Contractions Of Rat Vas Deferens Research Articles

Effects of RS17053 on α1 -adrenoceptors in rat vas deferens and aorta.

RS17053 is classed as an α1A -adrenoceptor selective antagonist. We have examined its profile of action at all subtypes of α1 -adrenoceptor. Noradrenaline (NA) evoked contractions of rat vas deferens involve α1D -adrenoceptors in phasic contractions and α1A -adrenoceptors in tonic contractions. Contractions of rat aorta to NA involve α1D - and α1B -adrenoceptors. RS17053 (10-5 M) shifted NA potency and virtually abolished tonic contractions to NA, with little or limited effect on phasic contractions. The α1D -adrenoceptor antagonist BMY7378 (3 × 10-7 M) significantly inhibited the remaining phasic component of the contractions, and the α1A -adrenoceptor antagonist RS100329 (10-7 M) inhibited further the residual tonic contraction. Hence, RS17053 shows high selectivity for α1A -adrenoceptors over α1D -adrenoceptors in rat vas deferens. However, RS17053 (10-5 M) produced a large shift in the potency of NA in rat aorta, with a pKB of 6.82. Large shifts of NA potency in rat aorta involve α1B -adrenoceptor blockade. Results in rat vas deferens demonstrate low potency of RS17053 at α1D -adrenoceptors, but results from rat aorta can only be explained as demonstrating α1B -adrenoceptor antagonism by RS17053. RS17053 may be a useful pharmacological tool when reclassified as a mainly α1A - and to a lesser extent α1B -adrenoceptor antagonist with little effect at α1D -adrenoceptors.

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.

Evidence that the α1L‐adrenoceptor is the native α1A‐adrenoceptor in rat vas deferens

A 4th functional subtype of α1‐adrenoceptor, the α1L‐adrenoceptor, present in rat vas deferens, has been proposed at which prazosin has low potency (Ohmura et al., 1992). The subtypes of α1‐adrenoceptor mediating contractions of rat vas deferens to norepinephrine (NE) have been examined employing α1A‐antagonist RS100329 and α1D‐antagonist BMY7378 and the non‐selective antagonist prazosin. In presence of cocaine (3 μM) to block the NE transporter, NE potency (6.14±0.15, n=34) was significantly increased (P<0.05) as compared to in the absence of cocaine (5.30±0.10, n=21). Cocaine amplified contractions to low concentrations of NE. BMY7378 was more potent against contractions to NE in the presence of cocaine, whereas RS100329 was more potent in absence of cocaine. Prazosin, like BMY7378, was more potent in the presence of cocaine, suggesting α1D‐adrenoceptor selectivity. Prazosin pA2 values were 8.34 (slope ‐ 0.78±0.07) in absence of cocaine and 9.01 (slope −0.93±0.12) in presence of cocaine, with the lower value indicative of α1A‐adrenoceptor potency, and the higher value α1D‐adrenoceptor potency. Hence, it is concluded that the α1L‐adrenoceptor reported in rat vas deferens is not a functional isoform of the α1A‐adrenoceptor, it is the native α1A‐adrenoceptor at which prazosin shows lower potency.

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.

Contraction of rat vas deferens by cocaine.

Contraction of rat vas deferens by cocaine.

Ketanserin potentiates the prejunctional inhibitory effect of 5-hydroxytryptamine on rat vas deferens.

5-Hydroxytryptamine (5-HT) slightly inhibited the twitch contractions of rat vas deferens caused by single pulse field stimulation at 0.1 Hz. The inhibitory effect of 5-HT was much less in the epididymal portion than in the prostatic portion of the vas deferens. Ketanserin potentiated the prejunctional inhibitory effect of 5-HT and attenuated its stimulatory effect. This potentiation was observable only in the epididymal portion, of the vas deferens. Cyproheptadine and mianserin, but not methysergide, had essentially similar potentiating effects to those of ketanserin. These results suggest that the 5-HT receptor that mediates prejunctional inhibition is not of the 5-HT2 type, and that ketanserin acts by suppressing the 5-HT-induced stimulatory effect, which is possibly mediated by a postjunctional 5-HT2 receptor, thus unmasking the inhibitory effect of 5-HT.

