AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 1 203-R207, Copyright © 1984 by American Physiological Society
Role of conjugation and red blood cells for inactivation of circulating catecholamines
N. Alexander, S. Yoneda, N. D. Vlachakis and R. F. Maronde
We investigated the extent of catecholamine (CA) conjugation in plasma and
accumulation inside red blood cells (RBCs) after forced immobilization of
the rat. A control blood sample was obtained from undisturbed rats resting
in home cages via an indwelling aortic catheter. Then rats were immobilized
for 2 h, and blood samples were taken during stress at 15 min and 2 h and
at 30 min poststress. Both sulfate and glucuronide conjugates were
deconjugated by enzymatic hydrolysis and measured by radioenzymatic
thin-layer chromatographic methods. In plasma of resting rats, the major
conjugate of norepinephrine (NE) is sulfate and that of epinephrine (E) and
dopamine (DA) is glucuronide; total conjugates in plasma are 53, 57, and
97% of total NE, E, and DA, respectively. During stress, sulfate conjugates
of NE, E, and DA increased significantly along with free NE, E, and DA. DA
glucuronide unexpectedly declined at 2 h of stress and 30 min poststress.
Concentrations of free CAs rose in RBCs during stress, as did NE sulfate,
the only conjugate present in RBC lysate. We conclude that both CA
conjugation and RBC accumulation are enhanced when large amounts of free CA
enter the circulation as a result of immobilization stress and that the
relative importance of these inactivation pathways is different for the
three CAs.
