[Mode of action of proteinase inhibitors in rats. 2. Effect of leupeptin on N-balance and biological half-life in ad lib feeding].

During a 15-day period, growing Wistar rats (75 g) were fed ad lib. a whole-egg diet containing 10% crude protein (control group) and the same diet + a daily subcutaneous injection of 1 mg of leupeptin per animal (experimental group), respectively. To investigate the influence of the peptide aldehyde leupeptin on the M-metabolism, N-balance trials were carried out between the 1st and the 6th, and the 10th and the 15th experimental days. Leupeptine was not found to influence the true N-digestibility. However, the intermediary N-utilization, characterized by the biological value of the dietary protein, deteriorated in comparison with the control group. The peptide aldehyde under study resulted in an extension of the biological half-life of the proteins in the tissue of the small and large intestine. It was measured via the decline of radioactivity in protein following application of L-guanidino-14 C-arginine and L-(4,5-3H)-leucine. The amino acid utilization appears to have been increased as well. In connection with previous studies (SIMON et al., 1976) i, which, under somewhat different experimental conditions, leupeptine resulted in a higher intermediary N-utilization, the mentioned agent is supposed to be able to influence N-utilization. However, additional studies are required to make statements regarding the influence of dosis and metabolic situation.