In vitro and in vivo alpha-blocking activity of thymoxamine and its two metabolites.

The alpha-adrenoceptor potency of thymoxamine and its two metabolites deacetylthymoxamine and demethyldeacetylthymoxamine were determined on the contraction of rat vas deferens induced by noradrenaline, the blood pressure increase induced by noradrenaline given i.v. to dogs and the contraction of the nictitating membrane induced by electrical stimulation in cats. In vivo the three drugs were administered at 6.35 x 10(-6) mol kg-1 intravenously. Deacetylthymoxamine presented nearly the same alpha-blocking activity as the parent drug. This was ascribed in vivo to the rapid deacetylation of thymoxamine. Demethyldeacetylthymoxamine was less active. In vitro its pA2 was 6.20 +/- 0.09 compared with 6.75 +/- 0.20 for thymoxamine and 6.57 +/- 0.13 for deacetylthymoxamine. In vivo, it was inactive in dog and less active than the other two drugs soon after its administration in the cat. The oral LD 50 values in the mouse for the three drugs were respectively 0.81, 0.71 and 1.14 mmol kg-1 for thymoxamine, deacetylthymoxamine and demethyldeacetylthymoxamine.

Effects of novel tacripyrines ITH12117 and ITH12118 on rat vas deferens contractions, calcium transients and cholinesterase activity

We have recently synthesized a new series of hybrid compounds having the moieties of tacrine, a potent inhibitor of brain and peripheral acetylcholinesterase (AChE), and nimodipine, a blocker of L-type voltage-dependent calcium channels (VDCCs). These compounds were designed to target AChE and L calcium channels in the brain, as potential therapeutic agents in Alzheimer's disease. We performed the present study to determine the main peripheral side effects of two of these compounds, ITH12117 and ITH12118. We have here shown that in rat vas deferens these compounds inhibited AChE with a potency about 1000-fold lower than that of physostigmine or tacrine. Furthermore, the hybrid compounds enhanced contractions evoked by acetylcholine, with a potency about 100-fold lower than that of physostigmine or tacrine. Additionally, contractions induced by Ca2+ on depolarized vas deferens were blocked by nimodipine with greater efficacy, compared with ITH12117 and ITH12118. Compound ITH12118 (1μM) caused a pronounced inhibition of the tonic (but not phasic) contraction elicited by electrical field stimulation. Furthermore, the same dose of nimodipine and ITH12118 blocked by 75% cytosolic Ca2+ elevations produced by acetylcholine, noradrenaline, or ATP. As a matter of comparison, we showed that rat brain cortex AChE was inhibited by ITH12118 with a potency 10 to 20-fold higher than that for vas deferens. This study shows that ITH12118 could be a paradigmatic multitarget compound having selective brain effects with smaller peripheral side effects. This may help to orient the search of new neuroprotective compounds with potential therapeutic application in Alzheimer's disease.

Regarding Article “Receptor Activity-Modifying Protein-1 Augments Cerebrovascular Responses to Calcitonin Gene-Related Peptide and Inhibits Angiotensin II-Induced Vascular Dysfunction”

