This experiment was performed to investigate differential effects of continuous and intermittent restraint stress on noradrenaline (NA) turnover in brain regions of male Wistar rats by measuring levels of a major metabolite of NA, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) levels, as well as by measuring levels of plasma corticosterone and organ weights of the thymus, spleen, and adrenal glands. Rats in the 15-min and 30-min intermittently stressed groups showed significantly larger increases in MHPG-SO4 levels in most brain regions relative to those in the 90-min and 180-min continuously stressed groups, even though the total stress duration was equal or shorter. Body weight loss and loss of relative thymus weight in the 15-min intermittently stressed groups were the most marked among the five treatment groups. These findings suggest that stress-rest cyclicity is critical in determining the extent of stress-induced brain NA turnover and peripheral physiological responses.
