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Dry and persistent cough is one of the commonest side effects experienced by patients treated with angiotensin-converting enzyme (ACE) inhibitors for the therapy of hypertension and congestive heart failure. The present study investigated the effect of zofenopril and ramipril on cough induced by citric acid in guinea pig and the involvement of bradykinin (BK) and prostaglandin E2 (PGE2) in mediating the responses of these drugs. Zofenopril (10 mg/kg) or ramipril (3-10 mg/kg), which is threefold more potent than zofenopril, on a mg basis, in lowering blood pressure, was orally administered daily in drinking water for 2 weeks. At the end of this period, aerosol of citric acid solution (0.1 M) was performed and the number of cough counted for 10 min. The role of the kinin B(2) receptor was also investigated. BK and PGE2 levels in the bronchoalveolar lavage (BAL) fluid were measured after repeated oral treatment with zofenopril or ramipril (10 mg/kg). Ramipril (3-10 mg/kg) increased citric acid-induced cough by 40% and 60%, respectively, as compared to the vehicle control group (15.0 ± 1.8), while zofenopril (10 mg/kg) was without effect. The enhancement of citric acid-induced cough caused by ramipril (10 mg/kg) was reduced by the kinin B(2) receptor antagonist MEN16132 (0.25 mg/kg ip). BK and PGE2 levels in the BAL fluid were increased, in comparison to the control group, after ramipril treatment, while they were unchanged after zofenopril administration. Zofenopril, contrary to ramipril, did not affect either citric acid-induced cough in the guinea pigs or BK and PGE2 production in the airways.

We have investigated the effect of intravaginal application of capsaicin on micturition reflex in female rats. Urinary bladder contractility was measured by transurethral pressure recording at isovolumetric and subthreshold conditions in anaesthetized rats. The intravaginal application of capsaicin (15 microg/50 microl rat) induced reproducible bladder phasic contractions, without desensitization upon repeated applications, that were blocked by intravenous atropine (1 mg/kg) or hexamethonium (5 mg/kg) and prevented by removal of paracervical ganglia or systemic capsaicin pretreatment (125 mg/kg, s.c.). The inhibition of sympathetic transmission by guanethidine (30 mg/kg, s.c.) produced significant increase of the bladder reflex contractions activated by intravaginal capsaicin. Intravenous administration of the TRPV1 antagonist, capsazepine (3 mg/kg), significantly reduced the excitatory reflex response to capsaicin. Intravaginal administration of capsaicin (15 microg/50 microl), during distension-induced reflex bladder contractions, produced a transient block of reflexes, unaffected by guanethidine pretreatment. In conclusion, the stimulation of capsaicin-sensitive sensory nerve endings in the rat cervix-vagina induced a dual excitatory or inhibitory bladder response in anaesthetized female rats depending on the degree of bladder distension.

