SARAFOTOXIN EXPRESSION IN THE BRONCHOPULMONARY TRACT - IMMUNOHISTOCHEMICAL OCCURRENCE AND COLOCALIZATION WITH ENDOTHELINS

The immunohistochemical occurrence of sarafotoxin (SRTX), a snake veno m peptide under strong evolutionary control, was investigated in the p ulmonary diffuse neuroendocrine system (PDNES) of newborn cats and rat s. By applying the avidin-biotin-peroxidase complex method on serial l ung sections, we have demonstrated its distribution and colocalization with different endothelin (ET) isoforms. A light microscopic study re vealed apparent immunostaining for SRTX in neuronal components and smo oth muscle tissue and in neuroepithelial bodies (NEB), while isolated neuroendocrine cells (NEC) remain unlabelled. Comparison of the SRTX r eactivity pattern with that of different ET peptides on adjacent lung sections showed colocalization of SRTX-b with ET-3 in NEB, intrapulmon ary ganglion cells and nerve fibres, on the one hand, and with ET-1 in airway and vascular smooth muscle cells, on the other. These findings , in addition to the remarkable functional and structural similarities between SRTX and ET peptides, suggest a common evolutionary origin an d biological significance of sarafotoxin and endothelins. Moreover, th is is the first time that a toxic peptide has been demonstrated in the PDNES.