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