Differential release of calcitonin gene‐related peptide and neuropeptide Y from the isolated heart by capsaicin, ischaemia, nicotine, bradykinin and ouabain

The influence of various drugs as well as total ischaemia on the outflow of calcitonin gene-related peptide (CGRP), which is present in sensory nerves, and neuropeptide Y (NPY), which is co-stored with noradrenaline (NA), from the isolated guinea-pig heart, was studied in vitro. Capsaicin exposure and total ischaemia for 5-30 min induced a Ca2+-dependent increase in the outflow, suggesting release, of CGRP- but not NPY-like immunoreactivity (LI) from the heart. When characterized by high performance liquid chromatography (HPLC), the CGRP-LI present in heart extracts and the released CGRP-LI by capsaicin eluted in a major peak corresponding to synthetic CGRP. Incubation with morphine, indomethacin or reserpine pretreatment did not influence the capsaicin-evoked release of CGRP-LI. Capsaicin pretreatment depleted the cardiac content of CGRP-LI but not NPY-LI. The increase in perfusate volume observed after 30 min ischaemia in controls was reduced after capsaicin pretreatment. Nicotine exposure induced release of CGRP- as well as NPY-LI in a concentration- and Ca2+-dependent manner. The increased outflow of NPY-LI was not influenced by capsaicin pretreatment. Among other agents tested, bradykinin and ouabain caused increased outflow of CGRP but not of NPY-LI. Noradrenaline, tyramine, histamine, vasopressin, alpha,beta methylene ATP, ATP or adenosine induced changes in cardiac contractility or flow but did not evoke any detectable release of CGRP- or NPY-LI. In conclusion, the release of multiple neuropeptides can be studied in combination with contractile recordings using the isolated perfused guinea-pig whole heart preparation. Activation of cardiac sensory nerves by capsaicin, nicotine, bradykinin and ouabain, as well as ischaemia, induced release of CGRP while nicotine also evoked NPY release.