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The Mg, Ca and immunoreactive parathyroid hormone (PTH) serum levels were determined in 22 uremic patients on chronic hemodialysis with different Mg concentrations in the dialysate. Baseline levels of PTH, Ca and Mg were obtained over a 4-month-period whilst on Mg dialysis of 1.5 mEq/l. Patients were then divided into three groups: 10 patients were dialyzed for 6 months with 0.5 mEq/l of Mg, 7 patients with 1.5 mEq/l, and 5 patients with 2.5 mEq/l Mg. At the end of the 6-month period with differentiated Mg dialysis the three groups were characterized by significantly different Mg serum levels. On the contrary, no significant changes were observed in the PTH or the Ca serum levels. The results of this study indicate that PTH secretion in uremic patients on regular hemodialysis is not appreciably influenced by the Mg serum levels.

1. Methylguanidine administered orally to normal volunteers was almost completely recovered in the urine, indicating that it is absorbed in the gastrointestinal tract and is not converted into other compounds. In normal persons at least, its urinary output therefore corresponds to its metabolic production rate plus the amount ingested. 2. In normal persons, diets based on foods not containing methylguanidine (e.g. vegetarian, protein-free and milk-egg) caused a fall in the urinary output of methylguanidine as compared with the output of the same subjects on a free diet. Conversely, higher amounts of methylguanidine were excreted on a diet rich in broth and in boiled beef, which contain large amounts of methylguanidine formed from the oxidation of creatinine, caused by boiling. 3. Oral administration of creatinine to normal volunteers induced an immediate and marked increase in urinary excretion of methylguanidine, and the ingestion of [methyl-14-C]creatinine by uraemic patients was followed by the urinary excretion of labelled methylguanidine. These findings indicate that creatinine is partly converted into methylguanidine in both normal and uraemic subjects and accounts for the high metabolic production of methylguanidine in patients with renal failure, in whom the body pool of creatinine is high. 4. Creatinine, incubated at 38 degrees C for 24 h in Krebs bicarbonate solution (pH 7-38) through which was bubbled oxygen with 15% carbon dioxide, was partially oxidized to methylguanidine. This raises the possibility that even in vivo such a conversion may occur "non-enzymatically".

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Plasma and erythrocyte magnesium (Mg) concentrations were measured in uremics on regular hemodialysis, in healthy persons and in patients with anemia due to causes other than renal failure. The mean plasma Mg concentration was found to be significantly higher in the uremic patients than in other subjects. The erythrocyte Mg concentration in anemic uremics and in nonuremic anemics was found to be higher than in normal subjects and a close inverse relationship was found between this figure and the hematocrit. It seems reasonable to argue that anemia, rather than renal failure, is related to the high concentration of Mg in erythrocytes.

The determination of whole blood magnesium concentration (MgT) was investigated in uremics on chronic dialysis with a broad range of hematocrit (Ht) and of plasma magnesium concentration (MgP). In view of the inverse correlation between erythrocyte magnesium concentration (MgC) and Ht in dialyzed uremics, as shown in our previous paper, it was possible to derive a formula which expressed MgT in terms of MgP and Ht. By exploring the predictive power of this formula, it can be concluded that MgT can be calculated directly from MgP and Ht.

The correlation between whole blood potassium concentration (Kt) and hematocrit (Ht) was investigated in subjects with a broad range of Ht. This relationship was found to be represented by a curve, and its form was derived by the manipulation of the formula concerning the inverse correlation between Ht and erythrocyte potassium concentration (Kc).