The transport of 14C-neostigmine from plasma to bile

The transport of 14C-neostigmine from plasma to bile was investigated in the rat. After i.v. injection of 14C-neostigmine, approximately 0.8 per cent of the administered radioactivity was recovered from bile within 4 hr. Concurrent infusion ofglycopyrronium or oxyphenonium did not modify the biliary excretion of radioactivity. However choleresis, induced by infusion of sodium dehydrocholate, significantly increased the excretion of radioactivity; approximately 1.3 per cent of the dose was detected in bile within 4 hr. In other experiments the concentration of radioactivity in plasma, liver cells, and bile was determined 30 min after intravenous 14C-neostigmine. The concentration of radioactivity in liver cell water was 3–15 times that in bile and 23–59 times that of plasma. Although neostigmine was concentrated 5-fold during transfer from plasma to bile, it was concluded that passive mechanisms were responsible for both the entry of the drug into liver cells and for its excretion in bile.