Renal handling of 125I-labelled homologous pancreatic lipase and amylase in the rat.

Experiments were carried out in vivo on rats and in vitro on tubular brush border vesicles in order to study the renal mechanisms of the elimination of pancreatic lipase and amylase from the circulation. Highly purified 125I-labelled homologous lipase, amylase or 125I-labelled di-iodo-tyrosine was injected intravenously in a single dose. The sieving coefficients of lipase and amylase were found to be 0.126 and 0.118 respectively. Less than 1% of the lipase activity but more than 10% of the radioactivity were found in the urine in the course of a 120 min experiment. In experiments with amylase, 16% of the enzyme activity and 19% of the radioactivity were present in the urine. Elimination of both enzymes showed first order kinetics and was of the same magnitude (17-24 min). The elimination curves of the radioactivity consisted of at least two components: a fast component immediately after the injection, which was identical with the decrease of the resp. enzyme activity; and a slow component (half-life 106 min), which in both cases proved to be identical with the half-life of di-iodo-tyrosine. In experiments with amylase, the excretion of protein-free 125I-activity started later than with lipase. The radioactivity of 125I-labelled lipase was taken up faster by brush-border-vesicles than that of 125I-amylase. Liberation of protein-free 125I-activity from both enzymes occurred at the same rate. At the end of the experiments the kidneys had no lipase or amylase activity, but they contained 5.4% (lipase), 3.8% (amylase) of the injected radioactivity.(ABSTRACT TRUNCATED AT 250 WORDS)