Atrial natriuretic peptide(ANP)-granules of the auricular cardiocytes in Syrian hamsters during the pre- and postnatal growth period.

Abstract

During pre-and postnatal development, the atrial natriuretic peptide (ANP)-granules in the right and left auricular cardiocytes of Syrian hamsters were studied immunohistochemically and by transmission electron microscopy. Moreover, the number and diameter of ANP-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, the ANP immunoreactivity was located primarily in the perinuclear region in auricular cardiocytes of the neonatal group, but was located diffusely in the cells of the fetal group. At the 15th day of gestation, the immunoreactivity was stronger than at the 13th day of gestation. The ANP immunoreactivity observed in the cardiocytes of the newborn was weaker than in the fetal group. During the postnatal growth period, the immunoreactivity became gradually stronger. Ultrastructurally, ANP-granules in the fetal cardiocytes were scattered in the cytoplasm with immature organelles. During the postnatal growth period, the granules were predominantly located in the perinuclear region associated with the Golgi apparatus. By ultrastructural morphometry, the number of granules in the right auricular cardiocytes was significantly greater than in the left auricular cardiocytes in all groups examined. In the newborn, the number of granules was significantly less than that in the fetal group. During the postnatal growth period, the granule number of cardiocytes significantly increased. There was no significant difference between the granule number of 10-day-old neonates and of 90-day-old neonates. During the postnatal period, the granule diameter in both auricles was significantly greater than in the fetal group. The granule size was not significantly different between the right auricular cardiocytes and the left ones in all groups examined. It is suggested that a large amount of ANP-granules is secreted at the perinatal period, resulting in granule depletion in both auricular cardiocytes.