Evidence for a functional alpha 1A- (alpha 1C-) adrenoceptor mediating contraction of the rat epididymal vas deferens and an alpha 1B-adrenoceptor mediating contraction of the rat spleen.

1. The alpha 1-adrenoceptor subtype mediating contraction of the rat epididymal vas deferens and rat spleen has been investigated by use of alpha 1-adrenoceptor antagonists that have shown selectivity between the different cloned receptor subtypes. 2. In the rat epididymal vas deferens the potency of noradrenaline and phenylephrine was increased in the presence of neuronal and extra-neuronal uptake blockers, cocaine and beta-oestradiol, but these did not alter that of methoxamine. The order of potency of the agonists in the presence or absence of uptake blockade was noradrenaline > phenylephrine > methoxamine. In the rat spleen the potency of these agonists was not altered in the presence of cocaine and beta-oestradiol, and their order of potency was the same as in the vas deferens. 3. The non subtype selective alpha 1-adrenoceptor antagonist prazosin (up to 1 x 10(-7) M) was found to antagonize contractions to noradrenaline in the vas deferens competitively (pA2 9.2), but only in a non competitive manner in the spleen. Contractions to phenylephrine in the spleen however were competitively antagonized by prazosin (up to 1 x 10(-7) M) with a pA2 of 9.2. This suggests that there is an alpha 1- and a non alpha 1-adrenoceptor response to noradrenaline in the rat spleen. 4. Pretreatment with chlorethylclonidine (10(-4) M for 30 min) did not alter the noradrenaline contractions in the vas deferens, but contractions to noradrenaline and phenylephrine in the spleen were shifted 30 and 300 fold to the right of the control curve, respectively. This suggests that only the contractions in the spleen were mediated by alpha 1B-adrenoceptors. 5.(ABSTRACT TRUNCATED AT 250 WORDS)     

Study of the in vivo and in vitro cardiovascular effects of (+)-glaucine and N-carbethoxysecoglaucine in rats.

1. The cardiovascular and vasorelaxant effects of (+)-glaucine and of a semisynthetic derivative (N-carbethoxysecoglaucine) were studied in rats. 2. N-carbethoxysecoglaucine did not modify either systolic arterial pressure or heart rate values in conscious (25 mg kg-1, p.o.) and anaesthetized normotensive rats (5 mg kg-1, i.v.). Furthermore, this compound showed no activity in the experiments carried out on rat isolated aorta [contractility and 45Ca2+ influx assays (5 microM)] and did not modify the rate and force of contraction in rat isolated atria (5 microM). 3. In conscious normotensive rats, oral administration of (+)-glaucine (25 mg kg-1) did not modify either systolic arterial pressure or heart rate. 4. In anaesthetized normotensive rats, (+)-glaucine (5 mg kg-1, i.v.) produced a remarkable fall in mean arterial pressure (MAP) accompanied by a significant decrease in heart rate. In the same preparation, (+)-glaucine (5 mg kg-1, i.v.) did not modify the cardiovascular effects induced by noradrenaline (NA) (5 micrograms kg-1) and 5-hydroxytryptamine (5-HT) (300 micrograms kg-1) but markedly inhibited those induced by nicotine (200 micrograms kg-1). 5. In isolated intact aorta of rat, (+)-glaucine (0.15-5 microM) competitively inhibited the contractions induced by NA (with a pA2 value of 7.14) and non-competitively those induced by 5-HT (in normal Krebs solution) and Ca2+ (in depolarizing Ca(2+)-free high-K+ 50 mM solution), with depression of the maximal response and with pD2 values of 5.56 and 5.26, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of several calcium channels modulators on the [3H]noradrenaline release and 45Ca influx in the rat vas deferens.

1. The effects of nifedipine (1 microM), CdCl2 (0.1 mM) and the Bay K 8644 enantiomers (1 microM) on [3H]noradrenaline release and 45Ca uptake in epididymal and prostatic rat vas deferens were investigated. 2. Nifedipine, CdCl2 and Bay K 8644 optical isomers did not affect the basal tritium release. However, the [3H]noradrenaline release evoked by high potassium (50 mM) from both portions of rat vas deferens was markedly inhibited by CdCl2, scarcely affected by nifedipine and not modified by Bay K 8644 enantiomers. 3. (-)-Bay K 8644 increased the basal and potassium (50 mM) induced 45Ca uptake whereas (+)-Bay K 8644, nifedipine and CdCl2 did not alter the basal 45Ca uptake. However, they strongly inhibited the uptake induced by potassium in both portions of rat vas deferens. 4. These results suggest that the calcium channels (mainly L type) are involved on the contractions in rat vas deferens epididymal and prostatic halves; these channels differ from those present in sympathetic nerve terminals (likely of N Type) which modulates the NA release. 5. This study also shows that Bay K 8644 optical isomers possess opposite effects on the L channels of bisected rat vas deferens smooth muscle.     

