Journal of Applied Physiology, Vol 67, Issue 1 239-242, Copyright © 1989 by American Physiological Society
Chronic CO inhalation and carotid body catecholamines: testing of hypotheses
S. Lahiri, D. G. Penney, A. Mokashi and K. H. Albertine
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104.
The purpose of this study was twofold: one concerns carotid blood flow and
tissue PO2 and the other the effect of chronic hypoxic hypoxia on enhanced
catecholamine content. The rationale was that chronic CO inhalation would
not mimic the effect of hypoxia on the carotid body if its tissue blood
flow is sufficiently high to counteract the effect of CO on O2 delivery
and, hence, on tissue PO2. The differential effects of CO on the carotid
body and erythropoietin-producing tissue would also indicate that the
effect of hypoxic hypoxia on the carotid body is the result of a direct
action of a local low O2 stimulus rather than secondary to a systemic
effect initiated by other O2-sensing tissues. To test these alternatives we
studied the effects of chronic CO inhalation on carotid body catecholamine
content and hematocrit in the rats, which were exposed to an inspired PCO
of 0.4-0.5 Torr at an inspired PO2 of approximately 150 Torr for 22 days.
The hematocrit of CO-exposed rats was 75 +/- 1.1% compared with 48 +/- 0.7%
in controls. Dopamine and norepinephrine content of the carotid bodies (per
pair) was 5.88 +/- 0.91 and 3.02 +/- 0.19 ng, respectively, in the
CO-exposed rats compared with 6.20 +/- 1.0 and 3.29 +/- 0.6 ng,
respectively, in the controls. Protein content of the carotid bodies (per
pair) was 18.4 +/- 1.6 and 20.5 +/- 0.9 micrograms, respectively. Thus,
despite a vigorous erythropoietic response, the CO-exposed rats failed to
show any significant stimulation of carotid body in terms of the content of
either catecholamine or protein. The results suggest that carotid body
tissue PO2 is not compromised by moderate carboxyhemoglobinemia because of
its high tissue blood flow and that the chronic effect of hypoxic hypoxia
on carotid body is direct.
