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C A Maggi

Publications and source records attributed to C A Maggi.

At least 127 records · Page 7Linked to original sources
PubMed1997

MEN 11420, a potent and selective tachykinin NK2 receptor antagonist in the guinea-pig and human colon.

We have characterized the action of the novel, water-soluble, tachykinin NK2 receptor antagonist MEN 11420 ([Asn(2-AcNH-beta-D-Glc)-Asp-Trp-Phe-Dap-Leu] c(2 beta-5 beta)) 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, [beta Ala8]neurokinin A (NKA) (4-10) with a pKB value of 8.1. Up to 1 microM 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 microM (dose ratio 5.3) was much smaller than that produced against [beta Ala8]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 microM) and contraction (IC50 = 0.32 microM) produced by [beta Ala8]NKA (4-10) (0.3 microM 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 [beta Ala8]NKA(4-10) with IC50s of 99 and 75 nM, respectively. MEN 11420 (1 microM) 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 microM) 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 microM) 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 microM). Up to 3 microM, 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 [beta Ala8]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 tachykininergi

Aged↗
PubMed1997

The tachykinin NK1 receptor. Part I: ligands and mechanisms of cellular activation.

The tachykinin NK1 receptor is widely expressed in the mammalian central and peripheral nervous system. Powerful pharmacological tools (agonists and antagonists) are now available to elucidate the physiological role of NK1 receptors at these levels, as well as to understand their role in diseases and establish the possible therapeutic usefulness of NK1 receptor antagonists for treatment of human diseases. The structure-activity studies that have led to the development of potent peptide and non-peptide ligands for the tachykinin NK1 receptor are here reviewed. Among the peptide agonists and antagonists, linear and cyclic sequences have been developed. The non peptide antagonists belong to different chemical classes, i.e. steroids, perhydroisoindolones, quinuclidines, piperidines and tryptophane derivatives. The first non peptide antagonists for NK1 receptors have been obtained by random screening of chemical compounds large collections. The resulting leads were optimized with 'classic' structure activity approaches, aiming at identifying 'common' motifs for interaction with the receptor by ligands of different chemical classes. The results derived from the recent application of molecular biology techniques were useful to drive the design of new ligands toward a precise structural definition of ligand-receptor bi-molecular interactions. Studies on mutant receptors have established that the sites of interaction of peptide agonists and non peptide antagonists with the tachykinin NK1 receptor are largely non overlapping. Moreover, data obtained from mutagenesis of the NK1 receptor further indicate that some amino acid residues in the NK1 receptor sequence are critical for determining the binding affinity of some but not all ligands. Therefore, different antagonists discovered from random screening may not possess common points of interaction or common structural and conformational characteristics for their interaction with the tachykinin NK1 receptor. The tachykinin NK1 receptor couples with G-proteins to determine its biological effects in target cells. Several G-proteins both sensitive (Go, Gi) and insensitive (Gq, G11) to pertussis toxin can mediate the action of NK1 receptors. Moreover, several second messanger signalling systems (elevation of intracellular calcium, stimulation of phosphoinositol turnover, arachidonic acid mobilization, cAMP accumulation) have to be activated following NK1 receptor signalling. Also a direct modulation of certain ion channels at membrane level has been proposed. The NK1 receptor undergoes prompt and significant tachyphylaxis upon exposure to the agonist: this has been shown to be linked with receptor internalization which also occurs physiologically when the NK1 receptor is stimulated by endogenous tachykinins.

Animals↗
PubMed1997

Effect of several bicyclic peptide and cyclic pseudopeptide tachykinin NK2 receptor antagonists in the human isolated ileum and colon.

