Opioid peptides in response to mental stress in asymptomatic dilated cardiomyopathy.

Fourteen asymptomatic dilated cardiomyopathy patients showing normal plasma levels of beta-endorphin, Met-enkephalin, dynorphin B, norepinephrine and endothelin-1 but elevated atrial natriuretic factor (ANF) levels underwent two Mental Arithmetic Tests (MAT), with placebo and naloxone hydrochloride infusion, respectively. MAT significantly (p < 0.01) increased blood pressure, heart rate, opioid peptides, norepinephrine, ANF, but not endothelin-1. Naloxone infusion significantly (p < 0.05) attenuated the increments produced by MAT in all measured parameters during placebo infusion. These results indicate that in asymptomatic dilated cardiomyopathy the endogenous opioid system, activated by stress-induced sympathoadrenergic hyperactivity, may further increase the sympathetic tone in a positive feedback that is interrupted by naloxone.