HomeStrokeVol. 42, No. 2Regarding Article “Receptor Activity-Modifying Protein-1 Augments Cerebrovascular Responses to Calcitonin Gene-Related Peptide and Inhibits Angiotensin II-Induced Vascular Dysfunction” Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessLetterPDF/EPUBRegarding Article “Receptor Activity-Modifying Protein-1 Augments Cerebrovascular Responses to Calcitonin Gene-Related Peptide and Inhibits Angiotensin II-Induced Vascular Dysfunction” Kazushi Tsuda, MD, FAHA Kazushi TsudaKazushi Tsuda Cardiovascular and Metabolic Research Center Kansai University of Health Sciences Osaka, Japan (Tsuda) Search for more papers by this author Originally published30 Dec 2010https://doi.org/10.1161/STROKEAHA.110.604272Stroke. 2011;42:e24Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: January 1, 2010: Previous Version 1 To the Editor:We read with great interest the recent article by Dr Chrissobolis and colleagues1 dealing with the cerebrovascular responses in the transgenic mice with overexpression of the receptor activity-modifying protein-1 (RAMP1) for calcitonin gene-related peptide (CGRP) receptors. The results of their study demonstrated that the responses to CGRP in carotid and basilar arteries in vitro as well as cerebral arterioles in vivo were selectively enhanced in human RAMP1 transgenic mice compared with controls. In addition, the authors presented that angiotensin II-induced oxidative stress and endothelial dysfunction was prevented after expression of RAMP1. The authors propose the hypothesis that RAMP1 may be an important mediator of vascular protection and a new therapeutic target in vascular disease.Several studies have reported that enhanced activity of the sympathetic nervous system might actively participate in the pathogenesis of vascular dysfunction. In a study we presented previously, the changes in norepinephrine release induced by CGRP was investigated in the rat central nervous system.2 In an in vitro study, we showed that CGRP inhibited the stimulation-evoked norepinephrine release in a dose-dependent manner. It was also demonstrated that a dihydropyridine-sensitive calcium channel agonist, Bay K 8644, significantly reversed the inhibitory effect of CGRP on norepinephrine release, indicating that CGRP might partially interact with dihydropyridine-sensitive calcium channels and modulate intracellular calcium mobilization. Furthermore, we showed that the inhibitory action on CGRP on norepinephrine release was significantly attenuated in spontaneously hypertensive rats compared with normotensive rats.3 In the peripheral tissues, Ohhashi and Jacobowitz4 observed that CGRP might have reduced the electric stimulation-induced contraction of rat vas deferens, suggesting that CGRP might inhibit norepinephrine release during adrenergic nerve stimulation. It can be speculated that the sympatholytic action of CGRP might be a defense against vascular dysfunction. Because angiotensin II may stimulate the sympathetic neurotransmission in the central nervous system,5 we would like to know whether changes in sympathetic nervous activity might be associated with the magnitude of the RAMP1 overexpression or whether CGRP might suppress the angiotensin II-induced sympathetic hyperactivity in the study of Dr Chrissobolis and colleagues. Further studies should be performed to assess more thoroughly the interactions between CGRP and the sympathetic nervous system and their role in the protective effect against the angiotensin II-induced vascular dysfunction in the RAMP1 transgenic mice.Kazushi Tsuda, MD, FAHA Cardiovascular and Metabolic Research Center Kansai University of Health Sciences Osaka, JapanDisclosuresNone.FootnotesStroke welcomes Letters to the Editor and will publish them, if suitable, as space permits. Letters must reference a Stroke published-ahead-of-print article or an article printed within the past 3 weeks. The maximum length is 750 words including no more than 5 references and 3 authors. Please submit letters typed double-spaced. Letters may be shortened or edited. Include a completed copyright transfer agreement form (available online at http://stroke.ahajournals.org and http://submit-stroke.ahajournals.org).

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.

Inhibition of rat vas deferens contractions by flavonoids in-vitro

Flavonoids are a large heterogeneous group of benzo-gamma-pyrone derivatives, which are abundantly present in our diet. In this study we investigated the effect of ten flavonoids (quercetin, kaempferol, morin, galangin, rutin, apigenin, flavone, naringenin, hesperitin and silybin) on the contractile response elicited by electrical field stimulation in the rat isolated vas deferens. All flavonoids tested inhibited vas deferens contractions. The relative order of potency of the tested flavonoids was naringenin > hesperitin > morin > kaempferol > apigenin > silybin > flavone > rutin > quercetin > galangin. Analysis of the chemical structures showed that the saturation of C-2-C-3 double bond and the presence of hydroxyl groups on the flavonoidic scaffold play an important role in the activity of flavonoids.

