Restraint stress-induced elevations in plasma corticosterone and beta-endorphin are not accompanied by alterations in immune function.

A variety of stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, thereby resulting in elevated levels of circulating ACTH, beta-endorphin and corticosterone. Since these hormones have been shown previously to alter measures of immune function, we determined whether presentation of a stressor which activates the HPA axis produces a concomitant alteration in immune function. Restraint stress resulted in significantly elevated levels of corticosterone and beta-endorphin without affecting either proliferative or cytolytic activities of lymphocytes. At concentrations similar to those achieved during stress, in vivo, corticosterone exhibited a dose- and time-dependent reduction in both lymphocyte proliferation as well as natural killer cytotoxicity, in vitro. beta-Endorphin, on the other hand, was without direct or modulatory effects. These results indicate that restraint stress-induced activation of the HPA axis occurs without accompanying alterations in immune function.