Neutral endopeptidase inhibitors potentiate substance P-induced contraction in gut smooth muscle

To determine the role of endogenous neutral endopeptidase (NEP), also called enkephalinase (EC 3.4.24.11), in regulating tachykinin-induced contraction of gut smooth muscle, we studied the effects of NEP inhibitors on the contractile responses to substance P (SP) in isolated longitudinal strips of ileum or duodenum in rats and ferrets. Leucine-thiorphan and phosphoramidon shifted the concentration-response curves of SP to lower concentrations in all tissues studied, but the sensitivity to SP was greater and the effect of leucine-thiorphan was less in the ferret, a finding that correlated with the observation that the ferret ileum contained substantially less NEP activity than rat ileum. Captopril, bestatin, MGTA, leupeptin, and physostigmine did not alter contractile responses to SP, suggesting that kininase II, aminopeptidases, carboxypeptidase N, serine proteinases, and acetylcholinesterase do not modulate the SP-induced effects. These studies suggest that, in the ileum and duodenum, NEP modulates the actions of SP and, furthermore, that the sensitivity of tissues may be determined, at least in part, by the amount of enzymatically active NEP present.

Download Full-text

Neutral endopeptidase modulates neurotensin-induced airway contraction

Journal of Applied Physiology ◽

10.1152/jappl.1989.66.5.2338 ◽

1989 ◽

Vol 66 (5) ◽

pp. 2338-2343 ◽

Cited By ~ 9

Author(s):

T. D. Djokic ◽

D. J. Dusser ◽

D. B. Borson ◽

J. A. Nadel

Keyword(s):

Smooth Muscle ◽

Serine Proteases ◽

Neutral Endopeptidase ◽

Smooth Muscle Contraction ◽

Response Curves ◽

Terminal Fragment ◽

Carboxypeptidase N

To determine the role of endogenous neutral endopeptidase (NEP) (also called enkephalinase, EC 3.4.24.11) in regulating neurotensin-induced airway contraction, we used phosphoramidon, a specific NEP inhibitor, in the guinea pig. In studies in vitro, neurotensin and the COOH-terminal fragment neurotensin-(8–13) contracted strips of bronchial smooth muscle in a concentration-dependent fashion (P less than 0.001). In contrast, the NH2-terminal fragment neurotensin-(1–11) and the COOH-terminal fragment neurotensin-(12–13), the main fragments of neurotensin hydrolysis by NEP, had no effect. Phosphoramidon (10(-5) M) did not change resting tension but shifted the concentration-response curves to neurotensin to lower concentrations (P less than 0.001), whereas inhibitors of kininase II, aminopeptidases, serine proteases, and carboxypeptidase N were without effect. Removing the epithelium increased the contractile response to neurotensin (P less than 0.001), and phosphoramidon further increased the response to neurotensin in these tissues (P less than 0.001). Similar results were obtained in studies in vivo using aerosolized neurotensin and phosphoramidon. These results suggest that endogenous NEP in the airways modulates the effects of neurotensin on airway smooth muscle contraction by inactivating the peptide.

Download Full-text

Enkephalinase inhibitor potentiates substance P- and electrically induced contraction in ferret trachea

Journal of Applied Physiology ◽

10.1152/jappl.1987.63.4.1401 ◽

1987 ◽

Vol 63 (4) ◽

pp. 1401-1405 ◽

Cited By ~ 92

Author(s):

K. Sekizawa ◽

J. Tamaoki ◽

J. A. Nadel ◽

D. B. Borson

Keyword(s):

Smooth Muscle ◽

Substance P ◽

Response Curve ◽

Electrical Field Stimulation ◽

Smooth Muscle Contraction ◽

Field Stimulation ◽

Electrical Field ◽

Contractile Responses ◽

Cholinergic Neurotransmission

To determine the role of endogenous enkephalinase (EC 3.4.24.11) in regulating peptide-induced contraction of airway smooth muscle, we studied the effect of the enkephalinase inhibitor, leucine-thiorphan (Leu-thiorphan), on responses of isolated ferret tracheal smooth muscle segments to substance P (SP) and to electrical field stimulation (EFS). Leu-thiorphan shifted the dose-response curve to SP to lower concentrations. Atropine or the SP antagonist [D-Pro2,D-Trp7,9]SP significantly inhibited SP-induced contractions in the presence of Leu-thiorphan. Leu-thiorphan increased the contractile responses to EFS dose dependently, an effect that was significantly inhibited by the SP antagonist [D-Pro2,D-Trp7,9]SP. SP, in a concentration that did not cause contraction, increased the contractile responses to EFS. This effect was augmented by Leu-thiorphan dose dependently and was not inhibited by hexamethonium or by phentolamine but was inhibited by atropine. Because contractile responses to acetylcholine were not significantly affected by SP or by Leu-thiorphan, the potentiating effects of SP were probably on presynaptic-postganglionic cholinergic neurotransmission. Captopril, bestatin, or leupeptin did not augment contractions, suggesting that enkephalinase was responsible for the effects. These results suggest that endogenous tachykinins modulate smooth muscle contraction and endogenous enkephalinase modulates contractions produced by endogenous or exogenous tachykinins and tachykinin-induced facilitation of cholinergic neurotransmission.

