Distribution of atrial natriuretic polypeptide (ANP)-containing cells in the rat heart and pulmonary vein. Immunohistochemical study and radioimmunoassay.

The distribution of atrial natriuretic polypeptide (ANP) was immunohistochemically surveyed in the rat heart and lung using an antiserum raised against alpha-human ANP. The ANP-immunoreactive cells were seen to be distributed in the atrial walls and proximal portions of the pulmonary vein and venae cavae, but were absent from the aorta, pulmonary arteries, trachea, bronchus, and alveolar cells. The immunoreactive cells were present in a narrow region just beneath the endothelium of the pulmonary vein and vena cavae, and, ultrastructurally and immunocytochemically, were seen to be striated muscle cells with ANP-containing specific granules similar to those seen in atrial cardiocytes. A radioimmunoassay for ANP revealed a content of 604 +/- 51 pg/mg wet weight in the pulmonary vein, and 3343 +/- 1620 pg/mg wet weight in the venae cavae. In addition to the atrial wall, the proximal portion of both the pulmonary vein and venae cavae are suggested to be constituents of an ANP-producing organ.