Nitric oxide synthase expression in AT2 receptor-deficient mice after DOCA-salt

Angiotensin II type 2 receptor-deficient mice (AT(2)-/y) provide an opportunity to study the relationship between the angiotensin II type 1 receptor (AT(1)) and nitric oxide synthase (NOS) isoforms without concomitant AT(2) receptor-related effects. To test this relationship, the expression of renal NOS isoforms (neural, inducible, and endothelial) in AT(2)-/y and AT(2)+/y mice was examined. The mice were challenged with deoxycorticosterone acetate (DOCA)-salt to stimulate NO generation.

Gene expression analyses by real-time polymerase chain reaction (PCR) (TaqMan) were performed in kidneys to characterize neuronal nitric oxide synthase (nNOS), epithelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and the AT(1) receptor. Pressure-natriuresis experiments were done to determine the physiologic background.

AT(2)-/y mice showed nNOS and iNOS up-regulation. DOCA-salt increased iNOS expression more in AT(2)-/y mice than in AT(2)+/y mice. Immunohistochemistry localized the iNOS expression with DOCA-salt mainly in the glomeruli. eNOS was not different between the groups, and was not affected by DOCA-salt. DOCA-salt increased mean arterial pressure more in AT(2)-/y mice than in AT(2)+/y mice. Concomitantly, the pressure-natriuresis relationship was shifted to the right in AT(2)-/y and AT(2)+/y mice after DOCA-salt. DOCA-salt decreased renal blood flow (RBF) and glomerular filtration rate (GFR) in both groups. iNOS blockade did not lower blood pressure.

We conclude that AT(2) receptor deletion and concomitant up-regulation of the AT(1) receptor is associated with up-regulation of nNOS and iNOS. Under DOCA-salt, renal iNOS expression was further increased. Because iNOS inhibition did not change blood pressure, iNOS may not be involved in the hemodynamics, but may contribute to organ damage.