The effects of calcitonin gene‐related peptide on tracheal smooth muscle of guinea‐pigs in vitro

Abstract

1 The effect of calcitonin gene-related peptide (CGRP) on airway smooth muscle is controversial. The aim of this study was to determine whether the action of CGRP on tracheal strips of guinea-pigs is modulated by epithelium and whether this peptide-induced action involves other mediators including nitric oxide (NO) and endothelin (ET)-1.2 CGRP produced a weak dose-dependent increase in guinea-pig tracheal tension in vitro (-logEC50 = 8.5 ± 0.1, maximum contraction = 8.3 + 1.2% of 50 mM KCl-induced contraction, n = 6). In epitheliumdepleted preparations, CGRP (10'-M)-induced contraction was significantly potentiated from 9.0+1.9% to 41.1+6.0% (n=6).3 L-NG-nitro-arginine methyl ester (L-NAME, 10-4 M), which inhibits NO synthesis, enhanced the contractile response to CGRP from 9.0+1.9% to 31.2+1.1% (n=6). Indomethacin (10-5M) also enhanced the response to CGRP, although the effect was weak (13.4+3.2%, n=6). 4 Anti-ET-1 serum changed the CGRP-induced contraction into a relaxation. After incubation of the trachea with ET-1 (10-' M) to attenuate ET-1-induced responses, the CGRP-induced contraction also changed into a relaxation. BQ-123 (an ETA receptor antagonist) and BQ-788 (an ETB receptor antagonist) caused the same conversion of the CGRP response, from contraction to relaxation, although the relaxing effect elicited by BQ-788 was more potent than that by BQ-123. Maximum inhibitory responses were -31.0 + 3.3% and -13.0 + 2.3% of 50 mM KCl-induced contraction, respectively (n = 6). 5 In primary culture, guinea-pig tracheal epithelial cells released ET-1, and CGRP (10-5 M) significantly increased the release of ET-1. 6 These data suggest that the action of CGRP is modulated by airway epithelium and this mechanism involves the release of NO and ET-1. Especially, the majority of contractile action elicited by CGRP consists of an action of ET-1 via the predominant ETB receptor.

Nitric Oxide in Health and Disease of the Respiratory System

“…Bradykinin, endothelin-1, substance P, adenosine, and calcitonin-gene related peptide, applied to the inside of intact tracheal tubes, provoke concentration-dependent relaxations (9,93,(101)(102)(103)316). The relaxations are reversed into contractions (or contractions are markedly potentiated) by NOS inhibitors, indicating that the relaxant effect in the airways is mediated by the release of endogenous NO (9,93,(101)(102)(103)316).…”

“…The relaxations are reversed into contractions (or contractions are markedly potentiated) by NOS inhibitors, indicating that the relaxant effect in the airways is mediated by the release of endogenous NO (9,93,(101)(102)(103)316). This effect was mimicked by removal of airway epithelium (111), suggesting that airway epithelium releases NO, which counteracts smooth muscle contraction induced by different spasmogens (9,93,(101)(102)(103)316). These striking results demonstrate the functional importance of epithelium in airway reactivity, not merely considered as a physical protective barrier between spasmogens and smooth muscle but as a modulator of bronchomotor tone via the release of relaxant substances (so-called epithelium-derived relaxing factors).…”

Multiple roles of nitric oxide in the airways

“…[55][56][57] Intraluminal perfusion of tracheal tube preparations has shown that bradykinin, endothelin-1, substance P, adenosine, and calcitonin gene related peptide applied to the inside of intact tracheal tubes provoke concentration dependent relaxation. [58][59][60][61][62][63] The relaxation is reversed into contractions (or contractions are markedly potentiated) by NOS inhibitors, indicating that the relaxant effect in the airways is mediated by the release of endogenous NO. [58][59][60][61][62][63] This effect was mimicked by removal of airway epithelium, suggesting that airway epithelium releases NO which counteracts smooth muscle contraction induced by different spasmogens.…”

Bronchoprotector Properties of Calcitonin Gene–related Peptide in Guinea Pig and Human Airways

“…For example, regardless of the origin of the airway preparation used (animal species and level of the tracheobronchial tree), most studies examining the effect of CGRP on the baseline tension of the airway smooth muscles resulted in identical data, as no contractile or relaxant response was observed (9, 10, 17-20, 23, 24, 26, 27, 29). In studies showing a contractile action for CGRP (for example, in guinea pig trachea), there is a consensus regarding the epithelium dependency for this effect of the peptide but the magnitude of the response evoked by CGRP was each time described as being weak and of minor importance: 30% of the maximum induced with 1.5 ϫ 10 Ϫ5 M of methacholine (20), 14% of the capsaicin (10 Ϫ5 M) maximum (21), and 8% of 50 mM KCl-induced contraction (31). Thus, when compared with SP and NKA, which Lung samples were collected in areas adjacent to the tissue preparations used for the bioassays.…”