CHARACTERIZATION OF ANGIOTENSIN RECEPTORS MEDIATING PROSTAGLANDIN SYNTHESIS IN C6-GLIOMA CELLS

The heptapeptide angiotensin (ANG)-(1-7) mimics some but not all the central actions of ANG II, suggesting that receptor subtypes may exist. The effects of ANG-(1-7), ANG II, and ANG I on prostaglandin (PG) E2 and prostacyclin (PGI2) synthesis were investigated in neurally derived rat C6 glioma cells. All three ANG peptides stimulated PG release in a dose-dependent manner with the order of potency ANG-(1-7) > ANG I > ANG II. PGE2 release induced by ANG-(1-7) (10(-7) M) was partially blocked by [Sar1,Ile8]ANG II (10(-6) M), [Sar1,Thr8]ANG II (10(-6) M), or the subtype 1 selective antagonist Du Pont 753 (10(-5) M) but not by the subtype 2 selective antagonist CGP 42112A (10(-7)-10(-5) M). PGI2 release was inhibited only by [Sar1,Thr8]ANG II. ANG II-induced PGE2 release was blocked by [Sar1,Thr8]ANG II (10(-6) M), [Sar1,Ile8]ANG II (10(-6) M), or Du Pont 753 (10(-7) M) but not by CGP 42112A (10(-7)-10(-5) M). In contrast, ANG II-induced PGI2 release was blocked by Du Pont 753 (10(-7) M) as well as [Sar1,Ile8]ANG II (10(-6) M) but not by [Sar1,Thr8]ANG II or CGP 42112A. Thus ANG II-stimulated PGE2 and PGI2 syntheses in C6 glioma cells are mediated via receptor subtype 1. ANG-(1-7)-induced PGE2 synthesis is also mediated via subtype 1 receptors; however, PGI2 release was blocked by [Sar1,Thr8]ANG II only. Moreover, [Sar1,Thr8]ANG II had no effect on ANG II-induced PGI2 release but was the only antagonist to block the action of ANG-(1-7) on PGI2 release. This differential ability of various antagonists to inhibit PGE2 vs. PGI2 release further suggests that separate receptor pathways lead to the increase in the two PGs.