Angiotensin-II Subtype 2 Receptor Agonist (CGP-42112) Inhibits Catecholamine Biosynthesis in Cultured Porcine Adrenal Medullary Chromaffin Cells

Abstract

Angiotensin II subtype 2 receptor (AT2-R) is abundantly expressed in adrenal medullary chromaffin cells. However, the physiological roles of AT2-R in chromaffin cells remain to be clarified. Therefore, we investigated the effects of CGP42112 (AT2-R agonist) on catecholamine biosynthesis in cultured porcine adrenal medullary cells. We initially confirmed AT2-R was predominantly expressed in porcine adrenal medullary cells by [125I]-Ang II binding studies. CGP42112 (≧1 nM) significantly inhibited cGMP production from the basal value. Tyrosine hydroxylase (TH) is a rate-limiting enzyme in the biosynthesis of catecholamine, and its activity is regulated by both TH-enzyme activity and TH-synthesis. CGP42112 (≧1 nM) significantly inhibited TH-enzyme activity from the basal value. These inhibitory effects of CGP42112 on TH-enzyme activity and-cGMP production were abolished by PD123319 (AT2-R antagonist) while CV-11974 (AT1-R antagonist) was ineffective. We also tested whether decrease of cGMP is involved in the inhibitory effect of CGP42112 on TH-enzyme activity. Pretreatment of 8-Br-cGMP (membrane-permeable cGMP analogue) prevented the inhibitory effect of CGP 42112 on TH-enzyme activity. Similar to that of TH-enzyme activity, CGP42112 (≧1 nM) significantly reduced TH-mRNA and TH-protein level from the basal value, and these inhibitory effects were abolished by PD123319 but not CV-11974. These findings demonstrate that CGP 42112 reduces both TH-enzyme activity and TH-synthesis and that these inhibitory effects could be mediated by decrease of cGMP production.