Nadler J L, Natarajan R, Stern N
Section of Endocrinology, University of Southern California/Los Angeles County Medical Center 90033.
J Clin Invest. 1987 Dec;80(6):1763-9. doi: 10.1172/JCI113269.
Angiotensin II (AII) 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 AII, 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 AII binding (91 +/- 6 to 36 +/- 4 ng/10(6) cells/h 10(-4) M, P less than 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 AII-stimulated levels of aldosterone (208 +/- 11% control, AII 10(-9) M vs. 222 +/- 38%, AII + U-60257). The LO blockers action was specific for AII since neither BW755c nor phenidone altered ACTH or K+-induced aldosterone secretion. AII stimulated the formation of the 12-LO product 12-hydroxyeicosatetraenoic acid (12-HETE) 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/10(5) cells, P less than 0.02). BW755c prevented the AII-mediated 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(-8) M) completely restored AII action during LO blockade. AII 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 AII-induced aldosterone secretion.
肾上腺球状带细胞中的血管紧张素II（AII）激活磷脂酶C，导致肌醇磷酸和富含花生四烯酸（AA）的二酰甘油形成。虽然球状带细胞可通过环氧化酶（CO）代谢AA，但该途径在醛固酮合成中作用甚微。最近的证据表明，脂氧合酶（LO）途径可能对内分泌组织如胰岛的激素分泌很重要。然而，球状带细胞合成LO产物的能力及其在醛固酮分泌中的作用尚不清楚。为研究此问题，在分离的大鼠球状带细胞中评估了非选择性和选择性LO抑制剂对AII、促肾上腺皮质激素（ACTH）和钾诱导的醛固酮分泌及LO产物形成的影响。非选择性LO抑制剂BW755c剂量依赖性地降低AII刺激的醛固酮水平，而不改变AII结合（从91±6降至36±4 ng/10⁶细胞/小时，10⁻⁴ M，P<0.001）。另一种非选择性LO阻滞剂非那吡啶以及更具选择性的12-LO抑制剂黄芩苷也观察到相同效果。相反，选择性5-LO抑制剂U-60257未改变AII刺激的醛固酮水平（208±11%对照, AII 10⁻⁹ M 对比 222±38%, AII + U-60257）。LO阻滞剂的作用对AII具有特异性，因为BW755c和非那吡啶均未改变ACTH或钾诱导的醛固酮分泌。AII刺激12-LO产物12-羟基二十碳四烯酸（12-HETE）的形成，在加载AA的细胞中通过紫外检测和高效液相色谱法（HPLC）以及在未标记细胞中通过特异性放射免疫分析（RIA）测定（从501±50增至990±10 pg/10⁵细胞，P<0.02）。BW755c阻止了AII介导的12-HETE形成增加。相反，ACTH和钾均未增加12-HETE水平。添加12-HETE或其不稳定前体12-HPETE（10⁻⁹或10⁻⁸ M）可在LO阻断期间完全恢复AII的作用。AII还使15-HETE形成增加，但15-LO产物对醛固酮分泌无影响。这些研究表明，12-LO途径作为AII诱导醛固酮分泌的一种新的特异性介质发挥关键作用。
