title: Naloxone-provoked vaso-vagal response to head-up tilt in men.
abstract: A double-blind paired protocol was used to evaluate, in eight male volunteers, the effects of the endogenous opiate antagonist naloxone (NAL; 0.05 mg.kg-1) on cardiovascular responses to 50 degrees head-up tilt-induced central hypovolaemia. Progressive central hypovolaemia was characterized by a phase of normotensive-tachycardia followed by an episode of hypotensive-bradycardia. The NAL shortened the former from 20 (8-40) to 5 (3-10) min (median and range; P < 0.02). Control head-up tilt increased the means of thoracic electrical impedance [from 35.8 (SEM 2.1) to 40.0 (SEM 1.8) omega; P < 0.01] of heart rate [HR; from 67 (SEM 5) to 96 (SEM 8) beats.min-1, P < 0.02], of total peripheral resistance [TPR; from 25.5 (SEM 3.2) to 50.4 (SEM 10.5)mmHg.min.1-1, P < 0.05] and of mean arterial pressure [MAP; from 96 (SEM 2) to 101 (SEM 2)mmHg, P < 0.02]. Decreases were observed in stroke volume [from 65 (SEM 12) to 38 (SEM 9) ml, P < 0.01], in cardiac output [from 3.7 (SEM 0.7) to 2.5 (SEM 0.5) 1.min-1, P < 0.01], in pulse pressure [from 55 (SEM 4) to 37 (SEM 3)mmHg, P < 0.01] and in central venous oxygen saturation [from 73 (SEM 2) to 59 (SEM 4)%, P < 0.01]. During NAL, mean HR increased from 70 (SEM 3); n.s. compared to control) to only 86 (SEM 9) beats.min-1 (P < 0.02 compared to control) and MAP remained stable.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Copenhagen Muscle Research Centre, Department of Anaesthesia, Rigshospitalet 2034, University of Copenhagen, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Madsen
authors.forename: M
authors.initials: M
authors.lastname: Klokker
authors.forename: H L
authors.initials: HL
authors.lastname: Olesen
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001919:Bradycardia / Q000209:etiology; D002302:Cardiac Output / Q000187:drug effects; D004311:Double-Blind Method; D004723:Endorphins / Q000502:physiology; D006257:Head / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D011187:Posture / Q000502:physiology*; D012737:Sex Factors; D012769:Shock / Q000209:etiology; D013610:Tachycardia / Q000209:etiology; D013997:Time Factors; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
chemical_list: D004723:Endorphins; D009270:Naloxone