Portion Of Rat Vas Deferens Research Articles

Stereoselectivity of butylidenephthalide on non-adrenergic prejunctional voltage-dependent Ca2+ channels in prostatic portion of rat vas deferens

The naturally occurring and synthetic butylinenephthalide (Bdph) has two geometric isomers. Z- and E-Bdph were reported to have geometric stereoselectivity for voltage-dependent calcium channels (VDCCs) in guinea-pig ileum. The aim of this study was to investigate whether the binding of Z- and E-Bdph on prejunctional VDCCs of rat vas deferens (RVD) is stereoselective. The twitch responses to electrical field stimulation (EFS, supramaximal voltage, 1 ms, 0.2Hz) were recorded on a polygraph. Z- and E-Bdph concentration-dependently inhibited the twitch responses to EFS in full tissue, prostatic portion and epididymal portion of RVD. The pIC50 value of Z-Bdph was greater than that of E-Bdph in the electrically stimulated prostatic portion of RVD, suggesting that the binding of Bdph on the non-adrenergic prejunctional VDCCs of cell membrane is stereoselective. In the prostatic portion, exogenous Ca2+ only partially reversed the twitch inhibition by Z-Bdph, but effectively reversed those by Ca2+ channel blockers, such as verapamil, diltiazem and aspaminol, suggesting that the action mechanisms may be different from those of Ca2+ channel blockers. K+ channel blockers, such as tetraethylammonium (TEA) and 4-aminopyridine (4-AP), may prolong duration of action potential to allow greater Ca2+ entry and induced more release of transmitters. Therefore both blockers via their prejunctional actions reversed the twitch inhibition induced by Z-Bdph in all preparations of RVD by a non-specific antagonism.

Effects of desipramine on prazosin potency at α1A- and α1D-adrenoceptors in rat vas deferens: Implications for the α1L-adrenoceptor subclassification

This study investigates the interaction between cocaine, desipramine and prazosin at α1-adrenoceptor subtypes mediating contractions to noradrenaline in epididymal portions of rat vas deferens. Noradrenaline potency was not significantly affected by desipramine (0.1–1.0μM) and reduced by desipramine (10μM), but was increased by the presence of cocaine (3.0–30μM), particularly in terms of phasic contractions to low concentrations of noradrenaline. In vehicle experiments, prazosin exhibited relatively low potency as an antagonist against the predominantly α1A-adrenoceptor mediated response (pKB 8.50). In the presence of cocaine, prazosin exhibited higher potency against the revealed α1D-adrenoceptor mediated component (e.g. pKB 9.12). In the presence of desipramine, the potency of prazosin was either unchanged or indeed decreased. Cocaine (0.3–30μM) significantly increased the single pulse nerve-stimulation-evoked contraction, with a maximum increase to 156±12% of control (n=9). In contrast, desipramine in low concentrations (0.1–0.3μM) produced a small but significant increase to 126.6±5.5% (n=11), but higher concentrations failed to increase the response. In conclusion, desipramine fails to produce sufficient noradrenaline transporter block in low concentrations (0.1μM) and produces α1-adrenoceptor antagonism in slightly higher concentrations (0.3–1μM), and so is unsuitable for use in α1-adrenoceptor subclassification studies. Contractions of rat vas deferens are mediated by α1A- and α1D-adrenoceptors, and prazosin has selectivity for α1D- over α1A-adrenoceptors. The α1L-adrenoceptor previously identified in rat vas deferens is the native α1A-adrenoceptor. The range of prazosin potencies and receptor subtypes previously reported in rat vas deferens may be explained by the choice of cocaine or desipramine as noradrenaline transporter blocker.

Prazosin has low potency at α1A‐adrenoceptors and high potency at α1D‐adrenoceptors in rat vas deferens

