Psychophysical responses to a speech stressor: correlation of plasma beta-endorphin levels at rest and after psychological stress with thermally measured pain threshold in patients with coronary artery disease.

Objectives: We tested the hypothesis that psychological stress alters plasma levels of opioid peptides and that these plasma levels are related to pain perception in patients with coronary artery disease.

Background: Public speaking psychological stress has previously been shown to be associated with silent ischemia.

Methods: After instrumentation and a 30-min rest period, venous blood samples for beta-endorphin were obtained before and immediately after psychological stress in 20 patients with coronary artery disease. Pain threshold was then assessed using a thermal probe technique at baseline and immediately after stress. Patients gave three brief speeches lasting a total of 15 min about real-life hassle situations.

Results: Psychological stress significantly increases plasma beta-endorphin levels (4.3 +/- 0.9 pmol/liter [mean +/- SE] at rest to 8.3 +/- 2 pmol/liter after stress, p < 0.05). There was a significant positive correlation between pain threshold and beta-endorphin levels after stress (r = 0.577, p = 0.008). This significant positive correlation was still present while rest blood pressure and change in blood pressure during stress were controlled for by analysis of covariance techniques.

Conclusions: In patients with coronary artery disease and exercise-induced ischemia, public speaking produces psychological stress manifested by increased cardiovascular reactivity and causes an increase in plasma beta-endorphin levels that is significantly correlated with pain thresholds. These findings may explain the predominance of silent ischemia during psychological stress in patients with coronary artery disease.