We have characterized the contractile responses produced by stimulation of the tachykinin NK2 receptor in the hamster urinary bladder in vitro and in vivo. In isolated bladder strips, neurokinin A (NKA, pD2 7.40, Emax 71% of the response to 80 mM KCl) and the synthetic tachykinin NK2 receptor selective agonist [betaAla8]NKA(4-10) (pD2 7.48, Emax 77% of the response to KCl) both induced a concentration-dependent contraction, whereas the tachykinin NK1 and NK3 receptor selective agonists, [Sar9]substance P sulfone and senktide, respectively, produced a negligible contractile effect. The bicyclic peptide antagonists MEN 11420 and MEN 10627 behaved as competitive antagonists of the response to [betaAla8]NKA(4-10) with apparent pK(B) values of 9.3 and 9.7, respectively. Comparable apparent pK(B) values were estimated against NKA (pK(B) 9.2 and 9.4 for MEN 11420 and MEN 10627, respectively). Under isovolumetric recording of the intravesical pressure, the nicotinic receptor agonist DMPP (0.6 micromol/kg i.v.) produced a phasic contraction of the hamster bladder in vivo that was abolished by hexamethonium (110 micromol/kg i.v.) or by surgical ablation of pelvic ganglia. In vivo [betaAla8]NKA(4-10) (10 nmol/kg i.v.) induced a tonic-type sustained bladder contraction with superimposed high frequency and small amplitude (12 mmHg) phasic contractions and, in about 70% of cases examined, a few high amplitude (20 mmHg) phasic contractions. Hexamethonium abolished the high amplitude phasic contractions, indicating their reflex origin. In animals subjected to the ablation of pelvic ganglia, the urinary bladder response to [betaAla8]NKA(4-10) was comparable to that observed after administration of hexamethonium. Moreover, hexamethonium did not affect the contractile responses to [betaAla8]NKA(4-10) in ganglionectomized animals. MEN 10627 and MEN 11420 produced a dose-dependent and long-lasting inhibition of the contractile response to [betaAla8]NKA(4-10): the least effective doses of the two antagonists were 30 and 3 nmol/kg i.v. for MEN 10627 and MEN 11420, respectively. An almost complete and long-lasting inhibition of the response to the agonist was produced at doses of 10 and 100 nmol/kg i.v. of MEN 11420 and MEN 10627. In urethane-anaesthetized hamsters the non-stop intravesical infusion of saline (50 microl/min) produced repetitive micturition cycles which were abolished by hexamethonium (110 micromol/kg i.v.) or by surgical removal of the pelvic ganglia. MEN 11420 (100 nmol/kg) had no significant effect on the volume-evoked micturition reflex in anaesthetized hamsters. In conclusion, the hamster urinary bladder is a suitable preparation for studying the action of tachykinin NK2 receptor antagonists in vivo: in this species, the stimulation of tachykinin NK2 receptors induces bladder contractions. Blockade of tachykinin NK2 receptors does not appreciably modify the volume-evoked micturition reflex in this species.

This study investigates the role of tachykinin NK1 and NK2 receptors in motor responses induced by the intravesical instillation of capsaicin in urethane-anaesthetized rats. SR 140,333 (1 micromol/kg, i.v.), a nonpeptide NK1 receptor antagonist, abolished urinary bladder contractions induced by the selective NK1 receptor agonist [Sar9]SP-sulfone (0.1-100 nmol/kg, i.v.) without affecting those induced by the NK2 receptor agonist [betaAla8]NKA(4-10). MEN 11,420 (100 nmol/kg, i.v.), a cyclic peptide NK2 receptor antagonist, abolished bladder contractions induced by [betaAla8]NKA(4-10) (0.3-300 nmol/kg, i.v.) without modifying those induced by [Sar9]SP-sulfone. Intravesical instillation of capsaicin (6 nmol/0.6 ml/rat) produced a motor response consisting in a primary contraction followed by a series of high amplitude phasic contractions. The intravesical instillation of saline (0.6 ml/rat) produced a primary contraction of lower amplitude with respect to that induced by capsaicin and the total area under the curve was also lower in saline-instilled rats, however the number and the amplitude of phasic contractions was similar to that induced by capsaicin. MEN 11,420 (100 nmol/kg, i.v.) did not modify motor responses induced by the intravesical administration of saline. In contrast, in capsaicin-instilled rats, MEN 11,420 (100 nmol/kg, i.v.) reduced the primary contraction, the area under the curve and also the number of phasic contractions. SR 140,333 (1 micromol/kg, i.v.) reduced the primary contraction but not other parameters. The combination of SR 140,333 (1 micromol/kg, i.v.) and MEN 11,420 (100 nmol/kg, i.v.) produced an additive inhibitory effect on the primary contraction but not a further inhibition on other parameters with respect to that observed with MEN 11,420 alone. In hexamethonium (110 micromol/kg, i.v.)-pretreated animals the intravesical instillation of capsaicin produced a tonic contraction having greater amplitude and area than that induced by saline. MEN 11,420, but not SR 140,333, significantly reduced the bladder response to capsaicin in hexamethonium-pretreated rats. Again, the combined administration of MEN 11,420 and SR 140,333 did not produce further inhibitory effect in comparison to MEN 11,420 alone. It is concluded that the motor responses induced by the intravesical instillation of capsaicin are mediated by the activation of peripheral tachykinin NK2 receptors.

