and whether a prazosin-induced blockade of extraneuronal uptake process may be involved. Cumulative additions of dopamine (1.8 x 10(-7)-4.4 x 10(-5) M) elicited slight (< 30%) but dose-related inhibition of electrically-evoked (0.05 Hz, 1 ms duration and supramaximal voltage) muscle twitches of the vas deferens. Pretreatment with cocaine (10 microM), prazosin (50 nM) or oestradiol (10 microM) produced comparable potentiation of the inhibitory responses of dopamine; the pD2 values to dopamine amounted to 4.47 +/- 0.20, 4.72 +/- 0.21 and 4.56 +/- 0.19, respectively. A lower concentration of prazosin (5 nM) failed to alter dopaminergic responses. Further potentiation of dopamine responses was demonstrated in tissues preincubated with a combination of cocaine plus prazosin (50 nM), or cocaine plus oestradiol (pD2, 5.40 +/- 0.11 and 5.42 +/- 0.05, respectively). However, a mixture of all three drugs failed to elicit any further increase in dopamine responses, a finding that may suggest an extraneuronal uptake blocking activity for prazosin. Inhibition of muscle twitches evoked by bromocriptine, a dopaminoceptor agonist which is not a substrate for extraneuronal uptake, was not affected by prazosin (50 nM) pretreatment. The findings presented in this study emphasize the role of dopamine in modulating noradrenergic neurotransmission in rat vas deferens. More importantly, the results suggest that prazosin may act to block the extraneuronal uptake at noradrenergic sites, an effect that may account for its capability to facilitate dopaminergic modulation of noradrenergic neurotransmission.

Presynaptic inhibition of neurotransmission in rat vas deferens by 2-(p-methoxyphenyl) adenosine, ethyl adenosine-5'-carboxylate and N-cyclopropyl adenosine-5'-carboxamide.

Presynaptic inhibition of neurotransmission in rat vas deferens by 2-(p-methoxyphenyl) adenosine, ethyl adenosine-5'-carboxylate and N-cyclopropyl adenosine-5'-carboxamide.

Nitric oxide as neuromodulator of sympathetic transmission in rat vas deferens.

1. Electrical field stimulation (EFS) of muscle strips in vitro elicited a tetrodotoxin (TTX)-sensitive biphasic contractile response consisting of a phasic component followed by a tonic one. 2. The amplitude of both components of the response was impaired by N omega-nitro-L-arginine and potentiated by sodium nitroprusside. Cystamine caused a reduction in amplitude of both phasic and tonic components of the response to EFS. Neither N omega-nitro-L-arginine, sodium nitroprusside, nor cystamine induced changes in the resting muscle tone, or in the contractile response to exogenous agonists ATP and noradrenaline (NA). 3. The nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, induced a reduction in amplitude of both components of the response to EFS. 4. These results reveal a facilitatory prejunctional modulatory role for nitric oxide in sympathetic neurotransmission in rat vas deferens. Endogenous nitric oxide released in the extracellular space is presumed to potentiate neurotransmission by acting at prejunctional level via cGMP.

The characteristics of endothelin receptor subtypes on muscle contraction and neuro-transmission in rat vas deferens.

We observed endothelin (ET)-induced contractile responses on prostatic and epididymal segments, as well as the facilitation of an electrically stimulated tone on prostatic segments of isolated rat vas deferens. In both segments, the selective ET(B)-receptor agonists, IRL 1620 and sarafotoxin S6c, produced only a small contraction or no contraction at a concentration of 1 microM. The rank order of contraction potencies (pD2 value) was ET-1 = ET-2 > ET-3 >> sarafotoxin S6c = IRL 1620. The maximum responses of ET-induced contractions in the prostatic segments were larger than those in the epididymal segments. The contractile response to ET-3 was antagonized by pretreatment for 30 min with BQ-123 (10 nM), a selective ET(A) receptor antagonist, and BQ-788 (1 microM), a selective ET(B) receptor antagonist. The contractile responses to ET-1 were antagonized by pretreatment with BQ-123 (10 microM), but not with BQ-788 (1 microM). The ET-3-induced facilitation on the twitch response to electrical stimulation in the prostatic segment of the vas deferens was antagonized by BQ-123 (0.1 microM) and BQ-788 (1 microM). The ET-1-induced facilitation was antagonized by pretreatment with BQ-123 (3 microM), but not with BQ-788 (10 microM). These results suggest that in rat vas deferens the ET(A) receptors are divided into BQ-123-sensitive ET(A1) and BQ-123-insensitive ET(A2) subtypes, and the production of a contractile response of smooth muscle as well as the facilitation of neurotransmission are accomplished through mediation by ET(A1)- and ET(A2)-subtypes.

