DOWN-REGULATION OF ADRENAL ATRIAL-NATRIURETIC-PEPTIDE RECEPTOR MESSENGER-RNAS AND PROTEINS BY PREGNANCY IN RATS

The main objective oi this study was to find out if the reported chang es in the aldosterone-suppressant activity of atrial natriuretic pepti de (ANP) during different hormonal states in rats are due to a modulat ion of ANP receptors. In zona glomerulosa cells, ribonuclease protecti on assay detected mRNAs for guanylate cyclase (GC)-coupled ANP GC-A an d 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 a ntibodies 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 recepto rs in zona glomerulosa cells. Pregnancy decreased GC-A receptor protei ns in zona glomerulosa cells, but these recovered to virgin values on day 2 postpartum. ANP receptor mRNAs in zona glomerulosa cells increas ed by postpartum day 2, but did not reach the values found in virgin r ats. Zona fasciculata mainly contained GC-A receptor mRNA. It is concl uded that ANP receptors in rat adrenal zona glomerulosa are modulated by pregnancy, oestrogen and progesterone; a decrease in ANP GC-A recep tors during pregnancy might explain the accompanying decrease in the a ldosterone-suppressant effects of ANP.