Pharmacological effects of solifenacin on human isolated urinary bladder

To investigate the effects of solifenacin on human detrusor smooth muscles, we evaluate the effects of solifenacin on the contractions induced by carbachol, KCl, CaCl2 and electrical field stimulation (EFS), and the EFS-induced acetylcholine release from detrusor smooth muscle strips by using the muscle bath and microdialysis technique. The effects of solifenacin were also compared with effects of other antimuscarinic agents (atropine, oxybutynin and propiverine). Pretreatment with various antimuscarinic agents caused parallel shifts to the right of the concentration-response curves to carbachol. The pA2 value of the Schild plots for solifenacin was similar to that for oxybutynin. Atropine did not inhibit the KCl- and CaCl2-induced contractions, while solifenacin, oxybutynin and propiverine significantly inhibited these contractions. EFS-induced contractions were inhibited by various antimuscarinic drugs in a concentration-dependent manner. In the presence of atropine, solifenacin tended to inhibit the residual atropine-resistant contractions induced by EFS, but it was not significant. However, oxybutynin and propiverine inhibited them under the same conditions. Although pretreatment with atropine and propiverine did not cause significant changes in EFS-induced acetylcholine release, solifenacin and oxybutynin caused significant decreases in acetylcholine release. The present results suggest that solifenacin inhibits contractions of human detrusor smooth muscles mainly by the antimuscarinic action and that the high concentration of solifenacin has Ca2+ channel antagonist action. Moreover, solifenacin may block not only postjunctional receptors, but also prejunctional receptors to modulate acetylcholine releases in cholinergic nerve endings in human detrusor smooth muscles. The findings support that muscarinic-receptor-inhibitory actions in human bladder mainly contribute to the usefulness of solifenacin as a therapeutic drug for overactive bladder.     

Pharmacological analysis of 5-hydroxytryptamine effects on electrically stimulated human isolated urinary bladder.

1. 5-Hydroxytryptamine (5-HT) is able to potentiate the contractions induced by electrical field stimulation of pieces of human isolated urinary bladder. On the basis of available selective 5-HT agonists and antagonists, we have further investigated the receptors involved and their site of action. 2. 5-HT produced a concentration-dependent increase of the contractile response to electrical field stimulation from 0.1 nM to 1 microM. At higher concentrations (up to 100 microM) the effect decreased. These activities were mimicked by a variety of 5-HT agonists, for which the following rank order of potency was found: 5-HT greater than alpha-methyl 5-HT greater than 5-methoxytryptamine greater than 5-carboxamidotryptamine greater than 2-methyl 5-HT much greater than GR 43175. In addition the gastro-prokinetics agents metoclopramide, cisapride and the 5-HT3 antagonist ICS 205-930 behaved as 5-HT agonists, their EC50 values being 2.3, 0.3, and 0.5 (microM) respectively. 3. The 5-HT potentiating effect was resistant to antagonism by ondansetron (1 microM) and cyanopindolol (1 microM), selective 5-HT3 and 5-HT1A/1B antagonists respectively. The 5-HT2 antagonists ketanserin (1 microM), spiperone (1 microM) and methysergide (1 microM) also showed a weak inhibitory activity. Methiothepin (0.1-1 microM) antagonized only the inhibitory effect of 5-HT. Metoclopramide (0.1-1 microM), cisapride (0.01-0.1 microM) and ICS 205-930 (0.3-3 microM) all produced a rightward displacement of the 5-HT response curve with concomitant reduction of the maximum response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological characterization of thromboxane and prostanoid receptors in human isolated urinary bladder

