Submitted on November 3, 2004
Accepted on May 9, 2005
Naloxone does not influence cardiovascular responses to mild mental stress in postmenopausal women
Brigitte Litschauer1, Georg Schaller2, and Michael Wolzt2*
1 Center of Physiology and Pathophysiology, Medical University Vienna, Vienna, Austria
2 Department of Clinical Pharmacology, Medical University Vienna, Vienna, Austria
* To whom correspondence should be addressed. E-mail: michael.wolzt{at}meduniwien.ac.at.
The interaction between central opioid activity, sex hormones, and the cardiovascular reactivity to stress is unknown. 28 healthy post-menopausal women, 16 without and 12 with hormone replacement therapy (HRT) participated in this randomised, double-blind, cross-over study. The opioid receptor antagonist naloxone or placebo were administered intravenously on two different days and mild mental stress was induced by the Stroop Color-Word Test. Cardiovascular responses were assessed non-invasively 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 (LH) concentrations, which were higher in non-HRT compared to 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 post-menopausal 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 post-menopausal women independent of their hormone substitution status.
