Complement studies in BN rats with mercuric chloride-induced immune glomerulonephritis

Whole complement haemolytic activity (CH50) changes were examined in 71 rats, developing and HgCl2-induced biphasic immune glomerulonephritis. In some rats, serum C4 level was also studied. Whole CH50 level was compared with proteinuria and C3 glomerular deposits. In control rats or in rats injected with low doses of HgCl2, there was no complement decrease. In rats injected with a high dose, after an initial increase (also observed in controls), CH50 level decreased between day 12 and day 20, sometimes dramatically. This decrease, observed during the first phase, was transient, CH50 levels returning to normal before day 30. Serum C4 level varied in accordance with CH50, indicating a classical pathway activation of complement. Fall in CH 50 and proteinuria was correlated: the heavier the proteinuria, the greater the fall in complement (p < 0.01). Whether proteinuria is or is not the consequence of the complement activation, remains to be demonstrated.