Specific action of the lipoxygenase pathway in mediating angiotensin II-induced aldosterone synthesis in isolated adrenal glomerulosa cells.

Abstract

Angiotensin II (All) in adrenal glomerulosa cells activates phospholipase C resulting in the formation of inositol phosphates and diacylglycerol rich in arachidonic acid (AA). Although glomerulosa cells can metabolize AA via cyclooxygenase (CO), this pathway plays little role in aldosterone synthesis. Recent evidence suggests that the lipoxygenase (LO) pathway may be important for hormonal secretion in endocrine tissues such as the islet of Langerhans. However, the capacity of the glomerulosa cell to synthesize LO products and their role in aldosterone secretion is not known. To study this, the effect of nonselective and selective LO inhibitors on All, ACTH, and potassium-induced aldosterone secretion and LO product formation was evaluated in isolated rat glomerulosa cells. BW755c, a nonselective LO inhibitor dose dependently reduced the AII-stimulated level of aldosterone without altering All binding (91±6 to 36±4 ng/106 cells/h 10-' M, P < 0.001). The same effect was observed with another nonselective LO blocker, phenidone, and a more selective 12-LO inhibitor, Baicalein. In contrast U-60257, a selective 5-LO inhibitor did not change the All-stimulated levels of aldosterone (208±11% control, All 10-9 M vs. 222±38%, All + U-60257). The LO blockers action was specific for All since neither BW755c nor phenidone altered ACTH or K+-induced aldosterone secretion. All stimulated the formation of the 12-LO product 12-hydroxyeicosatetraenoic acid as measured by ultraviolet detection and HPLC in AA loaded cells and by a specific RIA in unlabeled cells (501±50 to 990±10 pg/105 cells, P < 0.02). BW755c prevented the Allmediated rise in 12-HETE formation. In contrast, neither ACTH nor K+ increased 12-HETE levels. The addition of 12-HETE or its unstable precursor 12-HPETE (10-9 or 10' M) completely restored All action during LO blockade. All also produced an increase in 15-HETE formation, but the 15-LO products had no effect on aldosterone secretion. These studies suggest that the 12-LO pathway plays a key role as a new specific mediator of All-induced aldosterone secretion.

Novel Interactions between TGF-β1 Actions and the 12/15-Lipoxygenase Pathway in Mesangial Cells

“…Cell pellets were lysed and deacetylated. 12(S)-HETE levels in cell extracts and supernatants were quantitated by a specific RIA as described previously (29,34).…”

The Oxidized Lipid and Lipoxygenase Product 12(S)-Hydroxyeicosatetraenoic Acid Induces Hypertrophy and Fibronectin Transcription in Vascular Smooth Muscle Cells via p38 MAPK and cAMP Response Element-binding Protein Activation

“…12(S)-HETE was then extracted, and levels were quantitated using a specific radioimmunoassay as described previously (6,31).…”

Catalytic consumption of nitric oxide by 12/15- lipoxygenase: Inhibition of monocyte soluble guanylate cyclase activation

“…First, cell pellets were deacylated by treatment with 1.5 ml 0.2 M NaOH in methanol, 50 M n-propyl gallate under N 2 for 45 min. The solution was then diluted to 15% methanol and extracted, and LOX products in the cell pellets and supernatants were quantified by using a specific RIA (41).…”