The biliary excretion of trypsin in rats

The serum half-life of bovine [3H]acetyltrypsin was estimated to be 9 min following intravenous administration in rats. This was maintained when six successive doses of 200 micrograms each were given at 1-h intervals. The enzyme was removed from the circulation after complexing with alpha 2-macroglobulin (alpha 2-M). The amount of 3H label appearing in bile increased with each successive dose and this was associated with breakdown products ( less than 10,000 daltons) of the alpha 2-M/[3H]acetyltrypsin. Intact alpha 2-M/[3H]acetyltrypsin was recovered from bile but represented only 0.06% of the administered dose of active enzyme.