Aloamaka C P, Ezimokhai M, Morrison J, Cherian T
Department of Obstetrics and Gynaecology, Faculty of Medicine and Health Sciences, UAE University, Al Ain.
Cardiovasc Res. 1993 Sep;27(9):1629-33. doi: 10.1093/cvr/27.9.1629.
There is evidence for involvement of the endothelium in magnesium induced vasodilatation. In view of the use of magnesium in the treatment of women with pre-eclampsia, and because the mechanism of the vascular effects of magnesium in pregnancy is not fully understood, this study examined the dilator response to magnesium of aortic rings from pregnant and non-pregnant rats. The role of the endothelium was also evaluated.
Rings from descending thoracic aorta of pregnant and non-pregnant rats, contracted with either 10(-7) M phenylephrine or 40 mM potassium chloride, were relaxed with increasing concentrations of MgSO4 in the presence or absence of 10(-6) M indomethacin or endothelium. The rings were also contracted to 10(-5) M phenylephrine, in calcium-free medium containing 0, 1.2, or 4.8 mM MgSO4.
The relaxation of aortic rings from pregnant rats to MgSO4 was greater when stimulated with potassium chloride but that of rings from non-pregnant rats was greater when stimulated with phenylephrine. Neither the presence of MgSO4 nor pregnancy had any effect on intracellular calcium dependent contraction. The relaxations of rings from either pregnant or non-pregnant rats to MgSO4 were not significantly altered by de-endothelialisation or pretreatment with 10(-6) M indomethacin.
The effect of pregnancy on magnesium induced relaxation of rat aortic smooth muscle was dependent on the agent used to induce contraction in the tissue, probably because pregnancy exerted different actions on receptor and voltage operated calcium channels. This effect of pregnancy was independent of either endothelial function or prostaglandin synthesis. Neither pregnancy nor the presence of magnesium affected the release of intracellular stored calcium.
有证据表明内皮细胞参与了镁诱导的血管舒张过程。鉴于镁用于治疗先兆子痫女性，且由于孕期镁的血管效应机制尚未完全明确，本研究检测了妊娠和非妊娠大鼠主动脉环对镁的舒张反应。同时也评估了内皮细胞的作用。
将妊娠和非妊娠大鼠胸降主动脉环用10⁻⁷ M去氧肾上腺素或40 mM氯化钾收缩后，在有或无10⁻⁶ M吲哚美辛或内皮细胞存在的情况下，用递增浓度的硫酸镁使其舒张。这些环也在含0、1.2或4.8 mM硫酸镁的无钙培养基中用10⁻⁵ M去氧肾上腺素收缩。
氯化钾刺激时，妊娠大鼠主动脉环对硫酸镁的舒张反应更大，而去氧肾上腺素刺激时，非妊娠大鼠主动脉环的舒张反应更大。硫酸镁的存在或妊娠对细胞内钙依赖性收缩均无影响。妊娠或非妊娠大鼠主动脉环对硫酸镁的舒张反应，经去内皮或用10⁻⁶ M吲哚美辛预处理后均无显著改变。
妊娠对镁诱导的大鼠主动脉平滑肌舒张的影响取决于用于诱导组织收缩的药物，这可能是因为妊娠对受体和电压门控钙通道产生了不同作用。妊娠的这种影响独立于内皮功能或前列腺素合成。妊娠和镁的存在均不影响细胞内储存钙的释放。