(1) We have investigated α1 -adrenoceptor subtypes mediating contractions to noradrenaline in epididymal portions of rat vas deferens. (2) Contractions to noradrenaline were investigated in the absence or presence of the noradrenaline transporter blocker cocaine. (3) In the absence of cocaine, contractions to noradrenaline were potently antagonized by RS100329, but not by BMY7378, and so are mediated mainly by α1A -adrenoceptors. (4) In the presence of cocaine, noradrenaline potency was increased, particularly in terms of low concentrations and phasic contractions. Contractions to low concentrations of noradrenaline in the presence of cocaine were resistant to RS100329 but potently antagonized by BMY7378, demonstrating that α1D-adrenoceptors are additionally involved in contractions amplified by cocaine. (5) In the absence of cocaine, prazosin exhibited relatively low potency as an antagonist against the α1A-adrenoceptor-mediated component to the response. In the presence of cocaine, prazosin exhibited higher potency against the α1D-adrenoceptor-mediated component. (6) In conclusion, prazosin has previously unreported selectivity for α1D-over α1A -adrenoceptors in functional studies of rat vas deferens. Contractions of rat vas deferens are mediated by α1A-and α1D -adrenoceptors. The range of prazosin potencies and of receptor subtypes previously reported in rat vas deferens may be explained by the presence of these two subtypes.

Contractions of rat vas deferens are mediated by α1A‐ and α1D‐adrenoceptors

The subtypes of α1‐adrenoceptor mediating contractions of rat vas deferens to exogenous noradrenaline have been examined employing the α1A‐adrenoceptor antagonist RS100329 and α1D‐adrenoceptor antagonist BMY7378. In the presence of cocaine (3 μM) to block the noradrenaline transporter, the potency of noradrenaline at producing contractions was significantly increased in epididymal but not prostatic portions, and the effect was mainly in terms of phasic contractions. RS100329 produced approximately parallel shifts in the potency of noradrenaline at producing tonic contractions in epididymal portions in the absence of cocaine, but produced non‐parallel shifts in the presence of cocaine. In epididymal portions, BMY7378 showed high potency against phasic contractions to noradrenaline in the presence but not the absence of cocaine. It is concluded that the predominant tonic contraction to noradrenaline in epididymal portions of rat vas deferens is mediated by α1A‐adrenoceptors, but α1D‐adrenoceptors are additionally involved in phasic contractions. These phasic contractions are amplified by cocaine, suggesting that blockade of the noradrenaline transporter makes α1D‐adrenoceptors available to exogenous noradrenaline.

Effects of St−587 on the α-adrenoceptors in the Bisected Rat Vas Deferens

The effects of the alpha-adrenoceptor agonist St-587 have been studied on the twitch responses induced by field stimulation in the prostatic portion of rat vas deferens. Moreover the drug's influence on the unstimulated prostatic and epididymal halves of rat vas deferens has also been determined. Alone and after addition of yohimbine (0.3 microM) it enhanced in a concentration-dependent manner the twitch responses in the prostatic half. Prazosin competitively antagonized (pA2 = 8.41 +/- 0.03) this effect. The enhancing effect of St-587 was not reduced in reserpinized animals. These results suggest that post-synaptic alpha 1-adrenoceptors are involved in the potentiation of twitch responses induced by St-587. When alpha 1-adrenoceptors were blocked by prazosin (0.1 microM), St-587 partially inhibited the twitch responses of the prostatic portion of rat vas deferens (Emax = 49.5 +/- 3.5%). Yohimbine completely reversed the inhibitory effects of both St-587 and clonidine. Furthermore St-587 antagonized the inhibitory effects of clonidine on twitch responses. Thus it appears that St-587 also behaves as a partial agonist of presynaptic alpha 2-adrenoceptors in this portion of rat vas deferens, but it did not induce contractions in the unstimulated prostatic half of the vas deferens. However, it competitively antagonized the alpha 1-adrenoceptor agonist phenylephrine by acting as an antagonist of prostatic postsynaptic alpha 1 adrenoceptors. These alpha 1-adrenoceptors are probably different from those that mediate the twitch enhancing response to St-587 in that portion. On the other hand, St-587 was a partial agonist of alpha 1-adrenoceptors in the epididymal half.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of T‐type calcium channel blockers and thalidomide on contractions of rat vas deferens

