Mineral Metabolism in Diabetes Mellitus: Changes Accompanying Treatment with a Portable Subcutaneous Insulin Infusion System*

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Abstract
To define abnormalities that might account for the osteopenia of diabetes we investigated mineral metabolism n i seven juvenile-onset diabetic patients. Each wasstudied before and after normal or near-normal plasma glucose levels had been achievedby 7–14 days of treatment with a portable infusion system delivering insulin scMean basal urinary calcium excretion fell from 0.075 ± 0.06 mg/dl glomerular filtrate (GF) on conventional therapy to 0.023 ± 0.02 mg/dl GF during pump therapy (P < 0.025). Serum phosphorus rose from 4.09 ± 0.09 to 5.01 ± 0.8 mgdl (P < 0.001) due to a rise in the renal tubular threshold for phosphate reabsorption from 3.89 ± 1.2 to 5.49 ± 1.1 mg/dl (P < 0.001). Incremental urinary calcium excretion after a standard oral calcium load (a measure of calcium absorption) did not change significantly. Similarly, there wereno significant changes in the immunoreactive parathyroid hormone concentration (61 ± 25 vs. 63 ± 20 μleq/ml) or in nephrogenous cAMP excretion (1.37 ± 0.7 vs. 1.18 ± 0.6 pmol/dl GF). There was no significant change in the 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentration (38 ± 9 pg/ml on conventional therapy)vs. 31 ± 12 pg/ml on insulin pump therapy). We conclude that the restoration of normoglycemia over 7-14 days in these diabetic patients led to a reduction in urinary calcium and phosphorus excretion. The reduction in calciuria was not associated with changes in concentrations of immuno-reactive parathyroid hormone and (1,25-(OH)2D,hormones, which govern calcium homeostasis. There was also a striking rise i n the renal tubular threshold for phosphate reabsorption. Phosphate depletion due to excess urinary phosphate losses in poorly controlled diabetes may contribute significantly to the development of diabetic osteopenia.