Effect of magnesium on red blood cell deformability in pregnancy

Red blood cell (RBC) deformability is an important factor in determining movement of red blood cells through the microcirculation. In preeclampsia and some cases of intrauterine growth restriction (IUGR), RBC deformability and microcirculation are reduced. Magnesium is administered to reduce the risk of seizures. The aim of this study was first to detect the effect of intravenous magnesium application (2 g/h) on the deformability of RBCs in pregnancies with normal RBC deformability, receiving magnesium as tocolytic agent. The second aim was to examine the effect of calcium-antagonists (magnesium, nifedipin) on the deformability of RBC of preeclamptic patients in vitro.

Part 1: magnesium (2 g/h), fenoterol (270 microg/h)+verapamil (0.2 mg/h) or placebo (NaCl 0.9%) was administered intravenously to pregnant women with premature contractions to test the tocolytic effect. RBC-deformability was measured by laser diffractoscopy in all three groups. Blood samples were taken before, after 1 h and after 24 h of administration. Magnesium-plasma-levels were measured. Part 2: Blood samples from patients with preeclampsia were incubated in vitro with magnesium (2 mmol), nifedipine (0.25 mg/ml), or placebo (NaCl 0.9%). RBC deformability was measured before and 15 min, 1 h, 2 h, 6 h, and 10 h after start of the incubation.

Part 1: The initial RBC-deformability was the same in all groups (E=0.232+/-0.017 in NaCl, 0.232+/-0.023 in fenoterol+verapamil, 0.232+/-0.019 in magnesium). After 1 h of administration, RBC-deformability was significantly greater with magnesium (0.254+/-0.020) and Fenoterol+Verapamil (0.238+/-0.02) compared to placebo (0.231+/-0.015). After 24 h the effect on RBC deformability in the fenoterol+verapamil-group was gone (0.234+/-0.021 compared to 0.234+/-0.016 in placebo), while in the IV-magnesium-group RBC-deformability remained increased (E=0.241+/-0.019). Statistical analysis of the influence of magnesium-plasma-levels showed the maximum effect at concentrations of 1.95-2.15 mmol/l. Part 2: RBC-deformability in preeclampsia was reduced as predicted by previous studies (0.120+0.0086 versus 0.232 in normal pregnancy). In vitro incubation with magnesium enhanced RBC-deformability in preeclampsia. Even after 15 min, a statistically significant effect was seen (0.127+/-0.0091 versus 0.121+/-0.0091 in placebo). Maximum effect was reached after 6 h of incubation (0.159+/-0.0093 versus 0.133+/-0.0091). Incubation with Nifedipine also enhanced RBC deformability [0.127+/-0.0091 after 15 min, 0.149+/-0.010 after 6 h (maximum effect)], but the effect was less pronounced than with magnesium.

Intravenous magnesium therapy over a 24-hour period increases RBC-deformability even in pregnancies with normal RBC-deformability. In vitro measurements show an increase of RBC-deformability in preeclampsia in response to magnesium, which could offer additional therapeutic benefit for the treatment of reduced blood flow seen in most cases of preeclampsia.