High-dose naloxone modifies cardiovascular and neuroendocrine function in ambulant subjects

Abstract

To determine the role of the opioids in the control of the cardiovascular system in awake ambulatory subjects, eight healthy men were infused with a high dose of naloxone (10 mg bolus plus 7 mg/hr), or saline placebo, for 12 hr. Ambulatory monitoring of blood pressure and heart rate every 10 min indicated no differences between trials for blood pressure ( p>0.80), but a significant difference for the maximal heart rate response during stair climbing or 1 km walks ( p<0.02). Plasma cortisol concentration were increased during the naloxone trials ( p<0.05), as was total urinary epinephrine and dopamine output ( p=0.005 and <0.03, respectively). Plasma FSH and LH concentrations were elevated during naloxone infusion (FSH: p<0.02, LH: p<0.01), but neither exercise or mental tasks significantly altered their levels ( p>0.20). The cardiovascular responses during moderate mental tasks were not affected by naloxone ( p>0.05). These results indicate that in the normal ambulatory state the opioid system has a minor role in cardiovascular regulation, as demonstrated by the urinary catecholamines. Its role becomes more evident when considerable stress in imposed.