Effects of the alpha 1-adrenoceptor antagonist R-(-)-YM12617 on isolated human penile erectile tissue and vas deferens

The effects of the selective alpha 1-adrenoceptor antagonist, R-(-)-YM12617 (5-[2-[[2-(0-ethoxyphenoxy)ethyl]amino] propyl]-2-methoxybenzenesulphonamide HCl), were investigated in isolated human corpus spongiosum, corpus cavernosum, and vas deferens. R-(-)-YM12617 concentration dependently and competitively inhibited contractions induced by noradrenaline in human penile erectile tissue (pA2 value in corpus spongiosum = 9.92), and the drug was approximately 12 times more potent than prazosin (pA2 value = 8.83). In the vas deferens, R-(-)-YM12617 and prazosin inhibited electrically induced contractions concentration dependently, and abolished the contractions at 10(-6) and 10(-5) M, respectively. The -log IC50 values for R-(-)-YM1261 and prazosin were 8.46 and 7.50, respectively. It is concluded that R-(-)-YM12617 is a potent inhibitor of alpha 1-adrenoceptors in human penile erectile tissues and vas deferens, and that the drug, if injected intracavernosally, may be useful for the treatment of penile erectile dysfunction.     

Investigation of the subtypes of alpha 1-adrenoceptor mediating contractions of rat aorta, vas deferens and spleen.

1. The subtypes of alpha 1-adrenoceptor mediating contractions to exogenous noradrenaline (NA) or phenylephrine in rat vas deferens, spleen and aorta, and mediating contractions to endogenous NA in rat vas deferens have been examined. 2. In rat vas deferens, the competitive antagonists prazosin, WB 4101, benoxathian and 5-methyl-urapidil inhibited contractions to NA with pA2 values of 9.26, 9.54, 9.02 and 8.43, respectively. The irreversible antagonist chloroethylclonidine (CEC) (100 microM) failed to affect contractions to NA. 3. In rat vas deferens in the presence of nifedipine (10 microM), contractions to NA were significantly attenuated and under these conditions, CEC (100 microM) significantly reduced the maximum response to NA. 4. In rat spleen, the competitive antagonists prazosin, WB 4101 and benoxathian inhibited contractions to phenylephrine with pA2 values of 9.56, 8.85 and 7.60, respectively, and 5-methyl-urapidil had a KB of 6.62. CEC (100 microM) significantly reduced the maximum contraction to phenylephrine. 5. In rat aorta, the competitive antagonists, prazosin, WB 4101, benoxathian and 5-methyl-urapidil inhibited contractions to NA with pA2 values of 9.45, 9.21, 8.55 and 8.12, respectively. CEC (100 microM) produced an approximately parallel shift in the potency of NA, without significantly reducing the maximum response. 6. In epididymal portions of rat vas deferens in the presence of nifedipine (10 microM), the isometric contraction to a single electrical pulse was significantly reduced by CEC (100 microM), and by the competitive antagonists prazosin, WB 4101, benoxathian and 5-methyl-urapidil at concentrations of 1 nM.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of calcium channel inhibitors and other procedures affecting calcium translocation on drug-induced rhythmic contractions in the rat vas deferens.