Involvement of ATP-sensitive K + channels in the inhibitory effect of calcitonin gene-related peptide on neurotransmission in rat vas deferens

This study investigated the inhibitory action of human calcitonin-gene-related peptide (CGRP) on neurotransmission in rat isolated vas deferens. The electrically stimulated contractile responses, which were mediated predominantly by activation of postganglionic noradrenergic nerve fibers, were concentration-dependently inhibited by human CGRP (0.1–100 nM, IC 50=2.15±0.21 nM, n=17). Human CGRP at concentrations greater than 3 nM reduced the contractile responses to exogenous noradrenaline and ATP. The inhibitory effect of human CGRP on the electrically stimulated or agonist-induced contractions was antagonized by human CGRP-(8–37), the CGRP receptor antagonist. Glibenclamide (3–10 μM) decreased the effect of human CGRP at a concentration greater than 1 nM whilst glibenclamide did not affect the inhibitory effect of human CGRP on the agonist-induced contractions. These results indicate that human CGRP at low concentrations exerts its inhibitory action mainly by acting on CGRP receptors at the sympathetic nerve terminals supplying rat vas deferens and the activation of ATP-sensitive K + channels is at least in part involved in the action of human CGRP on neurotransmission.

Are imidazoline receptors involved in sympathetic neurotransmission in rat vas deferens

1. 1. An involvement of imidazoline receptors in the modulation of neurotransmitter release was investigated in the prostatic portion of the rat vas deferens stimulated transmurally at 0.2 Hz or by single pulses. 2. 2. Idaxozan and yohimbine induced a concentration-dependent potentiation of the contractile response to 0.2-Hz transmural stimulation in the epididymal and prostatic portion of the vas. 3. 3. After reserpine treatment, idazoxan, but not yohimbine, still potentiated the contractile response, suggesting a possible involvement of imidazoline receptors. 4. 4. Clonidine and rilmenidine, agonists with different affinities to α 2-adrenoceptors and imidazoline receptors, inhibited with the same potency the contractile responses to a single pulse transmural stimulation. 5. 5. Yohimbine (a selective α 2-adrenoceptor antagonist) antagonized the inhibitory concentration effect curve to rilmenidine in a competitive manner. pA 2 values for idaxozan (an antagonist to α 2-adrenoceptors and imidazoline receptors) were not different when noradrenaline or rilmenidine were used as agonists. Phenoxybenzamine blocked the effect of both agonists. 6. 6. Thus, the potency relationship of agonists, as well as the effect of the antagonists, did not favor the hypothesis that imidazoline receptors are involved in the idazoxan-potentiating effect in the rat vas deferens.

Functional properties of agmatine in rat vas deferens

Experiments were performed with rat vas deferens to verify whether agmatine, an endogenous ligand for adrenoceptors and imidazoline receptors, can influence sympathetic neurotransmission, with respect to contractions induced by transmural nerve stimulation, contractions induced by exogenous noradrenaline, and overflow of endogenous noradrenaline. It was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls, (b) shifted to the right the inhibitory concentration-response curves for clonidine on electrically induced twitches, indicating competitive antagonism at presynaptic α-adrenoceptors, with a pA 2 value of 4.12 ± 0.10, (c) shifted to the right the concentration-response curves for noradrenaline-induced contractions, indicating competitive antagonism at postsynaptic α-adrenoceptors as well, with a pA 2 value of 4.03 ± 0.10, and (d) caused a dose-dependent increase of KCl-induced overflow of noradrenaline, up to about 90% in relation to controls. It is concluded that agmatine has multiple effects on sympathetic neurotransmission in rat vas deferens.

Evidence for participation of nitric oxide in excitatory neurotransmission in rat vas deferens

A depression of the fast, non-adrenergic, and also of the slow, adrenergic, components of muscle contraction in response to intramural nerve stimulation was induced by the blocker of nitric oxide synthase N G-nitro-L-arginine methyl ester ( L-NAME), in rat vas deferens. Effects of exogenous noradrenaline or ATP were not reduced by L-NAME. However, L-arginine also caused an inhibition of electrically induced effects in most of the preparations, contrary to the expectations for a precursor of nitric oxide synthesis. In spite of these difficulties L-arginine antagonized the action of L-NAME. These results indicate that nitric oxide is involved in excitatory nerve-muscle transmission in vas deferens.

P-198 - Participation of adenosine 5’-triphosphate in sympathetic neurotransmission of rat vas deferens

P-198 - Participation of adenosine 5’-triphosphate in sympathetic neurotransmission of rat vas deferens

Post-natal development of functional neurotransmission in rat vas deferens.