1. Cumulative concentration-response curves (CRC) to prostaglandin E₁ (PGE₁), PGE₂, PGD₂ and PGF_2α (0.01–30 μM) and to the thromboxane A₂ (TXA₂) receptor agonist U-46619 (0.01–30 μM) were constructed in human isolated detrusor muscle strips both in basal conditions and during electrical field stimulation.
2. All the agonists tested contracted the detrusor muscle. The rank order of agonist potency was: PGF_2α>U-46619>PGE₂ whereas weak contractile responses were obtained with PGD₂ and PGE₁. Any of the agonists tested was able to induce a clear plateau of response even at 30 μM.
3. The selective TXA₂ antagonist, GR 32191B (vapiprost), antagonized U-46619-induced contractions with an apparent pK_B value of 8.27±0.12 (n=4 for each antagonist concentration). GR 32191B (0.3 μM) did not antagonize the contractile responses to PGF_2α and it was a non-surmountable antagonist of PGE₂ (apparent pK_B of 7.09±0.04; n=5). The EP receptor antagonist AH 6809 at 10 μM shifted to the right the CRC to U-46619 (apparent pK_B value of 5.88±0.04; n=4).
4. Electrical field stimulation (20 Hz, 70 V, pulse width 0.1 ms, trains of 5 s every 60 s) elicited contractions fully sensitive to TTX (0.3 μM) and atropine (1 μM). U-46619 (0.01–3 μM) potentiated the twitch contraction in a dose-dependent manner and this effect was competitively antagonized by GR 32191B with an estimated pK_B of 8.54±0.14 (n=4 for each antagonist concentration). PGF_2α in the range 0.01–10 μM (n=7), but not PGE₂ and PGE₁ (n=3 for each), also potentiated the twitch contraction of detrusor muscle strips (23.5±0.3% of KCl 100 mM-induced contraction) but this potentiation was unaffected by 0.3 μM GR 32191B (n=5).
5. Cumulative additions of U-46619 (0.01–30 μM) were without effect on contractions induced by direct smooth muscle excitation (20 Hz, 40 V, 6 ms pulse width, trains of 2 s every 60 s, in the presence of TTX 1 μM; n=3). Moreover, pretreatment of the tissue with 0.3 μM U-46619 did not potentiate the smooth muscle response to 7 μM bethanecol (n=2).
6. We concluded that TXA₂ can induce direct contraction of human isolated urinary bladder through the classical TXA₂ receptor. Prostanoid receptors, fully activated by PGE₂ and PGF_2α are also present. All these receptors are probably located post-junctionally. The rank order of agonist potency and the fact that GR32191B, but not AH6809, antagonized responses to PGE₂ seem to indicate the presence of a new EP receptor subtype. Moreover, we suggest the presence of prejuctional TXA₂ and FP receptors, potentiating acetylcholine release from cholinergic nerve terminals.

     

Pharmacological characterization of muscarinic receptors in mouse isolated urinary bladder smooth muscle

The pharmacological characteristics of muscarinic receptors in the male mice urinary bladder smooth muscle were studied. (+)-Cis-dioxolane, oxotremorine-M, acetylcholine, carbachol and pilocarpine induced concentration-dependent contractions of the urinary bladder smooth muscle (pEC(50)=6.6+/-0.1, 6.9+/-0.1, 6.7+/-0.1, 5.8+/-0.1 and 5.8+/-0.1, E(Max)=3.2+/-0.8 g, 2.7+/-0.4 g, 1.0+/-0.1 g, 2.7+/-0.3 and 0.9+/-0.2 g, respectively, n=4). These contractions were competitively antagonized by a range of muscarinic receptor antagonists (pK(B) values): atropine (9.22+/-0.09), pirenzepine (6.85+/-0.08), 4-DAMP (8.42+/-0.14), methoctramine (5.96+/-0.05), p-F-HHSiD (7.48+/-0.09), tolterodine (8.89+/-0.13), AQ-RA 741 (7.04+/-0.12), s-secoverine (8.21+/-0.09), zamifenacin (8.30+/-0.17) and darifenacin (8.70+/-0.09). In this tissue, the pK(B) values correlated most favourably with pK(i) values for these compounds at human recombinant muscarinic M(3) receptors. A significant correlation was also noted at human recombinant muscarinic m5 receptors given the poor discriminative ability of ligands between M(3) and m5 receptors. In recontraction studies, in which the muscarinic M(3) receptor population was decreased, and conditions optimized to study M(2) receptor activation, methoctramine exhibited an affinity estimate consistent with muscarinic M(3) receptors (pK(B)=6.23+/-0.14; pA(2)=6.16+/-0.03). Overall, these data study suggest that muscarinic M(3) receptors are the predominant, if not the exclusive, subtype mediating contractile responses to muscarinic agonists in male mouse urinary bladder smooth muscle.     

