Magnesium sulphate increases lymphocyte adenosine 3':5'-cyclic monophosphate in humans

We determined the effect of i.v. magnesium sulphate, which is often combined with beta 2-adrenoceptor agonists for tocolytic therapy, on lymphocyte cyclic AMP production, extracellular magnesium and blood calcium concentrations. Sixteen healthy volunteers received i.v. magnesium sulphate 1 g h-1 over 8 h; seven volunteers also had infusion of NaCl 18 mg h-1 as control. Venous blood was taken pre- and post-infusion to determine basal lymphocyte cyclic AMP and the increase evoked by 0.1 mM isoprenaline, as well as serum and plasma concentrations of total and non-protein-bound magnesium and calcium. Following magnesium sulphate there was a significant rise in the isoprenaline-evoked increase in cyclic AMP (P < 0.05) and in the magnesium concentrations (P < 0.01) and a decrease in the free calcium concentration (P < 0.01).