Calcitonin gene-related peptide augments parasympathetic contraction of rabbit tracheal smooth muscle in vitro.

The effect of calcitonin gene-related peptide (CGRP) on parasympathetic contraction of rabbit airway smooth muscle was studied under isometric conditions in vitro. CGRP (10(-7) M) did not contract tracheal smooth muscle, but it potentiated the contractile response to electrical field stimulation (EFS) in a dose-dependent manner, the maximal increase from the baseline response being 14.4 +/- 6.2%. In contrast, the contractile responses to exogenously administered acetylcholine were not altered by this peptide. The CGRP-induced potentiation of the contractile responses to EFS was further augmented by physostigmine (123.1%), but not influenced by phentolamine, propranolol, indomethacin, or thiorphan, an enkephalinase inhibitor. These results suggest that CGRP augments the neurally mediated contraction of rabbit airway smooth muscle probably through a prejunctional mechanism and that this effect may not be modulated by tissue enkephalinase.