Substance P- and leu-enkephalin-immunoreactive nerves before and after myocardial ischaemia, hypothermic chemical cardioplegia and reperfusion injury during open-heart surgery.

During open-heart surgery, myocardial biopsies were obtained before the start of extracorporeal circulation (from the right auricular appendage) and after weaning from the pump (from the right atrium), and processed for immunocytochemical demonstration of substance P- and leu-enkephalin-immunoreactive nerve fibres and for electron microscopy. Substance P-immunoreactive nerves were seen around blood vessels, between myocardial cells and forming large glomerulus-like loops, but were not numerous. Leu-enkephalin-immunoreactive nerves were very sparse. We therefore believe that both nerve types primarily are modulatory axons. In the post-weaning specimens, nerves of both types were more numerous (attributable to the different site of biopsy), and no change was seen in the immunofluorescence reaction. The ultrastructure (all types) of nerve terminals was well preserved, although myocardial damage was obvious in many specimens. Cardiac nerves, including peptidergic nerves, thus seem to be relatively resistant to ischaemia, hypothermic chemical cardioplegia and reperfusion injury.