Isolated Rat Vas Deferens Research Articles

ChemInform Abstract: SYNTHESIS AND ANTIHYPERTENSIVE ACTIVITY OF STEREOISOMERS OF 4‐PIPERIDYL‐1,3‐DIHYDRO‐2‐OXO‐2H‐BENZIMIDAZOLES. ENHANCED POTENCIES OF (+)‐ISOMERS

AbstractDie Verbindungen (I) werden in ihre (+)‐ und H‐Isomeren umgewandelt und auf hxgotensive sowie α‐adrenerge Rezeptoren‐blockierende Aktivität Lintersucht.

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. Channels activated by methoxamine are concentrated in the epididymal half, whereas those opened by barium are evenly distributed. However, although responses to methoxamine and barium are similar in form, differences in the effects of some of the drugs tested, together with the results of previous studies, indicate that they produce contractions by different mechanisms.

The effects of pancreatic polypeptides and neuropeptide Y on the rat vas deferens

In order to study the physiological significance of the coexistence of pancreatic polypeptide and norepinephrine (NE) in peripheral noradrenergic nerves, the effects of pancreatic polypeptides of several species were tested on the isolated rat vas deferens. Neuropeptide Y (NPY) was also studied because of its sequence homology to the pancreatic polypeptides. The contractile responses, which were mediated predominantly by activation of noradrenergic nerves following electrical stimulation, were inhibited by bovine pancreatic polypeptide (BPP), human pancreatic polypeptide (HPP), avian pancreatic polypeptide (APP) and NPY in a dose-dependent manner using a constant flow bath. The decreasing order of the inhibitory responses was as follows: BPP=HPP > NPY > APP. The inhibitory responses produced by BPP and HPP lasted more than 1 hr and displayed a marked tachyphylaxis. In contrast, the inhibitory effects induced by NPY and APP usually returned to the control level after 20–30 min and had minimal tachyphylaxis. The inhibitory action of NPY was still present during α-adrenergic blockade. Contractions produced by a single submaximal dose of exogenous NE or serotonin (5-HT) in unstimulated preparations were not affected by pretreatment with NPY. The amplitude of contractions was partially reduced 1 min after pretreatment with BPP or HPP; recovery occurred about 15 min after peptide pretreatment in a constant flow bath. These results suggest that an NPY receptor exists presynaptically in the rat vas deferens and that stimulation of the receptor by NPY inhibits the release of NE from noradrenergic nerves. It is concluded that both BPP and HPP act by a presynaptic inhibitory mechanism on noradrenergic nerve terminals and also have a nonspecific inhibitory action on smooth muscle cells.

Synthesis and antihypertensive activity of stereoisomers of 4-piperidyl-1,3-dihydro-2-oxo-2H-benzimidazoles. Enhanced potencies of (+)-isomers

To elucidate the relationship between the pharmacological activity and stereochemical structure, we resolved 1-[2-(3-,4,5-trimethoxyphenyl)-2-hydroxy-1-methylethyl]-4-(1,3-dihydro-2-oxo-2H -benzimidazol-1-yl)piperidine (1 and 2) and 1-[2-(3,4-dimethoxyphenyl)-2-hydroxy-1-methylethyl]-4-(1,3-dihydro-2-oxo-2H-benzimidazol-yl)piperidine (3), which produced hypotensive effects mainly through their alpha-blocking actions. Threo isomers 1 and 3 were resolved via diastereomeric carbamates. Erythro isomer 2 was obtained by an oxidation and reduction sequence from optically active 1. No significant difference was found between the pharmacological activities of the threo and erythro isomers of the corresponding compounds. However, a clear difference was found between the pharmacological activities of the optical isomers. Difference was most clearly shown in the hypotensive actions of normotensive rats and in alpha-adrenergic blocking activities of isolated rat vas deferens. In these actions, (+) isomers were always more potent than the corresponding (-) isomers.

The effects of the ionophore A-23187 on the rat vas deferens.

The calcium ionophore A-23187 induced spontaneous, rhythmic contractions in the rat isolated vas deferens in a concentration-dependent manner. Contractions were blocked by phentolamine and were abolished following pretreatment with reserpine. In tissues preloaded with [3H]noradrenaline, A-23187 (10 microM) caused a time-dependent increase in the release of tritium. The findings suggest that A-23187-induced contractions in the rat vas deferens are secondary to the release of endogenous noradrenaline from the adrenergic nerves, as are contractions induced in this preparation by X-537A (another calcium ionophore) described earlier by other investigators.

Feedback inhibition of responses of rat vas deferens to twin pulse stimulation

Application of a pair of identical pulses of field stimulation to the rat isolated vas deferens results in two responses, the second of which is always smaller than the first, the reduction being inversely related to the internal between the pulses. This effect is due, in part, to the negative feedback inhibition of noradrenaline release, an event which has been demonstrated in a variety of noradrenergically innervated tissues. The ratio of the second response to the first response (the B/A ratio), is increased by substances with antagonistic activity at prejunctional α 2-receptors, and decreased by inhibitors of the neuronal uptake process. The procedure allows an estimate of the relative activity of antagonists at prejunctional α-receptors.

