Hydrolysis and metabolism of N-benzoyl-L-tyrosyl-p-aminobenzoic acid in normal and pancreatic duct-ligated animals.

Hydrolysis and metabolism of N-benzoyl-L-tyrosyl-p-aminobenzoic acid (Bz-ty-PABA), a synthetic peptide used for the assessment of exocrine pancreatic function, were studied in normal and pancreatic duct-ligated rats and guinea pigs. Bz-ty-PABA was specifically cleaved by chymotrypsin to N-benzoyl-L-tyrosine and p-aminobenzoic acid (PABA) in mucosal homogenates of the intestine. Both of the resultant products were rapidly absorbed and excreted in the urine after oral administration of two kinds of radioactive Bz-ty-PABA (Bz[14C] and PABA[14C]) to animals. The absorption rate was correlated to the intestinal chymotrypsin activity obtained from in vitro studies. Benzoic acid and p-acetaminobenzoic acid were predominant in the urine after dosages of Bz-ty-PABA with Bz[14C] and PABA[14C], respectively, in both species. Additionally, a small amount of unchanged form of Bz-ty-PABA was excreted in the urine and bile without being cleaved by chymotrypsin. These results and the study using intravenous injections suggest that the absorption of this intact peptide may be almost 10% of the dose.