In rat vas deferens, nerve mediated-contractions to a single electrical stimulus consist of an early purinergic and a later adrenergic component with differing sensitivities to L-type calcium channel blockers. We have investigated the effects of the T-type calcium channel blockers mibefradil and (1S, 2S)-2-[2-[[3-(1H-benzimidazol-2-yl)propyl]methylamino]ethyl]-6-fluoro-1,2,3,4-tetrahydro-1-(1-methylethyl)-2-naphthalenyl cyclopropanecarboxylic dihydrochloride (NNC 55-0396) against contractions in rat vas deferens. In addition, the actions of thalidomide were examined. Prostatic and epididymal portions of rat vas deferens were stimulated with a single electrical stimulus every 5 min, and mouse whole vas deferens was stimulated with 40 pulses at 10 Hz every 5 min. Both mibefradil and NNC 55-0396 (100 microM) produced inhibition of contractions of epididymal portions (42 +/- 13%, n= 7, and 43 +/- 4%, n= 15, of control respectively). However, both agents produced small inhibitions of responses in prostatic portions, presumably by L-type calcium channel block. Thalidomide (100 microM) inhibited contractions in epididymal (55 +/- 4% of control, n= 17) but not in prostatic portions of rat vas deferens. Thalidomide (10-100 microM) also inhibited contractions in mouse vas deferens. The T-type calcium channel blockers mibefradil and NNC 55-0396 block particularly the adrenoceptor-mediated, nifedipine-resistant response to nerve stimulation in rat vas deferens, and this may suggest that this component involves T-type calcium channels. In addition, thalidomide has actions that resemble those of the T-type calcium channel blockers, in that it blocks nifedipine-resistant contractions in epididymal portions.

Assessment of the adrenergic effects of orphenadrine in rat vas deferens.

The peripheral adrenergic effects of orphenadrine, an antiparkinsonian drug, have been evaluated in the rat vas deferens to investigate whether these properties are the same as those of other phencyclidine ligands. In the low micromolar range, orphenadrine enhanced electrically-evoked and exogenous noradrenaline contractile responses in the epididymal portion of rat vas deferens. It also induced spontaneous activity that was inhibited by prazosin (1 microM) but not by atropine (20 nM). It inhibited accumulation of [3H]noradrenaline in rat vas deferens (IC50 = 14.2+/-2.3 microM). Orphenadrine competitively inhibited [3H]nisoxetine binding in rat vas deferens membranes (Ki = 1.05+/-0.20 microM). It can be concluded that orphenadrine, at low micromolar concentrations, interacts with the noradrenaline reuptake system inhibiting its functionality and thus potentiating the effect of noradrenaline.

Selective impairment of noradrenergic transmission in the bisected rat vas deferens following photochemically‐induced cerebral ischaemia

Cerebrovascular disease may impair the autonomic control of peripheral organs including the male urogenital tract. This study investigates the effect of cortico-parietal focal ischaemia on the adrenergic and purinergic transmission in isolated epididymal and prostatic portion of rat vas deferens. Focal brain ischaemia was induced in male rats by photochemical activation following rose bengal intravenous injection. Twenty-four hours following brain ischaemia, cumulative and non-cumulative concentration-response curves were obtained for noradrenaline and alpha,beta-methylene ATP in the right and left epididymal and prostatic portions of the vas deferens. Both portions were also stimulated by single-pulse or pulse trains at 2-30 Hz to produce isometric contractions. In both portions from ischaemic rats the response to exogenous noradrenaline was markedly depressed compared with controls. Acute cortico-parietal ischaemia almost completely abolished the adrenergic phase of the response to single-pulse stimulation in the epididymal portion of the vas deferens. In addition, brain ischaemia deeply depressed phasic and tonic contractions of the frequency-response curve in both portions of bisected vas deferens. Cortico-parietal ischaemia produces a selective noradrenergic impairment at the level of male sexual secondary organs that may contribute to sexual dysfunction after stroke.

Involvement of G-protein βγ subunits on the influence of inhibitory α 2-autoreceptors on the angiotensin AT 1-receptor modulation of noradrenaline release in the rat vas deferens

The influence of α 2-autoreceptors on the facilitation of [ 3H]-noradrenaline release mediated by angiotensin II was studied in prostatic portions of rat vas deferens preincubated with [ 3H]-noradrenaline. Angiotensin II enhanced tritium overflow evoked by trains of 100 pulses at 8 Hz, an effect that was attenuated by the AT 1-receptor antagonist losartan (0.3–1 μM), at concentrations suggesting the involvement of the AT 1B subtype. The effect of angiotensin II was also attenuated by inhibition of phospholipase C (PLC) and protein kinase C (PKC) indicating that prejunctional AT 1-receptors are coupled to the PLC–PKC pathway. Angiotensin II (0.3–100 nM) enhanced tritium overflow more markedly, up to 64%, under conditions that favor α 2-autoinhibition, observed when stimulation consisted of 100 pulses at 8 Hz, than under poor α 2-autoinhibition conditions, only up to 14%, observed when α 2-adrenoceptors were blocked with yohimbine (1 μM) or when stimulation consisted of 20 pulses at 50 Hz. Activation of PKC with 12-myristate 13-acetate (PMA, 0.1–3 μM) also enhanced tritium overflow more markedly under strong α 2-autoinhibition conditions. Inhibition of G i/o-proteins with pertussis toxin (8 μg/ml) or blockade of Gβγ subunits with the anti-βγ peptide MPS-Phos (30 μM) attenuated the effects of angiotensin II and PMA. The results indicate that activation of AT 1-receptors coupled to the PLC–PKC pathway enhances noradrenaline release, an effect that is markedly favoured by an ongoing activation of α 2-autoreceptors. Interaction between α 2-adrenoceptors and AT 1-receptors seems to involve the βγ subunits released from the G i/o-proteins coupled to α 2-adrenoceptors and protein kinase C activated by AT 1-receptors.