In this study we have characterized the role of sensory fibers and of the sensory peptides, neurokinin A (NKA) and calcitonin gene-related peptide (CGRP), on the contractile responses evoked by single pulse electrical field stimulation (EFS) in the hamster urinary bladder. EFS of the hamster isolated urinary bladder produced twitch contractions which were unaffected by atropine but abolished by tetrodotoxin. The P2 purinoreceptor antagonist PPADS (30 microM) inhibited twitches by 66+/-4% on its own and by 78+/-3% in the presence of atropine. The selective tachykinin NK2 receptor antagonist nepadutant produced a slight but consistent reduction of twitch amplitude (-21+/-3%) at 1 microM. Addition of nepadutant to atropine and PPADS did not further increase their inhibitory effect. The application of hCGRP (10-300 nM) produced a concentration-dependent inhibition of twitches (Emax -38+/-3%, EC50=12 nM) and a small reduction of tone (0.5+/-0.09 mN). Similar effects were obtained with capsaicin (0.1-10 microM) which inhibited EFS-evoked contractions with an EC50 of 100.0 nM and a maximal effect of 34+/-4% inhibition at 1 microM. Under submaximal parameters of stimulation NKA (10 nM) increased the amplitude of twitches by 45+/-6% and produced a concentration-dependent tonic contraction (EC50=55.9 nM). The CGRP1 receptor subtype antagonist, hCGRP(8-37), increased by 29+/-8% the EFS-evoked contractions and significantly reduced the response to 0.1 microM CGRP. Capsaicin (10 microM) increased both CGRP-LI and NKA-LI release from superfused slices of hamster urinary bladder by about sixfold and by about 70%, over baseline, respectively. A second application of capsaicin was ineffective, indicating a complete desensitization of sensory nerve efferent function. In the hamster urinary bladder the sensory neuropeptides NKA and CGRP are co-released by sensory fibers after stimulation either by EFS or capsaicin. However, the role of CGRP appears functionally predominant.

In isolated strips of the hamster urinary bladder the selective tachykinin NK2 receptor agonist [betaAla8]NKA(4-10) induced a concentration-dependent (1 nM-10 microM) contraction (EC50 104 nM) associated with significant release of prostaglandin E2 (PGE2, 50+/-17 pg/mg tissue). In mucosa-free bladder strips [betaAla8]NKA(4-10) was as potent as in the presence of mucosa (EC50 46 nM), although the evoked PGE2 release was significantly less than in controls (6+/-1.7 pg/mg tissue). Dexketoprofen (10 microM) produced a significant but limited rightward shift of the concentration/response curve to [betaAla8]NKA(4-10) both in the presence and absence of the mucosal layer: the EC50 for [betaAla8]NKA(4-10) was increased five- and threefold, respectively. The evoked PGE2 release was abolished in both cases. The selective tachykinin NK2 receptor antagonist, nepadutant (10 nM-1 microM) produced a concentration-dependent and even inhibition of both contraction and PGE2 release induced by [betaAla8]NKA(4-10). The L-type calcium channel blocker, nifedipine (1 microM) and the non-selective cationic channel blocker SKF 96365 (30 microM) both inhibited the contractile response to [betaAla8]NKA(4-10) (89+/-2 and 83+/-2% inhibition, respectively). The evoked PGE2 release was not affected by nifedipine but was almost abolished by SKF 96365. Arachidonic acid (100 microM) induced a contractile response (5.9+/-0.7 mN) associated with a large production of PGE2 (383+/-78 pg/mg tissue). The contractile response to arachidonic acid was inhibited by both nifedipine (1 microM) and SKF 96365 (30 microM) (83+/-5 and 79+/-3% inhibition, respectively). The PGE2 production induced by arachidonic acid was markedly inhibited by SKF 96365 only (about 94% inhibition). Exogenous PGE2 contracted hamster bladder strips in the presence of dexketoprofen (EC50 1 microM) and strongly potentiated the contractile response to a submaximal concentration of [betaAla8]NKA(4-10). In anaesthetized hamsters the administration of [betaAla8]NKA(4-10) (10 nmol/kg, i.v.) produced a contractile response of the urinary bladder (13+/-0.4 mmHg) that was inhibited partly by dexketoprofen (25+/-3 and 35+/-4% inhibition for 0.2 and 2 mg/kg, i.v. dexketoprofen, respectively). We conclude that activation of tachykinin NK2 receptors determines prostanoid synthesis/release in the hamster urinary bladder and that this effect is largely ascribable to structures present in the bladder mucosa. Prostanoids generated following NK2 receptor activation amplify the direct contractile effect of NK2 receptor agonists. This latter response is largely due to activation of L-type calcium channels (nifedipine-sensitive) although this source of calcium apparently is not essential for activation of prostanoid synthesis.