The affinities of the monocyclic pseudopeptides MEN10,508, MEN10,573, MEN10,581, MEN10,612, MEN10,619 and MEN10,677, and the bicyclic peptides MEN10,627, MEN10,692, MEN10,771, MEN10,882 and MEN10,993 were evaluated at the tachykinin NK2 receptors of the human isolated ileum and colon circular muscle preparations, by using [betaAla8]neurokinin A(4-10) as an agonist. All of the antagonists tested produced a concentration-dependent and competitive antagonism of [betaAla8]neurokinin A(4-10)-mediated contractions in both preparations. MEN10,612 (pKB = 8.1) and MEN10,627 (pKB = 8.4-8.8) were among the most potent analogs within their chemical classes. In general, the bicyclic peptide antagonists were more potent than the monocyclic peptide compounds, showing a nanomolar affinity for the human NK2 receptor. By comparing the affinities shown by the antagonists under study at NK2 receptors of the human gut with the affinities measured at NK2 receptors of the rabbit isolated pulmonary artery and hamster isolated trachea, a high degree of pharmacological homology was found between human and rabbit NK2 receptors. The present results point out the class of NK2 receptor antagonists bearing a bicyclic peptide structure, like MEN10,627, as candidates for testing in pathological conditions characterized by exaggerated gut motility, in which tachykinins might play a role as non-cholinergic excitatory neurotransmitters.

Adult↗
PubMed1997

Tachykinin NK1 and NK2 receptors mediate non-adrenergic non-cholinergic excitatory neuromuscular transmission in the human ileum.

Tachykinin NK1 and NK2 receptor selective antagonists and agonists were used to study excitatory non-adrenergic non-cholinergic (NANC) transmission in circular muscle strips from human ileum by the sucrose-gap method. In the presence of atropine (1 microM), guanethidine (3 microM), indomethacin (3 microM), apamin (0.1 microM), and N omega-nitro-L-arginine (L-NOARG, 30 microM), electrical field simulation (EFS) produced a NANC inhibitory junction potential (i.j.p.) followed by NANC excitatory junction potential (e.j.p.) with superimposed action potentials and contraction of the circular muscle of human ileum. The selective tachykinin NK1 receptor antagonist, GR 82334 (0.1-3 microM) produced a concentration-dependent inhibition of the EFS-evoked NANC e.j.p. (IC50 = 0.21 microM) and contraction (IC50 = 0.21 microM). The selective tachykinin NK2 receptor antagonist, MEN 10627 (0.01-1 microM), likewise produced a concentration-dependent inhibition of the EFS-evoked NANC e.j.p. (IC50 = 0.07 microM) and contraction (IC50 = 0.03 microM). Either antagonist was more effective in inhibiting the mechanical than the electrical response to EFS. Neither GR 82334 nor MEN 10627 had any effect on the apamin- and L-NOARG-resistant NANC i.j.p. Activation of the NK1 or NK2 receptors by the selective receptor agonists, [Sar9]substance P (SP) sulfone and [beta Ala8]neurokinin A (NKA) (4-10), respectively (0.3 microM for 20 s each), produced depolarization with superimposed action potentials and contractions. GR 82334 selectively inhibited the responses to [Sar9]]SP sulfone, without affecting the responses to [beta Ala8]NKA (4-10). MEN 10627 inhibited the responses to [beta Ala8]NKA (4-10), without affecting the responses to [Sar9]SP sulfone. We conclude that both tachykinin NK1 and NK2 receptors co-operate in producing NANC excitation and contraction of the circular muscle in human ileum.

Aged↗
PubMed1997

Sequential activation of the triple excitatory transmission to the circular muscle of guinea-pig colon.

