S-Mg Does Not Change Inversely to S-FFA During Acute Stress Situations

The apparently divergent changes in serum magnesium (S-Mg) and serum free fatty acids (S-FFA) in stress situations associated with ele vated levels of circulating adrenaline were studied experimentally in 12 healthy volunteers, who were each given three adrenaline infusions (0.05 μg/kg bw/min over one hundred twenty minutes). Before the adrena line infusions the volunteers were treated for three days with either a non-selective beta-blocking agent (propranolol) or a beta-1-selective agent (atenolol) or with placebo.

Six of the volunteers underwent a fourth adrenaline infusion after pretreatment with a beta-2-selective beta-blocking agent (ICI 118551). S- Mg and S-FFA were determined every fifteen minutes. After pretreatment with placebo, adrenaline infusion caused an increase in S-FFA from 0.22 ± 0.20 mmol/L (mean ± SD) to max 0.59 ± 0.39 mmol/L after thirty minutes of adrenaline infusion (p < 0.001). At one hundred twenty minutes S-FFA had decreased to 0.35 ± 0.26 mmol/L. Thirty minutes after cessation of the adrenaline infusion, S-FFA had returned to the same level as before the infusion. S-Mg before the adrenaline infusion was 0.83 ± 0.05 mmol/L, rose to 0.85 ± 0.05 at fifteen minutes, and then decreased to 0.78 ± 0.05 at one hundred thirty- five minutes (p < 0.05). Pretreat ment with atenolol did not change this pattern, although the changes in S-FFA and S-Mg were of a smaller magnitude but still statistically sig nificant. No statistically significant changes in S-FFA or S-Mg were seen after pretreatment with either pro pranolol or ICI 118551.

The results show that the adrena line-induced changes in S-FFA and S-Mg disappear after blockade of the beta-2-adrenoceptor. The changes in S-FFA were not opposite to the changes in S-Mg, and although the changes in S-Mg could be explained in part by a binding of Mg to FFA in serum, there are probably other mechanisms at work too, such as a transport from the extracellular to the intracellular compartment.