Endogenous opioids modulate the cardiovascular response to mental stress

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Endocrinology

Background:

• The cardiovascular system's response to mental stress involves complex hormonal and neural pathways.
• Endogenous opioids are implicated in modulating physiological responses, including stress.
• Understanding the role of endogenous opioids is crucial for managing stress-related cardiovascular conditions.

Purpose of the Study:

• To investigate the role of endogenous opioids in mediating cardiovascular, hormonal, and psychological responses to mental stress.
• To determine if naloxone, an opiate antagonist, alters the physiological and psychological effects of acute mental stress.

Main Methods:

• Two controlled studies were conducted involving mental stress tasks and non-stressful control tasks.
• Participants received either naloxone (8 mg) or a saline placebo in a single-blind or double-blind manner.
• Cardiovascular (heart rate, blood pressure), hormonal (epinephrine, norepinephrine, cortisol, ACTH), and psychological (anxiety) measures were collected.

Main Results:

• Naloxone significantly enhanced the heart rate response to mental stress but did not affect blood pressure or anxiety levels.
• Plasma levels of epinephrine and norepinephrine were not altered by naloxone during stress.
• Naloxone increased plasma cortisol and ACTH levels irrespective of the task (stressful or control).

Conclusions:

• An endogenous opioid mechanism appears to inhibit the cardiovascular response, specifically heart rate, during mental stress.
• Opioid antagonism with naloxone unmasks or enhances the heart rate reactivity to stress.
• These findings highlight a novel inhibitory role for endogenous opioids in the acute stress response.