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Research ArticleCARDIOVASCULAR

Acute Cardiovascular Effects of Magnesium and Their Relationship to Systemic and Myocardial Magnesium Concentrations after Short Infusion in Awake Sheep

D. Zheng, R. N. Upton, G. L. Ludbrook and A. Martinez
Journal of Pharmacology and Experimental Therapeutics June 2001, 297 (3) 1176-1183;
D. Zheng
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R. N. Upton
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G. L. Ludbrook
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A. Martinez
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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.

Footnotes

  • Send reprint requests to: Da Zheng, Anesthesia and Intensive Care, The University of Adelaide, Adelaide, Australia, SA 5005. E-mail: da.zheng{at}adelaide.edu.au

  • This research was supported by grants from National Health and Medical Research Council of Australia.

  • Abbreviations:
    IVC
    inferior vena cava
    CO
    cardiac output
    MAP
    mean arterial blood pressure
    CVP
    central venous pressure
    LV dP/dtmax
    maximum positive rate of change of left ventricular pressure
    HR
    heart rate
    MVO2
    myocardial oxygen consumption
    MBF or Qh
    myocardial blood flow
    SVR
    systemic vascular resistance
    pO2
    blood oxygen tension
    pCO2
    blood carbon dioxide tension
    SO2
    blood oxygen saturation
    MSC
    model selection criteria
    SV
    stroke volume
    Cart
    arterial magnesium concentration
    Ccs
    coronary sinus magnesium concentration
    Vh
    apparent distribution volume of magnesium in the myocardium
    • Received November 21, 2000.
    • Accepted February 14, 2001.
  • The American Society for Pharmacology and Experimental Therapeutics
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Journal of Pharmacology and Experimental Therapeutics: 297 (3)
Journal of Pharmacology and Experimental Therapeutics
Vol. 297, Issue 3
1 Jun 2001
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Research ArticleCARDIOVASCULAR

Acute Cardiovascular Effects of Magnesium and Their Relationship to Systemic and Myocardial Magnesium Concentrations after Short Infusion in Awake Sheep

D. Zheng, R. N. Upton, G. L. Ludbrook and A. Martinez
Journal of Pharmacology and Experimental Therapeutics June 1, 2001, 297 (3) 1176-1183;

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Research ArticleCARDIOVASCULAR

Acute Cardiovascular Effects of Magnesium and Their Relationship to Systemic and Myocardial Magnesium Concentrations after Short Infusion in Awake Sheep

D. Zheng, R. N. Upton, G. L. Ludbrook and A. Martinez
Journal of Pharmacology and Experimental Therapeutics June 1, 2001, 297 (3) 1176-1183;
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