Defective nitric oxide production and functional renal reserve in patients with type 2 diabetes who have microalbuminuria of African and Asian compared with white origin.

Diabetic nephropathy is a leading cause of end-stage renal failure. Its incidence is higher and is increasing in persons of Indo-Asian and African-Caribbean (African-Asian) compared with those of white origin. Nitric oxide deficiency is associated with progressive renal disease. It was hypothesized that differences in the capacity to increase glomerular filtration (functional renal reserve) would exist between these racial groups in relation to nitric oxide availability. Patients with type 2 diabetes of African-Asian (n = 9) and white (n = 9) origin with microalbuminuria were studied under euglycemic conditions. Glomerular filtration, renal plasma flow, and clearance of the stable metabolites of nitric oxide, nitrite, and nitrate were measured before and after a renal vasodilatory stimulus of a mixed amino acid intravenous infusion. There were no significant differences in age, duration of diabetes, and baseline glomerular filtration (57.1 [14.1] versus 55.8 [10.1] yr; P = 0.82, 14.5 [10.2] versus 9.1 [7.0] yr; P = 0.19 and 125.9 [30.9] versus 127.2 [44.6] ml/min per 1.73 m(2); P = 0.94) between the African-Asian and white groups. Functional renal reserve, change in renal plasma flow, and percentage change in nitrate and nitrite clearance was significantly higher in the white compared with the African-Asian group (21.9 [45.7] versus -2.5 [28.2] ml/min per 1.73 m(2); P = 0.043, 155.8 [205.9] versus -90.1 [146.0]; P = 0.03 ml/min per 1.73 m(2) and 26.7 [85.1] versus -44.7 [16.9] %; P = 0.013, respectively). The differences in functional reserve were not confounded after adjustment for diabetes duration (P = 0.034). The data suggest that these patients with type 2 diabetes of African and Asian origin lose functional renal reserve earlier in the evolution of nephropathy than whites. The differences appear to be due to defective nitric oxide production or bioavailability and might explain some of the propensity to develop end-stage renal disease.