DEMONSTRATION OF ATRIAL-NATRIURETIC-PEPTIDE IMMUNOREACTIVITY AND ULTRASTRUCTURALLY RELATED SECRETORY GRANULES IN MYOBLASTS OF THE CHICK MYOTOME

In this study, an ultrastructural and immunohistochemical examination was carried out on the presence of an 'atrial-natriuretic-peptide (ANP )-like factor' in the myoblasts of the brachial myotome of chicken emb ryos at Hamburger and Hamilton stages 17 +/- to 19. The results of the immunohistochemical study indicate that, at these stages of their dev elopment, the myoblasts of the brachial myotome show ANP immunoreactiv ity. The ultrastructural analysis of the myoblasts shows the presence of 'granules' or 'secretory vesicles', similar to the secretory granul es which contain natriuretic peptides. The demonstration of immunoreac tivity to ANP in the myotome and the specific localization of secretor y vesicles in myoblasts, as the first evidence relating ANP with skele tal muscle development, reveal a new site at which an ANP-like factor may be synthesized. The hypothesis of a paracrine and/or autocrine fun ction(s) during myogenesis is suggested.