Effects of pregnancy and magnesium sulfate infusion on blood pressure and plasma catecholamines.

Magnesium sulfate (MgSO4) infusion often lowers blood pressure, but the responsible mechanisms are not clear. Since catecholamines play a major role in blood pressure regulation, we studied the effects of MgSO4 infusion on blood pressure, pulse rate, and plasma catecholamines in late pregnant and in nonpregnant New Zealand white rabbits. Pregnancy was associated with higher levels of dopamine (P less than 0.01) and epinephrine (P less than 0.001). MgSO4 treatment decreased mean arterial pressure (P less than 0.001), increased pulse rate (P less than 0.01), decreased dopamine (P less than 0.01) and decreased epinephrine (P less than 0.001). No significant effect on norepinephrine levels was noted, and there was no evidence that the effect of MgSO4 treatment was influenced by pregnancy. Further investigation is needed to clarify the role of catecholamines in mediating the effects of pregnancy and MgSO4 treatment on blood pressure regulation.