In vitro and in vivo profiling of fadolmidine, a novel potent α 2-adrenoceptor agonist with local mode of action

Alpha2-adrenergic receptors (α2-adrenoceptors) mediate various physiological actions of endogenous catecholamines in the central and peripheral nervous systems being involved in alertness, heart rate regulation, vasomotor control and nociceptive processing. In the present study, the pharmacological profile of a novel α2-adrenoceptor agonist, fadolmidine, was studied in various in vitro and in vivo assays and compared to the well characterised α2-adrenoceptor agonist, dexmedetomidine. Fadolmidine displayed high affinity and full agonist efficacy at all three human α2-adrenoceptor subtypes (A, B and C) in transfected CHO cells with EC50 values (nM) of 0.4, 4.9 and 0.5, respectively. Fadolmidine inhibited also electrically evoked contractions in rat vas deferens demonstrating the activation of rodent presynaptic α2D-adrenoceptors with an EC50 value of 6.4 nM. Moreover, fadolmidine was a full agonist at human α1A-adrenoreceptor (EC50 value 22 nM) and α1B-adrenoreceptor (EC50 value 3.4 nM) in human LNCaP cells and transfected HEK cells, respectively. Agonism at the α1-adrenoceptor was also observed in rat vas deferens preparations although at lower potency (EC50 value 5.6 μM). Fadolmidine demonstrated potent α2-adrenoceptor agonist activity also in vivo by inhibiting electrically induced tachycardia in pithed rats and increasing mean arterial pressure in anaesthetised rats. However, after systemic administration, fadolmidine had considerably weaker CNS-mediated effects (mydriasis and sedation) compared to dexmedetomidine possibly due to limited penetration through the blood brain barrier by fadolmidine. In a conclusion, fadolmidine is a potent full agonist at all three α2-adrenoceptor subtypes with a pharmacological profile compatible with a therapeutic value e.g. after spinal administration.

Synthesis and biological activity of nociceptin/orphanin FQ(1–13)NH 2 analogues modified in 9 and/or 13 position

The purpose of the present study was the synthesis and the biological screening of new analogues of N/OFQ(1–13)NH 2, the minimal sequence maintaining the same activity as the natural peptide nociceptin. In order to investigate the role of Lys, we substituted Lys at positions 9 and/or 13 by Orn, Dab (diaminobutanoic acid) or Dap (diaminopropanoic acid). The new N/OFQ(1–13)NH 2 analogues exerted strong and naloxone-resistant inhibition of electrically evoked contractions of rat vas deferens. Lys replacement with Orn maintained or even enhanced the inhibitory activity, while replacements with Dab and Dap decreased inhibitory activity.

Effects of MDMA, MDA and MDEA on blood pressure, heart rate, locomotor activity and body temperature in the rat involve α‐adrenoceptors

The effects of injection of 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA) and N-ethyl-3,4-methylenedioxyamphetamine (MDEA) (all 20 mg kg(-1)) on blood pressure, heart rate, core body temperature and locomotor activity in conscious rats were investigated using radiotelemetry. MDMA and MDA produced a prolonged increase in both systolic and diastolic pressures, with MDA causing the most marked rise. MDEA produced a transient but nonsignificant fall in diastolic pressure. The pressor response produced by MDA was accompanied by bradycardia. All three amphetamine derivatives caused an initial hypothermic response; however, MDA also produced a subsequent hyperthermia, and the speed of recovery from hypothermia was MDA>MDMA>MDEA. The alpha2A-adrenoceptor antagonist 2-((4,5-dihydro-1H-imidazol-2-yl)methyl)-2,3-dihydro-1-methyl-1H-isoindole (BRL 44408) (1 mg kg(-1)) prolonged the hypothermic response to MDMA. Only MDA induced locomotor activity when given alone, but in the presence of BRL 44408, MDMA produced increased locomotor activity. The order of potency for producing isometric contractions of rat aorta (alpha1D) and vas deferens (alpha1A) was MDA>MDMA>MDEA, with MDEA acting as an alpha1-adrenoceptor antagonist with a pK(B) of 4.79+/-0.12 (n = 4) in aorta. The order of potency for prejunctional inhibition of stimulation-evoked contractions in rat vas deferens (alpha2A-adrenoceptor mediated) was MDA>MDMA>MDEA. Blood pressure actions of the three amphetamine derivatives may be at least partly due to alpha1-adrenoceptor agonism or antagonism. The reversal of the hypothermic actions are at least partly due to alpha2A-adrenoceptor agonism since the hypothermic response was more prolonged with MDEA which exhibits low alpha2A-adrenoceptor potency, and effects of MDMA after alpha2A-adrenoceptor antagonism were similar to those of MDEA.

