title: Effect of morphine on sympathetic nerve activity in humans.
abstract: There are conflicting reports for the role of endogenous opioids on sympathetic and cardiovascular responses to exercise in humans. A number of studies have utilized naloxone (an opioid-receptor antagonist) to investigate the effect of opioids during exercise. In the present study, we examined the effect of morphine (an opioid-receptor agonist) on sympathetic and cardiovascular responses at rest and during isometric handgrip (IHG). Eleven subjects performed 2 min of IHG (30% maximum) followed by 2 min of postexercise muscle ischemia (PEMI) before and after systemic infusion of morphine (0.075 mg/kg loading dose + 1 mg/h maintenance) or placebo (saline) in double-blinded experiments on separate days. Morphine increased resting muscle sympathetic nerve activity (MSNA; 17 +/- 2 to 22 +/- 2 bursts/min; P < 0.01) and increased mean arterial pressure (MAP; 87 +/- 2 to 91 +/- 2 mmHg; P < 0.02), but it decreased heart rate (HR; 61 +/- 4 to 59 +/- 3; P < 0.01). However, IHG elicited similar increases for MSNA, MAP, and HR between the control and morphine trial (drug x exercise interaction = not significant). Moreover, responses to PEMI were not different. Placebo had no effect on resting, IHG, and PEMI responses. We conclude that morphine modulates cardiovascular and sympathetic responses at rest but not during isometric exercise.
authors.affiliation: Division of Cardiology, Department of Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Carter
authors.forename: Charity L
authors.initials: CL
authors.lastname: Sauder
authors.forename: Chester A
authors.initials: CA
authors.lastname: Ray
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology; D018737:Hand Strength / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007511:Ischemia / Q000503:physiopathology; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation* / Q000502:physiology / Q000503:physiopathology; D011957:Receptors, Opioid / Q000819:agonists; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology / Q000503:physiopathology
chemical_list: D000701:Analgesics, Opioid; D011957:Receptors, Opioid; D009020:Morphine