Translocation of orally administered rat salivary cystatin into serum and kidney

This translocation was followed by means of a sensitive enzyme immunoassay. Salivary cystatin could be detected in serum, oesophagus, stomach, small intestine and kidney 15 min after oral administration. The salivary cystatin level in serum and kidney extract was maximal 15–60 and 30–60 min, respectively, after its administration and increased dose-dependently. Chromatography showed that the cystatin molecule in serum was identical to that in the submandibular saliva used for oral administration, but differed from that in kidney extract. These results suggest that salivary cystatin is absorbed intact by the gastrointestinal tract and reaches the bloodstream, from which it is taken up by the kidney and modified.