Inhalation of f-Met-Leu-Phe (FMLP) produces dose-dependent increases in pulmonary resistance (RL) in rabbits. We hypothesized that inhibition of neutral endopeptidase (NEP), which has high affinity for FMLP, would augment the response to FMLP inhalation. We found the increase in RL above baseline in response to FMLP to be reduced from 56 ± 18 to 8 ± 10% (P < 0.01) by phosporamidon (1 mg/kg) and to 15 ± 6% (P < 0.02) by thiorphan (3 mg/kg). The geometric mean dose of FMLP producing a 20% rise in RL (PC20RL FMLP) was increased by phosphoramidon from 1.1 to 4.5 mg/ml (P < 0.05). Enkephalins, which are also NEP substrates, modulate cholinergic neurotransmission in the airway. Inhibition of the FMLP response by phosphoramidon was reversed by coadministration of naloxone (0.1 mg/kg); after atropine (2 mg/kg) the change in RL in response to FMLP was reduced to 7 ± 4% (P < 0.01), whereas morphine (0.15 mg/kg) increased PC20RL FMLP to 5.1 mg/ml (P < 0.05). FMLP-induced bronchoconstriction in the rabbit is vagally mediated, and reduced responses after NEP inhibition may reflect modulation of cholinergic bronchoconstriction by enkephalins. Changes in airway NEP activity may influence the activity of a wide range of its substrates, of which some are bronchoconstrictors and others bronchodilators.
|Number of pages||5|
|Journal||Journal of Applied Physiology|
|Publication status||Published - 1991|
- bacterial peptides
- cholinergic bronchoconstriction
- membrane metalloendoproteinase
- substance P