The α1D‐adrenoceptor antagonist BMY 7378 is also an α2C‐adrenoceptor antagonist

1 We have investigated the actions of the alpha(1D)-adrenoceptor selective antagonist BMY 7378 in comparison with yohimbine at alpha(1)- and alpha(2)-adrenoceptors. 2 In rat aorta (alpha(1D)-adrenoceptor), BMY 7378 (pA(2) of 8.67) was about 100 times more potent than yohimbine (pA(2) of 6.62) at antagonizing the contractile response to noradrenaline. 3 In human saphenous vein (alpha(2C)-adrenoceptor), BMY 7378 (pA(2) of 6.48) was approximately 10 times less potent than yohimbine (pA(2) of 7.56) at antagonizing the contractile response to noradrenaline. 4 In prostatic portions of rat vas deferens, BMY 7378 (10 mum) did not significantly affect the concentration-dependent inhibition of single pulse nerve stimulation-evoked contractions by xylazine (an action at prejunctional alpha(2D)-adrenoceptors). 5 In ligand-binding studies, BMY 7378 showed 10-fold selectivity for alpha(2C)-adrenoceptors (pK(i) of 6.54) over other alpha(2)-adrenoceptors. 6 It is concluded that BMY 7378, in addition to alpha(1D)-adrenoceptor selectivity in terms of alpha(1)-adrenoceptors, shows selectivity for alpha(2C)-adrenoceptors in terms of alpha(2)-adrenoceptors.

Interaction between adenosine A 2B-receptors and α 2-adrenoceptors on the modulation of noradrenaline release in the rat vas deferens: Possible involvement of a group 2 adenylyl cyclase isoform

In the prostatic portion of rat vas deferens, activation of adenosine A 2B-receptors, β 2-adrenoceptors, adenylyl cyclase or protein kinase A caused a facilitation of noradrenaline release. Blockade of α 2-adrenoceptors with yohimbine (1 μM) attenuated the facilitation mediated by adenosine A 2B-receptors and by direct activation of adenylyl cyclase with forskolin but not that mediated by β 2-adrenoceptors or by direct activation of protein kinase A with 8-bromoadenosine-3′,5′-cyclicAMP. The adenosine A 2B- and the β 2-adrenoceptor-mediated facilitation was prevented by the adenylyl cyclase inhibitors, 2′,5′-dideoxy-adenosine (3 μM) and 9-cyclopentyladenine (100 μM), at concentrations that also attenuated the release enhancing effect of forskolin, but were not changed by the phospholipase C inhibitor 1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione (U-73122, 1 μM). Facilitation of noradrenaline release mediated by adenosine A 2B-receptors was also attenuated by activation of protein kinase C with the phorbol ester 12-myristate 13-acetate (1 μM) and by inhibition of Gβγ subunits with an anti-βγ peptide; facilitation mediated by β 2-adrenoceptors was mainly attenuated by the calmodulin inhibitor calmidazolium (10 μM) and by the calmodulin kinase II inhibitor ( N-[2-[ N-(4-chlorocinnamyl)- N-methylaminomethyl]phenyl]- N-(2-hydroxyethyl)-4-methoxybenzene-sulfonamide phosphate (KN-93, 5 μM). The results suggest that adenosine A 2B- but not β 2-adrenoceptor-mediated facilitation of noradrenaline release is enhanced by an ongoing activation of α 2-adrenoceptors. They further suggest that adenosine A 2B-receptors and β 2-adrenoceptors are coupled to distinct adenylyl cyclase isoforms what may explain the different influence of α 2-adrenoceptor signalling pathway on the facilitatory effects mediated by the two adenylyl cyclase coupled receptors.

