[Action of proteinase inhibitors. 4. Effect of short-term application of chymostatin on nitrogen metabolism in the digestive tract and protein metabolism in tissue].

Chymostatin is an effective inhibitor of intracellular proteinases in vitro. In the present experiment male rats were injected intraperitonealy during a 3 days period twice daily with a solution containing 0,9 mg Chymostatin per 100 g live weight. Reference animals received a control injection containing the same solvents but no chymostatin. During this period a daily nitrogen balance was made and metabolic faecal nitrogen and true digestibility of nitrogen were estimated using 15N-labelled animals. Furthermore, apparent biological half lives of proteins in liver and intestinal tissues were determined following the decay curves for radioactivity in proteins 48 hours after injection of L-[5-3H]-arginine und L-[guanido-14C]-arginine. The fractional rate of protein synthesis in tissues was measured by a 6 hours continuous infusion technique with L-[U-14C]-tyrosine and L-[U-14C]-leucine. Among the parameters estimated only the apparent biological half lives of proteins in liver and intestinal tissues were influenced by chymostatin. However, the prolonged half lives seemed to be rather an effect of an increased reutilisation of amino acids resulting from the intracellular protein breakdown than a decreased rate of protein degradation. The in vivo effect of the proteinase inhibitor was by far inferior compared with the action in vitro. Factors like distribution, degradation and excretion of the inhibitor could be responsible for the moderate in vivo action of chymostatin.