Inhibitory mechanism of ANP on aldosterone production in human adrenocortical cells

The aldosterone-suppressing effect of natriuretic peptides (NPs) has been demonstrated in experiments using adrenocortical cells from various animal species. 3',5'-cyclic guanosine monophosphate (cGMP), which is produced by atrial natriuretic peptide (ANP), is recognized as a suppressor of aldosterone production. However, it has also been reported that cGMP does not exhibit the same aldosterone-suppressing effect as ANP. Therefore, we examined the effect of ANP on aldosterone suppression using various inhibitors and agonists, including a cGMP agonist.

We investigated the expression of ANP receptors in human adrenocortical cells. Next, we examined aldosterone synthesis gene expressions and the effects of various inhibitors, agonists, and siRNAs for the two ANP receptors on the aldosterone-suppressing action of ANP using human adrenocortical H295R cells, precultured with Ang-II. We also investigated inhibitory G (Gi) protein signaling as a cGMP-independent factor.

The human adrenocortical cell line H295R was shown to express the guanylyl cyclase A receptor (NPR1). Treatment with a neprilysin inhibitor ameliorated ANP-induced suppression of aldosterone production. Aldosterone production elevated by cyclic adenosine monophosphate (cAMP) agonist was significantly reduced by inhibitors of cAMP signaling. Conversely, cGMP alone had no significant aldosterone-suppressing effect. By suppressing the expression of receptors NPR1 and guanylyl cyclase C receptor (NPR3), aldosterone production increased in the presence of ANP. The suppression of aldosterone production by ANP was abolished by blocking Gi signaling by pertussis toxin (PTX).

These results suggest that ANP suppresses aldosterone production in H295R cells through NPR1 and NPR3, and this suppression is partially mediated by a cGMP-independent Gi signaling.