Actions of R‐ and S‐verapamil and nifedipine on rat vascular and intestinal smooth muscle

1 We have investigated the actions of the calcium entry blockers nifedipine, R-verapamil and S-verapamil in rat aorta, colon and vas deferens. 2 In aorta and colon, these agents produced concentration-dependent relaxations of KCl (80 mM)-induced contractions. In both tissues, the order of potency was nifedipine > S-verapamil > R-verapamil. However, nifedipine showed selectivity for aorta (potency ratio, colon/aorta: 4.36), S-verapamil showed no selectivity (0.62), but R-verapamil showed selectivity for colon (0.19). 3 In prostatic portions of rat vas deferens, nifedipine (10 microM) abolished the contraction to a single electrical stimulus, but R- and S-verapamil were without effect. In epididymal portions of rat vas deferens, R- and S-verapamil inhibited alpha1-adrenoceptor-mediated contractions to a single electrical stimulus at concentrations of 10 microM and above. 4 In conclusion, R-verapamil may prove useful as an intestinal selective calcium entry blocker in the treatment of intestinal disease with a hypermotility component, e.g. irritable bowel syndrome.

Coupling to protein kinases A and C of adenosine A 2B receptors involved in the facilitation of noradrenaline release in the prostatic portion of rat vas deferens

In the prostatic portion of rat vas deferens, the non-selective adenosine receptor agonist NECA (0.1–30 μM), but not the A 2A agonist CGS 21680 (0.001–10 μM), caused a facilitation of electrically evoked noradrenaline release (up to 43±4%), when inhibitory adenosine A 1 receptors were blocked. NECA-elicited facilitation of noradrenaline release was prevented by the A 2B receptor-antagonist MRS 1754, enhanced by preventing cyclic-AMP degradation with rolipram, abolished by the protein kinase A inhibitors H-89, KT 5720 and cyclic-AMPS-Rp and attenuated by the protein kinase C inhibitors Ro 32-0432 and calphostin C. The adenosine uptake inhibitor NBTI also elicited a facilitation of noradrenaline release; an effect that was abolished by adenosine deaminase and attenuated by MRS 1754, by inhibitors of the extracellular nucleotide metabolism and by blockade of α 1-adrenoceptors and P2X receptors with prazosin and NF023, respectively. It was concluded that adenosine A 2B receptors are involved in a facilitation of noradrenaline release in the prostatic portion of rat vas deferens that can be activated by adenosine formed by extracellular catabolism of nucleotides. The receptors seem to be coupled to the adenylyl cyclase–protein kinase A pathway but activation of the protein kinase C by protein kinase A, may also contribute to the adenosine A 2B receptor-mediated facilitation of noradrenaline release.

Coupling to protein kinases A and C of adenosine A2B receptors involved in the facilitation of noradrenaline release in the prostatic portion of rat vas deferens

In the prostatic portion of rat vas deferens, the non-selective adenosine receptor agonist NECA (0.1–30 μM), but not the A 2A agonist CGS 21680 (0.001–10 μM), caused a facilitation of electrically evoked noradrenaline release (up to 43±4%), when inhibitory adenosine A 1 receptors were blocked. NECA-elicited facilitation of noradrenaline release was prevented by the A 2B receptor-antagonist MRS 1754, enhanced by preventing cyclic-AMP degradation with rolipram, abolished by the protein kinase A inhibitors H-89, KT 5720 and cyclic-AMPS-Rp and attenuated by the protein kinase C inhibitors Ro 32-0432 and calphostin C. The adenosine uptake inhibitor NBTI also elicited a facilitation of noradrenaline release; an effect that was abolished by adenosine deaminase and attenuated by MRS 1754, by inhibitors of the extracellular nucleotide metabolism and by blockade of α 1 -adrenoceptors and P2X receptors with prazosin and NF023, respectively. It was concluded that adenosine A 2B receptors are involved in a facilitation of noradrenaline release in the prostatic portion of rat vas deferens that can be activated by adenosine formed by extracellular catabolism of nucleotides. The receptors seem to be coupled to the adenylyl cyclase–protein kinase A pathway but activation of the protein kinase C by protein kinase A, may also contribute to the adenosine A 2B receptor-mediated facilitation of noradrenaline release.

ATP modulates noradrenaline release by activation of inhibitory P2Y receptors and facilitatory P2X receptors in the rat vas deferens.

