Roy D R
Division of Nephrology, Royal Victoria Hospital, Montréal, Qué., Canada.
Can J Physiol Pharmacol. 1987 Sep;65(9):1918-22. doi: 10.1139/y87-298.
To determine the contribution of the juxtamedullary loop of Henle to magnesium reabsorption during magnesium deficiency, we performed two-phase micropuncture studies of end-descending limbs in a group of magnesium-deficient rats (n = 7) and in a pair-fed control group (n = 8) given MgCl2 in their drinking water. In the magnesium-deficient rats, daily excretion of magnesium fell to very low values (1.2 +/- 0.2 vs. 52 +/- 12 microM.day-1.100 g body weight-1, p less than 0.05). Plasma magnesium concentration and fractional magnesium excretion during the control phase were nearly 52 and 27%, respectively, of the values observed in pair-fed controls. Fractional magnesium delivery to the end-descending limb did not differ significantly between the two groups. During the acute magnesium repletion phase, fractional magnesium excretion and fractional magnesium delivery to the end-descending limb increased by a similar value in the two groups of rats, despite a lower filtered load of magnesium in the magnesium-deficient group. Absolute magnesium reabsorption upstream to the end-descending limb was lower in the magnesium-deficient rats but was otherwise tightly coupled to the filtered load of magnesium (Y = 0.91 + 0.37 x, r = 0.82, p less than 0.05). Similar observations were made with regards to whole kidney magnesium reabsorption. Our results suggest that, in young magnesium-deficient rats, magnesium reabsorption is tightly coupled to the filtered load of magnesium both in segments upstream to the juxtamedullary end-descending limb and in the whole kidney, and that a reabsorptive defect for magnesium is not evident in this setting.
为了确定在镁缺乏期间亨利氏髓旁袢对镁重吸收的贡献，我们对一组镁缺乏大鼠（n = 7）和一组饮用含MgCl₂ 水的配对喂养对照组大鼠（n = 8）的髓袢降支末端进行了两阶段微穿刺研究。在镁缺乏大鼠中，镁的每日排泄量降至非常低的值（1.2±0.2对52±12μmol·天⁻¹·100 g体重⁻¹，p<0.05）。对照期的血浆镁浓度和镁排泄分数分别约为配对喂养对照组所观察值的52%和27%。两组之间向髓袢降支末端的镁输送分数没有显著差异。在急性镁补充期，尽管镁缺乏组的镁滤过负荷较低，但两组大鼠的镁排泄分数和向髓袢降支末端的镁输送分数增加的值相似。镁缺乏大鼠髓袢降支末端上游的绝对镁重吸收较低，但在其他方面与镁滤过负荷紧密相关（Y = 0.91 + 0.37x，r = 0.82，p<0.05）。关于全肾镁重吸收也有类似的观察结果。我们的结果表明，在年轻的镁缺乏大鼠中，髓袢降支末端上游节段和全肾的镁重吸收都与镁滤过负荷紧密相关，并且在这种情况下镁重吸收缺陷不明显。