In the rat isolated vas deferens, methoxamine 8.1 microM produced an initial phasic response that declined towards baseline and was followed by rhythmic contractions that continued until wash-out. These responses were predominant in the epididymal half. BaCl2 1 mM produced a similar type of response which was not mediated by noradrenaline release or activation of alpha-adrenoceptors. The barium responses were similar in the epididymal and prostatic halves. Incubation in nominally Ca2+-free solution caused abolition or near abolition of rhythmic contractions produced by barium or methoxamine. The initial phasic response to methoxamine was abolished in Ca2+-free solution, whereas that produced by barium persisted. Rhythmic contractions produced by methoxamine or barium were inhibited by Mg2+ (2.4-20 mM) and by La3+ (1-5 mM). Mg2+ had selectivity for inhibition of the frequency of methoxamine- but not barium-induced rhythmic contractions. Despite their dependence on [Ca2+]o, barium- and methoxamine-induced rhythmic contractions were resistant to inhibition by calcium channel inhibitors. Verapamil, nifedipine and flunarazine inhibited the amplitude of rhythmic contractions more readily than the frequency (methoxamine IC50 for verapamil: amplitude = 29.8 +/- 5.40 microM, n = 6, frequency = 96.7 +/- 31.0 microM, n = 5, for nifedipine: amplitude = 2.42 +/- 0.34 microM, n = 7, frequency = 3.24 +/- 0.75 microM, n = 7, and for flunarizine: amplitude = 15.9 +/- 5.95 microM, n = 7, frequency = 153 +/- 28.6 microM, n = 7). There was no differentiation between inhibition of methoxamine and barium-induced responses. Like Mg2+, methoxyverapamil selectively inhibited the frequency of methoxamine-induced contractions (IC50: amplitude = 16.8 +/- 2.86 microM, n = 5, frequency = 2.07 +/- 0.81 microM, n = 5) but not barium-induced contractions (IC50: amplitude = 13.9 +/- 1.95 microM, n = 5, frequency = 48.5 +/- 8.98 microM, n = 5). Diazoxide (43.3-2167 microM) and nitroprusside (3.36-6712 microM) had only a small effect on barium contractions, but produced a dose-related reduction in the amplitude of methoxamine-induced responses. Diazoxide and nitroprusside caused methoxamine contractions to occur in groups, although they had no effect on their overall frequency. It is concluded that barium- and methoxamine-induced rhythmic contractions in the rat vas deferens are mediated by the entry of [Ca2+]o via membrane calcium channels that have a lower affinity (10-100 X) for calcium channel inhibitors than those mediating the KCl response.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

(-)-Discretamine, a selective alpha 1D-adrenoceptor antagonist, isolated from Fissistigma glaucescens.

1. The selectivity of (-)-discretamine for alpha 1-adrenoceptor subtypes was investigated by use of functional and binding studies in rat vas deferens, spleen and aorta, and in cultured DDT1MF-2 and A10 cells. 2. In prostatic portions of rat vas deferens, the competitive antagonists (-)-discretamine, 5-methylurapidil (5-MU) and prazosin inhibited contractions to noradrenaline (NA) with pA2 values of 6.21, 8.71 and 9.27, respectively. The irreversible antagonist, chloroethylclonidine (CEC, 100 microM) failed to affect contractions to NA while nifedipine (1 microM) blocked them almost completely. 3. In rat spleen, the competitive antagonists (-)-discretamine, 5-MU and prazosin inhibited contractions to phenylephrine with pA2 values of 6.44, 7.19 and 9.45, respectively. CEC (100 microM) significantly reduced the maximum contraction to phenylephrine while nifedipine (1 microM) did not affect it. 4. In rat aorta, the competitive antagonists (-)-discretamine, 5-MU and prazosin inhibited contractions to NA with pA2 values of 7.60, 8.00 and 9.40, respectively. CEC also antagonized the contractions to NA in a competitive manner with a pA2 value of 6.10. 5. The specific binding of [3H]-prazosin to DDT1MF-2 and A10 cells was concentration-dependent and saturated at 3-5 nM with KD values of 0.24 +/- 0.02 and 0.20 +/- 0.02 nM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of indoramin in rat vas deferens and aorta: concomitant alpha1-adrenoceptor and neuronal uptake blockade.

1. The actions of the alpha1-adrenoceptor antagonist indoramin have been examined against the contractions induced by noradrenaline in the rat vas deferens and aorta taking into account a putative neuronal uptake blocking activity of this antagonist which could result in self-cancelling actions. 2. Indoramin behaved as a simple competitive antagonist of the contractions induced by noradrenaline in the vas deferens and aorta yielding pA2 values of 7.38+/-0.05 (slope=0.98+/-0.03) and 6.78+/-0.14 (slope=1.08+/-0.06), respectively. 3. When the experiments were repeated in the presence of cocaine (6 microM) the potency (pA2) of indoramin in antagonizing the contractions of the vas deferens to noradrenaline was increased to 8.72+/-0.07 (slope=1.10+/-0.05) while its potency remained unchanged in the aorta (pA2=6.69+/-0.12; slope=1.04+/-0.05). 4. In denervated vas deferens, indoramin antagonized the contractions to noradrenaline with a potency similar to that found in the presence of cocaine (8.79+/-0.07; slope=1.09+/-0.06). 5. It is suggested that indoramin blocks alpha1-adrenoceptors and neuronal uptake in rat vas deferens resulting in Schild plots with slopes not different from unity even in the absence of selective inhibition of neuronal uptake. As a major consequence of this double mechanism of action, the pA2 values for this antagonist are underestimated when calculated in situations where the neuronal uptake is active, yielding spurious pKB values.     

