Magnesium sulfate infusion during late gestation does not elicit a peripheral vascular steal and preserves placental perfusion.

Abstract

Despite proven efficacy in interrupting uterine smooth muscle contraction for periods of 24-48 h, a recent clinical study concluded that the adrenergic beta-receptor agonist, ritodrine hydrochloride (Yutopar) had significant detrimental side effects. Our previous preclinical studies have shown that ritodrine reduces placental blood flow via a vascular steal phenomenon. Moreover, ovarian blood flow is reduced by approximately 40% by ritodrine treatment. Reduced ovarian blood flow during tocolytic treatment presented the possibility for a blood-flow-mediated decrease in progesterone secretion which would have negative effects on uterine quiescence. Pharmacological agents such as calcium channel blockers and magnesium sulfate have tocolytic potential. Magnesium sulfate infusion has a long clinical history of safety and efficacy; however, the possibility for latent detrimental hemodynamic and tissue/organ blood flow responses was unexamined. Therefore, the present studies examined hemodynamic and organ blood flow in near-term pregnant rats given intravenous MgSO4. Our results show that (a) peripheral vascular steal is not induced, and (b) placental perfusion is preserved during MgSO4 infusion. However, ovarian blood flow is significantly reduced and blood-flow mediated decrease in progesterone secretion requires consideration during implementation of tocolysis via MgSO4 infusion.