TGF-beta and oxidant stress have been considered to play key roles in the pathogenesis of diabetic vascular complications; however, the stimulus for these factors in humans is not clear. The purpose of this in vivo study was to determine whether transient hyperglycemia in humans is sufficient to increase renal production of TGF-beta1 and urinary isoprostanes in normal humans. A hyperglycemic clamp procedure was performed on 13 healthy volunteers. An infusion of glucose was delivered to maintain the plasma glucose between 200 and 250 mg/dl for 120 min. Timed urine samples, collected on an overnight period before the study, at each void on completion of the procedure, and the following overnight, were assayed for TGF-beta1, F2-isoprostanes, and creatinine. Plasma samples were assayed for TGF-beta1 before and at timed intervals throughout hyperglycemia. Mean baseline TGF-beta1 in plasma was 4.57 +/- 0.22 ng/ml, and no change in plasma TGF-beta1 levels was detected throughout the hyperglycemia period. Baseline urine TGF-beta1 was 4.14 +/- 1.16 pg/mg creatinine. The fractional urine samples showed a sharp increase in TGF-beta1 excretion in the 12-h period after exposure to hyperglycemia, with a mean peak TGF-beta1 of 30.43 +/- 8.05 pg/mg (P = 0.002). TGF-beta1 excretion in the subsequent overnight urine sample was not different from baseline (4.62 +/- 1.21 pg/mg). Urinary isoprostanes increased from a baseline of 4.92 +/- 0.74 to 13.8 +/- 3.37 ng/mg creatinine. It is concluded that 120 min of hyperglycemia in normal humans is sufficient to induce an increase in renal TGF-beta1 and isoprostane production.