Naloxone does not influence cardiovascular responses to mild mental stress in postmenopausal women

The interaction between central opioid activity, sex hormones, and the cardiovascular reactivity to stress is unknown. Twenty-eight healthy postmenopausal women, 16 without, and 12 with hormone replacement therapy (HRT) participated in this randomized, double-blind, cross-over study. The opioid receptor antagonist naloxone or placebo was administered intravenously on 2 different days and mild mental stress was induced by the Stroop Color-Word Test. Cardiovascular responses were assessed noninvasively by impedance cardiography. Stress significantly increased stroke volume, cardiac output, blood pressure, and heart rate, which was not influenced by opioid receptor blockade. Whereas naloxone increased cortisol plasma concentrations irrespective of HRT status, luteinizing hormone concentrations, which were higher in non-HRT compared with HRT women, were increased by naloxone in women with HRT only. These data suggest that the opioidergic tone of the hypothalamus-pituitary-adrenal axis persists in postmenopausal women, irrespective of HRT use, while the opioidergic tone on the hypothalamus-pituitary-gonadal axis seems to depend on an estrogenic milieu. Naloxone does not alter cardiovascular mental stress reactions in postmenopausal women independent of their hormone substitution status.