Cardiac Musculature of the Intrapulmonary Venous Wall as an Endocrine Organ of Atrial Natriuretic Polypeptide in Watase's Shrew (Crocidura watasei) and Musk Shrew (Suncus murinus)

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Both Watase's Crocidura watasei and musk Suncus murinus shrews possess cardiac myocytes in the tunica media of the intrapulmonary venous walls. Cardiac musculature was found even in the small intrapulmonary veins. Immunohistochemical studies demonstrated the presence of atrial natriuretic polypeptide (ANP) in the musculature. ANP-immunoreactivity was observed in the cardiac myocytes of intrapulmonary veins of more than 200 μm in diameter. It is suggested that pulmonary venous cardiac musculature evolved as an endocrine apparatus in insectivores such as Crocidura and Suncus.