Effect of hypoxia and hypercapnia on catecholamine content in cat carotid body

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Abstract
The content of catecholamines (CA) in the cat carotid body was determined before and after 0.5 h exposures to normoxic normocapnia [arterial O2 partial pressure (PaO2) 126 .+-. 28 Torr, aterial 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 3 exposures were indistinguishable among themselves as were the decreases in E. The decrease in CA content is probably attributable to increased release. The release of CA during the chemoreception of hypoxia apparently is different from that during the chemoreception of hypercapnia and the concept of different mechanisms for the chemoreception of hypoxia and hypercapnia is supported.