title: Acute cardiovascular effects of magnesium and their relationship to systemic and myocardial magnesium concentrations after short infusion in awake sheep.
abstract: The temporal relationship between the systemic and myocardial concentrations of magnesium and some of its acute cardiovascular effects were examined after short i.v. infusion administration of magnesium (30 mmol over 2 min) in five awake chronically instrumented sheep. Magnesium decreased mean arterial blood pressure and systemic vascular resistance (SVR) by 23 and 41% from baseline, respectively. These hemodynamic changes were consistent with magnesium producing primary reductions in SVR with partial heart rate (HR)-mediated compensation of blood pressure. Cardiac output and HR increased by 38 and 38% from baseline, respectively. Magnesium had little effect on myocardial contractility, but substantially increased myocardial blood flow (MBF, 77% above baseline) primarily due to direct myocardial vasodilation. The peak arterial and coronary sinus serum magnesium concentrations were 6.94 +/- 0.26 (mean +/- S.E.M.) and 6.51 +/- 0.20 mM, respectively, at 2 min. Both arterial and coronary sinus magnesium concentrations at the end of the study were still more than 3 mM, whereas all the cardiovascular effects were back to baseline. The myocardial kinetics of magnesium was consistent with rapid equilibration of magnesium (half-life 0.4 min) with a small distribution volume (71 ml) consistent with the extracellular space of the heart. In conclusion, magnesium was shown to have a rapid equilibration between the plasma/serum concentrations of magnesium and its extracellular concentration in the myocardium. However, the primary cardiovascular effect of magnesium (reductions in SVR) preceded its extracellular concentrations, and was a direct function of its arterial concentration. A "threshold" model for changes in SVR was preferred when linked to the arterial magnesium concentration.
authors.affiliation: Anaesthesia and Intensive Care, Royal Adelaide Hospital/University of Adelaide, North Terrace, Adelaide, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Zheng
authors.forename: R N
authors.initials: RN
authors.lastname: Upton
authors.forename: G L
authors.initials: GL
authors.lastname: Ludbrook
authors.forename: A
authors.initials: A
authors.lastname: Martinez
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects*; D002319:Cardiovascular System / Q000187:drug effects*; D003326:Coronary Circulation / Q000187:drug effects; D005110:Extracellular Space / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D007262:Infusions, Intravenous; D008274:Magnesium / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics*; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D012756:Sheep; D014655:Vascular Resistance / Q000187:drug effects; D014851:Wakefulness
chemical_list: D008274:Magnesium