Localization of fmrfamide-like immunoreactivity in the peripheral organs and its cross reaction with neuropeptide Y in the rat.

The molluscan cardioexcitatory peptide (FMRFamide) is a tetrapeptide. Neuropeptide Y (NPY) is a 36 amino acid peptide. Functionally, NPY is classified as a co-transmitter in the vasculatures of many organs and shows potent vasoconstriction. Coexistence of FMRFamide with NPY has been demonstrated in the central nervous system. The localization and distribution of NPY in the peripheral organs have been demonstrated mainly by radioimmunoassay. The localization and distribution, however, have not been investigated by immunohistochemistry. Therefore we present and compare the distribution of NPY- and FMRFamide-like immunoactivities in several peripheral organs of rats. Analysis of these data will reflect whether there is a cross reaction of FMRFamide with NPY antiserum or not. We have demonstrated both NPY- and FMRFamide-like nerve fibers in the vasculatures of the kidney, liver, pancreas, spleen, submandibular gland, lung and small intestine. The distribution pattern of these immuno-reactivities of the peripheral organs showed some extent of similarity. Radioimmunoassay indicated that FMRFamide possessed the ability to react with NPY-antiserum. This study demonstrated that the presence of FMRFamide immuno-reactivity in rat peripheral organs represents cross-reactivity of NPY with the FMRFamide anti serum. Such a result can be explained if antisera against NPY and FMRFamide recognize the carboxy-terminal sequence of -Arg-X-amide in the respective peptides.