Effects of Heptanol on Neurogenic Contractions of Vas Deferens: A Comparative Study of Stimulation Frequency in Guinea Pig and Rat

This study examines the role of gap junctional communication in smooth muscle in relation to the frequency of stimulation and the innervation density of the tissue in the generation of neurogenic contractions. Toward this end the effects of heptanol, a gap junctional blocker, on the neurogenic contractions of guinea pig and rat vas deferens at different frequencies of stimulation (single pulse, 5, 10, 20, 40, 60, and 80 Hz) were studied. In both the prostatic and epididymal halves of these tissues, heptanol abolished the neurogenic contractions at the lower frequencies of stimulation. At higher frequencies, contractions were resistant to heptanol action. The effect of heptanol on the neurogenic contractions was found to decrease with increasing stimulation frequency. The neurogenic contractions of rat vas deferens were more resistant to heptanol than those of guinea pig vas deferens. Our data indicate that gap junctional communication is significant in the generation of neurogenic contractions in both guinea pig and rat vas deferens in a frequency-dependent manner, and we discuss the mechanisms underlying these findings.

Effect of heptanol on noradrenaline-induced contractions in rat vas deferens

We have studied the effects of 1-heptanol and nifedipine on noradrenaline (NA)-induced contractions in order to explore the role of gap junctions and their interactions with L-type Ca2+ channel mediated [Ca2+]o entry in the generation of NA-induced contractions in the rat vas deferens. Application of 20 microM NA to rat vas deferens resulted in contractions with three different components, an initial phasic component followed by a tonic component overlapped with an oscillatory component. Heptanol (0.01-2 mM) induced a concentration dependent reduction of the contractions. 2 mM heptanol reduced the phasic component by 32.9 +/- 4.4% and the tonic component by 93.8 +/- 1.9% of control, while the oscillatory component was completely abolished (n=7). Nifedipine (2 microM) reduced the phasic component by 34.5 +/- 4.1% and the tonic component by 89.5 +/- 3.8% of control and abolished the oscillatory component (n=6). In the presence of heptanol and nifedipine together, the phasic component was reduced by 61.3 +/- 8.3% and the tonic component by 94.5 +/- 1.0% of control. The oscillatory component was completely abolished (n=6). These results allow the conclusion that phasic contraction is mainly due to the direct action of NA, independent of gap junctions, while the tonic and oscillatory contractions may depend significantly on cell-to-cell communication. These in turn may depend critically on the availability of extracellularly derived Ca2+.

Effects of Mondia whitei extracts on the contractile responses of isolated rat vas deferens to potassium chloride and adrenaline