Responses of the rat vas deferens to drugs and to field stimulation were examined in sexually immature rats. The vasa from immature rats often exhibited spontaneous contractions and displayed greater sensitivity to the contractile effects of alpha-adrenoceptor agonists. The responses of the vasa from immature rats to single pulse field stimulation lacked the adrenergic component of the response although the non-adrenergic component was present. The responses were antagonized by alpha 2-adrenoceptor agonists. In the presence of cocaine, an adrenergic component of the response did appear. During trains of pulses the pre- and postjunctional effects of adrenergic transmission which are found in adult rats were absent in vasa from immature rats. Electron microscopic studies showed no qualitative differences in adrenergic innervation in vasa from immature and adult rats. It is concluded that a state of 'pre-innervation supersensitivity' associated with a lack of functional adrenergic transmission exists in the vas deferens of immature rats. The supersensitivity disappears and functional transmission develops during the period in which testosterone secretion increases in the rat. The reason for the lack of functional transmission at a time when the innervation appears to be morphologically mature is not clear but may be due to the noradrenaline release mechanism not being fully operative.

Radioenzymatic assay measurement of yohimbine's influence on adrenergic neurotransmission of rat vas deferens: Unique consequence of using normetanephrine as an uptake 2-blocking agent

The effect of the α 2-receptor antagonist, yohimbine on norepinephrine overflow was studied in the transmural-stimulated isolated rat vas deferens. A radioenzymatic assay was used to measure the endogenous norepinephrine overflow. In initial studies conducted in the presence of uptake 1 blocker desipramine (10 −6 M) and uptake 2 blocker, normetanephrine (10 −5 M) there was an apparent uncoupling of the influence of yohimbine on nerve-stimulated contractile response from norepinephrine overflow. These results were found to be due to the electrolytic O-demethylation of normetanephrine with the resultant generation of large quantities of norepinephrine obscuring the influence of yohimbine on nerve-stimulated norepinephrine overflow from the vas deferens. These findings serve as a warning to the use of normetanephrine as an uptake 2 blocker when radioenzymatic assay is used to measure norepinephrine overflow from transmural-stimulated isolated tissue preparations. Yohimbine (10 −6 M), in the absence of uptake blockade, causes a 3-fold enhancement of nerve-stimulated norepinephrine overflow at 1 Hz and a 2-fold enhancement at 10 Hz. This report demonstrates utilization of a radioenzymatic assay to study endogenous norepinephrine overflow from rat vas deferens. Results for yohimbine are complementary to others using measurement of 3H-label overflow from [ 3H]norepinephrine prelabeled isolated tissue.

Presynaptic inhibitory actions of 2-substituted adenosine derivatives on neurotransmission in rat vas deferens: Effects of inhibitors of adenosine uptake and deamination

In the isolated rat vas deferens, various 2-substituted adenosine derivatives and adenosine inhibited contractions elicited by field stimulation but had little effect on responses to exogenous noradrenaline. 2-Chloroadenosine, 2-bromoadenosine, 2-hydroxyadenosine and 2-fluoroadenosine were all more potent than adenosine. Theophylline antagonized the action of the 2-substituted derivatives. The inhibitory action of adenosine was potentiated by dipyridamole, 2-amino-6-[(2-hydroxy-5-nitro)benzylthio]-9-beta-D-ribofuranosylpurine (HNBTG) or 2'-deoxycoformycin while that of 2-choloroadenosine was not altered by any of these drugs or by phenoxybenzamine, atropine or indomethacin. Pretreatment of the vas deferens with both HNBTG and 2'-deoxycoformycin eliminated the difference in inhibitory potency between adenosine and 2-chloroadenosine. These results indicate that 2-substituted adenosine derivatives, like adenosine, produce inhibition of transmission by acting on a presynaptic site which can be blocked by theophylline. The high apparent potency of 2-chloroadenosine compared to adenosine appears to be due to the former being neither taken up nor deaminated, while the apparent potency of adenosine is masked by uptake and deamination in this tissue.

Structure activity relations for inhibition of neurotransmission in rat vas deferens by adenosine

Adenosine inhibits the isometric contractions of the rat vas deferens in response to field stimulation in vitro by presynaptic inhibition of transmitter release. In the present study the structure activity relations for the inhibition of neurotramsmission in the rat vas deferens by adenosine were examined. Adenosine and adenosine-N 1-oxide were the most potent inhibitors studied. 6-Methylaminopurine riboside, 6-hydroxylaminopurine riboside, 5′-deoxyadenosine and 5′-nitroadenosine were slightly less potent inhibitors. The common structural requirements for activity include a primary or secondary amine function at C 6 of the purine ring with little tolerance for major steric changes or substitutions on the sugar moiety. None of the analogues studied prevented the presynaptic inhibitory action of adenosine.

Uptake and metabolism of adenosine by human erythrocyte ghosts.

Uptake and metabolism of adenosine by human erythrocyte ghosts.