ATRIAL-NATRIURETIC-FACTOR AND ANGIOTENSIN-II STIMULATE NITRIC-OXIDE RELEASE FROM HUMAN PROXIMAL TUBULAR CELLS

1. It has been recently reported that angiotensin II can enhance atria l natriuretic factor-stimulated cyclic GMP release from brain capillar y endothelial cells and stimulate directly the release of cyclic GMP b y Neuro 2a cells. A possible mechanism mediating such cyclic GMP relea se could be via the production of nitric oxide and the resultant stimu lation of soluble guanylate cyclase. 2. The ability of angiotensin II, atrial natriuretic factor and c((4-23)) atrial natriuretic factor to stimulate nitric oxide production was investigated in primary cultures of human proximal tubular cells. 3. Freshly prepared human proximal t ubular cells were seeded onto 6-well plates and allowed to reach confl uence, Cells were then incubated with incremental concentrations of ei ther angiotensin II, atrial natriuretic factor or c((4-23)) atrial nat riuretic factor alone for 1, 4, 12 or 24 h or in the presence of the n itric oxide synthase inhibitor N-G-monomethyl-L-arginine. Angiotensin II was also incubated with human proximal tubular cells in the presenc e of the AT(1) and AT(2) receptor antagonists DuP 753 and PD 123319. 4 . Incubation of human proximal tubular cells with angiotensin II, atri al natriuretic factor or c((4-23)) atrial natriuretic factor produced a dose- and time-dependent increase in nitric oxide production, which was inhibited in the presence of N-G-monomethyl-L-arginine, A similar increase in nitric oxide production was observed after incubation with atrial natriuretic factor or c((4-23)) atrial natriuretic factor. 5. The angiotensin-induced increase in nitric oxide production was not in hibited in the presence of either the angiotensin AT(1) or AT(2) recep tor antagonists DuP 753 or PD 123319. 6. This study demonstrates that primary cultures of human proximal tubular cells can be stimulated to produce nitric oxide by both atrial natriuretic factor and angiotensin II, Furthermore, the atrial natriuretic factor-induced response appea rs to be mediated via the atrial natriuretic factor-C receptor, while the angiotensin II-induced response appears to be mediated by a novel, as yet unidentified, angiotensin II receptor.