Chemical stimulation of primary afferent nerves in the rat urinary bladder in vivo with topical capsaicin (1 microg in 50 microl saline) determines a dual motor response, consisting of a contractile effect mediated by tachykinins released from sensory nerves in the bladder wall and a transient activation of a bladder-to-bladder micturition reflex organized at the supraspinal level (chemoceptive micturition reflex). Both responses undergo complete desensitization upon repeated applications of capsaicin. The i.v. administration of the novel neuropeptide nociceptin (100 nmol/kg) produced a long-lasting protection from capsaicin desensitization of afferent nerves which mediate the chemoceptive micturition reflex. In fact a chemoceptive micturition reflex could be repeatedly evoked by topical capsaicin in nociceptin-pretreated rats. In sharp contrast, nociceptin did not influence the development of desensitization of the local response to capsaicin, corresponding to the 'efferent' function of capsaicin-sensitive afferent neurons. These results suggest that the afferent and 'efferent' function of capsaicin-sensitive primary afferent neurons (CSPANs) in the rat bladder are differentiated by nociceptin. Alternative mechanisms underlying this phenomenon are discussed.

We have characterized the action of the novel, water-soluble, tachykinin NK2 receptor antagonist MEN 11420 ([Asn(2-AcNH-β-D-Glc)-Asp-Trp-Phe-Dap-Leu] c(2β–5β)) on the circular muscle of the guinea-pig and human colon in vitro and on the guinea-pig colon in vivo. In organ bath experiments on guinea-pig colon MEN 11420 produced a concentration-dependent rightward shift of the concentration-response curve to the NK2 receptor selective agonist, [βAla8]neurokinin A (NKA) (4–10) with a pKB value of 8.1. Up to 1 μM MEN 11420 had no effect on the concentration-response curve to methacholine, to the NK1 receptor selective agonist, [Sar9]substance P (SP) sulfone, to the NK3 receptor selective agonist, senktide, or on the response to exogenous SP. The response to exogenous NKA was inhibited, although the shift of the concentration-response curve to NKA produced by MEN 11420 at 1 μM (dose ratio 5.3) was much smaller than that produced against [βAla8]NKA (4–10) (dose ratio 102), presumably because NKA also stimulates NK1 receptors at relatively low concentrations. In sucrose gap, MEN 11420 concentration-dependently inhibited both depolarization (IC50 0.34 μM) and contraction (IC50 = 0.32 μM) produced by [βAla8]NKA (4–10) (0.3 μM for 10 s) in the guinea-pig colon without affecting the corresponding responses produced by [Sar9]SP sulfone. When similar experiments were performed in the circular muscle of the human colon MEN 11420 concentration-dependently inhibited both depolarization and contraction induced by [βAla8]NKA(4– 10) with IC50s of 99 and 75 nM, respectively. MEN 11420 (1 μM) had no effect on the nonadrenergic noncholinergic (NANC) depolarization and contraction produced by a short period of electrical field stimulation (EFS, 10 Hz for 1 s) in the guinea-pig colon and selectively inhibited the sustained component of depolarization produced during a prolonged period of EFS (3 Hz for 3 min), without affecting the concomitant depolarization. Nifedipine (1 μM) eliminated the NANC contraction to a short period of EFS and the phasic contraction in response to a prolonged period of EFS. MEN 11420 (1 μM) abolished the nifedipine-resistant NANC contraction produced by prolonged period of electrical field stimulation (EFS, 3 Hz for 3 min). All electrical and mechanical NANC responses to EFS which were resistant