CO2 ASPHYXIA INCREASES PLASMA NOREPINEPHRINE IN RATS VIA SYMPATHETIC-NERVES

The objective of this study was to determine whether the plasma norepi nephrine (NE) increase in rats exposed to CO2 asphyxia was due to adre nal gland release or sympathetic nerve ending (SNS) release. Plasma NE was measured by high-performance liquid chromatography in hypertensiv e and normotensive rats using the following protocol: control session, CO2 exposure, N-2 exposure, reserpine + CO2, and adrenalectomy + CO2. Four strains of male and female rats were used: spontaneously hyperte nsive rats, Wistar-Kyoto rats, and two congenic strains with different Y chromosomes. The same rats were used throughout the experiment (n = 80). Blood pressure measured by aortic telemetry increased similar to 50-60 mmHg in response to CO2 in all strains. CO2 increased NE 6-10x in all strains and both genders. N-2 produced a significant increase i n NE (73% of CO2 response). Reserpine significantly decreased (67%) pl asma NE after CO2. Adrenalectomy did not significantly reduce the NE r esponse to CO2. In conclusion, the increase in plasma NE after CO2 was associated with SNS release and not adrenal medullary release, was ma inly due to hypoxia, and was not a specific response to CO2.