Effects of environmental temperature on atrial natriuretic peptide (ANP)-granules of auricular cardiocytes and plasma ANP level in pregnant rats.

The atrial natriuretic peptide (ANP) levels of auricular cardiocytes and plasma were examined by immunohistochemistry, ultrastructural morphometry, and radioimmunoassay (RIA) in pregnant rats (4th, 12th, 20th day of gestation) under 22 degrees C and 33 degrees C environmental conditions. Immunohistochemically, ANP immunoreactivity was stronger on the 20th day of gestation in the 22 degrees C environmental groups, but weaker on the 12th and 20th days of gestation in the 33 degrees C environmental groups. According to the results of ultrastructural morphometry, the number of ANP-granules had increased significantly by the 20th day of gestation in the 22 degrees C environmental groups, but was decreased on the 12th and 20th days of gestation in the 33 degrees C environmental groups. RIA demonstrated that the maternal plasma ANP concentration decreased gradually during pregnancy in the 22 degrees C environment. The plasma ANP concentration in the 33 degrees C environmental groups tended to be lower than that at the same stage of pregnancy in the 22 degrees C environmental groups.