Perinatal expression of the atrial natriuretic factor gene in rat cardiac tissue.

The expression of the atrial natriuretic factor (ANF) gene was examined in the perinatal rat ventricle. The late fetal ventricle (day -3 relative to parturition) demonstrated a modest level of ANF gene expression. This expression increased at the time of birth and peaked on day +1 after birth. Atrial ANF immunoreactivity (irANF) increased gradually during the postpartum period (day +1 to 2-3 wk of age), while ventricular irANF as well as ventricular ANF mRNA levels fell over the same interval. This decrease in ANF gene expression resulted from a decrease in activity of the same major transcription start site employed in the adult atria and ventricle. Plasma irANF levels were very high in the neonatal period and decreased over the ensuing 2-3 wk, a profile similar to that seen for ventricular ANF gene expression. In situ hybridization histochemistry revealed that, while adult rat ventricular ANF mRNA was predominantly confined to the subendocardial layer, neonatal ventricles expressed the ANF gene throughout approximately 50% of the inner wall thickness. These findings suggest that the ANF gene is responding to regulatory stimuli that appear at or near the time of parturition and dissipate in the early neonatal period.