Inhibition of mouse-liver microsomal enzyme function after oral administration of sodium nitrite

The effect of a single oral dose of sodium nitrite on mouse-liver microsomal-enzyme activity was studied. Sodium nitrite (100 mg/kg) produced a rapid and marked inhibition of both aminopyrine-demethylase and aniline-hydroxylase activity. Inhibitory effects of approximately 50% were observed as early as 15 min after treatment and were still persisting at 90 min. The responses at 45 min after treatment were dose-dependent, no response being observed at 25 mg/kg. Daily oral administration of 25 or 50 mg sodium nitrite/kg for 8 days produced no subacute inhibition of microsomal-enzyme activity. The mechanism of this response involves non-competitive inhibition of enzyme activity. While 300 mg sodium nitrite/kg had little effect on the K m of aminopyrine demethylase. V was decreased from 2·35 to 1·54 μmols formaldehyde/g liver/hr.