The aim of this study was to resolve the temporal relationships of the triple excitation of the circular muscle of guinea-pig colon that occurs in response to activation of the intrinsic excitatory nerves by using atropine and tachykinin NK1 and NK2 receptor selective antagonists to define the relative contribution of the transmitters involved. In organ bath experiments, performed in the presence of blockers of inhibitory innervation, a train of electrical pulses at 5 Hz for 300 s produced a sustained contraction of the circular muscle of guinea-pig colon: the sequential addition of atropine (1 microM), of the tachykinin NK1 receptor antagonist, SR 140333 (0.3 microM) and of the tachykinin NK2 receptor antagonist, MEN 11420 (1 microM) produced a cumulative inhibitory effect and progressively delayed the onset of the contractile response to nerve stimulation. In the presence of peptidase inhibitors, atropine was less effective in inhibiting the contractile response for prolonged periods of stimulation: however, the pattern of inhibition of the evoked response produced by the sequential addition of blocker drugs was not substantially affected. The selective tachykinin NK3 receptor agonist, senktide, produced a concentration-dependent contraction of guinea-pig colon. The sequential addition of atropine (1 microM), SR 140333 (0.3 microM) and MEN 11420 (1 microM) reproduced the effect of the same drugs on the response to electrical nerve stimulation. The peptide blocker of N-type voltage-dependent calcium channels, omega-conotoxin (0.1 microM) produced a partial inhibitory effect of the response to senktide. The omega-conotoxin-resistant response to 1 microM senktide was inhibited and delayed by the progressive application of atropine, SR 140333 and MEN 11420, similar to the effect observed in the absence of omega-conotoxin. In sucrose gap, single-pulse electrical field stimulation produced a fast excitatory junction potential which was largely (90%) inhibited by atropine; application of a low concentration of the potassium channel blocker, 4-aminopyridine (30 microM), markedly enhanced the atropine-resistant excitatory junction potential which was abolished by the NK1 receptor antagonist, GR 82334. We conclude that, during prolonged electrical or chemical stimulation of excitatory motorneurons, there is a sequential, time-dependent activation of the three excitatory mechanisms in the circular muscle of guinea-pig colon: the pattern of activation is relatively independent of the intensity of stimulation and/or the mechanisms of secretion of released transmitters. Postjunctional factors predominate in determining the relative contribution of the three transmitters, acetylcholine, substance P and neurokinin A, in producing excitation of the circular muscle.

4-Aminopyridine↗
PubMed1997

Tachykinin NK1 and NK2 receptors mediate non-adrenergic non-cholinergic excitatory neuromuscular transmission in the guinea-pig stomach.

By using selective tachykinin NK1 and NK2 receptor antagonists and agonists, we studied the excitatory non-adrenergic non-cholinergic transmission to the circular muscle of the corpus of guinea-pig stomach by the sucrose-gap method. After elimination of inhibitory junction potentials by apamin (0.1 microM), L-nitroarginine (30 microM) and tetraethylammonium (10 mM), electrical field stimulation (10 Hz) in the presence of atropine (1 microM) and nifedipine (1 microM) evoked a pure excitatory junction potential and contraction. The selective tachykinin NK2 receptor antagonist, MEN 11420, concentration-dependently inhibited the non-adrenergic non-cholinergic excitatory junction potential (EC50=0.09 microM) and contraction (EC50=0.04 microM) evoked by electrical field stimulation. On the other hand, the selective NK1 receptor antagonist GR 82334 (3 microM) only slightly (by about 30%) inhibited the excitatory junction potential while leaving the contraction unaffected. The combined administration of GR 82334 (1 microM) and MEN 11420 (0.3 microM) produced an additive inhibition of the excitatoryjunction potential, significantly larger than that produced by each antagonist alone. In the presence of both GR 82334 (1 microM) and MEN 11420 (0.3 microM), the P2 purinoreceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (30 microM) remarkably inhibited the fast component of the excitatory junction potential. In the presence of atropine (1 microM), indomethacin (3 microM) and guanethidine (3 microM) either the selective NK2 receptor agonist, [betaAla8]neurokinin A (4-10) (0.01 microM), or the selective NK1 receptor agonist, [Sar9]substance P sulfone (0.3 microM), produced tetrodotoxin-(1 microM) and nifedipine-(1 microM) resistant depolarization and contraction. The [Sar9]substance P sulfone (0.3 microM)-induced contraction, but not that induced by [betaAla8]neurokinin A (4 10) (0.01 microM), was potentiated by apamin (0.1 microM) plus L-nitroarginine (30 microM). In the presence of atropine (1 microM), indomethacin (3 microM), guanethidine (3 microM), apamin (0.1 microM) and L-nitroarginine (30 microM), the selective tachykinin NK2 and NK1 receptor agonists, [betaAla8]neurokinin A (4-10) and [Sar9]substance P sulfone, both produced a concentration-dependent depolarization and contraction of the circular muscle. MEN 11420 inhibited the responses to [[Ala8]neurokinin A (4-10) without affecting the responses to [Sar9]substance P sulfone, while GR 82334 inhibited the responses to [Sar9]substance P sulfone but not that to [betaAla8]neurokinin A (4-10). These data provide evidence that tachykinin NK2 receptors predominantly mediate the non-adrenergic non-cholinergic excitatory transmission to the circular muscle of the corpus of guinea-pig stomach. In addition, after blocking the non-adrenergic non-cholinergic inhibitory junction potential by apamin, L-nitroarginine and tetraethylammonium, the fast component of the non-adrenergic non-cholinergic excitatory junction potential could be mediated by adenosine triphosphate.

