Dopamine and norepinephrine dynamics in rat carotid body during long-term hypoxia

The contents of dopamine (DA), norepinephrine (NE) and 3,4-dihydroxyphenylacetic acid (DOPAC), and the utilization rates (secretion plus breakdown) of DA and NE were measured in carotid bodies of rats exposed, to normobaric hypoxia (10% O2 + 90% N2) for 0, 2, 7, 14 or 28 days. Long-term hypoxia elicited gradual increase in DA, NE and DOPAC contents, which after 28 days were increased 27, 51 and 4.6 fold, respectively. The DA utilization rate estimated after blockade of biosynthesis by alpha-methyl-p-tyrosine gradually increased from two days to the end of hypoxic exposure. The utilization rate of NE was unaltered within the first 7 days but was greatly increased after 14 and 28 days. It was concluded that the utilization rates of both DA and NE were increased by long-term hypoxia but these increases had different time courses. Dopamine, whose utilization increased in the early stage of hypoxia, might exert neurochemical effects on the chemoreceptors throughout the exposure, whereas NE, whose utilization was stimulated after two weeks of hypoxia, might play a significant role only after a delay.