EFFECTS OF INFUSION OF PARATHYROID-HORMONE AND PRIMARY HYPERPARATHYROIDISM ON FORMATION AND BREAKDOWN OF TYPE-I COLLAGEN

The influence of chronic and acute exposure to parathyroid hormone (PTH) on formation and breakdown of type I collagen, using two recently developed radioimmunoassays for serum PICP (the carboxyterminal propeptide of type I procollagen) and serum ICTP (the carboxyterminal telopeptide of type I collagen), have been evaluated. Fasting morning values were obtained from 18 women with primary hyperparathyroidism (HPT) and an equal number of age-matched, healthy controls. A 24-hour infusion of synthetic human parathyroid hormone (PTH 1-38) was performed in 14 healthy females. The patients with HPT had higher values for serum ICTP than the controls (6.0 +/- 3.0 and 4.1 +/- 2.1 mu g/liter; P < 0.05), whereas the serum PICP concentrations were not different (170 +/- 72 and 151 +/- 65 mu g/liter; n.s.). During infusion of PTH in healthy subjects, there was an increase of the serum ICTP concentrations (from 3.6 +/- 1.3 to 4.4 +/- 1.8 mu g/liter; P < 0.001) whereas those of serum PICP decreased (from 185 +/- 78 to 118 +/- 42 mu g/liter; P less than or equal to 0.0001). The increase of serum ICTP during infusion of PTH was positively related to the increase of serum calcium and other indices of bone resorption, i.e., fasting urinary excretions of hydroxyproline and calcium. The decrease of serum PICP was also related to the changes of serum ICTP and hydroxyproline in urine, serum calcium, and alkaline phosphatase but not to osteocalcin, an established marker of osteoblastic activity. The findings support the fact that serum ICTP is a valuable method for evaluating bone resorption and is also easy to perform. Furthermore, the discordant results for the different markers of osteoblastic activity indicate that they reflect different functions of the cell.