Effects of controllable vs. uncontrollable chronic stress on stress-responsive plasma hormones.

We have previously reported effects of chronic stress on circadian rhythms of temperature, eating, and locomotor activity. These studies were conducted using an around-the-clock signalled intermittent footshock paradigm in which some rats have control over shock termination while other rats are yoked to the rats with control. Although this paradigm is stressful, as suggested by decreases in food intake and disrupted circadian rhythms, rats tolerate the paradigm well, continuing to eat, drink, gain weight, and groom. In the present studies, rats were sacrificed following 3 or 14 days of stress, and plasma was collected for hormonal assays. After 3 days of stress, plasma corticosterone and prolactin levels were elevated in both stress groups compared to controls; yoked rats had higher levels of corticosterone than rats in the group with control over shock termination, while prolactin levels in both stressed groups were similar. ACTH levels were similar in stressed and control rats. After 14 days of stress, ACTH and corticosterone levels in both stress groups were similar to control levels. Prolactin levels were elevated in the yoked experimental group compared to levels in control or controllable stress groups. These data support previous studies suggesting that control over stressors attenuates the effects of stress on physiology and demonstrate that two hormones with diverse biological effects are elevated by chronic stress.