1. The distribution of intact parathyroid hormone-(1–84) [PTH-(1–84)] and of its COOH-terminal fragments was determined in human serum by column chromatography. In addition to PTH-(1–84) (peak I), COOH-terminal fragments having molecular weights of approximately 4000–7000 (peak II) and immunoreactive components co-eluting with human PTH-(1–12) (peak III) were observed.

2. Mean concentrations of intact PTH-(1–84) and of its COOH-terminal fragments were significantly raised in chronic renal failure as compared with those of normal subjects. Mean amounts of peak II were higher in patients with chronic renal insufficiency than in nutritional vitamin D deficiency, in pseudohypoparathyroidism and in primary hyperparathyroidism, despite comparable amounts of PTH-(1–84).

3. In chronic renal failure as well as in a group of patients with vitamin D deficiency, pseudohypoparathyroidism and primary hyperparathyroidism and in controls, significant linear relations were found between the serum concentrations of calcium and log (peak II/peak I). Our findings suggest that the conversion of intact PTH-(1–84) into COOH-terminal fragments by the parathyroid glands (resulting in a raised secretion of fragments) and/or in peripheral organs may be directly related to the serum concentration of calcium. However, the degradation of the fragments may also be suppressed in a calcium-dependent manner.

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