AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 1 139-R145, Copyright © 1993 by American Physiological Society
Fate of circulating amino-terminal propeptide of type III procollagen in conscious pigs
L. T. Jensen, J. H. Henriksen, J. Risteli, H. P. Olesen, M. D. Nielsen and I. Lorenzen
Department of Rheumatology, University of Copenhagen, Hvidovre Hospital, Denmark.
The amino-terminal propeptide of type III procollagen (PIIINP, M(r) 42,000)
is a promising marker for the formation of type III collagen of granulation
tissue in experimental and clinical studies. The disposal kinetics of
circulating PIIINP is, however, almost unknown. In conscious pigs with a
thoracic duct-venous shunt, 125I-labeled PIIINP was injected intravenously.
The initial distribution volume was 2.2 liters, which was 1.7 times the
plasma volume (P < 0.01). The disappearance curve was three-phased, with
an initial steep decline (t1/2 58 min), followed by two slower phases (t1/2
239 min and 289 h). Consecutive gel filtrations showed that the initial
slope of the plasma disappearance curve corresponded to the plasma
clearance of the intact PIIINP. The initial plasma clearance was 26.5 ml
plasma/min, whereas the urinary clearance was 8.7 ml plasma/min (P <
0.01). The other components of the plasma disappearance curve originated
from the formation and disappearance of a high and a low molecular weight
(MW) fraction as part of the degradation of PIIINP. The high MW fraction
(approximately M(r) 90,000) was similar to a previously described, but not
further characterized, PIIINP immunoreactive component. The existence of
the low MW fraction (approximately M(r) 20,000) has not been reported
before. The lymphatic recirculation of intact PIIINP was rapid, and the
lymph-serum ratio was almost constant within 1 h of injection. We conclude
that the t1/2 of circulating PIIINP is 58 min, that PIIINP escapes the
circulation very quickly, and that the degradation of PIIINP includes at
least two intermediary steps.