to MEN 11420, either in the absence or presence of nifedipine, were abolished by the subsequent application of the NK1 receptor antagonist, SR 140333 (1 μM). Up to 3 μM, MEN 11420 had no significant effect on the cholinergic excitatory junction potential or the NANC inhibitory junction potential evoked by single pulse EFS, nor did it affect membrane conductance. In urethane-anaesthetized guinea-pigs MEN 11420 (10– 100 nmol/kg i.v.) produced a dose-dependent and long lasting (> 3 h) inhibition of the contractile response (15 ± 2 mmHg) of the proximal colon induced by [βAla8]NKA (4–10) (3 nmol/kg i.v.). MEN 11420 (300 nmol/kg i.v.) did not affect the contraction produced by [Sar9]SP sulfone. MEN 11420 (300 nmol/kg) produced a limited (Emax about 40% inhibition) and transient (recovery within 60 min) inhibition of the atropine- and hexamethonium-sensitive phasic contractions of the proximal colon induced by threshold distension of a colonic balloon. On the other hand, MEN 11420 (10–300 nmol/kg i.v.) produced a dose-dependent complete and prolonged (> 2 h from administration) inhibition of the atropine-resistant and hexamethonium-sensitive phasic contraction induced by suprathreshold distension of the colonic balloon. We conclude that MEN 11420 is a potent and selective tachykinin NK2 receptor antagonist devoid of significant inhibitory activity toward excitatory transmission mediated via tachykinin NK1 or muscarinic receptors. The present findings indicate that SP and NKA are likely involved in the preferential activation of NK1 and NK2 receptors during tachykininergic transmission, although NKA can act as an effective NK1 receptor ligand.

The study aimed to establish the possible role of tachykinins as mediators of atropine-resistant reflex contractions evoked by balloon distension in the proximal duodenum of urethane-anesthetized, guanethidine (34 mumol/kg s.c.)-pretreated rats. Distension of the balloon with a small amount (0.2-0.3 ml) of saline induced the appearance of phasic rhythmic contractions (about 11 mmHg in amplitude) which were promptly suppressed by either atropine (3 mumol/kg i.v.) or hexamethonium (28 mumol/kg i.v.). Despite the continuous i.v. infusion of atropine (2 mumol/h), low-amplitude rhythmic phasic contractions recovered, which were promptly suppressed by hexamethonium, to indicate the involvement of an atropine-resistant excitatory reflex. The amplitude of these atropine-resistant contractions was increased to about 4-5 mmHg by further distension of the balloon (0.4-0.6 ml) : under these conditions, the atropine-resistant contractions undergo a progressive fading. The fading was prevented by i.v. administration of the nitric oxide (NO) synthase inhibitor, L-nitroarginine methyl ester (L-NAME, 55 mumol/h), to provide a suitable baseline (amplitude of contractions was 7-8 mmHg) for studying the effect of tachykinin receptor antagonists. I.v. administration of the selective tachykinin NK2 receptor antagonists, MEN 10,627 (10-100 nmol/kg) and SR 48968 (100-300 nmol/kg) or of the selective NK1 antagonist SR 140333 (100 nmol/kg), at doses which do not affect the duodenal contractions induced by acetylcholine (5.5 mumol/kg i.v.), produced a prompt and long lasting suppression of the atropine-resistant reflex duodenal contractions produced by balloon distension in urethane-anesthetized rats, whilst SR-48965 (300 nmol/kg), the enantiomer of SR-48968 devoid, of NK2 receptor blocking activity, was without effect. I.v. administration of the selective NK1 receptor agonists [Sar9] substance P sulfone and septide or of the NK2 receptor selective