Animals↗
PubMed1997

Evidence for the involvement of P2-purinoceptors in the cholinergic contraction of the guinea-pig ileum.

In the isolated ileum of the guinea-pig the P2-purinoceptor antagonists PPADS and suramin: (a) strongly inhibited the cholinergic contractile effect of alpha,beta-methylene ATP, (b) did not influence contractions evoked by exogenous acetylcholine (ACh) but, (c) moderately (by about 30%) inhibited cholinergic contractions due to electrical field stimulation (EFS), in a non-additive manner. These results suggest that an endogenous ligand that stimulates P2-purinoceptors (possibly ATP) is involved in the contractile effect of EFS, as a positive modulator of ACh release.

Acetylcholine↗
PubMed1997

Characterization of receptors mediating contraction induced by tachykinins in the guinea-pig isolated common bile duct.

1. We studied the effect of the natural tachykinins and of synthetic agonists selective for the tachykinin NK1, NK2 and NK3 receptors, on the motility of guinea-pig isolated common bile duct longitudinally-oriented smooth muscle. 2. All the tachykinins tested (both natural and synthetic) produced a concentration-dependent contractile response of the guinea-pig isolated common bile duct: these effects underwent a marked tachyphylaxis, especially the responses elicited by NK1 and NK3 receptor-selective agonists. 3. Among the natural tachykinins neurokinin B (EC50 = 3.2 nM; 95% c.l. = 2.0-5.1; n = 4) was the most potent, being about 40 and 25 fold more potent than substance P (EC50 = 121.6 nM; 95% c.l. = 94-157; P < 0.01; n = 4) and neurokinin A (EC50 = 83.4 nM; 95% c.l. = 62-112; P < 0.01; n = 4), respectively. Among the synthetic analogues the NK3 receptor-selective agonist senktide (EC50 = 1.1 nM; 95% c.l. = 0.7-1.8; n = 8) was the most potent, being about 120, 110 and 20 fold more potent than [Sar9]substance P sulfone (NK1 receptor-selective) (EC50 = 130.4 nM; 95% c.l. = 99-172; P < 0.01; n = 8), [beta Ala8]NKA (4-10) (NK2 receptor-selective) (EC50 = 120.1 nM; 95% c.l. = 95-151; P < 0.01; n = 8) and septide (NK1 receptor-selective) (EC50 = 22.6 nM; 95% c.l. = 18-28; P < 0.01; n = 8), respectively. All tachykinins (natural or synthetic receptor agonists) produced a similar Emax, averaging about 50% of that produced by KCl (80 mM). 4. Atropine (1 microM) did not affect the responses to either NK1 or NK2 receptor-selective agonists, whereas it reduced the Emax of senktide by about 50%, without affecting its potency (EC50). Tetrodotoxin (1 microM) totally blocked senktide-induced contractions, as did the combined pretreatment with atropine plus the tachykinin NK1 and NK2 receptor-selective antagonists GR 82334 and MEN 11420 (1 microM each), respectively. 5. GR 82334 (1 microM) blocked with apparent competitive kinetics septide- (apparent pKB = 7.46 +/- 0.10; n = 5) and [Sar9]substance P sulfone- (apparent pKB = 6.80 +/- 0.04; n = 4) induced contractions. MEN 11420 (30-300 nM), a novel potent NK2 receptor antagonist, potently antagonized [beta Ala8]NKA (4-10), with competitive kinetics (pKB = 8.25 +/- 0.08; n = 12: Schild plot slope = -0.90; 95% c.l. = -1.4; -0.35). The NK3 receptor-selective antagonist SR 142801 (30 nM) produced insurmountable antagonism of the senktide-induced contractions (Emax inhibited by 64%). None of the above antagonists, tested at the highest concentrations employed against tachykinins, affected the concentration-response curve to methacholine (0.1-300 microM). 6. We conclude that tachykinins produce contraction of the guinea-pig isolated common bile duct by stimulating NK1, NK2 and NK3 receptors. The responses obtained by activating NK1 and NK2 receptors are atropine-resistant. The contraction obtained by stimulating NK3 receptors is totally neurogenic, being mediated by the release of endogenous acetylcholine and tachykinins; the latter act, in turn, on postjunctional tachykinin NK1/NK2 receptors. The role of the NK3 receptor as prejunctional mediator of the excitatory transmission operated by tachykinins is discussed.