Pharmacological characterization of muscarinic receptors in dog isolated ciliary and urinary bladder smooth muscle

1. The pharmacological characteristics of muscarinic receptors mediating contraction of dog isolated ciliary muscle were determined and compared to those mediating contraction of dog urinary bladder smooth muscle. 2. (+)-Cis-dioxolane induced concentration-dependent contractions of ciliary muscle (pEC50=7.18+/-0.07, Emax=453+/-64 mg, n=19) and urinary bladder isolated smooth muscle (pEC50=6.55+/-0.07, Emax=11+/-1 g, n=19). These responses were antagonized by several muscarinic receptor antagonists (pKb values for the ciliary muscle and the bladder smooth muscle, respectively): atropine (8.25+/-0.14 and 9.21+/-0.09), pirenzepine (6.31+/-0.13 and 6.70+/-0.25), tolterodine (7.97+/-0.14 and 8.68+/-0.12), oxybutynin (7.40+/-0.08 and 7.88+/-0.12), zamifenacin (6.46+/-0.19 and 7.69+/-0.11), S-secoverine (6.66+/-0.14 and 8.13+/-0.07), AQ-RA 741 (6.16+/-0.15 and 7.08+/-0.23), p-F-HHSiD (7.10+/-0.27 and 7.35+/-0.07) and responses were not antagonized by PD 102807 (up to 100 nM). 3. In urinary bladder smooth muscle, the profile of antagonist pKB values correlated significantly with pK(i) values at human recombinant m3 muscarinic receptors, suggesting that M3 muscarinic receptors mediated the response. In the ciliary muscle, a significant (P<0.01) correlation was obtained with human recombinant m3 and m5 receptors. 4. Darifenacin displayed insurmountable antagonism at receptors in the bladder. At receptors in the ciliary muscle, it exhibited two phases of antagonism, comprising an initial low affinity (pKB<6) component and a high affinity phase (pKB>8). 5. The role of pigmentation in the atypical behaviour of darifenacin was examined. In blue coloured eyes, darifenacin produced apparent surmountable, competitive antagonism of the responses to (+)-cis-dioxolane (pKB=8.76+/-0.07). The antagonist profile obtained in this tissue suggested the involvement of a site which has the pharmacological attributes of the M5 receptor. 6. We suggest that the dog urinary bladder contracts in response to M3 muscarinic receptor activation. Contraction of the brown-eyed dog ciliary muscle is more complex and may include involvement of at least two receptors, possibly the M5 and M3 receptor, whereas blue-eyed dog ciliary muscle may involve a single population of M5 muscarinic receptors.     

Potent contractile activity of endothelin on the human isolated urinary bladder.

Endothelin (1 nM-0.3 microM) produced a concentration-related contraction of mucosa-free muscle strips excised from the dome of the human urinary bladder. The response to endothelin was unaffected by either atropine (1 microM) or nifedipine (1 microM) at concentrations that abolished the response to carbachol and KCl, respectively. These findings indicate that mechanisms other than activation of dihydropyridine- and voltage-sensitive calcium channels may be involved in the action of endothelin on smooth muscles.     

Pharmacological modulation of the contractile response to toluene diisocyanate in the rat isolated urinary bladder.

1. Toluene diisocyanate produced concentration-dependent contractions of the rat isolated urinary bladder. 2. The contractions were tetrodotoxin-resistant and were abolished by previous exposure of the strips to capsaicin. 3. Indomethacin (5 microM) and ruthenium red (30 microM) inhibited toluene diisocyanate-induced contractions. Responses expressed as a percentage of the response obtained with substance P, 30 nM, were respectively 141.6 +/- 24.8% and 20.1 +/- 5.1% in control and indomethacin-treated strips (P less than 0.005); 123.0 +/- 30.2% and 14.0 +/- 6.5% in control and ruthenium red-treated strips (0.01 less than P less than 0.05). 4. These results suggest that toluene diisocyanate-induced contractions of the rat isolated bladder are the result of the release of cyclo-oxygenase products which may act by activating the capsaicin receptor.     

