Effect of pH, substrate, and temperature on tryptic activity of duodenal samples.

Many tests of pancreatic exocrine function are based on the estimation of tryptic activity in duodenal juice. However, tryptic activity may be influenced by substrate, pH, and temperature. We studied the effect of substrate, pH, and temperature on tryptic activity of duodenal juice in vitro and in vivo. TAME yielded higher tryptic activity in vitro (11.25 times) and in vivo (4.54 times) compared to BAEE and BAME. Our in vitro studies also indicated that trypsin was denatured slowly between pH 6 and 4.25 and rapidly between 4.25 and 3.75. The rate of denaturation was faster at room temperature and slower in ice over a broad range of pHs. In our in vivo studies, hypersecretors showed tryptic activities consistently lower than normosecretors. The duodenal pHs of the hypersecretors were consistently lower than those of normosecretors, suggesting that the low tryptic activities were secondary to denaturation by acid. These studies indicate that the activity of trypsin in duodenal juice varies significantly with substrate, pH, and temperature. These factors must, therefore, be considered in the analysis and interpretation of trypsin.