Role of the lipoxygenase pathway in angiotensin II-mediated aldosterone biosynthesis in human adrenal glomerulosa cells.

Abstract

We studied the role of the lipoxygenase pathway of arachidonic acid metabolism in angiotensin II (AII)-stimulated aldosterone secretion in normal and adenomatous human adrenal glomerulosa tissue. In freshly isolated normal adrenal glomerulosa cells, the AII-mediated stimulation of aldosterone secretion was not altered by cyclooxygenase blockade with ibuprofen. In contrast, BW755c (10(-5) mol/L), a nonselective lipoxygenase inhibitor, and baicalein (10(-6) mol/L), a more selective 12-lipoxygenase blocker, inhibited AII-mediated aldosterone secretion, but did not alter basal aldosterone secretion. The glomerulosa cells produced the lipoxygenase products 12- and 15-hydroxyeicosatetraenoic acid (HETE) in the basal state, as measured by high pressure liquid chromatography and RIA. However, AII selectively stimulated only 12-HETE production [basal, 1329 +/- 207 (+/- SE) pg (3.99 +/- 0.62 pmol)/10(5) cells.h; AII, 2365 +/- 333 (7.09 +/- 1.0); n = 9; P less than 0.02], suggesting that 12-lipoxygenase activation may be involved in AII-mediated aldosterone secretion by normal cells. In addition, the lipoxygenase inhibitors that blocked AII-mediated aldosterone secretion also prevented AII-mediated 12-HETE formation. In contrast, neither ACTH nor K+ stimulated 12-HETE formation, suggesting that 12-lipoxygenase activation is primarily involved in AII action in normal glomerulosa cells. BW755c caused a marked dose-dependent inhibition of basal aldosterone secretion in freshly isolated cells from aldosterone-producing adenomas [APA; basal, 66 +/- 3 ng (182 +/- 8 pmol)/10(6) cells.h; 10(-5) mol/L BW755c, 49 +/- 2 (136 +/- 6); 10(-4) mol/L BW755c, 30 +/- 2 (83 +/- 6)]. In contrast, the cyclooxygenase inhibitor indomethacin and the selective 5-lipoxygenase inhibitor U60257 did not alter basal aldosterone secretion by these cells. The APA cells produced 12- and 15-HETE, and BW755c at the same dose that inhibited aldosterone secretion also inhibited the production of both 12- and 15-HETE. In the cultured APA cells, AII-stimulated aldosterone secretion was inhibited by BW755c [basal, 26 +/- 8 pg/mL (72.0 +/- 22.1 pmol/L); AII, 336 +/- 79 (930 +/- 218); AII plus BW755c, 92 +/- 38 (255 +/- 105) n = 13; P less than 0.01]. The lipoxygenase products 12- and 15-HETE restored the stimulatory effect of AII during inhibition by BW755c, indicating a role for these lipoxygenase pathways in AII-mediated aldosterone secretion in APA cells. These results suggest that the stimulatory effects of AII on aldosterone secretion are mediated by stimulation of the lipoxygenase pathway in human zona glomerulosa cells.