To study the occurrence of
atrial natriuretic peptide (
ANP) in overloaded ventricles, suprarenal
aortic coarctation was performed on adult rats (n = 60) to induce overloaded left ventricle. In 36 rats, the overloads were released in 2 weeks. The hearts (6 rats in each group) were examined 2, 7, and 14 days after overload and 2, 7, 19, 47, and 77 days after overload release. Another group of 6 rats was coarctated for the second time for 1-6 days after 14 days of coarctation and 7 days of release.
ANP immunoreactivity was examined by light and electron microscopic immunocytochemistry.
ANP mRNA was studied by
RNA-
RNA tissue in situ hybridization.
ANP immunoreactivity and
ANP mRNA were found in the left ventricle 2 days after coarctation, and their amounts increased in proportion to the intraventricular pressure and the duration of coarctation. Two days after release,
ANP and its
mRNA began to decrease, but at 77 days
ANP-containing granules still existed in the ventricular myocytes, whereas its
mRNA became undetectable. The second coarctation triggered the release of the remaining ventricular
ANP from the first overload and induced another cycle of increased
ANP synthesis. Specific granules that do not contain
ANP were found in overload-released ventricles, indicating the possible existence of other
peptide hormones. These findings suggest that the extents of ventricular
ANP gene expression and
ANP synthesis and release are regulated by intraventricular pressure, and the occurrence of
ANP in overloaded ventricles may not be a transient, immediately reversible phenomenon.