The precursor for rat
vasoactive intestinal polypeptide (
preproVIP) is processed by proteolytic cleavage into a
signal peptide and five further functional domains:
preproVIP 22-79,
peptide histidine isoleucine (PHI),
preproVIP 111-122, VIP, and
preproVIP 156-170. To investigate the biosynthetic processing of
preproVIP in peripheral parasympathetic neurons, the sphenopalatine
ganglion and one of its projection areas, the nasal mucosa, were used. By immunohistochemistry it was shown that in the sphenopalatine
ganglion,
preproVIP-derived
peptides are localized mainly in neuronal cell bodies, whereas in the nasal mucosa immunoreactivity was found only in nerve fibers and terminals. The
peptides were quantified and characterized by radioimmunoassay, HPLC, and gel chromatography using
antisera specific for the different precursor products. In the rat sphenopalatine
ganglion, the different
peptides were found in approximately equimolar amounts, with the exception of PHI and its C-terminally extended variant, PHV, which were present at considerably lower concentrations. However, in the nasal mucosa there was a preferential accumulation of VIP to at least three times the concentration of any of the other
peptides. Our results suggest that all
preproVIP-derived
peptides are present and processed in the sphenopalatine
ganglion but that there is a selective accumulation of VIP in the nerve terminals. This indicates that VIP is physiologically the most important transmitter among the
preproVIP-derived
peptides in parasympathetic nerves originating in the sphenopalatine
ganglion.