Fate of insulin analogues in intact and nephrectomized rats
determined by their receptor binding constants.
Kruse, Viggo, Ivan Jensen, Lise Permin, and Anders Heding.
Novo Nordisk, Bagsvaerd, Denmark, and 1Hagedorn Research Institute,
Gentofte, Denmark
APStracts 4:0019E, 1997.
Following i.v. injection of 125I-labeled human insulin and analogues
in normal and nephrectomized rats we examined their kinetic fate by
Q-Sepharose separation into intact ligand, 'fragments' (genuine
fragments and protein-bound radioactivity), and iodide. Receptor
binding constants (kass; kdis) of the analogues were estimated
dynamically in vitro by BIAcore(tm). The very fast disappearance of
intact ligand from serum was found to be determined by (1) both kass
and kdis of receptor-bearing tissue - thus substantiating our primary
hypothesis -, (2) elimination by kidneys, and (3) fast
extravascularization. The rate of appearance of degradation products
from receptor-mediated intracellular processing seems determined by
kdis. With the possible exception of a truncated analogue, ligand
appears protected against degradation while the intracellular
receptor-ligand complex remains intact. Non-receptor mediated
processing in kidneys is slow, compared to the receptor-mediated
uptake and degradation of ligands with rate constants comparable to
those of insulin. We observed binding of insulin and analogues,
putatively to serum proteins; binding capacity and affinity appear
insignificant for insulin, but considerable for some analogues.
Received 23 September 1996; accepted in final form 16 January
1997.
APS Manuscript Number E479-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 19 February 1997