Plasma electrolyte concentrations in women and the effects of oestrogen administration

Age-related changes in the concentrations of the main plasma electrolytes and in the urinary excretion of some of these ions have been examined in 436 pre-menopausal and 117 post-menopausal women. The main changes up to the menopause were decreases in the mean plasma potassium, calcium and total protein concentrations, accompanied by increases in the renal excretion of calcium and inorganic phosphate. The decrease in plasma total calcium concentration was completely accounted for by the fall in albumin and globulin concentrations. The main changes observed at the menopause were increases in plasma sodium, total calcium, inorganic phosphate and magnesium concentrations, an increase in the plasma "anion gap" and increases in the renal excretion of sodium, magnesium and inorganic phosphate. All these changes were reversed by treatment with ethinyl oestradiol. The causes and significance of some of these changes are discussed, particularly the menopausal rises in plasma sodium concentration and in the plasma "anion gap".