Resistance artery vasodilation to magnesium sulfate during pregnancy and the postpartum state

This study compared the vasodilatory responses to magnesium sulfate (MgSO4) of cerebral and mesenteric resistance arteries and determined whether the responses varied between different gestational groups. Third-order branches (4 (1.2 mM) HEPES buffer solution with increasing concentrations of MgSO4 (4, 6, 8, 16, and 32 mM) and measuring lumen diameter at each concentration. All groups exhibited concentration-dependent dilation to MgSO4, decreasing the amount of tone in the vessels. However, MA were significantly more sensitive to MgSO4 than PCA. Whereas there was no difference in the response between different gestational groups in MA, the PCA from the LP and PP groups showed a significantly diminished response to MgSO4. The percent dilation at 32 mM MgSO4 for PCA versus MA in NP, LP, and PP animals was 36 ± 2 vs. 51 ± 7% ( P < 0.05), 19 ± 9 vs. 54 ± 6% ( P < 0.01 vs. PCA and NP), and 12 ± 5 vs. 52 ± 11% ( P < 0.01 vs. PCA and NP). These results demonstrate that MgSO4 is a vasodilator of small resistance arteries in the cerebral and mesenteric vascular beds. The refractory responses of the PCA in LP and PP groups demonstrate changes in the cerebrovascular vasodilatory mechanisms with gestation. The greater sensitivity of the MA to MgSO4-induced vasodilation suggests that the prophylactic effect of MgSO4 on eclamptic seizures may be more closely related to the lowering of systemic blood pressure than to an effect on cerebral blood flow.