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

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 non-significant (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.