CARDIAC-LIKE MUSCULATURE OF THE INTRAPULMONARY VENOUS WALL OF THE LONG-CLAWED SHREW (SOREX-UNGUICULATUS), COMMON TREE SHREW (TUPAIA-GLIS) AND COMMON MARMOSET (CALLITHRIX-JACCHUS)

Background: The cardiac-like musculature is distributed not only in th e heart wall but also in the intrapulmonary venous wall in a few speci es of insectivores. It has been suggested that the evolutionary origin of venous cardiac-like musculature may be traceable to a basic stock of certain mammalian lines of descent. So, it is important to clarify whether the musculature may be a common structure in lower mammals fro m insectivores to primates and to examine the functional significance of the structure. Methods: The distribution of cardiac-like musculatur e in the intrapulmonary venous wall of the long-clawed shrew (Sorex un guiculatus), common tree shrew (Tupaia glis), and common marmoset (Cal lithrix jacchus) was observed by Light and electron microscopy. The pr esence of atrial natriuretic polypeptide (ANP) was examined in the mus culature by immunohistochemistry. Results: All three species contained cardiac-like myocytes in the tunica media of intrapulmonary venous wa ll. In the common tree shrew and the common marmoset, cardiac-like mus culature was found in the small intrapulmonary vein of 150-200 mu m in diameter, while, in the long-clawed shrew, it was distributed even in the intrapulmonary vein of 30 mu m in diameter. Ultrastructure of myo cytes was fundamentally similar to that of atrial myocytes in the long -clawed shrew and the common tree shrew, The presence of atrial natriu retic polypeptide (ANP) was also demonstrated by immunohistochemistry in the intrapulmonary venous walls of common tree shrews. Conclusions: The results indicate that the pulmonary venous cardiac-like musculatu re occurs in the lower eutherian mammals from insectivores to primitiv e primates. The musculature is thought to act as a regulatory pump in pulmonary circulation and as an endocrine apparatus of ANP. (C) 1997 W iley-Liss, Inc.