1. This study examined the influence of H2O2, interleukin-6 and platelet-derived growth factor on the proliferation of rat mesangial cells. Mesangial cells were exposed to either a single pulse or three daily pulses of H2O2 (10−8-10−4 mol/l), alone or in combination with interleukin-6 (5 ng/ml) and/or platelet-derived growth factor (10 ng/ml). Proliferation was assessed after 24 h and 72 h of incubation using [3H]thymidine incorporation and cell counts.

2. Although one pulse of H2O2 had no significant effect on mesangial cell proliferation, three daily pulses of 10−6 mol/l H2O2 resulted in a significant increase in [3H]thymidine incorporation of 31 (52.6, 10.3)% (median and 75th-25th interquartile range) (P <0.001). Both interleukin-6 and platelet-derived growth factor were also mitogenic to mesangial cells, [3H]thymidine incorporation increasing by 19 (36.7, −6.7)% (P <0.05) and 53.5 (107, 21.9)% (P <0.001), respectively. The mitogenic effect of interleukin-6 was enhanced by 10−6 mol/l H2O2 [49.9 (77.7, 12.3)%] (P <0.01), whereas the addition of 10−6 mol/l H2O2 to platelet-derived growth factor resulted in a summated increase in [3H]thymidine incorporation of 82.7 (113, 57.4)% (P <0.001). Incubation with all three substances simultaneously resulted in down-regulation of growth compared with H2O2 plus platelet-derived growth factor by 55.4 (77.7, 103)% (P <0.05).

3. These findings suggest that reactive oxygen species may play a major role in determining the mesangial cell proliferation that occurs in certain forms of glomerulonephritis, acting either alone or in combination with other growth factors.

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