ACE‐independent ANG II generating pathway in type II diabetic renal vascular disease

Abstract

The db/db mouse exhibits progressive type II diabetic renal disease. Studies were performed to test the hypothesis that ACE‐independent ANGII generation in the diabetic kidney contributes to afferent arteriole (AA) reactivity. Conscious non‐fasted blood glucose levels and body weight were elevated (523 ± 22 mg/dl, 54 ± 1g vs 161 ± 15 mg/dl, 30 ± 1g), while 24hr blood pressure measured by radiotelemetry was not different (108 ± 3 vs 107 ± 3 mmHg; n=5, 6) in db/db compared to db/m mice, respectively. Circadian rhythm for blood pressure was absent and heart rate was decreased in db/db mice (484 ± 16, 537 ± 12 bpm; P<0.05). AA were studied using the mouse in vitro blood perfused juxtamedullary nephron technique utilizing euglycemic (5mM) and hyperglycemic (30mM) solutions for db/m and db/db mice, respectively. AA responses to ANGI (1–1000nM) ± ACE inhibitor (1mM Captopril) ± Serine proteinase inhibitor (1mM PMSF) were measured. Baseline AA diameters of db/db (14.9 ± 0.5μm; n=22) were significantly larger than db/m (13.3 ± 0.6μm; n=19, P<0.05) mice. Significant vasoconstriction to 10, 100, 1000nM ANGI was observed in both groups (−10±2, −31±4, −30± 5% db/db, n=10; −11 ± 3, −30 ± 5, −30 ± 5 db/m, n=8) due to conversion of ANGI→ANGII. There were similar responses to ANGI in db/m and db/db mice. Vasoconstriction produced by ANGI→ANGII was significantly attenuated by Captopril and Captopril + PMSF in db/m mice (−30 ± 5, −10 ± 3, −2 ± 7%; n=8, 3, 3 at 1μM ANGI); however, there was no significant difference between ANGI and ANGI + Captopril in db/db mice. Interestingly, ANGI responses in db/db were blocked by ACE + chymase inhibition (−30 ± 5, −30 ± 7, −7 ± 5 %; n=10, 3, 3 at 1μM ANGI). Vasoconstictor responses to 100nM ANGII were intact in the presence of inhibitors (−17 ± 7, −15 ± 3%). These data suggest that intrarenal ANGII may be formed from ANGI by increased chymase activity in diabetes. NIDDK‐62003 & P20RR018766