Inhibitory effect of serotonergic drugs on contractile response of the rat vas deferens to electrical nerve stimulation: in vivo study

PURPOSE: To evaluate, in vivo, the inhibitory effects of certain serotonergic drugs on the contractile response of the rat seminal tract to electrical stimulation of the hypogastric nerve. MATERIALS AND METHODS: Twenty-five Sprague Dawley rats (250 to 300 gm. each) were equally divided into 5 groups based on experimental agent; normal saline, clomipramine, sertraline, paroxetine, and fluoxetine. The hypogastric nerve was electrically stimulated and the intraluminal pressure of the vas deferens was measured, both pretreatment and 30 minutes after intravenous injection of four different doses (0.1 to 20 x the therapeutic dose) of each agent. Variations of responses relative to the time after administration of each agent (at 10- and 20-fold concentration) were also observed. RESULTS: All serotonergic drugs caused dose-dependent inhibition of elevation in intraluminal pressure of the vas deferens (p <0.05). The inhibitory effect of clomipramine was significantly better (p <0. 05) than that of fluoxetine at a 1-fold dose, while no significant differences were noted among clomipramine, sertraline and paroxetine. At doses of 10- and 20-fold, clomipramine had the strongest inhibitory effect, followed by sertraline and paroxetine, then fluoxetine (p <0.05). No differences were found in the inhibitory effects of the drugs studied, as a function of the time after injection. CONCLUSIONS: Clomipramine was the most potent drug for inhibition of elevation in intraluminal pressure of the rat vas deferens induced by electrical stimulation of the rat hypogastric nerve. The stronger inhibitory effect of clomipramine than the selective serotonin reuptake blockers suggests a possible peripheral action of clomipramine in addition to its central serotonergic action.     

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

AIM: 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. METHODS: 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). RESULTS: 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. CONCLUSION: 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.     

Hormonal influence on the neurogenic response of the hamster vas deferens

The effect of castration on in vitro contractility of smooth muscle of the vas deferens and body of the bladder has been studied in the hamster. Castration produced supersensitivity to in vitro electrical stimulation and norepinephrine in the vas deferens, but had no effect on the body of the bladder. Castration also increased the maximum contractile response of the vas deferens to electrical stimulation, norepinephrine, ATP, acetylcholine and histamine. The changes in contractility of smooth muscle of the vas deferens developed slowly and may be explained by specific effects upon adrenergic and purinergic neurotransmission and/or non-specific effects upon smooth muscle cell membranes.     

Analysis of the contractions evoked by sympathetic nerve stimulation, and thermal effect on the guinea-pig vas deferens--study as a model for the thermotherapy of benign prostatic hyperplasia

BACKGROUND: The present study was designed to investigate the mechanism of thermotherapy on benign prostatic hyperplasia (BPH), using the guinea-pig vas deferens as a model for BPH. The components of contractions elicited by electrical field stimulation and nicotine were analyzed, and the thermal effect on the vas deferens was examined. METHODS: The vas deferens was dissected, suspended vertically through two silver ring electrodes, and attached to an isometric transducer. The electrical stimulation of 10 constant current pulses (10 mA) with 0.3 msec in duration of 5, 10, and 40 Hz was achieved under air-gap condition. Drugs were added directly to a 5 ml Magnus tube containing Tyrode solution (36 degrees C) gassed with a 95% O2-5% CO2 mixture. The components of contractions evoked by electrical stimulation and nicotine were investigated by tetrodotoxin (TTX), and blocking agents of alpha 1-adrenoceptors and/or purinoceptors. Thermal effect on electrically evoked contractions was examined at incubation temperature of 25 degrees C (control), 43 degrees C, 45 degrees C, 46 degrees C and 47 degrees C for 1 hour. RESULTS: Nicotine (200 microM) elicited biphasic contractions, which were triggered by corelease of noradrenaline (NA) and ATP (N-ATP) from sympathetic nerve terminals by activation of prejunctional nicotine receptors. NA and N-ATP caused the corresponding contractions, alpha 1 and N-ATP components, respectively. Combined application of prazosin (1 microM) and suramin (50 microM) abolished these contractions. Activation of post-junctional alpha 1-adrenoceptors by NA caused release of ATP from muscle cells to produce the contraction (alpha 1-ATP component), which was sensitive to both suramin and prazosin. N-ATP and alpha 1 components attributed to fast and slow part of the contraction, respectively. Electrical field stimulation caused biphasic contractions which consisted of both neurogenic (TTX-sensitive) and non-neurogenic (TTX-insensitive) components. An increase in stimulation frequency (5 to 40 Hz) increased the neurogenic components, which contained alpha 1 and N-ATP components, as well as the case of nicotine. The non-neurogenic components consisted of alpha 1-ATP, muscle-derived ATP (m-ATP) and unknown substance 'X' components. Nifedipine (10 microM). L-type Ca2+ channel blocker, markedly reduced the contractions induced by bath applied phenylephrine (alpha 1-agonist, 100 microM) but only partially blocked the contractions produced by bath applied ATP (500 microM). The contractile force in amplitude and neurogenic components induced by electrical field stimulation did not change at 43 degrees C, but both declined significantly above 45 degrees C. The neurogenic components at 45 degrees C and 46 degrees C were suppressed to 22 +/- 6% and 14 +/- 3% (mean +/- SD) of control, respectively. All the contractile responses were abolished at 47 degrees C. CONCLUSION: The contractions of the guinea-pig vas deferens evoked by electrical field stimulation consisted of alpha 1, N-ATP, alpha 1-ATP, m-ATP and X components. Sympathetic nerve fibers in the muscles were completely inactivated by thermal exposure at 47 degrees C for 1 hour. The results suggest that the minimal temperature for thermotherapy of BPH should be 47 degrees C.     

