High altitude influence on the level and turn-over time of cardiac norepinephrine in rats.

In rats exposed to an altitude of 2,900 meters the level of endogenous cardiac norepinephrine decreases after the 5th day of exposure. The turner-over time of the amine proceeds in 3 steps which are probably related to periods of stress and adaptation: initial increase, important decrease from the 5th day and return to a normal value from the 12th day.