Effects of oxypertine on the isolated vas deferens of the rat.

1 The isolated vas deferens of the rat was used to examine the peripheral action of oxypertine, a psychotropic-anxiolytic drug. 2 Oxypertine (4.4 X 10(-10) M to 2.6 X 10(-5) M) antagonized competitively the effects of noradrenaline (pA2 = 7.2), 5-hydroxytryptamine (pA2 = 8.6) and dopamine (pA2 = 9.8). 3 Oxypertine (8.8 X 10(-9) M to 2.6 X 10(-5) M) antagonized the effects of low concentrations of acetylcholine and enhanced the contractions elicited by high concentrations of acetylcholine. 4 The contractions evoked by transmural stimulation of the vas deferens were reduced by oxypertine. 5 Oxypertine failed to antagonize the responses to potassium chloride. 6 These findings are compared with the effects of other antidepressant drugs.     

Inhibition of neuroeffector transmission in human vas deferens by sildenafil

Sildenafil (0.1 - 30 microM), a cyclic GMP phosphodiesterase 5 (PDE 5) inhibitor, induced inhibition of electrically evoked contractions of ring segments of human vas deferens from 34 vasectomies. Zaprinast (0.1 - 100 microM), another PDE 5 inhibitor, and the nitric oxide (NO) donor sodium nitroprusside (SNP) (0.1 - 100 microM) had no effect on neurogenic contractions. The inhibition induced by sildenafil was not modified by the inhibitor of guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) (1 - 30 microM) but it was abolished by the K(+) channel blockers tetraethylammonium (TEA, 1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM). Sildenafil, zaprinast and SNP did not affect the contractions induced by noradrenaline. SNP (10 microM) caused elevation of cyclic GMP levels that was potentiated by sildenafil (10 microM) and zaprinast (100 microM). ODQ (10 microM) inhibited the increase in cyclic GMP. Sildenafil inhibits adrenergic neurotransmission in human vas deferens. The inhibition is not related to accumulation of cyclic GMP but is probably due to activation of prejunctional large-conductance Ca(2+)-activated K(+) channels.     

Pharmacological effects of (+)-nantenine,an alkaloid isolated from Platycapnos spicata,in several rat isolated tissues

In this work, the potential activity of (+)-nantenine (a natural aporphin alkaloid) in several rat isolated tissues was studied. In rat isolated intact aorta, (+)-nantenine (0.05 - 0.5 microM) competitively antagonized with almost equal effectiveness the contractions produced by phenylephrine (PE) and 5-hydroxytryptamine (5-HT) in normal Krebs solution. However, at higher concentrations (2 microM), the alkaloid also reduced the maximal effect induced by these two agonists. In depolarizing Ca2+-free high KCl 50 mM solution, (+)-nantenine (1.5 - 6 microM) inhibited, in a non-competitive way, the increase in tension evoked by Ca2+ with depression of the maximum response. On the other hand, (+)-nantenine (3 - 30 microM) did not affect the contractile effect caused by okadaic acid (OA, 1 microM) while, however, this alkaloid totally relaxed, in a concentration-dependent fashion, the contractions produced by phorbol 12-myristate 13-acetate (PMA, 1 microM) in endothelium-containing rat aortic rings. (+)-Nantenine (1 - 30 microM) reversed and competitively antagonized the inhibitory action induced by B-HT 920 in electrically-stimulated rat vas deferens. In isolated rat atria, (+)-nantenine (3 - 10 microM) diminished the contraction frequency. (+)-Nantenine (3 microM) significantly reduced the depolarization (voltage)-activated transient (T-type) and sustained (long-lasting, L-type) barium inward currents [ IBa(T) and IBa(L) ] recorded in whole cell-clamped rat aortic myocytes. These results indicate that the pharmacological effects of (+)-nantenine observed at concentrations lower than 1 microM can be attributed to alpha 1 -adrenergic and 5-HT 2A receptor blocking properties whereas at higher concentrations (> 1 microM) the pharmacological activity of this natural compound may be also due to a decrease of Ca2+ influx through transmembrane calcium channels (calcium antagonist activity), to an inhibition of PKC actions and/or to an alpha 2 -adrenoceptor blockade.     

