An oral test of pancreatic chymotrypsin activity using N-acetyl-L-tyrosyl-p-amino-benzoic acid in rats.

After a single dose of up to 50 mg/kg body weight (optimal amount for the test) of p-aminobenzoic acid or the corresponding amount of synthetic chymotrypsin substrate N-acetyl-L-tyrosyl-p-aminobenzoic acid, the urinary excretion of p-aminobenzoic acid in rats increases approximately linearly during 24 h. Higher doses do not cause any further significant increase in the amount of urine excreted p-aminobenzoic acid. Compared with a 24 h collecting period, 82% of p-aminobenzoic acid and 77% of p-aminobenzoic acid from N-acetyl-L-tyrosyl-p-aminobenzoic acid were excreted in the urine during the first 6 h after oral application of these substances. Therefore it is sufficient for practical purposes to determine p-aminobenzoic acid in 6 h urine samples. Stimulation of pancreatic secretion by application of 2.5 U of pancreozymin and 2.5 U of secretin failed to bring about significant increase in the cleaved p-aminobenzoic acid in the urine.