Effect of raised plasma β endorphin concentrations on peripheral pain and angina thresholds in patients with stable angina

Abstract

Objective - To determine whether changes in plasma concentrations of β endorphins alter angina threshold and peripheral pain threshold in patients with stable angina. Design - Latin square design comparison of angina thresholds by exercise treadmill test and peripheral pain thresholds using a radiant heat source in eight patients with stable angina under control conditions, after stimulation of pituitary β endorphin release by ketoconazole, after suppression of pituitary β endorphin release by dexamethasone, and after blockade of opioid receptors by intravenous naloxone. Results - An approximately fivefold increase in circulating concentrations of β endorphins was found after administration of ketoconazole (mean (SEM): 13.9 (1.2) v 73.8 (6.2) pg/ml; p < 0.05), which was associated with an increase in peripheral pain threshold to a radiant heat source (time to onset of pain perception 72 (19) v 123 (40) seconds; p < 0.05), but no significant difference in angina threshold. A reduction in circulating concentrations of β endorphins after pretreatment with dexamethasone was statistically nonsignificant (13.9 (1.2) v 9.0 (1.5) pg/ml; NS) and was not associated with any change in either peripheral pain or angina thresholds. No effects were seen after blockade of opioid receptors by previous administration of intravenous naloxone. Conclusions - Increased plasma concentrations of β endorphins alter peripheral pain threshold but not angina threshold in patients with stable angina pectoris.