Abstract
Phosphate depletion in the rat is associated with the rapid development of marked magnesuria (1, 2). This phenomenon has been attributed to a decrease in the renal tubular transport of magnesium since the magnesuria occurred in the face of falling filtered load of this ion.
However, it is also possible that magnesium secretion by the renal tubule occurs during phosphate depletion and contributes to the magnesuria. The present study was undertaken to examine this question.
Methods. Male Sprague-Dawley rats weighing 220–280 g and 7 to 10 weeks old were housed individually in metabolic cages. During an adaptation period of 7 days, all rats were fed control diet containing 0.44% phosphate, 0.4% sodium, 0.41% calcium, and 0.03% magnesium (I.C.N. Pharmaceutical Co., Cleveland, Ohio). The rats were then randomly allocated to the phosphate-depleted group or the control group. The phosphate-depleted group (PD) received a diet identical to the control diet except that its phosphate content was reduced to 0.03%. Control animals continued to receive the control diet ad libitum. The rats had free access to deionized water.
Phosphate depletion lasted for 6 to 8 days. During this period both phosphate-depleted rats and the control animals were placed in plastic restraining cages several hours each day for adaptation. The day prior to the experiment, silastic catheters were placed in the left carotid artery and the right jugular vein and a blood sample was taken from the vein for the analysis of phosphate. Only PD animals with plasma phosphates less than 6.5 mg% were used in the study. On the morning of the experiment, the rats were anesthetized with halothane (Surital, Ayerst Laboratories, New York), a bladder catheter was placed and was connected to an extension which led out through the abdominal wall.
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