Pharmacological characterization of muscarinic receptors in rabbit isolated iris sphincter muscle and urinary bladder smooth muscle

1. The pharmacological characteristics of muscarinic receptors in the rabbit iris sphincter muscle were studied and compared to M₃ receptors in rabbit urinary bladder smooth muscle.
2. (+)-Cis-dioxolane induced concentration-dependent contractions of the iris sphincter muscle (pEC₅₀=6.41±0.10, E_max=181±17 mg, n=38) and urinary bladder smooth muscle (pEC₅₀=6.97±0.04, E_max=4.28±0.25 g, n=54). These contractions were competitively antagonized by a range of muscarinic receptor antagonists (pK_B values are given for the iris sphincter muscle and the bladder smooth muscle, respectively): atropine (9.30±0.07 and 9.40±0.04), AQ-RA 741 (6.35±0.04 and 6.88±0.03), darifenacin (9.56±0.05 and 9.12±0.05), methoctramine (5.75±0.07 and 5.81+0.06), oxybutynin (8.10±0.09 and 8.59±0.06), pirenzepine (6.79±0.05 and 6.89±0.04), secoverine (7.54±0.05 and 7.66±0.05), p-F-HHSiD (7.55±0.09 and 7.50±0.05) and zamifenacin (8.69±0.10 and 8.36±0.06). A significant correlation between the pK_B values in the bladder and the pK_B values in the iris was obtained.
3. In both tissues, the pK_B values correlated most favorably with pK_i values for these compounds at human recombinant muscarinic m3 receptors. A reasonable correlation was also noted at human recombinant muscarinic m5 receptors given the poor discriminative ability of ligands between m3 and m5 receptors.
4. Overall, the data from this study suggest that the muscarinic receptors mediating contraction of the rabbit iris sphincter muscle and urinary bladder smooth muscle are similar and equate most closely with the pharmacologically-defined muscarinic M₃ receptor.

     

Inhibitory effect of nicorandil on the contraction of isolated human urinary bladder detrusor muscle

This study was performed to determine whether the antianginal drug nicorandil relaxes isolated human detrusor muscle. Ten strips of detrusor muscle obtained from 10 pediatric patients who underwent surgery on the urinary bladder were contracted with 80 mM potassium chloride (KCl) before and after incubation with four concentrations of nicorandil (100, 200, 400 and 800 microM). The percent inhibition by nicorandil of the height and area under the curve (AUC) of KCl-induced contractions of the detrusor strips was calculated. The effect of glibenclamide (10 microM) on nicorandil (800 microM)-induced inhibition of KCl-induced detrusor contractions was also studied. Nicorandil caused a concentration-dependent inhibition of KClinduced contractions of the detrusor strips. The percent inhibition of the height of KCl-induced contractions of the detrusor by nicorandil was significant at concentrations of 200, 400 and 800 microM. The percent inhibition of the AUC for KCl-induced detrusor contractions was significant at all four concentrations of nicorandil used. Glibenclamide reversed the inhibitory effect of 800 microM nicorandil on KCl-induced detrusor contractions. These results suggest that nicorandil inhibits KCl-induced contractions of isolated human detrusor muscle and may therefore be useful in clinical conditions requiring detrusor muscle relaxation.     

Bioassay of vasopressin on the rabbit isolated urinary bladder

The rabbit isolated urinary bladder contracted in the presence of Lys⁸-vasopressin from threshold concentrations of 5 to 30 μ ml^?1 (0·02 to 0·11 ng ml^?1). Responses were proportional to the dose used. The tissue gave satisfactory results either fresh or after storage for several days in cold Tyrode or Krebs solution (3–4°). The preparation also contracted in the presence of oxytocin, but it was 7 to 20 times less sensitive to this peptide. A number of other peptides and amines known to stimulate smooth muscle showed low activity on the rabbit urinary bladder and, occasionally, intense tachyphylaxis.     

