Vitamin C or L-ascorbate is an effective endogenous reducing agent inf
luencing the functions that are involved with the redox mechanism. Det
ection of oxygen tension changes by the carotid body chemoreceptors is
one such function. In this study we investigated the hypothesis that
the level of ascorbate, if present, could change in the carotid body a
s a result of ascorbate's interaction in the chemosensing process, whi
ch would be reflected in the production of the ascorbyl radical. We ad
dressed this issue by examining changes of the ascorbyl radical: using
the in vitro electron spin resonance spectroscopy (ESR), in the carot
id bodies dissected from pentobarbitone anesthetized cats exposed in v
ivo to three eucapnic, breathing gas mixtures of different O-2 concent
ration: normoxic, 21% O-2; hypoxic, 7% O-2; and hypoxic-reoxygenated,
7% O-2 followed by 100% O-2. Each group consisted of five cats, yieldi
ng five pairs of carotid bodies for the ESR signal recording. We found
that the intensity of ESR signals, measured as peak-to-peak amplitude
, was diminished by 39 and 43% in the hypoxic and hypoxic-reoxygenated
groups, respectively, compared with that in normoxia. The study shows
that ascorbate was present in the normoxic carotid body and was deple
ted by hypoxia. We conclude that ascorbate is part of free radical mec
hanisms operative in the carotid body in hypoxia. (C) 1997 Elsevier Sc
ience B.V.