Adaptation to chronic stress. Temporal pattern of immune and neuroendocrine correlates.

Stress-inducing stimuli are associated with a suppression of immune function. In this study, the relationship between pituitary-adrenal hormone release and natural cytoxicity was examined in the rat during single and repeated instances of chronic stress. Increased plasma concentrations of both adrenocorticotropic hormone (ACTH) and beta-endorphin/lipotropin were correlated with increases in natural killer (NK) activity following a single period of immobilization. After 4 days of repeated daily immobilization (2.5 hours/day), the secretory response of beta-endorphin/lipotropin was similar to that on day 1, but NK activity was lower than on day 1. These observations suggest a complex interaction between pituitary-adrenal responses to stress and changes in natural cytoxicity.