A novel pathway underlying the inhibitory effects of melatonin on isolated rat urinary bladder contraction

The aim of the present study was to elucidate the direct effects of melatonin on bladder activity and to determine the mechanisms responsible for the detrusor activity of melatonin in the isolated rat bladder. We evaluated the effects of melatonin on the contractions induced by phenylephrine (PE), acetylcholine (ACh), bethanechol (BCh), KCl, and electrical field stimulation (EFS) in 20 detrusor smooth muscle samples from Sprague-Dawley rats. To determine the mechanisms underlying the inhibitory responses to melatonin, melatonin-pretreated muscle strips were exposed to a calcium channel antagonist (verapamil), three potassium channel blockers [tetraethyl ammonium (TEA), 4-aminopyridine (4-AP), and glibenclamide], a direct voltage-dependent calcium channel opener (Bay K 8644), and a specific calcium/calmodulin-dependent kinase II (CaMKII) inhibitor (KN-93). Melatonin pretreatment (10(-8)~10(-6) M) decreased the contractile responses induced by PE (10(-9)~10(-4) M) and Ach (10(-9)~10(-4) M) in a dose-dependent manner. Melatonin (10(-7) M) also blocked contraction induced by high KCl ([KCl](ECF); 35 mM, 70 mM, 105 mM, and 140 mM) and EFS. Melatonin (10(-7) M) potentiated the relaxation response of the strips by verapamil, but other potassium channel blockers did not change melatonin activity. Melatonin pretreatment significantly decreased contractile responses induced by Bay K 8644 (10(-11)~10(-7) M). KN-93 enhanced melatonin-induced relaxation. The present results suggest that melatonin can inhibit bladder smooth muscle contraction through a voltage-dependent, calcium-antagonistic mechanism and through the inhibition of the calmodulin/CaMKII system.     

Capsaicin-like effects of N-arachidonoyl-dopamine in the isolated guinea pig bronchi and urinary bladder

A capsaicin-like endogenous ligand of vanilloid (VR1) receptors, N-arachidonoyl-dopamine, was recently identified in bovine and rat nervous tissue, and found to be almost as potent as capsaicin, and 5-10-fold more potent than anandamide, on these receptors, both in isolated cells and in vivo. Here we have investigated if N-arachidonoyl-dopamine also exerts other capsaicin-like effects at VR1 receptors in some isolated organ preparations. N-arachidonoyl-dopamine exerted a potent contractile response of guinea pig isolated bronchi (EC50=12.6 +/- 1.7 microM, Emax=69.2 +/- 2.4% of carbachol Emax), which was blocked by pre-treatment with capsaicin or with the VR1 antagonist capsazepine, as well as by a combination of tachykinin NK1 and NK2 receptor antagonists. In this assay, N-arachidonoyl-dopamine was less and more potent and/or efficacious than capsaicin (EC50=40.0 nM; Emax=93.5%) and anandamide (EC50=15.2 microM, Emax=38.0%), respectively. Unlike capsaicin and anandamide, forskolin or ethanol did not enhance N-arachidonoyl-dopamine effect in this preparation, whereas epithelial denudation resulted in a 2.5-fold increase in potency without affecting the efficacy. N-arachidonoyl-dopamine also contracted the isolated guinea pig urinary bladder, although in this preparation, as well as in the isolated rat urinary bladder, the potency (EC50=3.7 +/- 0.3 and 19.9 +/- 0.1 microM) and/or efficacy (Emax=12.0 +/- 0.1% and 20.7 +/- 0.7% of carbachol Emax) of the compound were significantly lower than those of both capsaicin and anandamide. These data suggest that the extent to which exogenous N-arachidonoyl-dopamine activates VR1 receptor in isolated organs is largely dependent on pharmacodynamics and bioavailability.     

Pharmacological analysis of contractile effects of eletriptan and sumatriptan on human isolated blood vessels