Download Full-text

Neurokinin receptors mediating substance P-induced contraction in adult rabbit airways

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1990.258.2.l99 ◽

1990 ◽

Vol 258 (2) ◽

pp. L99-L106 ◽

Cited By ~ 1

Author(s):

J. A. Cook ◽

S. L. Brunner ◽

D. T. Tanaka

Keyword(s):

Smooth Muscle ◽

Substance P ◽

Regional Differences ◽

Receptor Agonist ◽

Neutral Endopeptidase ◽

Ringer Solution ◽

Adult Rabbit ◽

Isometric Contractions ◽

Neurokinin Receptors ◽

Contractile Responses

Airway contractile responses to substance P (SP) were examined in isolated adult rabbit bronchial (BSM) and tracheal smooth muscle (TSM) segments. The tissues were placed in organ baths containing modified Krebs-Ringer solution, and isometric contractions to SP were monitored in the presence of phosphoramidon, an inhibitor of neutral endopeptidase (NEP). Under these conditions, BSM segments were significantly more reactive and more sensitive to SP than TSM segments. Removal of SPs cholinergic component with atropine (ATP) eliminated these regional differences in reactivity without affecting sensitivity. In considering the basis for these observations, it has been suggested that SP activates up to three different neurokinin (NK) subset receptors. Accordingly, we examined the regional airway contractile responses to Senktide, a selective NK-3 receptor agonist, and Septide, a selective NK-1 receptor agonist. In the presence of ATR, Senktide was inactive in both BSM and TSM, whereas Septide produced significantly greater contractions in BSM than in TSM. Subsequent desensitization of NK-1 receptors with Septide virtually eliminated the regional differences in airway sensitivity to SP. These findings indicate that 1) endogenous NEP activity can mask significant regional airway differences in SP-mediated contraction; and 2) these latter differences are the result of cholinergic, NK-1, and NK-2 receptor influences.

Download Full-text

Role of neutral endopeptidase and kininase II on substance P-induced increase in nasal obstruction in patients with allergic rhinitis.

American Journal of Respiratory and Critical Care Medicine ◽

10.1164/ajrccm.149.1.7509244 ◽

1994 ◽

Vol 149 (1) ◽

pp. 113-117 ◽

Cited By ~ 5

Author(s):

A Lurie ◽

J A Nadel ◽

G Roisman ◽

H Siney ◽

D J Dusser

Keyword(s):

Allergic Rhinitis ◽

Substance P ◽

Nasal Obstruction ◽

Neutral Endopeptidase ◽

Kininase Ii

Download Full-text

Tachykinin recovery during postmortem bronchoconstriction in guinea pig lungs

Journal of Applied Physiology ◽

10.1152/jappl.1991.70.3.1215 ◽

1991 ◽

Vol 70 (3) ◽

pp. 1215-1219 ◽

Cited By ~ 7

Author(s):

M. A. Martins ◽

S. A. Shore ◽

J. M. Drazen

Keyword(s):

Substance P ◽

Guinea Pig ◽

Neutral Endopeptidase ◽

Neurokinin A ◽

Opening Pressure ◽

Airway Opening ◽

Isolated Lungs ◽

Peak Value

We examined the role of substance P (SP) and neurokinin A (NKA) in the postmortem bronchoconstriction in guinea pig lungs using isolated lungs superfused via the trachea. Airway opening pressure (Pao) during superfusion was monitored and the superfusate collected for analysis of SP- and NKA-like immunoreactivities (SP-LI and NKA-LI, respectively). Peak Pao (39.0 +/- 3.9 cmH2O) was reached 10 min after starting superfusion; Pao decreased slowly thereafter, reaching only 9.9 +/- 2.2% of the peak value 2 h after starting superfusion (P less than 0.005); 12.6 +/- 2.6 and 34.0 +/- 9.7 fmol of SP-LI and NKA-LI, respectively, were found in the fraction corresponding to 10-20 min of superfusion. Recovered immunoreactivities decreased to 5.2 +/- 0.3 and 9.3 +/- 1.8 fmol of SP-LI and NKA-LI, respectively, in the fraction corresponding to 110-120 min of superfusion (P less than 0.05). Inhibition of neutral endopeptidase with thiorphan resulted in significantly greater increases in Pao (P less than 0.005) and augmentation of the recovery of SP-LI and NKA-LI (P less than 0.05 and P less than 0.001, respectively). Capsaicin treatment of animals 7-10 days before the removal of their lungs abolished the increase in Pao during superfusion and resulted in a significant decrease in the amount of SP-LI and NKA-LI recovered. Our data confirm that tachykinin release occurs during postmortem bronchoconstriction in guinea pig lungs and, furthermore, that tachykinin degradation by NEP modulates the intensity of this response.

Download Full-text