Animals↗
PubMed1997

Pharmacological modulation of electromechanical coupling in the proximal and distal regions of the guinea-pig renal pelvis.

1. The effect of drugs affecting calcium and potassium channels and intracellular calcium handling/release on electromechanical coupling in the smooth muscle of the guinea-pig proximal vs. distal renal pelvis were investigated by using the single sucrose gap method. 2. Spontaneous action potentials discharged from the proximal renal pelvis were bell-shaped, did not show a pronounced plateau and had a small after-hyperpolarization. Spontaneous action potentials from the distal renal pelvis were characterized by a fast depolarization, a pronounced plateau and after-hyperpolarization. 3. Nifedipine (1 microM) suppressed action potentials in both regions of the renal pelvis. A submaximally effective concentration of nifedipine (50 nM) shortened action potential duration and reduced contractility in both regions of the renal pelvis. On the other hand Bay K 8644 (1 microM) markedly prolonged the duration of the action potential and increased contractility in both regions of the renal pelvis. 4. Tetraethylammonium (0.5 mM) markedly prolonged the action potential duration and contraction in the distal renal pelvis without affecting action potentials in the proximal renal pelvis. Similar effects were produced by a slightly higher concentration of tetraethylammonium (2 mM) in the proximal renal pelvis. 5. Charybdotoxin (30 nM) markedly prolonged the duration of action potential and increased and prolonged the contraction in both the proximal and distal renal pelvis. 6. 4-aminopyridine (1 mM) selectively increased the frequency of action potentials in the distal renal pelvis without affecting other parameters of the action potential nor contractility. 4-aminopyridine had no effect in the proximal renal pelvis. 7. The inhibitor of sarcoplasmic reticulum Ca-ATPase, cyclopiazonic acid (10 microM) transiently increased the frequency of action potentials in both regions of the renal pelvis; CPA markedly delayed the repolarizing phase of the action potential in both the proximal and distal renal pelvis and, in parallel, increased contractility. 8. We conclude that action potentials generated from the proximal and distal regions of the guinea-pig renal pelvis are evenly dependent upon the availability of L-type Ca channels; that Ca-dependent maxi K channels provide a major contribution to the repolarization of action potentials in both regions of the renal pelvis, thus regulating duration/intensity of Ca influx and contraction; that release of Ca from the internal store is not important in providing activator Ca for contraction but regulates duration of the action potential and may be involved in setting the frequency of discharge of pacemaker cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1997

Effect of cyclopiazonic acid on contractions produced by tachykinin NK1 and NK2 receptor agonists in the circular muscle of guinea-pig colon.

