Selective vasodilator effect of magnesium sulfate in human placenta

Problems: To determine if magnesium sulfate (MgSO₄) attenuates the vasoconstrictor effect of angiotensin II (Ag II), endothelin-1 (ET-1) and thromboxane mimetic (TX) in the human fetal-placental vasculature and if interleukin-1 beta (IL-1β) is involved in this process. Study Design: Isolated placental cotyledons (n = 18) were dually perfused with fetal perfusion pressure used as an index of vascular response. The vasoconstriction effect of bolus injection of various concentrations of Ag II (10^-10-10^-6 M) or ET-1 (10^-10-10^-4 M) or TX (10^-10-10^-5 M) was established in the absence or presence of MgSO₄ (7 mg% constant infusion during 10 hr). Statistical significance was determined by paired t-test and ANOVA. Results: MgSO₄ significantly attenuates the vasoconstrictor effect of Ag II in the fetal-placental vasculature in the human placenta (P = 0.02). Moreover, significant attenuation of vasoconstrictor response to ET-1 (10^-10-10^-5 M) was observed in the presence of MgSO₄ (P = 0.02). However, no attenuation of the vasoconstrictor response to TX was noted in the presence of MgSO₄ (P > 0.5). Ag II and TX were shown to induce IL-1β secretion by placental tissue. This effect was completely reduced by perfusion of MgSO₄ (7 mg%; constant infusion). Conclusions: MgSO₄ significantly attenuates the vasoconstrictor effect of Ag II and ET-1 in the fetal-placental vasculature in the human placenta, but not that of TX. Inhibition of local production of IL-1β could be one of the mechanisms used by MgSO₄ to reduce the vasoconstrictory effect of Ag II and TX in human placental cotyledone.