Acute stress and the brain norepinephrine uptake mechanism in the rat

The kinetic constants for norepinephrine uptake in cerebral cortical homogenates were determined in vitro immediately following an acute stress consisting of either forced immobilization, cold-wet exposure, combined cold-plus-restraint, swim stress, or electric footshock in the rat. The kinetic constants, apparent Km and Vmax, for uptake of 3H-l-norepinephrine were significantly increased only following 10 min swim at 22 degrees or following 5 min electric footshock. When severe hypothermia accompanied the stress, the findings suggested that a profound reduction in body temperature was associated with depressed responsiveness of brain noradrenergic mechanisms to stress including decreased uptake kinetic constants. In a series in which the duration of electric footshock was varied from 2 to 30 min, it was noted that the NE uptake kinetic constants were increased at 5 min, but were similar to paired controls at 2, 10 and 30 min following the onset of footshock. It was concluded that various acute stresses did not elicit a generalized response of the cortical NE uptake mechanism to stress in the rat. Furthermore, when uptake kinetic constants did change with stress, the values were often within the range of normal values seen in the rat.