AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 6 1520-R1525, Copyright © 1995 by American Physiological Society
Effects of hypoxia and hypercapnia on whole body release and clearance of choline
D. J. Jenden and O. U. Scremin
Department of Pharmacology, University of California Los Angeles School of Medicine 90095, USA.
We have recently demonstrated an increase in arterial blood choline (Ch)
concentration in normocapnic hypoxia and apnea. This could be due to
enhanced release of free Ch from tissues, to decreased Ch clearance, or
both. The present investigations was undertaken to determine the individual
contributions of these processes to the whole body balance of Ch, using an
intravenous infusion of tracer quantities of [2H4]Ch to assess the
bidirectional flux between the central pool and peripheral pools. Rats were
subjected to normocapnic hypoxia or hypercapnia; release and clearance of
Ch were calculated using a simple model. Hypoxia caused an increase in Ch
production and a decrease in Ch clearance. At severe levels of hypoxia, Ch
clearance was essentially zero. Hypoxia was attended by progressive
acidosis that was related to the magnitude of the hypoxic challenge. To
determine the possible effects of acidosis per se on the variables
measured, respiratory acidosis with normoxia was provoked by controlled
administration of CO2. Under these conditions, parallel decreases in Ch
production and Ch clearance were observed.
