Comparison of the effects of epithelium removal and of an enkephalinase inhibitor on the neurokinin‐induced contractions of guinea‐pig isolated trachea

1 The ability of peptidases to restrict neurokinin 1 receptor (NK1R) activation by exogenously applied or endogenously released neurokinins was investigated by measuring NK1R internalization in rat spinal cord slices. 2 Concentration -response curves for substance P and neurokinin A were obtained in the presence and absence of 10 mM thiorphan, an inhibitor of neutral endopeptidase (EC 3.4.24.11), plus 10 mM captopril, an inhibitor of dipeptidyl carboxypeptidase (EC 3.4.15.1). These inhibitors significantly decreased the EC 50 of substance P to produce NK1R internalization from 32 to 9 nM, and the EC 50 of neurokinin A from 170 to 60 nM. 3 Substance P was significantly more potent than neurokinin A, both with and without these peptidase inhibitors. 4 In the presence of peptidase inhibitors, neurokinin B was 10 times less potent than neurokinin A and 64 times less potent than substance P (EC 50 ¼ 573 nM). 5 Several aminopeptidase inhibitors (actinonin, amastatin, bacitracin, bestatin and puromycin) failed to further increase the effect of thiorphan plus captopril on the NK1R internalization produced by 10 nM substance P. 6 Electrical stimulation of the dorsal root produced NK1R internalization by releasing endogenous neurokinins. Thiorphan plus captopril increased NK1R internalization produced by 1 Hz stimulation, but not by 30 Hz stimulation. 7 Therefore, NEN and DCP restrict NK1R activation by endogenous neurokinins when they are gradually released by low-frequency firing of primary afferents, but become saturated or inhibited when primary afferents fire at a high frequency.

Section: Jcg Marvizón Et Al Effect Of Peptidases On Nk1r Internalisupporting

confidence: 83%

Effect of peptidases on the ability of exogenous and endogenous neurokinins to produce neurokinin 1 receptor internalization in the rat spinal cord

Marvizón¹,

Wang

Lao³

et al. 2003

“…Therefore, since no significant differences were observed between the 30 and 60min challenge period (P > 0.05), the 60 min period was selected for all subsequent experiments. The enkephalinase inhibitor, thiorphan has been shown to enhance the effector responses to exogenous and endogenous tachykinins in different muscle tissues (Devillier et al, 1988;Maggi et al, 1989). …”

Section: Chemicalsmentioning

confidence: 99%

Tachykinins activate guinea‐pig alveolar macrophages: involvement of NK₂ and NK₁ receptors

Brunelleschi

Vanni

Ledda

et al. 1990

105

1 The effects of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were evaluated on superoxide anion (0 1) production by guinea-pig alveolar macrophages (AM).2 SP dose-dependently (ED50 = 0.7 nM) evoked 01 production from guinea-pig AM; the N-terminal heptapeptide, SP(1-7), was ineffective. In the presence of thiorphan (10-M), an enkephalinase inhibitor, the stimulating effects of SP were not significantly modified. NKA and NKB were both able to induce 01 production from guinea-pig AM, ED50 values being 0.1 and 1.3 nm, respectively. Therefore, the rank order of activity of natural tachykinins was NKA > SP > NKB. Tachykinin-evoked effects were quantitatively similar to those elicited by the autacoid mediator PAF-acether and less than those induced by the synthetic peptide N-formylmethionyl-leucyl-phenylalanine (FMLP). 3The NK2 receptor agonist [fi-Ala8]-NKA (4-10) dose-dependently evoked 01 production from guinea-pig AM; the NK1 receptor agonist [Pro9]-SP sulphone acted only at high concentrations, while the NK3 receptor agonist [Me,Phe7]-NKB was ineffective. 4 These findings indicate that guinea-pig AM possess NK2 and possibly some NK1 tachykinin receptors and further suggest tachykinin involvement in lung pathophysiology.

“…Removal of epithelium from tracheal or bronchial strips potentiates the contractile response to SP and NKA by inhibiting tachykinin cleavage and inactivation (Devillier et al, 1988;Frossard et al, 1989). In addition, pretreatment of airway tissue with phosphoramidon, a potent inhibitor of NEP, significantly enhances tachykinin-induced contraction of the smooth muscle (Black et al, 1988;Lotvall et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by substance P, neurokinin A and VIP

Ben‐Jebria

Marthan

Rossetti

et al. 1993

1 The effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by the following neuropeptides substance P (SP), neurokinin A (NKA) and vasoactive intestinal peptide (VIP) was studied both in the absence and in the presence of the neutral endopeptidase (NEP) inhibitor, phosphoramidon. 2 Cumulative concentration-response curves (CCRC) to these neuropeptides were constructed in human passively sensitized isolated bronchial rings and compared to those in paired controls. Passively sensitized human isolated bronchial rings were tissues incubated overnight in serum from asthmatic patients atopic to Dermatophagoides pteronyssinus and paired controls were tissues originating from the same lung specimens but incubated overnight in serum from healthy donors. 3 In the absence of phosphoramidon, passive sensitization significantly increased the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 50 ± 5% to 76 + 6% (n = 5, P<0.05) and from 70 ± 7% to 101 ± 6% (n = 5, P<0.05) of the maximal response to acetylcholine, respectively. Passive sensitization significantly shifted to the left the CCRC for both tachykinins as measured by the geometric means dose-ratios which were 8.5 (95% confidence limits (CL): 3.1-13.9) and 7.3 (95% CL: 4.2-10.3) for SP and NKA, respectively. 4 In the presence of phosphoramidon (10 gM), passive sensitization still increased significantly the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 74 ± 4% to 115 + 7% (n = 5, P<0.05) and from 104 ± 9% to 146 + 16% (n = 5, P<0.05) of the maximal response to acetylcholine, respectively. Passive sensitization still significantly shifted to the left the CCRC for both tachykinins as measured by the dose-ratios which were 9.0 (95% CL: 4.3-13.6) and 5.4 (95% CL: 2.9-7.9) for SP and NKA, respectively. 5 The relaxant response to the maximal concentration of VIP given in tissues precontracted with histamine (0.5 mM) was significantly reduced by passive sensitization from 41 ± 4% to 25 + 3% (n = 5, P <0.05) of the amplitude of the precontraction in the absence of phosphoramidon and from 72 + 1% to 49 ± 4% (n = 5, P<0.05) in the presence of phosphoramidon (10 4M). Passive sensitization significantly shifted to the right the CCRC for VIP as measured by the dose-ratios which were 10.4 (95% CL: 6.6-14.1) and 6.4 (95% CL: 3.0-9.8) in the absence and in the presence of phosphoramidon, respectively. 6 We conclude that passive sensitization enhances the mechanical response to neuropeptides which contract human isolated bronchial smooth muscle and reduces that to a neuropeptide which relaxes it. The mechanism of passive sensitization-induced changes in the mechanical activity appears to be independent of a decrease in NEP activity since these changes persist in the presence of the NEP inhibitor, phosphoramidon.