title: Effects of morphine and time of day on pain and beta-endorphin.
abstract: Clients report more pain at some times of day than at others due, in part, to the temporal variation of the body's inhibitory pain response. The analgesic effectiveness of morphine varies with the time of day, perhaps due to the inhibiting or enhancing effects of the drug on plasma beta-endorphin (BE). This experiment was designed to examine the timed effects of morphine on the pain-induced BE response. Six groups of treatment mice (injected with morphine sulfate) and 6 groups of control mice (injected with saline) were exposed to an acute pain stimulus at 4-h intervals, and blood was collected. Plasma BE was analyzed using radioimmunoassay. Control mice showed a robust circadian BE-response rhythm with a peak at 0000 and a nadir at 1200, whereas the BE response of mice that received morphine was arrhythmic. Animals that received morphine tolerated the noxious stimulus longer, but the analgesia varied with time of day. These results indicate that morphine abolishes the rhythmic BE response to pain and does not inhibit pain equally at all times of day. Morphine doses should be titrated to maximize the endogenous pain control system while achieving analgesia with decreased dosages.
authors.affiliation: College of Nursing, University of Nebraska Medical Center, 985330 Nebraska Medical Center, Omaha, NE 68198-5330, USA. nrasmuss@unmc.edu
authors.forename: Natalie Ann
authors.initials: NA
authors.lastname: Rasmussen
authors.forename: Lynne A
authors.initials: LA
authors.lastname: Farr
mesh_terms: D000208:Acute Disease; D000701:Analgesics, Opioid / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D021081:Chronobiology Disorders / Q000188:drug therapy* / Q000378:metabolism*; D019454:Chronotherapy; D004195:Disease Models, Animal; D004353:Drug Evaluation, Preclinical; D016903:Drug Monitoring; D006801:Humans; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D009020:Morphine / Q000494:pharmacology / Q000627:therapeutic use*; D010146:Pain / Q000188:drug therapy* / Q000378:metabolism*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D011863:Radioimmunoassay; D011930:Reaction Time; D013997:Time Factors; D016896:Treatment Outcome; D001615:beta-Endorphin / Q000097:blood* / Q000187:drug effects*
chemical_list: D000701:Analgesics, Opioid; D001615:beta-Endorphin; D009020:Morphine