gr-82334 and septide

1. The presence of tachykinin NK1 receptors have been shown in the epithelium and smooth muscle of guinea-pig airways. Previous data showed that substance P (SP), and the NK1 receptor agonist, [Sar9, Met (O2)11]-SP, relax guinea-pig tracheal tube preparations by stimulation of epithelial NK1 receptors and via nitric oxide (NO) release. However, the selective tachykinin NK1 receptor agonist, septide, was unable to produce this effect. The aim of the present study was to investigate the ability of a series of SP analogues to stimulate NK1 receptors of guinea-pig airway epithelium. 2. Isometric tension was recorded in isolated tracheal tube preparations in which compounds were administered intraluminally in the presence of phosphoramidon, indomethacin (both 1 microM) and the tachykinin NK2 receptor antagonist, SR 48,968 ((S)-N-methyl N-(4-acetyl-amino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl)benzam ide) (0.1 microM). Cumulative concentration-response curves were obtained in preparations under resting tone or in preparations precontracted with acetylcholine (ACh, 10 microM). 3. Contractile responses to low concentrations (0.1-10 nM) of substance P (SP) and the selective agonist of NK1 receptors, [Pro9]-SP. in non precontracted tracheae were higher in preparations pretreated with the NO-synthase inhibitor, NG-monomethyl L-arginine (L-NMMA, 100 microM) than in preparations pretreated with its inactive enantiomer D-NMMA (100 microM). Tracheal tube preparations precontracted with ACh and pretreated with D-NMMA were relaxed by low concentrations of SP and [Pro9]-SP (0.1-10 nM). In contrast, after pretreatment with L-NMMA, SP and [Pro9]-SP contracted tracheae at all the concentrations tested. 4. Concentration-response curves to the NK1 receptor agonists, SP methyl ester, [Apa9-10]-SP and [pGlu6] SP (6-11) obtained in non-precontracted tracheae were similar in the presence of either D-NMMA or L-NMMA. SP methyl ester, [Apa9-10]-SP and [pGlu6] SP (6-11) did not produce any relaxation, but instead, cause contractions in tracheal tube preparations precontracted with ACh and pretreated with D-NMMA. Concentration-response curves produced by all these agonists were similar in preparations precontracted with ACh and pretreated with L-NMMA or D-NMMA. 5. In guinea-pig tracheal tube preparations two groups of NK1 receptor agonists can be distinguished: one group, including [Pro9]-SP, stimulator epithelial NK1 receptors, the other group, including SP methyl ester, [Apa9-

Topics: Animals; Dose-Response Relationship, Drug; Epithelium; Guinea Pigs; Male; Muscle, Smooth; Neurokinin-1 Receptor Antagonists; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Peptide Fragments; Physalaemin; Piperidines; Pyrrolidonecarboxylic Acid; Quinuclidines; Receptors, Neurokinin-1; Substance P; Tachykinins; Trachea

Intravenous administration of the undecapeptide [Sar9]substance P (SP) sulfone (1.5 nmol/kg) and the hexapeptide [Glp6,Pro9]SP(6-11) (septide; 0.4 nmol/kg) produced a comparable (about 30-40% of maximal effect) increase of insufflation pressure (bronchospasm) in anesthetized guinea-pigs. The non peptide NK-1 receptor antagonist, (+/-)CP 96,345 and the peptide NK-1 receptor antagonist, GR 82,334 antagonized dose-dependently the response to both agonists. Both antagonists were more potent against septide than against [Sar9]SP sulfone (9 and 4 fold difference in ED50 for (+/-)CP 96,345 and GR 82,334, respectively). These findings indicate that a 'septide-sensitive' mechanism mediates bronchoconstriction in vivo and it influences the estimate of the potency of NK-1 receptor antagonists.

Topics: Animals; Biphenyl Compounds; Bronchial Spasm; Bronchoconstriction; Dose-Response Relationship, Drug; Guinea Pigs; Hypnotics and Sedatives; Male; Peptide Fragments; Physalaemin; Pyrrolidonecarboxylic Acid; Receptors, Tachykinin; Substance P; Sulfones

In the guinea-pig ileum tissue, [Pro9]substance P, a tachykinin NK1 receptor selective agonist and septide, [pGlu6,Pro9]-substance P-(6-11), do not interact with the same receptor as shown by the different inhibitory profiles of GR 72251 and [D-Pro9,Pro10,Trp11]substance P. Substitution at position 10 of the D-Pro9-Pro10 moiety with bulky N-methylated amino acids increased the antagonist potency for the tachykinin NK1 receptor without affecting that for the 'septide-sensitive receptor'. The incorporation of a trans-beta-L-substituted proline in position 10, for example a benzyl group (beta-benzyl-L-proline), afforded a potent antagonist active in the nanomolar range. For GR 82334, this increase in potency was obtained at the expense of selectivity for tachykinin NK1 and 'septide-sensitive' receptors.

Topics: Amino Acid Sequence; Animals; Guinea Pigs; Ileum; In Vitro Techniques; Male; Molecular Sequence Data; Muscle Contraction; Muscle, Smooth; Neurokinin-1 Receptor Antagonists; Peptide Fragments; Physalaemin; Pyrrolidonecarboxylic Acid; Rabbits; Rats; Receptors, Neurokinin-1; Structure-Activity Relationship; Substance P

The neuromodulatory actions of Septide, a selective neurokinin-1 (NK-1) agonist, and substance P (SP) were investigated in isolated rabbit tracheal smooth muscle (TSM) segments. The tissues were placed in organ baths containing modified Krebs-Ringer solution and contracted with either the agonists or electrical field stimulation (ES) with frequencies ranging from 1 to 50 Hz. The neutral endopeptidase (NEP) inhibitor, phosphoramidon (10(-6) M), had no significant effect on Septide-mediated contractions. Septide-mediated contractions were augmented in the presence of neostigmine, eliminated in the presence of atropine, and diminished in the presence of tetrodotoxin. Both SP and Septide increased ES-induced contractions in a dose-dependent manner. On the other hand, the presence of both Septide and SP did not further augment this neuromodulatory action. After NK-1 desensitization, Septide-mediated contractions were also virtually eliminated; however, the peptide's neuromodulatory action was unaffected. In contrast, the presence of GR-82334, a selective NK-1 antagonist, eliminated Septide's neuromodulatory activity. These findings provide evidence that 1) NK-1 receptors facilitate both the direct release of ACh as well as augment the release of ACh by ES and 2) the cholinergic pathways involved with these two processes may represent different mechanisms.

Topics: Acetylcholine; Animals; Electric Stimulation; In Vitro Techniques; Muscle Contraction; Muscle, Smooth; Nervous System Physiological Phenomena; Parasympathetic Nervous System; Peptide Fragments; Physalaemin; Pyrrolidonecarboxylic Acid; Rabbits; Receptors, Neurokinin-1; Substance P; Synaptic Transmission; Tetrodotoxin; Trachea