Effects of K(+)-free solution of 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.     

Effects of methoxamine and barium on 45Ca2+ fluxes in the rat vas deferens.

The aim of this study was to determine whether methoxamine and barium stimulate 45Ca2+ uptake or efflux in the rat vas deferens in a manner that correlates with their contractile activity, and whether 45Ca2+ movements are inhibited by verapamil or nifedipine. Basal La(3+)-resistant (cellular) 45Ca2+ uptake was significantly greater in the epididymal half (791 +/- 27 nmol g-1) than in the prostatic half (654 +/- 14 nmol g-1) of the rat vas deferens and was unaffected by verapamil (61 microM) or nifedipine (14 microM). Methoxamine (8 microM) was without effect on 45Ca2+ uptake in either half but BaCl2 (1 mM) increased 45Ca2+ uptake by 31% in the prostatic half and by 22% in the epididymal half. The barium-induced increases in 45Ca2+ uptake were markedly reduced or abolished by verapamil (2 microM) or nifedipine (0.3 microM), which at these concentrations have no effect on the rhythmic contractions but abolish the initial small phasic contraction induced by barium. The basal rate of 45Ca2+ efflux from the intact vas deferens (into Ca2+ containing Krebs-Henseleit solution or into Ca-free Krebs-Henseleit solution +/- EGTA 0.05 mM) was not affected by verapamil (61 microM) or nifedipine (14 microM). Methoxamine (8 microM) produced a marked, transient and reversible increase in 45Ca2+ efflux into 2.5 mM CaCl2 Krebs-Henseleit in 50% of the intact vasa deferentia examined which was augmented by verapamil (61 microM). BaCl2 (1 mM) produced a small increase in 45Ca2+ efflux into Ca(2+)-containing and Ca(2+)-free Krebs-Henseleit solutions from some intact vasa deferentia and this was not inhibited by nifedipine (14 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Nantenine blocks muscle contraction and Ca2+ transient induced by noradrenaline and K+ in rat vas deferens

The effect of nantenine, an aporphine alkaloid isolated from Ocotea macrophylla H.B.K., was studied on contractions and Ca(2+) translocation induced by noradrenaline, Ca(2+), or K(+) in the isolated rat vas deferens from reserpinized animals. Concentration-response curves of calcium chloride (CaCl(2)) were performed in the vas deferens, in a Ca(2+)-free nutrient solution, using potassium chloride (KCl, 80 mM) as a depolarizing agent. In these conditions, nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly reduced the maximum contractions (E(max)) of Ca(2+) (IC(50)=2.6 x 10(-4) M) and noradrenaline (IC(50)=2.9 x 10(-4) M). The contractile responses were totally recovered after the withdrawal of nantenine. In addition, experiments performed to measure simultaneously the contraction and the increase of intracellular Ca(2+) induced by noradrenaline (10(-5) M) or KCl (80 mM) showed that nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly decreased both effects. The results suggest that a reversible block of Ca(2+) entry could be involved on the non-competitive-like antagonism of nantenine in rat vas deferens.     

Investigation of the subtypes of alpha1-adrenoceptor mediating contractions of rat vas deferens

