Relative low serum levels of
parathormone (PTH) and low incidence of
secondary hyperparathyroidism have been reported in diabetic uremic patients. The pathogenesis of this reported resistance to uremic
secondary hyperparathyroidism in diabetes remains controversial. We have measured the serum C-terminal
parathormone (C-PTH) renal
phosphorus threshold (TmPO4) and nephrogenous
cyclic AMP (N-cCAMP), in 2-hour urine collection in 22 patients with
diabetic nephropathy with moderate
chronic renal failure and in 27 controls with similar
creatinine clearance values (18.16 +/- 9.14 and and 19.1 +/- 8.47 ml/min). In spite of the lower levels of serum C-PTH (1.07 +/- 0.43 ng/ml) diabetic patients exhibited an increased
phosphaturia (TmPO4: 1.97 +/- 0.9 mg/100 ml GFR) when compared with the control group (C-PTH: 2.01 +/- 1.17 mg/ml, and TmPO4: 2.5 +/- 0.7 ml GFR). When the C-PTH values were plotted against the logarithm of
creatinine clearance values, both groups showed a significant linear relationship reflecting the progressive increase in PTH when GFR fell. This progressive parathyroid stimulus was also present in diabetic patients but in a lower intensity. We believe that increased
phosphaturia in diabetics with moderate
chronic renal failure may be a major factor in precluding the appearance of
secondary hyperparathyroidism in these patients once they reach the dialysis and
transplantation programs.