Eletriptan, a second-generation triptan with high affinity for 5-HT(1B/1D) receptors, is highly effective in migraine, with or without aura. We compared the effects of eletriptan and sumatriptan on the human isolated middle meningeal and coronary arteries and saphenous vein, used as models for therapeutic efficacy and potential side effects, and have investigated the role of 5-HT(1B/1D) receptors in contractions induced by these triptans. Concentration-response curves to eletriptan and sumatriptan were constructed in the absence or presence of a selective 5-HT(1B/1D) receptor antagonist, N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-3-methyl-4-(4-py rid yl) benzamide (GR125743). All three blood vessels constricted in response to eletriptan and sumatriptan, but the middle meningeal artery relaxed following the highest concentration (100 microM) of eletriptan. In the middle meningeal artery, GR125743 antagonised the contractions induced by both eletriptan (pEC(50): 7.34+/-0.13) and sumatriptan (pEC(50): 6.91+/-0.17) to a similar degree (pA(2): 8. 81+/-0.17 and 8.64+/-0.21, respectively). In the human coronary artery and saphenous vein, sumatriptan-induced contractions (pEC(50): 6.24+/-0.14 and 6.19+/-0.12, respectively) were also potently antagonised by GR125743 (pA(2): 8.18+/-0.27 and 8.34+/-0.12, respectively). The eletriptan-induced contractions of the human saphenous vein (pEC(50): 6.09+/-0.13) were antagonised less effectively by GR125743 (pK(B): 7.73+/-0.18), and those of the human coronary artery (pEC(50): 5.54+/-0.22) remained unaffected by GR125743 up to a concentration of 100 nM. These results suggest that (i) based on the differences in pEC(50) values, the cranioselectivity of eletriptan (63-fold) is higher than that of sumatriptan (5-fold) in coronary artery, (ii) the contractile effects of sumatriptan and eletriptan (lower concentrations) in the three blood vessels are mediated via the 5-HT(1B) receptor, and (iii) additional mechanisms seem to be involved in coronary artery and saphenous vein contractions and middle meningeal artery relaxation following high concentrations of eletriptan.     

Histamine receptors in guinea-pig isolated urinary bladder

Spasmogenic action of histamine, 2-(2-aminoethyl) pyridine (H1 receptor agonist) and 4 methyl-histamine (H2 receptor agonist), have been studied in guinea pig isolated urinary bladder in the presence of mepyramine (H1 antagonist) and metiamide (H2 antagonist) to identify the presence of H1 and H2 receptors. The study suggested the presence of H1 as well as H2 receptors in this preparation.     

Pharmacological action of nicotine in the isolated urinary bladder from rabbit: special reference to the chronic nicotine treatment

1. A mode of action of nicotine and a change of the responsiveness to nicotine following chronic nicotine treatment in the urinary bladder of rabbit were investigated. 2. Nicotine induced only a contraction in the urinary bladder of rabbit, and the response to nicotine was reduced by hexamethonium, atropine and capsaicin. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and partially due to the release of acetylcholine and tachykinins. 3. Tetrodotoxin did not inhibit the contractile response to nicotine in the rabbit detrusor muscle, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 4. Nicotine-induced contraction was reduced following the chronic nicotine treatment without a change of its pharmacological properties. These findings suggest that chronic nicotine treatment might cause a decrease of the amounts of nicotinic receptors and also receptors for mediators released by nicotine.     

Pharmacological characterization of urinary bladder smooth muscle contractility following partial bladder outlet obstruction in pigs

Partial bladder outlet obstruction of the pig is considered as a valuable preclinical model for evaluating the profile of compounds for the treatment of bladder overactivity. In this study, we characterized the pharmacological properties of isolated bladder smooth muscle from pigs following partial outlet obstruction and its sensitivity to potassium channel openers. Bladder strips from obstructed animals showed significantly lower maximal efficacy (E(max)) and sensitivity to stimulation by ATP and carbachol, but not to those evoked by serotonin, compared to age-matched controls. Tissue strips from obstructed animals also showed a 2.5-fold increase in the potency and significantly reduced maximum response following K+ depolarization. With respect to spontaneous activity, bladder strips from control strips demonstrated little spontaneous phasic activity at all preloads examined. In contrast, bladder strips from obstructed animals showed large preload-dependent increases in spontaneous phasic activity at preload values of 16-32 g. The potencies of K(ATP) channel openers to relax carbachol-evoked contractions showed a good 1:1 correlation (r(2)=0.90) between obstructed and control bladder strips. These studies demonstrate that obstructed pig bladders show enhanced spontaneous phasic activity especially at elevated preloads, which may underlie unstable myogenic bladder contractions reported in cystometrographic measurements in vivo. The impaired responses to electrical field stimulation could be attributed to reduced efficacies and/or lower sensitivities of muscarinic and purinergic signaling pathways. K(ATP) channel sensitivities remain essentially unimpaired in the obstructed bladder and could be effectively modulated by openers with potential for the treatment of overactive bladder secondary to outlet obstruction.     