Effect of extracellular Mg concentration on electrically induced contractions of rat vas deferens in vitro

Contraction of smooth muscles of the vas deferens plays an important role in the propulsion of sperm into the pelvic urethra. This study examined the influence of external Mg2+ concentration on reactivity of the rat vas deferens to electrical stimulation in vitro. Vasa deferentia isolated from adult male rats were set up in tissue baths containing physiological salt solution at 37 degrees C and were stimulated electrically. Thereafter, increasing concentrations of Mg2+ were added to the bath and their effects on electrically evoked contractions were recorded. The effect of external Mg2+ depletion on evoked contractions was also examined. External Mg2+ depletion enhanced the contractile response to electrical stimulation while increasing external Mg2+ concentration inhibited the contractions. The inhibitory effect of Mg2+ was partially reversed by increasing extracellular Ca2+ concentration and was not additive with nifedipine. The results indicate that reactivity of the vas deferens to electrical stimulation is modulated by extracellular Mg2+ concentration. The possible relevance of these data to sperm transport through the vas deferens is discussed.     

Calcium channel blockade and contractile responses in the isolated human vas deferens

The effects of removal of extracellular calcium and of the calcium channel blockers nifedipine, verapamil and diltiazem were studied on contractions induced by electrical field stimulation and high K+-solution in isolated preparations of the human vas deferens. Electrically induced contractions were blocked by tetrodotoxin and alpha-adrenoceptor blockade. They were abolished in calcium-deficient medium, and suppressed by the calcium channel blockers in the order of potency nifedipine greater than verapamil greater than diltiazem. The maximum blocking effect of nifedipine was approximately 40%. All the blockers practically abolished K+-induced contractions. It is concluded that even if the contractile response of the human vas deferens to electrical stimulation is dependent on extracellular calcium, calcium channel blockers seem to have only a limited effect on this contraction and their capability of impairing the function of the vas deferens in patients is questioned.     

The evaluation of sympathetic system-related contractile activity of the rat vas deferens after ligation and intra-abdominal placement of the testis.

OBJECTIVE: To evaluate the contractile response of the vas deferens in a model of stress, to determine any changes in sympathetic activity as a result of stress in the ipsilateral testis, which decreases blood flow to the contralateral testis. MATERIALS AND METHODS: The study comprised two groups of six rats each; group 1 underwent a sham operation, and in group 2 the right testis was placed into the abdominal cavity and the vas deferens ligated. After 30 days, the vasa deferentia were resected bilaterally and their isometric contractions recorded. Electrical-field stimulation (EFS) was applied through a pair of platinum electrodes and concentration-response curves constructed for noradrenaline at 37 degrees C and to a solution containing 80 mmol/L K+. RESULTS: The vasa deferentia in both groups showed similar contractile responses to EFS, which were frequency-dependent and maximal at 80 Hz. Noradrenaline-induced contractile activity was lower in amplitude in the vasa deferentia of group 2 than in the contralateral and ipsilateral vasa deferentia of group 1, which were not significantly different from each other. All groups responded similarly to high K+. CONCLUSION: Intra-abdominal placement of the testes with vas deferens ligation decreased the contractile response to noradrenaline in the ipsilateral vas deferens without altering the contractile response to EFS and high K+. This difference could be caused by a reduction in the number of postjunctional alpha-adrenergic receptors or decreased receptor sensitivity. Both possibilities suggest that the vas deferens may initiate sympathetic activity, which may be responsible for contralateral testicular deterioration.     

