Protease inhibitors in the alimentary tract of the medicinal leech Hirudo medicinalis: in vivo and in vitro studies.

In individual leeches the flux of labeled serum through the digestive tract was monitored to measure the rate of digestion. A mean value of 10 mg of the original serum (or 2-3 mg of the contents of the foregut) per individual per day was found, which was constant during 10 weeks. On average the serum remained in the intestinum for 20 days. Occurrence and concentrations of eglin and bdellin, specific proteinase inhibitors of Hirudo, were analyzed after various periods following the ingestion of a meal. In the foregut they were present immediately after feeding. Their quantities increased several-fold within a few weeks. In the intestinum the tests for these inhibitors were always negative. The inhibition of the proteolytic activity of intestinum preparations by eglin, bdellin, and foregut extract was tested in vitro. Using azo-albumin as (an unspecific) substrate, inhibition by eglin was maximally 25% and by bdellin 60%. When the quantitative relations presumably representing in vivo conditions were applied, only a slight inhibition of proteolysis occurred. A hypothetical role of the inhibitors in the preservation of the blood stored in the foregut is discussed.