agonist, [beta Ala8] neurokinin A(4-10) produced dose-dependent contractions of the duodenum. SR 140333 (100 nmol/kg i.v.) selectively antagonized the duodenal contractions produced by [Sar9] substance P sulfone and septide without affecting those produced by [beta Ala8] neurokinin A(4-10). On the other hand, MEN 10,627 (30-100 nmol/kg i.v.) and SR 48968 (100-300 nmol/kg i.v.) but not SR 48965 (300 nmol/kg i.v.) antagonized, at a comparable extent, duodenal contractions induced by both the selective NK2 and NK1 receptor agonists. We conclude that endogenous tachykinins are involved in mediating atropine-resistant reflex contractions evoked by distension of the rat duodenum in vivo: both NK1 and NK2 receptors are activated by endogenous ligands to produce NANC contractions of rat duodenum in vivo. However, the contractile response to i.v. administered NK1 receptor agonists, [Sar9] substance P sulfone and septide, may involve the release of mediators producing smooth muscle contraction via NK2 receptors.

1. In the presence of atropine and guanethidine (3 μmol/l each), electrical field stimulation (1–20 Hz) produced frequency-dependent relaxations of the histamine-(3 μmol/l) induced vascular tone in isolated rings from the guinea-pig pulmonary artery. The electrically-evoked relaxations were abolished by tetrodotoxin (1 μmol/l). The amplitude of these nerve-mediated, nonadrenergic non-cholinergic (NANC) relaxations was unaffected by removal of the vascular endothelium produced through rubbing of the internal surface. 2. Capsaicin (1 μmol/l) produced a prompt and sustained relaxation of the histamine-induced tone which was unaffected by removal of the endothelium. A second application of capsaicin 60–120 min later had no further relaxant effect, indicating desensitization. After in vitro capsaicin desensitization, the electrically-evoked NANC relaxations were abolished, both in the presence or absence of the vascular endothelium. 3. Substance P evoked a prompt and transient relaxation in precontracted arterial rings with intact endothelium and a transient small contraction in rings in which the endothelium had been mechanically removed. The selective NK-1 receptor agonist, [Pro9]-substance P sulfone closely mimicked the relaxation produced by substance P while the selective NK-2 or NK-3 receptor agonists had no relaxant effect. Tachyphylaxis to substance P did not modify the amplitude of the capsaicin-induced relaxation. 4. Human alpha calcitonin gene-related peptide (CGRP) produced a prompt and sustained relaxation both in the presence and absence of the vascular endothelium. 5. Ruthenium red (10 μmol/l) blocked the relaxation to capsaicin while leaving unaffected the relaxation to electrical field stimulation or CGRP (0.1 μmol/l). 6. Both substance P (SP)-and CGRP-like immunoreactivities (LI) were detected in extracts of the guinea-pig pulmonary artery. Capsaicin (1 μmol/l) evoked a prompt and simultaneous outflow of both SP- and CGRP-LI. A second application of capsaicin 60 min later failed to increase SP- or CGRP-LI outflow, indicating complete desensitization. A small but clearly detectable release of both SP-LI and CGRP-LI was also evoked by electrical field stimulation. 7. These findings provide evidence that the neurogenic NANC vasodilation in the guinea-pig pulmonary artery is due to antidromic activation of peripheral endings of capsaicin-sensitive primary afferents. Endogenous CGRP is a likely mediator for this vasodilation. No evidence was found that endogenous SP might contribute to vasodilation by activating NK-1 receptors on endothelial cells.