1 The subtypes of alpha1-adrenoceptor mediating contractions of rat vas deferens to endogenous and exogenous noradrenaline and to the exogenous agonists methoxamine, phenylephrine and A61603 have been examined. 2 The effects of antagonists on the shape of concentration-response curves, both tonic and phasic, to the four agonists were analysed. Prazosin produced parallel shifts in all cases. Particularly for RS 17053 against noradrenaline, there was some evidence for a resistant component of the agonist response. High concentrations of RS 17053 (1-10 microM) virtually abolished tonic contractions but phasic contractions were resistant. 3 A series of nine antagonists (the above and WB4101, benoxathian, phentolamine, BMY 7378, HV 723, spiperone) were investigated against contractions to noradrenaline. The correlation with the potency of the series of alpha1-adrenoceptor antagonists against contractions to noradrenaline was significant only for the alpha1A-adrenoceptor ligand binding site (r=0.88, n=9, P<0.01). 4 In epididymal portions (nifedipine 10 microM), the isometric contraction to a single electrical pulse is alpha1-adrenoceptor mediated. The correlation with ligand binding sites for 11 antagonists (the above plus ARC 239 and (+)-niguldipine) was significant only for the alpha1D-adrenoceptor subtype (r=0.65, n=11, P<0.05). 5 In conclusion, tonic contractions of rat vas deferens produced by exogenous agonists are mediated predominantly by alpha1A-adrenoceptors, although a second subtype of receptor may additionally be involved in phasic contractions. Nerve-stimulation evoked alpha1-adrenoceptor mediated contractions seem to predominantly involve non-alpha1A-adrenoceptors, and the receptor involved resembles the alpha1D-receptor.     

Paradoxical effects of thioridazine on electromechanical coupling in the human and rat vas deferens

The effects of thioridazine on the responses of isolated human and rat vas deferens to high [K+]0, A23187 and caffeine were examined. In the presence of Ca2+ (2.5 mM), thioridazine (1-10 microM) induced spontaneous contractions but caused a dose-related inhibition of the phasic and secondary parts of the response to high [K+]0 (136 mM). The relaxation phase of the high [K+]0 response of the human vas deferens was unaffected by thioridazine (up to 10 microM). In Ca2(+)-free/EGTA (0.5 mM) media, thioridazine caused a dose-related potentiation, shortened the latency and prolonged the duration of high [K+]0 responses. Contractions to caffeine (20 mM) and A23187 (20-50 microM) were relatively unchanged by thioridazine (10 microM). The spontaneous activity caused by thioridazine (10 microM) was sensitive to the Ca2(+)-channel blockers nifedipine (10 microM) or verapamil (10 microM). These results indicate that the action of thioridazine during electromechanical coupling in the human and rat vas deferens may involve more than its blockade of voltage gated Ca2+ channels.     

Effects of St-587 on the alpha-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)     

The lack of utility of the rat vas deferens as a functional bioassay for sigma ligands

The present study examined the utility of the rat vas deferens preparation as a bioassay for sigma site ligands. sigma Ligands such as (+/-)-pentazocine, phencyclidine (PCP) and (+)-SK&F 10047 potentiated neurogenic twitch contractions. However, neither the order of potency nor the absolute potency of (+/-)-pentazocine and (+)-SK&F 10047 correlated with their affinity at central sigma sites. Furthermore, another potent sigma ligand, ditolyl-ortho guanidine (DTG) neither affected neurogenic twitch contractions nor inhibited twitch potentiation by PCP or (+)-SK&F 10047 at concentrations up to 30 mumol/l. These data indicate that the rat vas deferens is not a useful bioassay for the evaluation of sigma ligands. PCP, (+)-SK&F 10047 and (+/-)-pentazocine probably enhance neurogenic contractions in rat vas deferens primarily by inhibition of the neuronal uptake of noradrenaline.     

Effect of PCP and sigma ligands on both noradrenaline- and electrically-induced contractions and on [3H]-noradrenaline uptake in rat vas deferens

1 Electrically induced contractions of the epididymal portion of rat vas deferens were potentiated in concentration-dependent manner (0.1–30 μm ) by different sigma and PCP receptor ligands (PCP, TCP, (+)-MK-801, dextromethorphan and (+)-3-PPP); dextrorphan did it in a minor extent. 2 Sigma and PCP receptor ligands also potentiated the effect of noradrenaline, inducing a reduction of the noradrenaline EC₅₀ value in the rat vas deferens. The rank order of potencies was: PCP > TCP > (+)-3-PPP > (+)-MK-801 > dextrorphan > > > dextrometorphan. 3 In contrast, haloperidol (1 μm ), a sigma receptor ligand, inhibited both the neurogenic and noradrenaline-induced responses in this tissue. 4 The effect of PCP and sigma receptor ligands on noradrenaline uptake was evaluated. All compounds tested, including haloperidol, inhibited the tritiated noradrenaline incorporation to the tissue. IC₅₀ values were in the micromolar range, between 1.09 μm for dextrophan and 18 μm for dextrometorphan. 5 It is concluded that a direct interaction with the noradrenaline uptake system is involved in the potentiating effect of some sigma and PCP receptor ligands in the epididymal portion of rat vas deferens.