Mediation of contraction by cholinergic muscarinic receptors in the ureterovesical junction

EFFECTS OF CHOLINERGIC DRUGS ON URETERAL FUNCTION IN ANESTHETIZED DOGS

PURPOSE

We evaluated the effects of the nonselective muscarinic receptor agonist carbachol (CCh) and its antagonist atropine on ureteral function in anesthetized dogs.

MATERIALS AND METHODS

Drug effects were evaluated on elevated pressure in a completely obstructed ureter and peristalsis in its partially obstructed fellow ureters as well as on intravesical isovolumetric pressure.

RESULTS

CCh (0.1 to 1.0 microg/kg intravenously) dose dependently decreased elevated pressure and peristalsis in completely and partially obstructed ureters, respectively, and increased intravesical isovolumetric pressure. On the other hand, atropine (0.1 to 1.0 mg/kg intravenously) had no significant effects on these 3 variables. Prior administration of atropine (1.0 mg/kg intravenously) completely inhibited the described CCh induced effects.

CONCLUSIONS

Our results demonstrate that in anesthetized dogs cholinergic receptor stimulation has a suppressive effect on ureteral pressure and peristalsis in obstructed ureters, in contrast to its activation of bladder smooth muscle.

Distribution and functional effects of neuropeptide Y on equine ureteral smooth muscle and resistance arteries

The distribution of neuropeptide Y (NPY)-immunoreactive (IR) nerves, as well as the functional effects of NPY and the Y1- and Y2-receptor agonists, [Leu31,Pro34]NPY and NPY(13-36), respectively, have been investigated in vitro in both visceral and arterial smooth muscle of the horse intravesical ureter. NPY-IR nerve fibres were widely distributed along the entire length of the ureter, although the intravesical part was the most richly innervated region, and the only one where NPY-IR ganglion cells were found. NPY (10(-7) M) did not affect either basal tone or spontaneous rhythmic contractions of the isolated intravesical ureter, but significantly enhanced the increases in both tone and frequency of phasic activity elicited by noradrenaline (10(-6) and 10(-5) M). The Y1-receptor agonist, [Leu31,Pro34]NPY (10(-7) and 10(-6) M) did not significantly alter either ureteral basal tone or the contractile activity induced by noradrenaline, whereas the Y2-receptor agonist, NPY(13-36) (10(-7) M), mimicked the potentiating effect of NPY on noradrenaline responses. In ureteral resistance arteries (effective lumen diameters of 130-300 microm), NPY (10(-10) to 10(-7) M) elicited concentration-dependent contractions, which were inversely correlated with the arterial lumen diameter. Submaximal concentrations of NPY (10(-8) M) significantly increased the sensitivity of ureteral arteries to noradrenaline. [Leu31,Pro34]NPY (10(-10) to 10(-7) M), but not NPY(13-36), induced a contractile effect of similar magnitude and potency as those of NPY, and also potentiated noradrenaline responses. The present results demonstrate a rich NPY-innervation in the intravesical ureter and reveal functional effects of the peptide enhancing motor activity in both ureteral and arterial smooth muscles, although the receptors mediating such effects seem to be different. Thus, NPY potentiates the phasic contractions and tone elicited by noradrenaline through Y2-receptors, whereas it both contracts and potentiates noradrenaline vasoconstriction in ureteral arteries via Y1-receptors.

Involvement of a glibenclamide-sensitive mechanism in the nitrergic neurotransmission of the pig intravesical ureter