In vivo rat model to measure hypogastric nerve stimulation-induced seminal vesicle and vasal pressure responses simultaneously

This study presents a modified in vivo model in which the intraluminal pressures of the seminal vesicle and vas deferens can be measured simultaneously. Male Sprague-Dawley rats were grouped based on agent administered: serotonin, clomipramine, fluoxetine, sertraline, paroxetine, prazosin, terazosin, and tamsulosin. The control responses to hypogastric nerve stimulation (HNS) were recorded in each animal, and HNS was repeated after each drug administration. Serotonergic agents resulted in concentration-dependent inhibition of the HNS-induced seminal vesicle pressure increases (clomipramine>serotonin>fluoxetine>sertraline approximately paroxetine). On the other hand, only serotonin and clomipramine significantly inhibited vasal pressure responses. alpha-Adrenergic blockers inhibited both intraluminal pressure responses in a concentration-dependent manner. This model illustrates the importance of the hypogastric nerve for the stimulation of the seminal tract, with attention focused on the seminal vesicle. This model may be useful for the evaluation of drugs for the treatment of premature ejaculation.     

Effects of the antidepressant St. John's wort (Hypericum perforatum) on rat and human vas deferens contractility

PURPOSE: Since sexual dysfunction related to vas deferens smooth muscle contractility is a possible side effect of St. John's wort (SJW) (Hypericum perforatum) we evaluated the effect of this herbal antidepressant on rat and human vas deferens contractility. MATERIALS AND METHODS: The effect of SJW was evaluated on contractions induced by electrical field stimulation or exogenous agonists (alpha,beta-methylene adenosine triphosphate and phenylephrine) in isolated rat and human vas deferens. RESULTS: SJW (1 to 300 microM) decreased in a concentration dependent manner the amplitude of electrical field stimulation and agonist induced contractions with the same potency, suggesting direct inhibition of rat vas deferens smooth muscle. Of the chemical constituents of SJW tested hyperforin but not hypericin or the flavonoids quercitrin, rutin and kaempferol inhibited phenylephrine induced contractions. SJW and hyperforin also inhibited phenylephrine induced contractions in human vas deferens CONCLUSIONS: The results of our study demonstrate that SJW directly inhibits rat and human vas deferens contractility. If confirmed in vivo, these results suggest that SJW might affect sexual function in humans. These results might explain delayed ejaculation described in patients receiving SJW.     

Differences in the physiological response and ultrastructure of human and guinea pig vas deferens. Effects of prostaglandins, irradiation, and temperature

Marked differences were observed in the mechanical reactions of human and guinea pig vas deferens to prostaglandins, irradiation, and cooling. In human preparations prostaglandin E1 (0.1-1 ng/ml) had an augmentory effect on the contractile response after electrical neurostimulation (10 Hz, 0.3 ms, 3 s), but no visible influence (at concentrations ranging from 1 ng to 10 micrograms/ml) on the contractile response after electrical muscle stimulation (10 Hz, 40 ms, 3 s). In contrast, in guinea pig preparations (PGE1 (0.1-1 ng/ml) had an inhibitory effect on the contractile response after electrical neurostimulation and an augmentory effect (0.1-1 micrograms/ml) on the contractile response after electrical muscular stimulation. Human vas deferens showed higher radiosensitivity than guinea pig preparations. The neurotransmitters acetylcholine and catecholamines increased the radiosensitivity of guinea pig preparations, but not of human ones. Vas deferens reacted to short-time (15-120 s) cooling with an immediate temporary contraction, at 25 degrees C of short (seconds), at 5 degrees C of long (minutes) duration; after rewarming (5-37 degrees C) a second contraction appeared in guinea pig preparations, but not in human ones. Whereas the contraction to electrical neurostimulation (10 Hz, 0.3 ms, 3 s) was abolished in human preparations by cooling, it was only inhibited in guinea pig vas deferens. Electron microscopy showed differences in the ultrastructure of human and guinea pig vas deferens. Muscle cells were more widely separated in human vas deferens (generally 400 nm or more) than in guinea pig (approximately 100-200 nm), and the intracellular space in human preparations contained more collagen. The axons in human preparations contained predominantly large granular and agranular vesicles, those in guinea pig preparations small granular and agranular vesicles. The possible correlation between the physiological response of human and guinea pig vas deferens and the ultrastructural differences is discussed. The results indicate the possibility that other pharmacophysiological and toxicological phenomena could be essentially different in human and guinea pig material.     

