be linked to endogenous endorphins as well (Bandura, O'Leary, Taylor, Gautheir, & Gossard, 1987). Aerobic conditioning such as that achieved by long-distance runners is associated with high betaendorphin levels. High beta-endorphin levels (or some concomitant) in long-distance runners may have psychological consequences. Those who are aerobically conditioned are less likely to respond to a mental stressor with elevated blood pressure and strong autonomic nervous system activation. Perhaps endogenous opioids play a role for people who engage in aerobic exercise in creating resistance to the effects of stress (Fiatarone et al., 1988; McCubbin, Cheung, Montgomery, Bulbulian, & Wilson, 1992). Consistent with the hypothesis that high beta-endorphin levels enhance the body's stress resilience, Post, Pickar, Ballenger, Naber, and Rubinow (1984) found lower plasma beta-endorphin levels in trait anxious persons. Studies linking psychological states with enhanced immune system functioning have appeared. In these studies the chemical mediators (for example, betaendorphin) of better immune system functioning were not identified. However, the picture is consistent with the view that a sense of efficacy (a correlate of high beta-endorphin levels) enhances the immune system. Heisel, Locke, Kraus, and Williams (1986) found that college students with lower elevations on the Minnesota Multiphasic Personality Inventory (Hathaway & McKinley, 1967) distress scales displayed stronger natural killer cell activity. Levy, Herberman, Maluish, Schlien, and Lippman (1985) found that cancer patients exhibiting a fighting spirit and greater optimism displayed stronger natural killer cell activity. Examination of the effects of behavioral and psychological interventions on endogenous opioids is in its infancy. The studies on runners have examined beta-endorphin specifically. The studies on systematic desensitization have established that the success of the procedure ...