1. The present study was designed to investigate whether potassium (K+) channels are involved in the relaxations to nitric oxide (NO) of pig intravesical ureteral preparations suspended in organ baths for isometric tension recordings. In ureteral strips treated with guanethidine (10(-5) M) and atropine (10(-7) M) to block adrenergic neurotransmission and muscarinic receptors, respectively, NO was either released from nitrergic nerves by electrical field stimulation (EFS, 0.5-10 Hz., 1 ms duration, 20 s trains), or exogenously-applied as an acidified solution of sodium nitrite (NaNO2, 10(-6)-10(-3) M). 2. Incubation with an inhibitor of guanylate cyclase activation by NO, methylene blue (10(-5) M) did not change the basal tension of intravesical ureteral strips but inhibited the relaxation induced by EFS or exogenous NO on ureteral preparations contracted with the thromboxane analogue U46619 (10(-7) M). 3. Incubation with charybdotoxin (3 x 10(-8) M) and apamin (5 x 10(-7) M), which are inhibitors of large and small conductance calcium (Ca2+)-activated K+ channels, respectively, did not modify basal tension or the relaxations induced by EFS and exogenous NO. Treatment with charybdotoxin or apamin plus methylene blue (10(-5) M) significantly reduced the relaxations to EFS and exogenous NO. However, in both cases the reductions were similar to the inhibition evoked by methylene blue alone. The combined addition of charybdotoxin plus apamin did not change the relaxations to EFS or exogenously added NO of the porcine intravesical ureter. 4. Cromakalim (10(-8) 3 x 10(-6) M), an opener of ATP-sensitive K+ channels, evoked a dose-dependent relaxation with a pD2 of 7.3 +/- 0.2 and maximum relaxant effect of a 71.8 +/- 4.2% of the contraction induced by U46619 in the pig intravesical ureter. The blocker of ATP-sensitive K+ channels, glibenclamide (10(-6) M), inhibited markedly the relaxations to cromakalim. 5. Glibenclamide (10(-6) M) had no effect on the basal tone of ureteral preparations but significantly reduced the relaxations induced by both EFS and exogenous NO. Combined treatment with methylene blue (10(-5) M) and glibenclamide (10(-6) M) did not exert an effect greater than that of methylene blue alone on either EFS- or NO-evoked relaxations of the pig ureter. 6. The present results suggest that NO acts as an inhibitory neurotransmitter in the pig intravesical ureter and relaxes smooth muscle through a guanylate cyclase-dependent mechanism which seems to favour the opening of glibenclamide-sensitive K+ channels.

Muscarinic binding sites of the pig intravesical ureter

1. Muscarinic receptors in the pig intravesical ureter were characterized by binding assays in which the muscarinic receptor antagonist, (-)-[3H]-quinuclidinyl benzylate ([3H]QNB) was used as radioligand. 2. The specific binding of [3H]-QNB (about 90% of the total binding, as defined with 10(-5) M unlabelled atropine) was dependent on protein concentration, saturable, and of high affinity (KD = 0.13 +/- 0.02 nM). 3. Displacement of [3H]-QNB specific binding by the M1-selective antagonist, pirenzepine, described a two-component curve, with a minor (17%) high affinity component (pKiH = 8.75), and a major (83%) low affinity one (pKiL = 6.34). The M3-preferential antagonists, hexa-hydro-sila-difenidol (HHSid) and p-fluoro-HHSiD (p-F-HHSiD) delineated also two sites, with pKiH of 8.91 and 8.57 and pKiL of 6.94 and 7.05, respectively. However, the M2-selective antagonists, 11-(2-(diethyl-amino)methyl-1-piperidinylacetyl)-5,11-dihydro-6H-p yrido-(2,3-b)- (1,4)-benzodiazepin-6-one (AF-DX 116, pKi = 6.72) and methoctramine (pKi = 8.34), as well as the M4-selective antagonists, tropicamide (pKi = 7.15) and himbacine (pKi = 8.65) fitted best to a single population of sites. Moreover, 4-diphenyl-acetoxy-N-methyl-piperidine methiodide (4-DAMP), a muscarinic antagonist that discriminates the M1 and M3 versus the M2 subtypes, also delineated one site (pKi = 8.36). 4. The antagonist profile clearly indicates the existence of an M2 population in the porcine intravesical ureter. In addition, the presence of a minor non-M2 population, which may be formed by a mixture of several muscarinic subtypes (i.e. M1, M3 and/or M4) can not be discounted. 5. The present work confirms the results obtained in previous functional studies where the stimulation of muscarinic receptors by carbachol evoked the contraction of the pig isolated intravesical ureter.

Histochemical and functional evidence for a cholinergic innervation of the equine ureter

The distribution of acetylcholinesterase (AChE)-positive nerve fibers and cells, as well as the effects of acetylcholine (ACh) on ureteral smooth muscle and small resistance arteries were investigated in the equine ureter by means of histochemical, classic organ baths and myograph techniques. AChE-positive nerve fibers were widely distributed throughout the ureteral wall forming muscular, subepithelial and perivascular nerve plexuses, whose density was highest at the intravesical ureter. AChE-positive nerve cells were also identified grouped as adventitial or intramural ganglia. ACh increased concentration-dependently both the frequency of phasic contractile activity and basal tone of the isolated intravesical ureter, the pD2 values being 6.31 +/- 0.18 and 6.59 +/- 0.13, respectively. The ACh-induced motor effects in ureteral smooth muscle were blocked by atropine, giving pIC50 values of 8.58 +/- 0.08 and 9.68 +/- 0.05 for phasic activity and tone, respectively. Hexamethonium only inhibited ACh-evoked contractile activity at the highest concentration used. ACh elicited a potent endothelium-dependent relaxation of equine ureteral resistance arteries precontracted with 40 mM K-PSS, the pD2 value being 7.94 +/- 0.07. This relaxant response was abolished in the presence of the nitric oxide (NO) inhibitor, NG-nitro-L-arginine (L-NNA), the blockade being reversed by subsequent incubation with the NO exogenous substrate, L-arginine. The ACh-induced relaxation was competitively antagonized by atropine (pA2 = 10.05 +/- 0.18). The present results suggest the existence of a rich cholinergic innervation in the equine ureter which controls both ureteral smooth muscle and resistance arteries motor activity through the muscarinic effects of ACh. In addition, the ACh relaxant response in the ureteral resistance arteries seems to be mediated by NO.