Immunoreactive arginine vasopressin (AVP) and effects of AVP in the human vas deferens

Immunoreactive (IR) arginine vasopressin (AVP) was found to occur in the epididymal part of the human vas deferens. Segments from nine different subjects all contained IR-AVP in concentrations ranging from 37 to 717 fmol/gm. wet weight, concentrations severalfold higher than those normally found in the circulation. IR-AVP was shown by high performance liquid chromatography to elute in the same position as synthetic AVP. AVP added to isolated preparations of the human vas deferens induced concentration-related repetitive phasic contractions without significant changes of baseline tension. These contractions seemed to be mediated via stimulation of vasopressin V1-receptors and were abolished in the presence of vasopressin antagonists. Contractions induced by electrical field stimulation were frequency-dependent and sensitive to tetrodotoxin and prazosin. They were not affected by the vasopressin antagonists used. AVP increased the response to electrical field stimulation and this effect was inhibited by vasopressin antagonists. The results suggest either that circulating AVP is taken up and accumulated by the human vas deferens, and/or that AVP is synthesized locally. They do not suggest co-release of AVP and noradrenaline from nerve endings. The physiological role of the AVP occurring in the human vas deferens remains to be established.     

Lack of neuropeptide Y receptor detection in human bladder and prostate

OBJECTIVE: To investigate the presence of functional neuropeptide Y (NPY) receptors in human bladder and prostate (both richly endowed with NPY-containing nerve fibers) using peptide YY (PYY) as the agonist. Materials and methods Binding studies were conducted using [125I]PYY as the radioligand. Organ-bath studies were performed on isolated tissue strips for direct (postjunctional) contractile effects and for (prejunctional) inhibition of field stimulation effects. Any possible degradation of PYY was determined using high-performance liquid chromatography (HPLC). RESULTS: In the radioligand binding studies no quantifiable specific [125I]PYY binding was detected in human bladder or prostate, while specific high-affinity binding was readily seen in rat cerebral cortex. In organ-bath experiments, PYY (up to 1 micromol/L) caused no contraction of human prostate or bladder, whereas noradrenaline and carbachol, respectively, were effective; the potency or efficacy of noradrenaline and carbachol were not altered by PYY. Field stimulation-induced contraction was not affected by PYY in either human bladder or prostate, but was readily inhibited in rat vas deferens. HPLC detected no relevant PYY degradation by human bladder or prostate homogenates. CONCLUSION: Human bladder and prostate express only very few if any functional NPY receptors.     

Saw palmetto is an indirectly acting sympathomimetic in the rat-isolated prostate gland

BACKGROUND: To investigate whether saw palmetto that inhibits alpha1-adrenoceptor binding in vitro affects contractility of the rat prostate gland. METHODS: The effects of a commercially available saw palmetto extract were examined on the contractility of rat-isolated prostate glands. The extract was tested in the presence and absence of phentolamine, prazosin, yohimbine, propranolol, hexamethonium, cocaine, desipramine, nifedipine, guanethidine, atropine, and alpha,beta-methylene ATP to evaluate the mechanism of action. Isolated preparations of rat vas deferens and bladder were used for comparison. RESULTS: Unexpectedly, saw palmetto extract caused contractions of the rat prostate gland that could be attenuated by prazosin, phentolamine, nifedipine, guanethidine, cocaine, and desipramine but not by any of the other pharmacological tools. Similar contractile effects were observed in rat-isolated vas deferens preparations but not in rat-isolated bladder preparations. CONCLUSIONS: In the rat prostate gland, saw palmetto extract causes indirect alpha1-adrenoceptor-mediated contractions via the release of noradrenaline from sympathetic neurons.     