Effects of testosterone on neuromuscular transmission in rat isolated urinary bladder

Testosterone was examined for its effects on neuromuscular transmission in rat and shrew urinary bladder. In isolated preparations of detrusor muscle from sexually immature male rats (8-10 weeks old) at concentrations of 100-300 microM, it inhibited neuromuscular transmission in a concentration-dependent manner and it also inhibited responses to applied carbachol and diadenosine pentaphosphate (Ap(5)A, a P2X receptor agonist). Ethanol (at or above 38 mM), the solvent for testosterone, also caused significant inhibition of neurogenic contractions as well as carbachol- and Ap(5)A-induced contractions. In older, sexually mature male rats (over 16 weeks old), testosterone and ethanol had similar effects to those observed in the young male rat, although both were slightly less potent. In young virgin female rats (8-12 weeks old), testosterone and ethanol inhibited neuromuscular transmission; testosterone was approximately 1000 times more potent than in male rats, with a threshold concentration of 30 nM. In the insectivore, Suncus murinus, testosterone (0.1 microM-1 x mM) caused inhibition of neurogenic and chemogenic responses, but ethanol had no significant effect. Flutamide (50 microM), a genomic testosterone-receptor antagonist, did not inhibit any of the responses to testosterone. It is concluded that testosterone acts predominantly on a postjunctional nongenomic receptor to inhibit urinary bladder detrusor muscle contraction.     

盐酸丙哌维林对豚鼠离体膀胱平滑肌条的钙拮抗作用

目的　研究盐酸丙哌维林 (P 4)对豚鼠离体膀胱平滑肌条的钙拮抗作用及作用机制。方法　采用离体平滑肌条浴槽实验方法 ,以维拉帕米为对照 ,测定P 4对CaCl2 和组胺 (His)所致离体膀胱平滑肌条的收缩及对乙酰胆碱 (ACh)所致膀胱平滑肌依赖细胞内钙、外钙收缩的影响。结果　P 41～ 1 0 0 μmol·L- 1 使CaCl2 累积量效曲线非平行右移 ,最大反应降低 ,pD2 ′为 4 73± 0 1 4。P 41 μmol·L- 1 使His量效曲线平行右移 ,最大效应不变 ,pA2 为 5 44± 0 1 4 ;1 0～ 1 0 0μmol·L- 1 使His量效曲线非平行右移 ,最大效应降低 ,pD2 ′为 4 71± 0 1 0。P 41、1 0和 1 0 0 μmol·L- 1 对ACh所致依赖细胞内钙收缩的抑制率分别为 45 77%± 6 54 %、86 2 6 %± 5 59%和 90 55 %± 3 1 1 % ,对依赖细胞外钙收缩的抑制率分别为 7 30 %± 2 89%、49 1 6 %± 6 0 9%和 88 2 5 %±3 70 %。结论　P 4低浓度时竞争性拮抗His所致膀胱平滑肌条的收缩反应 ,明显抑制膀胱平滑肌条依赖细胞内钙释放的收缩反应 ;高浓度时非竞争性拮抗His和CaCl2 所致膀胱平滑肌条的收缩反应 ,明显抑制膀胱平滑肌条依赖细胞内钙释放和外钙经钙通道内流所致收缩反应     

The contractile effect of bombesin on the rat isolated urinary bladder

We have investigated and compared the myotropic effects of bombesin (BB) and carbachol (C) in the rat isolated urinary bladder. BB (0.5 x 10(-9) to 0.5 x 10(-5) M) and C (2.7 x 10(-8) to 5.4 x 10(-5) M) were found to produce dose-dependent increases of the basal tone of the rat detrusor muscle. The maximal contraction produced by C was about 4 times greater than that elicited by BB or substance P (SP). However, the threshold concentrations of BB and SP required to stimulate the detrusor muscle were much lower than those of C. The pD2 (-log ED50) values of BB, SP and C were respectively 7.63, 7.05 and 5.8. The tissues exposed to BB relaxed more slowly after washout than those challenged with C or SP. The contractile effects of medium range concentrations of BB were not affected by pretreating the tissues with tetrodotoxin, atropine, antihistaminics, indomethacin, alpha- and beta-adrenergic blockers, methysergide or 8-leucine-angiotensin II. Tissues desensitized with high concentrations of bradykinin maintained their sensitivity to BB. The result suggest that the contractile effect of BB on the rat isolated urinary bladder is likely to be the result of a direct effect on the smooth muscle cells.