DIFFERENTIAL REGULATION OF PROSTAGLANDIN SYNTHESIS BY ANGIOTENSIN PEPTIDES IN PORCINE AORTIC SMOOTH-MUSCLE CELLS - SUBTYPES OF ANGIOTENSIN RECEPTORS INVOLVED

We determined the role of AT1 and AT2 angiotensin receptors as mediato rs of prostaglandin (PG) release and mobilization of intracellular Ca+ in cultures of porcine vascular smooth muscle cells (VSMC) with subt ype-selective angiotensin (Ang) II receptor antagonists. The binding o f [I-125]Ang II to porcine VSMC showed an equilibrium constant (K(D)) of 0.52 nM and a binding capacity (B(max)) of 14.8 fmol/mg protein. Us ing the AT1 antagonists DuP 753, its metabolite EXP 3174, and L-1 58,8 09, [I-125]Ang II binding was displaced in a clearly biphasic manner, indicating the presence of two binding sites. Consistent with this, th e AT2 antagonist CGP 42112A also displayed a biphasic curve, whereas a nother AT2 antagonist, PD 123177, showed a 20% reduction in binding. A ng I, Ang II and Ang-(1-7) stimulated PGE2 as well as PGI2 synthesis i n a dose-dependent pattern. Ang II but not Ang I or Ang-(1-7) also cau sed an increase in the intracellular concentration of Ca++. Ca++ mobil ization by Ang II was blocked by the AT1 antagonist DuP 753, but not b y the AT2 antagonists. Ang II- and Ang I-stimulated (10 nM) PG product ion was attenuated by all three AT, antagonists. However, both CGP 421 12A (100 nM) and PD 123177 (100 nM) also attenuated PG release in resp onse to Ang II. The enhancement in PG release by Ang I (I 0 nM) was si gnificantly reduced by CGP 42112A (100 nM), but not by PD 123177 (1 mu M). Of the AT, antagonists, only high doses of DuP 753 or L-1 58,809 p artially reduced the Ang-(1-70-induced release of PG. CGP 42112A was i neffective for blocking Ang-(1-7)-stimulated PG release. Ang-(1-7)-sti mulated PGE2 and PGI2 production was significantly reduced by PD 12317 7. Unlike DuP 753 or L-1 58,809, but similar to the sarcosine antagoni sts, EXP 3174 (10 nM) abolished the angiotensin peptide-induced PG pro duction. These data show that Ang I and Ang II stimulate PGE2 and PGI2 release via activation of both AT1 and AT2 receptors in porcine VSMC. Ang II stimulates intracellular Ca++ mobilization via activation of A T1 receptors only. Because Ang-(1-7) enhanced PGE2 and PGI2 release vi a activation of angiotensin receptors having greater affinity for PD 1 23177 than CGP 42112A, although CGP 42112A showed a greater ability to block the Ang I response, these data further suggest differences in t hese two compounds at AT2 receptors. Moreover, differential activation of subtypes of angiotensin receptors linked to secretion of PG and to Ca++ mobilization may be important determinants in the local control of vascular tone.