Effects of castration and diabetes mellitus on cholinergic responsiveness and muscarinic receptors in the rat vas deferens

Studies were carried out to compare the effects of diabetes mellitus and castration on the muscarinic responsiveness of rat vasa deferentia. One and two months after castration or after streptozotocin-induced diabetes, there were significant decreases in serum testosterone levels, accompanied by significant decreases in vas deferens weights, protein contents, and protein concentrations. However, contractile responses of vasa deferentia from streptozotocin-diabetic or castrated rats to carbachol were significantly increased compared to controls. These changes were accompanied by increases in Kd and decreases in Bmax (pm/tissue) for 3H-quinuclidinyl benzilate (QNB) binding. Contractile responses and QNB binding were also studied in the spontaneously diabetic BB/W or rat, a less severely diabetic model than the streptozotocin-diabetic rat. Ninety days after the onset of diabetes in the BB rat, there was an increase in the contractile response to carbachol. There were qualitatively similar but smaller changes in vas deferens weights, protein contents, protein concentrations, and QNB binding than in the streptozotocin-diabetic rats. The data show that diabetes and castration increased the contractile responses of vasa deferentia despite decreases in protein content and in the number of muscarinic receptors. The results suggest that muscarinic receptor-effector coupling is more efficient in vasa deferentia from castrated or diabetic rats, resulting in a greater contractile response to cholinergic agonists.     

Stimulating and potentiating effects of sodium nitroprusside on the guinea-pig vas deferens and their comparison with the effects on the portal vein and the taenia coli

The effects of sodium nitroprusside on the electrical and mechanical properties of the guinea-pig vas deferens were studied and compared with those on the portal vein and the taenia coli. Sodium nitroprusside at concentrations higher than 0.5 mM caused depolarization of the membrane of the vas deferens and initiated spontaneous contractions, while spontaneous contractions of the portal vein were blocked by similar concentration of the drug. Noradrenaline- and carbachol-induced contractions of the vas deferens were markedly potentiated by sodium nitroprusside, whereas the noradrenaline-induced contraction of the portal vein was suppressed by the same concentration of the drug. Increasing the K+ concentration by 15 to 30 mM caused a similar potentiation of the contraction by noradrenaline or carbachol in the vas deferens. When sodium nitroprusside was applied during the course of noradrenaline- or carbachol-induced contracture, contraction was observed in the vas deferens, while relaxation was induced in the portal vein and taenia coli. In either case, however, the addition of Ca caused a relaxation of the preparations. These results suggest that the membrane depolarization may be involved in the stimulating effects sodium nitroprusside in the guinea-pig vas deferens.     

Effect of thyroxine on the contractile responses of the vas deferens to prostaglandin E2

The effects of prostaglandin E2 (PGE2) on the contractile activity of thyroidectomized and thyroxine-treated albino rats were studied in vitro. Thyroidectomy totally inhibited the contractile response of the vas deferens to PGE2. Thyroxine treatment, on the other hand, significantly (P < .001) potentiated the response of vasa deferentia to PGE2, when compared to controls. It is suggested that thyroid hormones play a role in the contractile response of the vas deferens to PGE2.     

Zinc content in the epididymis, vas deferens, prostate, and seminal vesicles of juvenile rhesus monkey (Macaca mulatta): effect of androgen and estrogen

The zinc content in the three segments of the epididymis (caput, corpus, and cauda), vas deferens, seminal vesicles, and prostate of juvenile monkeys was determined by atomic absorption spectrophotometry. Zinc content (micrograms/gm wet weight) was found to be maximum (328) in the vas deferens; in the other organs it measured in the following order: caput 191, corpus 238, cauda 193, prostate 133 and seminal vesicles 85. In order to investigate the endocrine control of the zinc in these organs, two groups of animals were treated with testosterone propionate (2 mg) or estradiol dipropionate (10 micrograms) once daily for 30 days. In response to androgen, a rise in both concentration and content of zinc was evident only in the prostate. The results further suggested that the prostatic zinc may be under dual hormonal control, but in the epididymis and vas deferens it may be under the influence of estrogen. It is concluded that the hormonal effects on zinc content and growth stimulation in accessory sex organs are quite separate and may be under different hormonal control.     