1 This study aimed to assess the effect of cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic reticulum calcium (Ca) pump, against contractile responses produced by selective tachykinin NK1 and NK2 receptor agonists, [Sar9]substance P (SP) sulfone and [beta Ala8]neurokinin A (NKA) (4-10), respectively, on the circular muscle of guinea-pig colon. All experiments were performed in the presence of atropine (1 microM) and indomethacin (10 microM). 2 In organ bath experiments, a submaximally equieffective concentration of the two agonists (10 nM) was selected: [Sar9]SP sulfone (10 nM) produced a biphasic contraction, the two amplitudes averaging 75 +/- 2 and 43 +/- 3% of the maximal response to KCl (80 mM) at 1 and 15 min from application of the agonist, respectively. CPA (3 microM for 60 min) slightly reduced the phasic response to [Sar9]SP sulfone (16 +/- 4% inhibition) and markedly suppressed the tonic component (89 +/- 3% inhibition). 3 The contraction produced by [beta Ala8]NKA (4-10) (10 nM) was more sustained than that induced by the NK1 receptor agonist: it averaged 69 +/- 5 and 73 +/- 4% of the response to KCl at 1 and 15 min from application of the agonist, respectively. CPA slightly and evenly depressed the response to [beta Ala8]NKA (4-10) (18 +/- 7 and 21 +/- 5% inhibition at 1 and 15 min). 4 In the presence of tachykinin NK1 and NK2 receptor antagonists (SR 140333 and MEN 10627, respectively, 1 microM each) and of L-nitroarginine (100 microM), KCl (40 mM) produced a distinct phasic and tonic contraction which was suppressed by 1 mM nifedipine. CPA (3 microM) did not affect the phasic contraction to KCl but abolished the tonic component of the response. 5 In the presence of 1 microM nifedipine, the response to [beta Ala8]NKA (4-10) was slightly depressed (32 +/- 6% inhibition) in its early component only, while the response to [Sar9]SP sulfone was abolished. CPA produced a slight inhibition (15 +/- 9 and 33 +/- 10% at 1 and 15 min, respectively) of the nifedipine-resistant response to [beta Ala8]NKA (4-10), an effect similar to that observed in the absence of nifedipine. Therefore, a large part of the response to [beta Ala8]NKA (4-10) persisted in the presence of both CPA and nifedipine. 6 In the sucrose gap, a prolonged superfusion with [Sar9]SP sulfone (0.1 microM for 5 min) produced sustained depolarization with superimposed spikes and contraction. CPA (3 microM) produced transient depolarization and contraction. In the presence of CPA, the initial responses (depolarization, spikes and contraction) to [Sar9]SP sulfone were unaffected but the sustained component of contraction was absent; the latter effect was accompanied by a suppression of spikes while the sustained depolarization was present. 7 We conclude that, during sustained depolarization produced by the NK1 receptor agonist, blockade of the sarcoplasmic reticulum Ca pump by CPA produces a faster Ca-dependent inactivation of Ca channels, thereby eliminating spikes and abolishing the tonic component of contraction. Ca mobilization/reuptake from a CPA-sensitive store seems to be of minor importance for regulating the NK2 receptor-mediated contractile responses.

Animals↗
PubMed1997

Nitric oxide promotes proliferation and plasminogen activator production by coronary venular endothelium through endogenous bFGF.

We reported previously that NO is responsible for the angiogenesis produced by endothelium-dependent vasodilating peptides. To investigate the mechanisms by which NO controls angiogenesis, NO was assessed for the ability to affect cell proliferation and upregulation of urokinase-type plasminogen activator (uPA) induced by basic fibroblast growth factor (bFGF) when added exogenously to or when produced endogenously by coronary venular endothelial cells (CVECs). The treatment of the cells with the NO donor sodium nitroprusside (NaNp) induced uPA upregulation and cell proliferation, which were prevented by anti-bFGF antibodies. Similarly, the NO-dependent mitogenic activity of the vasodilating peptide substance P (SP) was blocked by anti-bFGF antibodies, thus implicating endogenous bFGF in the NO-induced response. NaNp and SP induced bFGF expression as measured by Western blot analysis of CVEC extracts and by differential reverse transcriptase-polymerase chain reaction of bFGF mRNA. SP-induced upregulation of bFGF was prevented by the NO synthase inhibitor N omega-monomethyl-L-arginine. We conclude that NO promotes cell proliferation and uPA upregulation in CVECs by inducing endogenous bFGF and that this pathway mediates the angiogenetic response to the vasoactive neuropeptide SP. This signaling paradigm may provide an important link between shear rate, NO, bFGF, and coronary angiogenesis.

Cell Division↗
PubMed1997

Role of tachykinin NK1 and NK2 receptors on colonic motility in anesthetized rats: effect of agonists.

