In vivo and in vitro effects of sodium azide on mouse complement

A microtiter hemolytic assay was utilized to determine sodium azide (NaN3) modulation of B6C3F1 and C3H mouse serum complement levels in vivo and in vitro. Functional complement was expressed in CH50 units per milliliter. Experiments were performed to determine the in vitro effect of NaN3 on complement mediated lysis of IgM sensitized rabbit erythrocytes. Concentrations of 5, 10, 20, 30, 40, 60, and 80 mM NaN3 were added to microtiter wells containing Tris buffer, IgM sensitized rabbit erythrocytes, and serum complement from naive female C3H mice. Although NaCl and KCl controls had an inhibitory effect, NaN3 demonstrated a significant dose-dependent inhibition of complement-mediated lysis. In the three in vivo experiments, female B6C3F1 mice were exposed to NaN3 and physiological saline (vehicle control). Complement hemolytic ability was evaluated after a 1-day, single iv injection of 0.2, 2.0, and 20.0 mg/kg NaN3; at Days 1, 2, 3, 4, and 6 of a 6-day time course study after ip administration of 20 mg/kg NaN3; and at the end of an 11-day study involving daily injections of 10, 15, and 20 mg/kg NaN3 given ip. No significant changes in complement-mediated hemolysis were observed in the in vivo experiments. These studies indicate that NaN3 does not affect mouse complement levels in vivo. However, NaN3 suppresses in vitro complement hemolytic ability.