Effect of histamine and H 1- and H 2-agonists on the fractional outflow of radioactivity from the rat vas deferens preloaded with [ 3H]-noradrenaline

Histamine and relatively selective H 1- and H 2-receptor agonists caused a concentration-dependent increase in the fractional outflow of radioactivity from the rat isolated vas deferens preloaded with labelled noradrenaline. The evoked fractional outflow of radioactivity was not preferentially associated with either H 1- or H 2-selective agonists, nor was it related to the known potencies of the agonists within each group. The evoked fractional outflow caused by all compounds studied was independent of the extracellular Ca 2+ concentration. The study cautions against ascribing all the effects of histamine analogs to their respective histamine receptor stimulation.

Relationship between tyramine potentiation and selective inhibition of monoamine oxidase types A and B in the rat vas deferens.

1 The degree of selective monoamine oxidase (MAO) inhibition produced by (-)-deprenyl, clorgyline, LY51641 and tranylcypromine was examined in relation to modification of tyramine and noradrenaline contractile responses of the rat isolated vas deferens. 2 All inhibitors possessed reversible alpha-adrenoceptor blocking activity, determined against noradrenaline on the denervated vas deferens. For LY51641 and tranylcypromine, antagonism was competitive, with pA2 values of 6.17 and 5.16. 3 Clorgyline, LY51641 and (-)-deprenyl (10(-5) M) inhibited the tyramine response while present in the organ bath: LY51641, which was the most potent as an alpha-adrenoceptor blocker, produced this effect at 10(-6) M. Responses to tyramine and noradrenaline were potentiated on wishing out the inhibitors, but noradrenaline potentiation was seen only when tyramine had been present in the system. 4 Tranylcypromine (10(-6) M) potentiated responses to noradrenaline and tyramine while present in the organ bath. 5 Potentiation of tyramine responses by clorgyline and LY51641 occurred at 91% and 64% inhibition of MAO type A respectively, although full potentiation of the tyramine response was elicited only when substantial inhibition of both enzyme types occurred. Selective inhibition of MAO type B by 67% (with deprenyl) was not associated with tyramine potentiation.

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.

Adrenoceptor supersensitivity in the isolated rat vas deferens during barbital withdrawal

Long-term treatment with sodium barbital did not alter significantly the responsiveness of the isolated rat vas deferens to noradrenaline. However, three days after barbital withdrawal there was a 4.5-fold increase in the sensitivity and an enhanced maximum response to the neurotransmitter. Pharmacological analysis of the affinity of postjunctional adrenoceptors showed no alteration of the pA 2 of phentolamine, a decrease in the apparent dissociation constant ( K A) for noradrenaline and an increase in the fraction of adrenoceptors ( q) remaining active after exposure to phenoxybenzamine. Comparison between ED 50 and K A indicates the presence of spare receptors in the rat vas deferens. There was also a decrease in the blocking activity of phenoxybenzamine, in vasa deferentia obtained from rats three days after barbital withdrawal. These results suggest that an increased affinity of postjunctional adrenoceptors could be responsible, at least partially, for this supersensitivity to noradrenaline. The increased maximum response to the neurotransmitter could be the consequence of an improved coupling of adrenoceptor occupation to the final contractile response.

Structure-activity relationships for 2-substituted imidazoles as alpha 2-adrenoceptor antagonists.

Several 2-[(1,4-benzodioxan-2-yl)alkyl]imidazoles were prepared and evaluated for their blocking activity and relative selectivity on presynaptic (alpha 2) and postsynaptic (alpha 1) receptors in the isolated rat vas deferens. 1-Ethyl-2-[(1,4-benzodioxan 2-yl)methyl]imidazole (13) was the most selective alpha 2-adrenoceptor antagonist of the series and was, for practical purposes, devoid of alpha 1-adrenoceptor antagonist activity. The lipophilicity of 13 (log D = 2.31) indicated that it would have an excellent chance to enter the central nervous system. Compound 13 was selected for clinical evaluation as an antidepressant agent.

Preferential blockade of pre-synaptic alpha-adrenoceptors on the rat isolated vas deferens by cryptolepine, 7:studies on cryptolepine.

The twitch response of the rat isolated vas deferens to electrical field stimulation, (1 to 10 Hz, 1 to 2 m. sec.), reduced by noradrenaline (1 to 2 µg ml-1) was further enhanced by cryptolepine (5 to 10 µg ml-1). Cryptolepine (0.1 to 0.2 µg ml-1) antagonised the inhibition of the twitch produced by clonidine (1 to 2 ng ml-1) but did not antagonise the phenylephrine effect. Cryptolepine (1 to 2 µg ml-1) inhibited the potentiation of the twitch response and contraction of the muscle produced by phenylephrine (0.3 µg ml-1). Potentiation of the twitch produced by cocaine (1 to 5 µg ml-1) was also enhanced by Cryptolepine (1 to 2 µg ml-1).

