Possible compensatory role of parathyroid hormone-related peptide on maintenance of calcium homeostasis in patients with non-insulin-dependent diabetes mellitus.

Recent studies have revealed that altered mineral and vitamin D metabolism is observed in diabetic patients with the complication of osteopenia. In order to elucidate the role of parathyroid hormone-related peptide (PTHrP) on calcium homeostasis in diabetes, we have measured the serum level and urinary excretion of PTHrP as well as other serum calcium-regulating hormones in 106 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 43 control subjects. The serum concentration of intact PTH was 2.34 +/- 0.13 (mean +/- SEM) pmol/l in NIDDM patients, which is significantly lower than the value of 3.11 +/- 0.14 pmol/l in the controls (p < 0.01). Both serum calcium and calcitonin, however, were not statistically different from controls. On the other hand, circulating PTHrP in NIDDM was 40.1 +/- 1.4 pmol/l, which is significantly elevated when compared to 27.3 +/- 1.3 pmol/l in the controls (p < 0.01). Moreover, urinary excretion of PTHrP also was significantly higher in NIDDM (p < 0.01). In the present study, the circulating calcium level was well preserved in NIDDM patients, although the PTH levels were shown to be decreased. The elevated serum PTHrP might, therefore, have a physiologically compensatory role on the calcium regulatory systems in NIDDM. Furthermore, this elevation is most likely due to the excess production of this peptide and not to the decrease in urinary excretion.