Journal of Applied Physiology, Vol 54, Issue 5 1408-1413, Copyright © 1983 by American Physiological Society
Effect of hypoxia and hypercapnia on catecholamine content in cat carotid body
R. S. Fitzgerald, P. Garger, M. C. Hauer, H. Raff and L. Fechter
The purpose of this study was to determine the content of catecholamines
(CA) in the cat carotid body before and after 0.5 h exposures to normoxic
normocapnia [arterial O2 partial pressure (Pao2) 126 +/- 28 Torr, arterial
CO2 partial pressure (Paco2) 36.4 +/- 1.5 Torr], hypoxic normocapnia (Pao2
25 +/- 3 Torr, Paco2 36.7 +/- 3.3 Torr), and normoxic hypercapnia (Pao2 132
+/- 13 Torr, Paco2 = 98.2 +/- 7.6 Torr). CA synthesis was blocked using
alpha-methylparatyrosine methyl ester (AMPT) prior to alterations in the
inspired air. There was a significant decrease in carotid body content of
dopamine (DA), norepinephrine (NE), and epinephrine (E) 1 h after AMPT
administration. Analysis of variance and Duncan new multiple range
procedures revealed that during the subsequent 0.5-h exposures to normoxia,
hypoxia, or hypercapnia, only the decrease in DA during hypoxia was
significantly greater than that during normoxia; the loss during
hypercapnia was not. The decreases in NE during the three exposures were
indistinguishable among themselves as were the decreases in E. The decrease
in CA content is probably attributable to increased release. The data
reveal that the release of CAs during the chemoreception of hypoxia is
different from that during the chemoreception of hypercapnia and support
the concept of different mechanisms for the chemoreception of hypoxia and
hypercapnia.
