Hepatic and renal extraction of circulating type III procollagen amino-terminal propeptide and hyaluronan in pig.

Hepatic and renal clearance of the amino-terminal propeptide of type III procollagen (PIIINP) and of the glycosaminoglycan, hyaluronan (HA) were investigated in a catheterization study of seven healthy anesthetized pigs. Two assays were used, in order to distinguish between the metabolism of different PIIINP-related antigens. One was the PIIINP RIA Kit, which measures the intact propeptide. The other was the PIIINP Fab assay, in which the antibody has an equal affinity to the intact propeptide and to smaller fragments, of which the latter constitutes most of the antigenic activity in serum. Hepatic and gastrointestinal extraction were evaluated from measurements of serum concentrations in the artery, the portal vein and the hepatic vein. We found a significant hepatic extraction of the intact propeptide (extraction ratio 0.14) and of HA (extraction ratio 0.23), but not of smaller PIIINP fragments. No gastrointestinal extraction of any of the tested substances could be demonstrated. Only smaller PIIINP fragments (such as the col 1 fragment) were extracted by the kidneys (the extraction ratio in the PIIINP Fab assay was 0.19). The renal extraction ratio of HA was 0.14. The amounts of PIIINP fragments and of HA extracted by the kidneys were 50- and 3-times the amounts found in urine, respectively, indicating that the col 1 fragment and HA are degraded in the kidneys in addition to urinary excretion. Our results suggest a dynamic turnover of connective tissue-related components with a fast catabolism of circulating components in liver and kidneys.