Evidence for non-adrenergic non-cholinergic contractile responses in bovine and swine trachea

Non-adrenergic non-cholinergic (NANC) contraction of airway smooth muscle has been observed in some but not all animal species. The aim of this study was to investigate the NANC-contractile responses in bovine and swine trachea. Proximal and distal bovine and swine trachea were cut in strips and placed in 10 ml organ baths equilibrated in Krebs Henseleit (KH) solution and electrically stimulated (10 sec, 60 V, 2 ms, 4, 10 and 30 Hz). Contractile frequency response curves performed in the presence of the muscarinic antagonist, atropine (100 mM), the angiotensin converting enzyme inhibitor, captopril (1 microM) and the neutral endopeptidase inhibitor, thiorphan (1 microM), added 30 min prior to electrical field stimulation (EFS). In some tissues, incubated with atropine thiorphan and captopril, were also evaluated the effects of a pretreatment with capsaicin (10 microM) or a selective NK1 receptor antagonist, SR 14033 (100 nM) added to the baths 30 min prior to EFS. Bovine and swine proximal and distal tracheal preparations contracted in a frequency-dependent manner to EFS (4, 10 and 30 Hz). Some experiments were also performed with substance P (0.1 nM to 1 microM) in absence or in presence of SR 14033 (10 nM or 100 nM). At the maximum frequency tested (30 Hz), the contractile response elicited in bovine proximal and distal preparations was 194.5 +/- 17.1% and 229.7 +/- 24.1%, of ACh (100 microM), respectively. Similarly, the contractile response elicited by EFS (30 Hz) in swine proximal and distal preparations was 187.2 +/- 12.1% and 181.6 +/- 9.2% of ACh (100 microM), respectively. In tissues incubated with atropine, a significant decrease in smooth muscle sensitivity to EFS was observed (P < 0.05). When tissues were pretreated with captopril and thiorphan, a significant increase in the contractile response to EFS (30 Hz) was observed in all tested tissue preparations (bovine, proximal 210.1 +/- 14.4%, distal 264.3 +/- 16.2%; swine, proximal 199.3 +/- 14.9%, distal 206.3 +/- 16.2%, P < 0.05). In the presence of atropine, captopril and thiorphan a significant increase in the contractile response was observed in bovine and swine distal preparations compared with tissues incubated with atropine only (P < 0.05). These effects were antagonized by a pretreatment with a selective NK1 receptor antagonist, SR 14033. A pretreatment with capsaicin statistically (P < 0.05) enhanced EFS-induced contraction in all tested preparations respect to tissues incubated with atropine, thiorphan and captopril. Substance P induced a concentration dependent contraction of bovine and swine isolated tracheal preparations which was antagonized by a pretreatment with a selective NK1 receptor antagonist, SR 14033. No significant difference in the contractile potency (EC50) nor in maximum response (Emax) was observed to exogenously administered substance P between proximal and distal tracheal preparations. These data suggest that NANC contractile responses are present in bovine and swine trachea and are more evident in distal airways.