The role of ATP on the modulation of noradrenaline release elicited by electrical stimulation (100 pulses/8 Hz) was studied in the prostatic portion of rat vas deferens preincubated with [3H]noradrenaline. In the presence of P1 antagonists, the nucleotides 2-methylthioadenosine-5'-triphosphate (2-MeSATP), 2-methylthioadenosine 5'-diphosphate (2-MeSADP), ADP, and ATP decreased electrically evoked tritium overflow up to 44%, with the following order of potency: 2-MeSATP > 2-MeSADP > ADP > or = ATP. The P2Y antagonists reactive blue 2 (RB2) and 2-methylthioadenosine 5'-monophosphate (2-MeSAMP) increased, whereas the P2X antagonist pyridoxal-5'-phosphate-6-(2'-naphthylazo-6'-nitro-4',8'-disulfonate) (PPNDS) decreased evoked tritium overflow. The inhibitory effect of 2-MeSATP was antagonized by RB2 (10 microM) and by 2-MeSAMP (10 microM) but not by the selective P2Y1 receptor antagonist 2'-deoxy-N6-methyladenosine 3',5'-bisphosphate (MRS 2179; 10 microM). When, besides P1 receptors, inhibitory P2Y receptors were blocked with RB2, alpha,beta-methyleneadenosine 5'-triphosphate (alpha,beta-meATP), beta,gamma-imidoadenosine 5'-triphosphate (beta,gamma-imidoATP), beta,gamma-methyleneadenosine 5'-triphosphate (beta,gamma-meATP), 2-MeSATP, and ATP enhanced tritium overflow up to 140%, with the following order of potency: alpha,beta-meATP > 2-MeSATP = ATP = beta,gamma-meATP > or = beta,gamma-imidoATP. The facilitatory effects of alpha,beta-MeATP and beta,gamma-imidoATP were prevented by PPNDS. Under the same conditions, apyrase attenuated, whereas the ectonucleotidase inhibitor 6-N,N-diethyl-D-beta,gamma-dibromomethylene 5'-triphosphate enhanced tritium overflow, an effect that was prevented by PPNDS. In the prostatic portion of the rat vas deferens, endogenous ATP exerts a dual and opposite modulation of noradrenaline release: an inhibition through activation of P2Y receptors with a pharmacological profile similar to that of the P2Y12 and P2Y13 receptors and a facilitation through activation of P2X receptors with a pharmacological profile similar to that of P2X1 and P2X3, or PX2/P2X3 receptors.

New potential uroselective NO-donor alpha1-antagonists.

A recent uroselective alpha(1)-adrenoceptor antagonist, REC15/2739, has been joined with nitrooxy and furoxan NO-donor moieties to give new NO-donor alpha(1)-antagonists. All the compounds studied proved to be potent and selective ligands of human cloned alpha(1a)-receptor subtype. Derivatives 6 and 7 were able to relax the prostatic portion of rat vas deferens contracted by (-)-noradrenaline because of both their alpha(1A)-antagonist and their NO-donor properties.

Adenosine A2A receptor-mediated facilitation of noradrenaline release involves protein kinase C activation and attenuation of presynaptic inhibitory receptor-mediated effects in the rat vas deferens.

In the epididymal portion of rat vas deferens, facilitation of noradrenaline release mediated by adenosine A2A receptors, but not that mediated by beta2-adrenoceptors or by direct activation of adenylyl cyclase, was attenuated by blockade of alpha2-adrenoceptors and abolished by simultaneous blockade of alpha2-adrenoceptors, adenosine A1 and P2Y receptors. The adenosine A2A receptor-mediated facilitation was not changed by inhibitors of protein kinase A, protein kinase G or calmodulin kinase II but was prevented by inhibition of protein kinase C with chelerythrine or bisindolylmaleimide XI. Activation of protein kinase C with phorbol 12-myristate 13-acetate caused a facilitation of noradrenaline release that was abolished by bisindolylmaleimide XI and reduced by antagonists of alpha2-adrenoceptors, adenosine A1 and P2Y receptors. Activation of adenosine A2A receptors attenuated the inhibition of noradrenaline release mediated by the presynaptic inhibitory receptors. This effect was mimicked by phorbol 12-myristate 13-acetate and prevented by bisindolylmaleimide XI. It is concluded that adenosine A2A receptors facilitate noradrenaline release by a mechanism that involves a protein kinase C-mediated attenuation of effects mediated by presynaptic inhibitory receptors, namely alpha2-adrenoceptors, adenosine A1 and P2Y receptors.

