The main objective of this study was to find out if the reported changes in the aldosterone-suppressant activity of atrial natriuretic peptide (ANP) during different hormonal states in rats are due to a modulation of ANP receptors. In zona glomerulosa cells, ribonuclease protection assay detected mRNAs for guanylate cyclase (GC)-coupled ANP GC-A and GC-B receptors, and for ANP C receptors, which are not coupled to GC. Western analysis using polyclonal anti-GC-A and anti-GC-B receptor antibodies revealed the presence of GC-A but not GC-B receptor proteins in zona glomerulosa cells. Pregnancy (days 7, 16 and 21), oestradiol-17 beta and progesterone decreased mRNAs for all the three ANP receptors in zona glomerulosa cells. Pregnancy decreased GC-A receptor proteins in zona glomerulosa cells, but these recovered to virgin values on day 2 postpartum. ANP receptor mRNAs in zona glomerulosa cells increased by postpartum day 2, but did not reach the values found in virgin rats. Zona fasciculata mainly contained GC-A receptor mRNA. It is concluded that ANP receptors in rat adrenal zona glomerulosa are modulated by pregnancy, oestrogen and progesterone; a decrease in ANP GC-A receptors during pregnancy might explain the accompanying decrease in the aldosterone-suppressant effects of ANP.