title: Effects of naloxone on the haemodynamic and renal functional responses to plasma volume expansion in conscious rabbits.
abstract: We tested whether the opioid antagonist naloxone affects responses to plasma volume expansion (PVE) in conscious rabbits. Under basal conditions, naloxone (6 mg x kg-(1) plus 0.3 mg x kg(-1) x min(-1) i.v.) had no observable effect, except to slightly reduce heart rate. During vehicle treatment, PVE (Haemaccel; 1 ml x kg(-1) min(-1) for 30 min plus 0.2 ml x kg(-1) x min(-1) for 60 min i.v.) reduced haematocrit by 7.1+/-0.8% (from 34.8+/-1.1%), and increased central venous pressure by 3.0+/-0.9 mmHg (from -2.8+/-1.5 mmHg), cardiac output by 42+/-9 ml min(-1) x kg(-1) (from 152+/-17 ml x min(-1) x kg(-1)), systemic vascular conductance by 0.49+/-0.11 ml x min(-1) x mmHg(-1) kg(-1) (from 1.58+/-0.23 ml x min(-1) x mmHg(-1) x kg(-1)), urine flow by 0.13+/-0.04 ml x kg(-)x min(-1) (from 0.12+/-0.02 ml kg(-1) x min(-1)) and sodium excretion by 21+/-5 micromol x kg(-1) min(-1) (from 5+/-2 micromol x kg(-1) x min(-1)). During naloxone treatment, the PVE-induced changes in haematocrit and central venous pressure were similar to those during vehicle treatment, but the increases in cardiac output (24+/-7 ml kg(-1) min(-1)), systemic vascular conductance (0.25+/-0.05 ml min(-1) x kg(-1) x mmHg(-1)), urine flow (0.09+/-0.03 ml x kg(-1) min(-1)) and sodium excretion (11+/-4 micromol x kg(-1) x min(-1)) were 31-49% less. These observations indicate that endogenous opioids mediate some of the circulatory and renal excretory responses to PVE in conscious rabbits.
authors.affiliation: Department of Physiology, Monash University, Clayton, Victoria, Australia. amany.shweta@med.monash.edu.au
authors.forename: A
authors.initials: A
authors.lastname: Shweta
authors.forename: S C
authors.initials: SC
authors.lastname: Malpas
authors.forename: W P
authors.initials: WP
authors.lastname: Anderson
authors.forename: R G
authors.initials: RG
authors.lastname: Evans
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D001923:Brain Chemistry / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006400:Hematocrit; D006439:Hemodynamics / Q000187:drug effects*; D007668:Kidney / Q000187:drug effects*; D007677:Kidney Function Tests; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010953:Plasma Volume / Q000502:physiology*; D011817:Rabbits; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors; D012079:Renal Circulation / Q000187:drug effects; D012083:Renin / Q000097:blood; D012964:Sodium / Q000652:urine; D014563:Urodynamics / Q000187:drug effects
chemical_list: D009292:Narcotic Antagonists; D017465:Receptors, Opioid, delta; D009270:Naloxone; D009320:Atrial Natriuretic Factor; D012964:Sodium; D012083:Renin