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This Article Full Text Full Text (PDF) All Versions of this Article: 288/4/H1521    most recent 00994.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Euser, A. G. Articles by Cipolla, M. J. Search for Related Content PubMed PubMed Citation Articles by Euser, A. G. Articles by Cipolla, M. J.

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

Departments of Neurology, Obstetrics and Gynecology, and Pharmacology, University of Vermont College of Medicine, Burlington, Vermont

Submitted 28 September 2004 ; accepted in final form 30 November 2004

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 (<200 µm) of the posterior cerebral (PCA) and mesenteric arteries (MA) were dissected from nonpregnant (NP; n = 6), late pregnant (LP; day 19, n = 6), and postpartum (PP; day 3, n = 6) Sprague-Dawley rats. A concentration-response curve was performed by replacing the low-MgSO₄ (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.

eclampsia; cerebral arteries; mesenteric arteries; rat

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