G. Piedimonte

Neutral endopeptidase and kininase II mediate glucocorticoid inhibition of neurogenic inflammation in the rat trachea.

Glucocorticoids inhibit plasma extravasation induced in the rat tracheal mucosa by substance P and other tachykinins released from sensory nerves. This study was performed to determine whether this antiinflammatory effect of glucocorticoids is mediated by the tachykinin-degrading enzymes neutral endopeptidase (NEP) and kininase II (angiotensin converting enzyme, ACE). In addition, we studied the effect of dexamethasone on a nonpeptide inflammatory mediator, platelet-activating factor (PAF), which is not degraded by NEP or ACE. Adult male pathogen-free F344 rats were treated for 2 d with dexamethasone (0.5 mg/kg per d i.p.), or with the vehicle used to dissolve the steroid. The magnitude of plasma extravasation produced by an intravenous injection of substance P (5 micrograms/kg) or PAF (10 micrograms/kg) was then assessed by using Monastral blue pigment as an intravascular tracer. The role of NEP and ACE activities in the changes produced by dexamethasone was investigated by examining the effect of the selective inhibitors of these enzymes, phosphoramidon and captopril. Dexamethasone reduced the substance P-induced extravasation by 57% but did not affect the PAF-induced extravasation. The suppressive effect of dexamethasone on substance P-induced extravasation was completely reversed by simultaneously inhibiting NEP and ACE activities, but the inhibition of these enzymes had no effect on PAF-induced extravasation, regardless of whether the rats were pretreated with dexamethasone or not. These results suggest that NEP and ACE mediate a selective inhibitory effect of glucocorticoids on neurogenic plasma extravasation.

Neutral endopeptidase in the heart: Neutral endopeptidase inhibition prevents isoproterenol-induced myocardial hypoperfusion in rats by reducing bradykinin degradation

Peptide mediators may play a role in the control of myocardial perfusion. We found immunohistochemical evidence of the peptide-degrading enzyme neutral endopeptidase (NEP) in cultured rat myocytes. Therefore, we examined the effect of an NEP inhibitor, phosphoramidon, on myocardial perfusion in rats after (1) stimulating sensory nerves with capsaicin and (2) inducing myocardial hypoperfusion with isoproterenol, with or without pretreatment with selective antagonists of the substance P (NK1) and bradykinin (B2) receptors. Three to five sequential determinations of myocardial blood flow were made in anesthetized rats by injecting 100,000 radionuclide-labeled microspheres suspended in 70% dextrose into the left ventricle. Phosphoramidon doubled coronary blood flow in response to a dose of capsaicin that was ineffective in the absence of the inhibitor. Isoproterenol (50 mg/kg IP) caused an immediate fall in blood pressure and coronary blood flow; after 20 minutes, flow had returned to normal but pressure was still subnormal. Administration of phosphoramidon reduced the recovery of blood pressure but greatly increased coronary blood flow. These changes were not altered by a substance P NK1 receptor blocker but were completely abolished by a selective bradykinin B2 receptor blocker. Our data indicate that (1) NEP is present in the rat myocardium, (2) sensory nerve-induced coronary vasodilation is markedly potentiated by NEP inhibition, (3) isoproterenol-induced myocardial hypoperfusion is prevented by NEP inhibition, and (4) this effect of NEP inhibition is due to reduced degradation of bradykinin.

Ruthenium red, but not capsazepine reduces plasma extravasation by cigarette smoke in rat airways

1 Cigarette smoke increases vascular permeability in rat airways by activating release of tachykinin from capsaicin‐sensitive sensory nerves. However, the mechanism by which cigarette smoke induces secretion of sensory neuropeptides is unknown. Here we hypothesized that cigarette smoke activates sensory nerve endings via a mechanism similar to that of capsaicin. 2 We studied the effects of ruthenium red, an inorganic dye which blocks the cation influx promoted by capsaicin and of the capsaicin antagonist capsazepine on the increase in vascular permeability produced by cigarette smoke, capsaicin, hypertonic saline and substance P in the trachea of pentobarbitone anaesthetized rats. We also investigated the ability of cigarette smoke to desensitize sensory nerve fibres. 3 Ruthenium red (10 mm) by aerosol blocked the increase in vascular permeability induced by capsaicin (0.5 μm) and reduced the response to cigarette smoke (5 puffs) but did not affect responses evoked by hypertonic saline (7.2%) or by substance P (10 μm) (all given by aerosol). Aerosols of capsazepine (0.1 mm) prevented extravasation by capsaicin, but did not inhibit response to cigarette smoke, hypertonic saline or substance P. Finally, pre‐exposure to a high dose of cigarette smoke (10 puffs) prevented the extravasation caused by cigarette smoke (5 puffs) itself and by intravenous capsaicin (150 μg kg−1), but not that by intravenous substance P (10 nmol kg−1). 4 The present results show that cigarette smoke: (a) increases vascular permeability in the rat airways by a mechanism that is not antagonized by capsazepine, and is partially sensitive to rutheniun red; (b) produces desensitization of capsaicin‐sensitive sensory nerves. We propose that chemical(s) contained in or agent(s) produced by cigarette smoke in the airways share partially a common pathway with capsaicin to activate peptide release from capsaicin‐sensitive sensory nerves, but do not bind to the putative ‘capsaicin receptor’.