Different muscarinic receptor subtypes mediating the phasic activity and basal tone of pig isolated intravesical ureter

1. We have studied the effects of muscarinic cholinoceptor agonists and specific antagonists on both phasic activity and basal tone of the isolated intravesical ureter of the pig by means of isometric techniques in vitro. 2. Acetylcholine in the presence and absence of physostigmine increased both phasic activity and basal tone of ureteral strips in a concentration-dependent manner. Moreover carbachol, methacholine and oxotremorine-M increased both contractile parameters while bethanechol and McN-A-343 evoked only increases in tone without affecting the frequency of the phasic contractions. 3. The nicotinic receptor blocker, hexamethonium (10(-6)-10(-4) M), failed to modify the contractions evoked by a single dose of carbachol (10(-5) M), whilst the muscarinic antagonist, atropine inhibited both phasic and tonic responses. 4. The muscarinic M1 (pirenzepine), M2 (AF-DX 116 and methoctramine), M3 (4-DAMP, HHSiD and p-F-HHSiD), and putative M4 receptor (tropicamide) antagonists significantly reversed increases in both frequency of phasic activity and baseline tone induced by a submaximal dose of carbachol (10(-5) M). The pIC50 values for inhibition of the induced phasic activity were: atropine (10.16) > 4-DAMP (9.12) > HHSiD (8.22) = methoctramine (7.98) = p-F-HHSiD (7.88 > tropicamide (7.62) = pirenzepine (7.53) = AF-DX 116 (7.45) and for inhibition of basal tone were: atropine (10.73) > 4-DAMP (9.32) > HHSiD (8.65) = pirenzepine (8.43) = p-F-HHSiD (8.38) > methoctramine (7.79) > tropicamide (7.53) > AF-DX 116 (7.04). 5. The antagonist profile indicates that an M1 receptor mediates the tonic response while the phasic activity could involve either both M2 and M3 or an M4 muscarinic receptor. These results suggest that different muscarinic receptor subtypes mediate the phasic and tonic contractile activity induced by a submaximal concentration of carbachol in the porcine intravesical ureter.

Noradrenaline modulates smooth muscle activity of the isolated intravesical ureter of the pig through different types of adrenoceptors

1. We have studied the effects of alpha- and beta-adrenoceptor agonists and antagonists on both phasic peristaltic activity and basal tone of the isolated intravesical ureter of the pig by means of isometric techniques in vitro. 2. Spontaneous phasic activity was exhibited by 21% of pig intravesical ureter preparations manifested as rhythmic contractions with average frequency and amplitude of 2.54 +/- 0.18 min-1 and 1.48 +/- 0.16 g (n = 31), respectively. 3. Adrenaline, noradrenaline and phenylephrine induced concentration-dependent increases in both phasic activity and basal tone of ureteral preparations, all three agonists being more potent in modifying ureteral phasic activity than baseline tone. B-HT 920, B-HT 933 and clonidine had no significant effect. 4. Phentolamine (10(-9)-10(-7) M) and prazosin (3 x 10(-11)-3 x 10(-8) M) significantly inhibited increases in both frequency of phasic activity and baseline tone induced by a submaximal dose of noradrenaline. Rauwolscine (10(-9)-10(-7) M) affected only the tone evoked by noradrenaline and higher concentrations of this antagonist were needed to block phasic activity. 5. Pretreatment of ureteral strips with the beta-adrenoceptor antagonist, propranolol (10(-6) M), significantly increased the maximum contraction evoked by noradrenaline. After incubation with phentolamine (10(-6) M), noradrenaline (10(-7)-10(-6) M) decreased phasic activity induced by prostaglandin F2 alpha (10(-5) M). Isoprenaline and salbutamol also abolished PGF2 alpha-induced phasic activity. Pafenolol (10(-6) M) and butoxamine (10(-6) M) blocked the inhibitory effect of noradrenaline, isoprenaline, and salbutamol on PGF2 alpha-induced phasic activity. 6. These results suggest that noradrenaline may modulate both phasic peristaltic activity and basal tone of pig intravesical ureter through both alpha- and beta-adrenoceptors.