The development of immunoreactive
atrial natriuretic peptide (
ANP) was studied in fetal hearts of spontaneously hypertensive (SHR) and compared to normotensive Wistar-Kyoto (WKY) rats. While SHR fetal hearts were noticeably less developed than those of WKY
at 10 and 11 days gestation, both strains showed
ANP immunoreactive cells in some but not all primitive heart tubes. At 12 days additional
ANP immunoreactive cells appeared in formative trabeculae of the ventricle and atrium.
ANP cells were also observed in the myogenic layer of the truncus and bulbus arteriosus and their derivatives from 11 through 16 days, but not at 18 days. In both strains, there were more
ANP cells in the left ventricle than in right beginning at day 13. There were no obvious strain differences in the developmental pattern and timing of
ANP producing cells. However, on the day of birth, staining was reduced in hearts from some WKY newborn pups compared with hearts from SHR newborns and ventricular staining was reduced in both strains when compared to fetal hearts. These observations indicate that
ANP is one of the earliest
peptide hormones produced and that the predisposition to genetic
hypertension does not appear to influence the development of
ANP.