L-NAME诱发的高血压大鼠输精管的胆碱能收缩：西地那非的作用

高血压是引起勃起功能障碍的一个危险因素,但其对输精管收缩和射精反应的作用还未有详尽的描述。本研究用氮氧合酶抑制剂-NG-硝基-L-精氨酸甲酯（L-NAME）,诱导一氧化氮（NO）缺乏的高血压。研究目的是评估L-NAME诱导的高血压对大鼠输精管收缩性的影响,检测西地那非是否影响高血压大鼠输精管的收缩性。将36R雄性大鼠分为三组：（1）空白对照组,（2）L-NAME诱导的高血压组,（3）用西地那非处理经L—NAME诱导的高血压组。第二组给予L-NAME（每只老鼠每天40mg）,处理4周。第三组大鼠同时给予西地那非（每只老鼠每天5mg,经口腔灌胃）和L—NAME。输精管的前列腺段给予电刺激（EFS,1—20赫兹）,P2X2激动剂—α,β亚甲基ATP（α,β-meATP,100μmolL-1μmolL－1）和α1－肾上腺素受体激动剂苯福林（Phe,100μmolL^-1－1mmolL－1）用于构建浓度反应曲线。用P2X受体拮抗剂、pyridoxalphosphate-6－azophenyl-2,4＇-disulfonicacid（PPADS,30μmolL。）重复实验。L-NAME可以明显加强输精管对EFS,α,β—meATP和Phe的收缩反应。L—NAME组经西地那非治疗后,输精管对EFS的收缩反应（20Hz）明显加强。高血压大鼠再经PPADS处理后,被EFS和α,β-meATP加强的输精管收缩反应得以恢复。在慢性NO缺乏的大鼠模型中,胆碱能、肾上腺素能组分及EFS可以影响输精管的收缩性。胆碱能系统对输精管收缩反应的调节作用比。肾上腺素能更强,而且西地那非可能可以调节PE患者的射精反应。     

Effects of sodium metabisulphite on guinea pig contractile airway smooth muscle responses in vitro.

BACKGROUND--Sodium metabisulphite (MBS) is known to induce bronchoconstriction in asthmatic patients. The effects of MBS on guinea pig airway smooth muscle and on neurally mediated contraction in vitro have been examined. METHODS--Tracheal and bronchial airway segments were placed in oxygenated buffer solution and electrical field stimulation was performed in the presence of indomethacin (10(-5) M) and propranolol (10(-6) M) for the measurement of isometric tension. Atropine (10(-6) M) was added to bronchial tissues. RESULTS--Concentrations of MBS up to 10(-3) M had no direct effect on airway smooth muscle contraction and did not alter either tracheal smooth muscle contraction induced by electrical field stimulation at all frequencies or acetylcholine-induced tracheal smooth muscle contraction. There was a similar response in the absence of epithelium, except for potentiation of the response induced by electrical field stimulation at 0.5 Hz (24 (10)% increase). However, MBS (10(-5), 10(-6) and 10(-7) M) augmented neurally-mediated non-adrenergic non-cholinergic contractile responses in the bronchi (13.3 (3.2)%, 23.8 (9.6)%, and 6.4 (1.6)%, respectively). MBS had no effect on the contractile response induced by substance P, but at higher concentrations (10(-3) M and 10(-4) M) it caused a time-dependent attenuation of responses induced by either electrical field stimulation or exogenously applied acetylcholine or substance P. CONCLUSIONS--MBS had no direct contractile responses but enhanced bronchoconstriction induced by activation of non-cholinergic neural pathways in the bronchus, probably through increased release of neuropeptides. At high concentrations MBS inhibited contractile responses initiated by receptor or neural stimulation.     

Inhibition of the contractile responses of isolated human and rat bladders by clenbuterol

PURPOSE: We investigated the inhibition of the contractile responses of human continent and unstable detrusor muscle by the beta2 agonist clenbuterol as well as the inhibition of electrical field stimulation evoked contractile responses of isolated rat bladder muscle strips by orally administered clenbuterol. MATERIALS AND METHODS: The contractile responses of human continent and unstable detrusor muscle strips to electrical field stimulation (0.05 milliseconds, 0.5 to 80 Hz.) were measured before and after adding 10(-9) to 10(-4) M. clenbuterol in vitro. In addition, 6 rats per group were dosed orally with 2 microg x kg(-1) clenbuterol daily acutely (1 dose) or chronically (1 dose daily for 8 days), or with distilled water to serve as controls. The contractile response to electrical field stimulation of strips of isolated detrusor muscle was then measured. Serum clenbuterol levels were analyzed in duplicate by enzyme-linked immunosorbent assay and high performance liquid chromatography. RESULTS: In vitro clenbuterol significantly inhibited the electrical field stimulation evoked contractile responses of detrusor muscle strips from unstable but not continent human bladders. A significant inhibitory effect of clenbuterol on the electrical field stimulation evoked contractile response of rat detrusor muscle was observed after chronic but not acute oral dosing (p <0.01). Serum clenbuterol levels measured by enzyme-linked immunosorbent assay and high performance liquid chromatography were not significantly different. CONCLUSIONS: Clenbuterol or related beta2-adrenoceptor agonists may represent a useful therapeutic strategy for detrusor muscle overactivity.