AJP - Endocrinology and Metabolism, Vol 252, Issue 1 E96-101, Copyright © 1987 by American Physiological Society
Uptake of exogenous spermidine by rat lungs perfused in situ
D. E. Rannels and J. L. Addison
Uptake of the polyamine spermidine (SPD) from the pulmonary circulation was
characterized by using ventilated rat lungs perfused in situ with
Krebs-Henseleit-bicarbonate buffer containing 4.5% bovine serum albumin,
5.6 mM glucose, and 20 amino acids at plasma levels. [14C]SPD was
accumulated by the lungs in a time- and concentration-dependent manner. The
pathway of SPD uptake exhibited saturation kinetics with an apparent Km in
the range of 1 microM and a Vmax of 450-540 pmol/g lung min. SPD uptake was
inhibited by the naturally occurring polyamines putrescine and spermine
(SPM) and by the inhibitor of polyamine synthesis, methyglyoxal
bis(guanylhydrazone) (MGBG). Inhibition of SPD uptake by SPM followed
competitive kinetics; although MGBG was also a competitive inhibitor of SPD
uptake, MGBG was less effective than SPM. These observations indicate that
SPD is taken up from the pulmonary circulation by a carrier-mediated
pathway that is inhibited by other natural polyamines and by MGBG and
exhibits substrate affinity in the range of plasma SPD concentrations.