Objective: To investigate the effects of the methylene chloride:methanol (CH2Cl2:MeOH, 1:1) extract of the dried roots of Mondia whitei Linn and its hexane and methanol fractions on potassium chloride (KCl) and adrenaline (Adr)-induced contractions of rat vas deferens. Materials and Methods: Isolated strips of normal adult rat vas deferens were mounted in a Ugo Basile single-organ bath containing Krebs solution. Cumulative concentration-response curves of KCl (1-7 x 10-2 M ) and adrenaline (1.21-8.45 x 10-7 M ) were established in the absence and presence of M. whitei (50-400 µg/ml). In separate experiments, after obtaining a stable plateau of contractions with KCl (60 m M ), M. whitei samples (50-400 µg/ml) were added cumulatively to relax the preparation. In KCl (60 m M ), containing depolarizing medium, cumulative concentration-contraction curve to CaCl2 (2-14 x 10-2 M ) was elicited in the absence and presence of the hexane fraction of M. whitei (50-400 µg/ml). Results: All the M. whitei samples produced rightward shift of the concentration-response curves to KCl and Adr. At high concentration of the plant extracts (400 µg/ml), a decrease of the maximal response to the contractile agents was observed compared with that obtained with the control. All the three extracts produced concentration-dependent relaxation of the plateau of contraction induced by KCl and the hexane fraction appeared to be the more potent. In calcium-free physiological salt solution, the hexane fraction of M. whitei produced rightward shift to the concentration-response curve to CaCl2 and completely abolished the contractile effect of calcium at high concentration (400 µg/ml). Conclusion: It is concluded that M. whitei extracts antagonized the contractile responses to KCl and Adr in isolated rat vas deferens, which could be due to the blockade of voltage-operated calcium channels.

Neocuproine, a Copper (I) Chelator, Potentiates Purinergic Component of Vas Deferens Contractions Elicited by Electrical Field Stimulation

Effects of the specific copper (I) chelator, neocuproine, on the purinergic and adrenergic components of nerve-evoked contractions were investigated in the prostatic rat vas deferens. Electrical field stimulation (EFS; 4 Hz) induced bimodal contractions of vas deferens tissue in the presence of α₁-adrenoceptor antagonist prazosin (to isolate the purinergic component) or purinoceptor antagonist suramin (to isolate the adrenergic component). Neocuproine significantly potentiated the purinergic component of the contractile responses to EFS. However, the same agent failed to elicit any significant effect on the adrenergic component of nerve-evoked contractions. The copper (II) chelator cuprizone could not affect the purinergic component of contractions. The potentiating effect of neocuproine which was reversible after washout of the drug, did not occur following the application of the pre-prepared neocuproine-copper (I) complex. A nitric oxide synthase inhibitor, L-nitroarginine; a cyclooxygenase inhibitor, indomethacin or an α₂-adrenoceptor antagonist, yohimbine, failed to alter the responses to neocuproine on the purinergic component of the contraction to EFS. Neocuproine did not elicit any significant effect on preparations in which the purinergic receptors were desensitized with α,β-methylene ATP. In conclusion, our results suggest that neocuproine potentiates the purinergic component of rat vas deferens contractions elicited by EFS, presumably by facilitating purinergic neurotransmission and that copper (I)-sensitive mechanisms can modulate purinergic transmission in this tissue.

Possible role of sildenafil in inhibiting rat vas deferens contractions by influencing the purinergic system

To evaluate the effect of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-selective type 5 phosphodiesterase, on isolated rat vas deferens and its connections with the purinergic system. Epididymal and prostatic portions of isolated vas deferens were placed in organ baths containing Krebs' solution. Contractions were induced by noradrenaline (NA), adenosine triphosphate (ATP), alpha,beta-methylene ATP and electrical field stimulation (EFS). The effect of sildenafil on the contractions was compared with suramin and Evans blue (EB). NA, ATP, alpha,beta-methylene ATP and EFS caused contractions in both portions of vas deferens. NA-induced contractions were unaffected by sildenafil and suramin but potentiated by EB. ATP-induced contractions were non-competitively inhibited in both portions by sildenafil and suramin but potentiated by EB. alpha,beta-methylene ATP-induced contractions were unaffected by sildenafil but were inhibited in both portions by suramin and EB. EFS-induced contractions were inhibited by sildenafil and suramin while potentiated by EB. Sildenafil inhibited the contractions in both portions of vas deferens, as did suramin. We have suggested that purinergic system has a role in this antagonism and it seems to be mediated by an ATP-dependent mechanism instead of a receptor interaction.