BIOSYNTHETIC PROCESSING OF PREPROVASOACTIVE INTESTINAL POLYPEPTIDE INPARASYMPATHETIC NEURONS OF THE SPHENOPALATINE GANGLION

The precursor for rat vasoactive intestinal polypeptide (preproVIP) is processed by proteolytic cleavage into a signal peptide and five furt her functional domains: preproVIP 22-79, peptide histidine isoleucine (PHI), preproVIP 111-122, VIP, and preproVIP 156-170. To investigate t he 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, preproVlP-derived peptides are locali zed mainly in neuronal cell bodies, whereas in the nasal mucosa immuno reactjvity was found only in nerve fibers and terminals, The peptides were quantified and characterized by radioimmunoassay, HPLC, and gel c hromatography using antisera specific for the different precursor prod ucts. In the rat sphenopalatine ganglion, the different peptides were found in approximately equimolar amounts, with the exception of PHI an d its C-terminally extended variant, PHV, which were present at consid erably lower concentrations. However, in the nasal mucosa there was a preferential accumulation of VIP to at least three times the concentra tion of any of the other peptides. Our results suggest that all prepro VIP-derived peptides are present and processed in the sphenopalatine g anglion but that there is a selective accumulation of VIP in the nerve terminals. This indicates that VIP is physiologically the most import ant transmitter among the preproVIP-derived peptides in parasympatheti c nerves originating in the sphenopalatine ganglion.