Tachykinins fulfill general criteria to be considered as neurotransmitters-neuroeffectors in the mammalian enteric nervous system; however, little information is available about their role in the regulation of intestinal motility in vivo. The present study investigates the effect of selective tachykinin receptor agonists on colonic motility in urethane-anesthetized rats. Colonic motility was recorded by means of a balloon-catheter device (filled with 0.5 mL of water) inserted for 7 cm through the rectum. In atropine- and guanethidine-pretreated rats, the NK1 receptor agonist [Sar9]substance P sulfone (0.3-300 nmol/kg i.v.) dose dependently induced phasic contractions followed by an enhancement in the amplitude and frequency of spontaneous contractions. In three of six cases, a transient inhibition (3-5 min) of spontaneous motility was also evident after the phasic contraction. All these effects were reduced by the NK1 receptor antagonist SR 140333 (1 mumol/kg i.v.). In atropine- and guanethidine-pretreated rats and in the presence of SR 140333 (1 mumol/kg i.v.), the NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) (0.3-300 nmol/kg i.v.) induced a dose-dependent tonic contraction, but the amplitude and frequency of spontaneous contractions were not changed. NK2 receptor antagonists such as MEN 11420 (0.01-1 mumol/kg i.v.), MEN 10627 (1 mumol/kg i.v.), or SR 48968 (1 mumol/kg i.v.) reduced the effect of [beta-Ala8]neurokinin A-(4-10). The present results indicate that NK2 receptor stimulation evokes a pure excitatory effect on colonic motility whereas NK1 receptor stimulation induces both excitatory and inhibitory effects.

Anesthesia↗
PubMed1997

Tachykinin receptors and intestinal motility.

Substance P (SP) and neurokinin A (NKA) are synthesized by enteric cholinergic motorneurons that project to the longitudinal and circular muscle of the mammalian intestine. Thus, acetylcholine, SP, and NKA are the excitatory neuromuscular transmitters in the intestine. Tachykinin NK1 and NK2 receptors are expressed by smooth muscle cells in most regions of the intestine: the corelease of SP and NKA from nerves thus realizes paradigms of tachykininergic cotransmission. Examples have been found in which a cooperative model can be applied to account for the action of SP-NKA acting at NK1 and NK2 receptors (e.g., circular muscle of guinea-pig duodenum), as well as examples in which the message produced by activation of the two receptors diverges sharply in producing responses that have a markedly different time course and use different effector systems (e.g., circular muscle of guinea-pig colon). NK3 receptors are expressed on both excitatory and inhibitory motor neurons: indirect contractions (via release of acetylcholine and tachykinins) and relaxations (via release of nitric oxide) can be evoked in the gut by selective stimulation of NK3 receptors. Although a role of NK3 receptors in certain enteric reflexes has been evidenced, the importance of this system in mediating hexamethonium-resistant enteric transmission appears less important than previously speculated.

Animals↗
PubMed1996

A review of the design, synthesis and biological activity of the bicyclic hexapeptide tachykinin NK2 antagonist MEN 10627.

We review the reported data on the design, the conformational features and the pharmacological properties of the bicyclic peptide tachykinin NK2 receptor antagonist MEN 10,627 or cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2 beta-5 beta). MEN 10,627 possesses a highly constrained structure characterized by two consecutive beta-turns, as confirmed by the almost coincident results of NMR and X-ray analyses. The compound has been efficiently synthesized by solid-phase methodology using either Boc or Fmoc strategies. It is quite stable to metabolic degradation and is endowed with high affinity and selectivity for NK2 receptor expressed in various species. At the hamster NK2 receptor MEN 10,627 is about 30-fold more potent than the nonpeptide NK2 receptor antagonist, SR 48,968, while the converse is true for the rabbit NK2 receptor. MEN 10,627 and SR 48,968 show comparable affinities for the human NK2 receptor. MEN 10,627 produces a long lasting inhibition of the response to the selective NK2 receptor agonist [beta Ala8]NKA(4-10) in the rat urinary bladder in vivo after intravenous, intranasal and intraduodenal administration. Therefore different administration routes are possible for this compound that overcomes the usual drawbacks for the application of peptides as drugs.

Animals↗
PubMed1996

Effect of niflumic acid on electromechanical coupling by tachykinin NK1 receptor activation in rabbit colon.