Facilitation of noradrenaline release by adenosine A 2A receptors in the epididymal portion and adenosine A 2B receptors in the prostatic portion of the rat vas deferens

The adenosine-receptor modulation of noradrenaline release was compared in prostatic and epididymal portions of rat vas deferens. In both portions, tritium overflow elicited by electrical stimulation (100 pulses/8 Hz) was reduced by the adenosine A 1 receptor agonist, N 6-cyclopentyladenosine, and enhanced by the nonselective receptor agonist, 5′- N-ethylcarboxamidoadenosine, in the presence of the adenosine A 1 receptor antagonist, 1,3-dipropyl-8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 20 and 100 nM). The adenosine A 2A receptor agonist, 2- p-(2-carboxyethyl)phenethyl-amino-5′- N-ethylcarboxamidoadenosine, increased tritium overflow, but only in the epididymal portion. The enhancement caused by NECA was prevented by the adenosine A 2A receptor antagonist, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385; 20 nM), in the epididymal and by the adenosine A 2B receptor antagonist, alloxazine (1 μM), in the prostatic portion. Inhibition of adenosine uptake enhanced tritium overflow in both portions, an effect blocked by ZM 241385 in the epididymal and by alloxazine in the prostatic portion. The results indicate that adenosine exerts an adenosine A 1 receptor-mediated inhibition, in both portions, and facilitation mediated by adenosine A 2A receptors in the epididymal and by A 2B receptors in the prostatic portion.

Acute cerebral focal ischaemia alters the adrenergic and NANC responses in the bisected rat vas deferens.

1. Disturbances of the autonomic nervous system are common in right hemisphere stroke patients, including a marked decline in male sexual functions. There is a lack of information on the influence of stroke on male secondary sex organs such as the vas deferens. 2. This study investigates the effect of right brain focal ischaemia on the adrenergic and purinergic responses in isolated epididymal and prostatic portions of rat vas deferens. 3. In both epididymal and prostatic portions the concentration-response curves to noradrenaline are flattened resulting in a reduction (up to 67 - 76%) of the maximum contractile response in the tissue from ischaemic rats compared to the controls. In the prostatic portion from ischaemic rats the concentration-response curve to alpha,beta-methylene ATP was also depressed. 4. The first purinergic and the second delayed adrenergic phase to single pulse was not modified by brain ischaemia. In contrast both phasic and tonic components of the electrically induced contractions by trains of stimuli at high frequencies (2 - 30 Hz) were significantly depressed in the epididymal and prostatic portions from ischaemic rats. 5. These results demonstrate an autonomic imbalance at the level of male sexual secondary organs which may contribute to sexual impairment after stroke.

Effect of in vivo and in vitro ethanol on adrenergic and purinergic responses of the bisected rat vas deferens to low and high frequency pulses.

1. This study investigates the effect of acute in vivo and in vitro ethanol administration on the contractions evoked electrically and by exogenous noradrenaline and alpha,beta-methylene-ATP in the rat bisected vas deferens. 2. In vivo ethanol treatment (3 g kg(-1), i.p.) significantly potentiated the early purinergic (phase I) and the delayed adrenergic (phase II) phases evoked by single-pulse stimulation of the epididymal portion of the rat vas deferens, leaving unaffected both phases in the prostatic portion. In vitro 50 mM ethanol significantly depressed phase I leaving unaffected phase II in both portions from untreated rats. In vitro ethanol significantly depressed phase I in the epididymal portion from in vivo ethanol treated animals and potentiated phase II in both portions. 3. In vivo ethanol treatment (3.0 g kg(-1), i.p.) selectively impaired the response to noradrenaline only in the prostatic portion of rat vas deferens while it was devoid of any action on alpha,beta-methylene-ATP contractions. Ethanol 50 mM in vitro was devoid of any action on the response to exogenous noradrenaline and alpha,beta-methylene-ATP in both tissues. 4. In vivo ethanol treatment slightly but significantly increased the phasic response in the epididymal portion to trains of stimuli (2-30 Hz). In vitro 50 mM ethanol was ineffective against the phasic and tonic contractions elicited by the tetanus in both portions. 5. It is concluded that ethanol treatment affects purinergic and adrenergic pathways of transmission possibly leading to a disruption of physiological contractions necessary to seminal emission.