MORPHOLOGICAL RELATIONS BETWEEN HEME OXYGENASES, NO-SYNTHASE AND VIP IN THE CANINE AND FELINE GASTROINTESTINAL TRACTS

Carbon monoxide (CO), produced by haem oxygenase (HO), has been sugges ted as a messenger molecule in the central and peripheral nervous syst ems. In the present study, we have investigated the occurrence of the two isoforms of HO, HO-2 and HO-1 in the canine and feline gastrointes tinal tracts, including the small and large intestine and the gastroin testinal sphincters. An abundance of nerve cell bodies that contained immunoreactivity for HO-2 was found in the submucosal and myenteric pl exuses. HO-2 immunoreactivity was frequently co-localized with nitric oxide synthase (NOS) or vasoactive intestinal peptide (VIP) immunoreac tivities and was also observed in some nerve fibres, certain non-neuro nal cells dispersed among smooth muscle bundles, and in Vascular endot helium. The antiserum against HO-I revealed immunoreactivity in nerve cell bodies in the enteric plexuses, in nerve fibres and in non-neuron al cells in the smooth muscle layers. Some of the nerve structures wer e also NOS- or VIP-immunoreactive. These results demonstrate the prese nce of HO isoenzymes in nerves and other structures of the canine and feline gastrointestinal tracts and support the view that CO may have a role as a messenger molecule in the enteric nervous system. (C) 1997 Elsevier Science B.V.