Takekoshi K, Ishii K, Isobe K, Nanmoku T, Kawakami Y, Nakai T
Department of Clinical Pathology, University of Tsukuba, Ibaraki, 305-8575, Japan.
Biochem Biophys Res Commun. 2000 Jun 7;272(2):544-50. doi: 10.1006/bbrc.2000.2821.
Angiotensin II subtype 2 receptor (AT(2)-R) is abundantly expressed in adrenal medullary chromaffin cells. However, the physiological roles of AT(2)-R in chromaffin cells remain to be clarified. Therefore, we investigated the effects of CGP42112 (AT(2)-R agonist) on catecholamine biosynthesis in cultured porcine adrenal medullary cells. We initially confirmed AT(2)-R was predominantly expressed in porcine adrenal medullary cells by [(125)I]-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 (AT(2)-R antagonist) while CV-11974 (AT(1)-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.
血管紧张素II 2型受体（AT(2)-R）在肾上腺髓质嗜铬细胞中大量表达。然而，AT(2)-R在嗜铬细胞中的生理作用仍有待阐明。因此，我们研究了CGP42112（AT(2)-R激动剂）对培养的猪肾上腺髓质细胞中儿茶酚胺生物合成的影响。我们最初通过[(125)I]-血管紧张素II结合研究证实AT(2)-R在猪肾上腺髓质细胞中主要表达。CGP42112（≥1 nM）显著抑制基础值的cGMP生成。酪氨酸羟化酶（TH）是儿茶酚胺生物合成中的限速酶，其活性受TH-酶活性和TH-合成的调节。CGP42112（≥1 nM）显著抑制基础值的TH-酶活性。PD123319（AT(2)-R拮抗剂）可消除CGP42112对TH-酶活性和cGMP生成的这些抑制作用，而CV-11974（AT(1)-R拮抗剂）则无效。我们还测试了cGMP的降低是否参与了CGP42112对TH-酶活性的抑制作用。8-Br-cGMP（膜通透性cGMP类似物）预处理可防止CGP 42112对TH-酶活性的抑制作用。与TH-酶活性相似，CGP42112（≥1 nM）显著降低基础值的TH-mRNA和TH-蛋白水平，这些抑制作用可被PD123319消除，但不能被CV-11974消除。这些发现表明，CGP 42112降低了TH-酶活性和TH-合成，并且这些抑制作用可能是由cGMP生成的减少介导的。