We have investigated the effect of the Cl- channel blocker, niflumic acid, on the contractile response and electromechanical coupling activated by stimulation of the tachykinin NK1 receptor in the longitudinal muscle of rabbit proximal colon, in the presence of indomethacin (5 microM). The application of submaximal equieffective concentrations of the tachykinin NK1 receptor-selective agonist [Sar9]substance P sulfone (30 nM), of carbachol (300 nM) and KCl (40 mM), produced distinct phasic and tonic components of contraction. Niflumic acid (10-100 microM) preferentially and markedly inhibited the tonic component of the response to [Sar9]substance P sulfone and to carbachol, without affecting the response to KCl. Nifedipine (1 microM) abolished the response to KCl and greatly reduced the response to [Sar9]substance P sulfone and carbachol. The nifedipine-resistant response to [Sar9]substance P sulfone was attenuated by niflumic acid (100 microM), while that to carbachol was unaffected. In sucrose gap experiments, superfusion with niflumic acid (100 microM), in the presence of nifedipine (3 microM), produced membrane hyperpolarization, which was totally blocked by tetraethylammonium (10 mM). Niflumic acid inhibited both depolarization and contraction induced by [Sar9]substance P sulfone, both in the absence or in the presence of tetraethylammonium. The present findings support the idea that a niflumic acid-sensitive mechanism, probably an effect on Cl- channels, takes part in the post-receptorial events activated by tachykinin NK1 receptor stimulation in the longitudinal muscle of rabbit colon, and suggest that this mechanism would be more important for generating the sustained tonic than the phasic component of contraction.

Animals↗
PubMed1996

Calcitonin gene-related peptide (CGRP) in the circular muscle of guinea-pig colon: role as inhibitory transmitter and mechanisms of relaxation.

In the presence of 1 microM tetrodotoxin (TTX), human alpha calcitonin gene-related peptide (CGRP) produced a concentration-dependent relaxation (EC50 1.1 nM; Emax 86% of the relaxation to 1 microM isoprenaline) of mucosa-free circular muscle strips from the guinea-pig proximal colon. In the presence of TTX, the C-terminal fragment CGRP(8-37) produced a concentration (0.3-3 microM)-dependent rightward shift of the curve to CGRP. The TTX-resistant, receptor-mediated, CGRP-induced relaxation was unaffected by apamin (0.3 microM) and L-nitroarginine (L-NOARG, 100 microM), alone or in combination, as well as by glibenclamide (3 microM) or (S)-ketoprofen (10 microM). Tetraethylammonium (TEA, 1-10 mM) and cyclopiazonic acid (CPA, 3-10 microM) produced a concentration-dependent partial inhibition of the relaxant response to CGRP. The inhibitory effect of TEA on the maximal relaxation produced by CGRP was prevented by nifedipine (1 microM) which did not affect the CGRP-relaxation of its own. In the presence of atropine (1 microM), guanethidine (3 microM), SR 140,333 (0.3 microM), MEN 10,627 (1 microM), apamin (0.3 microM) and L-NOARG (100 microM), the application of 1 microM capsaicin produced a transient relaxation of the strips. This response was not reproduced upon a second application of capsaicin, 60 min later, indicating complete desensitization. CGRP(8-37) (0.3-1.0 microM) produced a partial inhibitory effect (about 50% inhibition) of the relaxant response to capsaicin. In the presence of atropine (1 microM), guanethidine (3 microM), SR 140,333 (0.3 microM), MEN 10,627 (1 microM), apamin (0.3 microM), L-NOARG (100 microM) and after capsaicin in vitro pretreatment (10 microM for 15 min), electrical field stimulation (EFS, 10 Hz for 5 s) produced a transient relaxation which was unchanged by CGRP(8-37) (1 microM) while being abolished by TTX. In sucrose gap, brief superfusion with 0.3 microM CGRP produced a TTX (1 microM)- resistant membrane hyperpolarization and relaxation: the hyperpolarization produced by CGRP was inhibited by about 50% by either TEA (10 mM) or CPA (10 microM), while being unaffected by glibenclamide (3 microM). The combined application of TEA and CPA was not more effective (65% inhibition) in inhibiting the CGRP-induced hyperpolarization than each drug alone. We conclude that CGRP produces a direct relaxation of the circular muscle of the guinea-pig proximal colon by activating receptors sensitive to blockade by CGRP(8-37). Activation of Ca-dependent potassium channels and Ca release/reuptake from internal store(s) appear both to be involved in the action of CGRP. Endogenous CGRP mediates part of the relaxant response evoked by stimulation of capsaicin-sensitive primary afferent nerves in the circular muscle of guinea-pig colon, while it is not involved in the apamin and L-NOARG-resistant nonadrenergic noncholinergic (NANC) relaxation produced by electrical field stimulation of intrinsic inhibitory nerves.

Amino Acid Sequence↗