Glucocorticosteroid effects on dog and rat serum complement

Inhibiting properties of glucocorticosteroids in vivo on the complement system are not fully recognized. Dexamethasone and prednisolone (10(-7)-10(-3)mol/l.) have no direct effects on serum complement of the dog, rat, human and guinea pig. Yet after subcutaneous application of dexamethasone (0.4 mg/kg) on two consecutive days to healthy beagle dogs the total functional complement is reduced to about 60% of the normal level within the next three days. This effect could be shown to be dose-dependent in male beagle dogs. Partial recovery of the depressed complement level (CH50 U/ml) occurs after the 6th day without treatment. In parallel a decrease in serum C3 is observed. The qualitative serum protein pattern documented by cellulose acetate film electrophoresis (CAF) reflects the decrease of C3 by a reduced beta 1-beta 2 level with a concomitant increase of the alpha 2 serum proteins. In contrast, serum complement, C3 and the serum CAF pattern in rats are not much altered by prednisolone (2 X 15 mg/kg s.c.) or dexamethasone (2 X 2 mg/kg s.c.). Thus the rat appears relatively insensitive to humoral changes induced by steroid alone. Altered liver protein synthesis of complement and other acute phase proteins appear responsible for the profound steroid effects observed in the dog.