P-244 - Influence of Ca content in the medium, and spasmolytics on response to the smooth muscle contractile agents in rat isolated vas deferens

P-244 - Influence of Ca content in the medium, and spasmolytics on response to the smooth muscle contractile agents in rat isolated vas deferens

Analysis of the effects of dopamine and noradrenaline in relation to the proposed postsynaptic dopamine receptor in rat vas deferens.

The contractile effects of dopamine and noradrenaline were compared in the rat isolated vas deferens, in order to obtain evidence for the presence or absence of postsynaptic dopamine receptors in this tissue. Attention was given to the role of several factors known to interfere with receptor characterization.

O-17 - Effect of indirectly-acting sympathomimetic drugs on the twitch response in isolated rat vas deferens

O-17 - Effect of indirectly-acting sympathomimetic drugs on the twitch response in isolated rat vas deferens

Developmental changes in alpha-adrenergic and muscarinic receptor-mediated contractions of rat vas deferens.

Studies were made on developmental changes in phasic contractions of isolated rat vas deferens in response to norepinephrine (NE) and acetylcholine (ACh), which are mediated by alpha-adrenergic and muscarinic cholinergic receptors (alpha-R and m-R). The ED50 values of both contractions were almost constant during development, but the maximum responses to NE and ACh per wet weight and the relative contractions by NE and ACh to that by 100 mM K+ decreased greatly between 3 and 8 weeks after birth. However, the alpha- and m-receptors, assayed by measuring binding of [3H]-WB4101 and [3H]-quinuclidinyl benzylate (QNB), increased quantitatively per g wet weight and per mg protein between 2 and 8 weeks after birth, but did not change qualitatively. Thus, a discrepancy between the increases of alpha- and m-receptors and decreases of the maximum responses to NE and ACh was found, and possible mechanisms for this are discussed.

DEVELOPMENTAL CHANGES IN α-ADRENERGIC AND MUSCARINIC RECEPTOR-MEDIATED CONTRACTIONS OF RAT VAS DEFERENS

AbstractStudies were made on developmental changes in phasic contractions of isolated rat vas deferens in response to norepinephrine (NE) and acetylcholine (ACh), which are mediated by α-adrenergic and muscarinic cholinergic receptors (a-R and m-R). The ED50 values of both contractions were almost constant during development, but the maximum responses to NE and ACh per wet weight and the relative contractions by NE and ACh to that by 100 mM K+ decreased greatly between 3 and 8 weeks after birth. However, the α- and m-receptors, assayed by measuring binding of [3H]-WB4101 and [3H]-quinuclidinyl benzylate (QNB), increased quantitatively per g wet weight and per mg protein between 2 and 8 weeks after birth, but did not change qualitatively. Thus, a discrepancy between the increases of α- and m-receptors and decreases of the maximum responses to NE and ACh was found, and possible mechanisms for this are discussed.

Biogenic amines and β-endorphin responses in the rat vas deferens

1. 1. Recent studies have demonstrated that activation of opioid peptide receptor by β-endorphin results in a change of bioamines in peripheral tissues. 2. 2. The present results could be interpreted assuming that the action of β-endorphin, on the smooth muscle of the isolated rat vas deferens, is independent of catecholaminergic, cholinergic and tryptaminergic neurotransmission. 3. 3. There is evidence that it is through a specific opioid ‘ϵ-receptor’ which have been shown a high degree of affinity for β-endorphin.

Castration alters the stimulatory and inhibitory adrenergic influences on isolated rat vas deferens

Responses to adrenoceptor agonistic drugs were examined in two regions of vasa deferentia (epididymal and prostetic) from adult intact and castrated rats. In the prostatic portion the stimulating alpha adrenergic responses following castration were greater than in the intact rats. On the other hand in the epididymal region the reactivity was smaller in preparations from castrated animals. A beta-adrenoceptor-inhibitory-mediated mechanism was only present in the epididymal segment of the castrated group; in which a clear spontaneous activity was observed. Testosterone treatment reversed the alpha and beta adrenergic effects detected after castration. Results show a relationship between testosterone and the spontaneous motility as well as an influence in the action of alpha and beta adrenergic agonists on their receptors.

3H-noradrenaline metabolism in the isolated epididymal and prostatic portions of the rat vas deferens

The spontaneous 3H-noradrenaline efflux from the isolated epididymal and prostatic portions of the rat vas deferens, was investigated. The spontaneous tritium efflux was higher in the epididymal portion than in the prostatic one from normal animals. Such differences were abolished after castration. On the other hand, acetylsalicylic acid enhanced the total tritium efflux only in the epididymal portion, whereas phentolamine and phenoxybenzamine increased the total tritium efflux from the two portions of the rat vas deferens in both experimental groups. The prostatic portion released a similar amount of 3H normetanephrine than the apididymal end, whereas other metabolic fractions (3,4-dihydroxyphenylglycol; 3,4-dihydroxymandelic acid and O-methylated deaminated metabolites) were smaller in the prostatic portion in comparison with the epididymal portion from control vas deferens. The results presented in the isolated rat vas deferens suggest the existence of a prostaglandin as well as an alpha adrenoceptive modulation of the spontaneous total tritium efflux.