Proof of chymotrypsin activity by a peroral test using a synthetic peptide with a C-terminal P-aminobenzoic acid residue.

The reciprocal relationship between the peroral dose and urinary excretion and the optimum testing load of para-aminobenzoic acid (PABA) and N-acetyl tyrosine peptide (Ac-L-Tyr-PABA), alone and after cholecystokinin-pancreozymin and secretin hormonal stimulation, was studied in rats. Between the peroral test dose of PABA and its urinary excretion there is a constant proportionality which is correlated to the size of the dose and is linear in the dose range up to 50 mg/kg b.w. The situation for Ac-L-Tyr-PABA is similar. Dosage of over 50 mg/kg b.w. do not lead to proportional excretion of the test substance in the urine. I.v. stimulation by cholecystokinin-pancreozymin and secretin, using peroral administration of Ac-L-Tyr-PABA, was not followed by a significant increase in urinary PABA excretion. The optimum peroral load of both PABA and Ac-L Tyr-PABA in the rat is 50 mg/kg b.w. With this dose, 82% of free PABA and 77% of the model peptide PABA excreted in 24 hours is found in the urine after 6 hours, so that for practical purposes this interval is adequate. The findings furnish important information on the possibilities of utilizing the given technique for diagnosing the state of exocrine pancreatic function in clinical practice.