Effects of Mg-load on the contraction of uterus in sponteneously diabetic mice

首先，我们以自发性糖尿病小鼠（KK/tA9）和非糖尿病小鼠（c57/BL）为实验对象，研究外源性镁（Mg）对Mg卸载状态下子宫收缩张力的影响。将KK/Ta和C57/BL小鼠分为3组：饲喂正常饲料组（n组）；1组饲喂正常饲粮，并辅以体育锻炼（旋转笼跑）（t组）；一组以限制饮食（正常体积的一半），并伴有体育锻炼（td组）。外用Mg降低了子宫收缩张力的振幅和频率，且呈浓度依赖性。Mg对两种小鼠的张力振幅和频率的IC_<50>均以n组最小，t组次之，td组次之。这种倾向在糖尿病小鼠中更为明显。其次，研究外源性Mg对小鼠子宫收缩张力的抑制作用，并与无Mg小鼠进行比较。mg负荷由1完成。p.注射2M MgCl_2 2 ~ 3周。Mg负荷KK/Ta小鼠血清Mg浓度显著高于Mg负荷C57/Bl小鼠，而子宫Mg浓度基本相同。在Mg卸载小鼠中，C57/BL子宫对外源Mg的敏感性高于KK/Ta子宫。然而，在Mg负荷小鼠中，KK/Ta和C57/BL的差异消失，表明组织收缩力与Mg浓度之间存在相关性。在催产素诱导的挛缩中，mg负荷抑制了挛缩幅度，显著缩短了挛缩峰时间。这些结果强烈提示Mg可能影响催产素与受体之间的亲和力以及受体的密度。

First, we investigated effects of external magnesium (Mg) on the contractile tension of uterus under the condition of Mg-unload, using spontaneously diabetic mice (KK/tA9 and the non-diabetic mice (c57/BL). Both KK/Ta and C57/BL mice were divided into the folloowing three groups : a group fed with normal diet (N-group) ; a group fed with normal diet, accompanied by pohysical exercice (whirl cage running)(T-group) ; a group fed with restricted diet (a half of normal volume), accompanied by the physical exercice (TD-group). External Mg decreased the amplitude and frequency of the contractile tension of uttlerus in a concentration dependent manner. IC_<50> of Mg in the amplitude and frequency of the tension in both mice was the smallest in N-group, followed by T-group and TD-group in the order. This tendency was more eminent in diabetic mice. Secondly, the inhibitive effects of external Mg on the contractile tension of utterus were studied, using Mg-load mice, and compared with Mg-unload mice. Mg-load was done by 1. p. injection of 2M MgCl_2 for 2 to 3 weeks. In Mg-load KK/Ta mice, serum Mg concentration was significantly higher than in Mg-load C57/Bl, whereas uterus Mg concentration was almost same in both mice. In Mg-unload mice, C57/BL uterus was more sensitive to external Mg than KK/Ta uterus. In Mg-load mice, however, the difference between KK/Ta and C57/BL disappeared, suggesting the relation between the contractility and the Mg concentration in the tissue. In oxytocin-induced contracture, Mg-load suppressed the amplitude of the contracture and significantly shortened the time to the peak contracture. These resyults strogly suggested that Mg may affect the affinity between oxytocin and the receptors, and the density of the receptors.