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 (PT H) on formation and breakdown of type I collagen, using two recently d eveloped radioimmunoassays for serum PICP (the carboxyterminal propept ide of type I procollagen) and serum ICTP (the carboxyterminal telopep tide 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 ICT P 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 s ubjects, 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 ser um PICP decreased (from 185 +/- 78 to 118 +/- 42 mu g/liter; P less th an 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 hydrox yproline and calcium. The decrease of serum PICP was also related to t he changes of serum ICTP and hydroxyproline in urine, serum calcium, a nd alkaline phosphatase but not to osteocalcin, an established marker of osteoblastic activity. The findings support the fact that serum ICT P is a valuable method for evaluating bone resorption and is also easy to perform. Furthermore, the discordant results for the different mar kers of osteoblastic activity indicate that they reflect different fun ctions of the cell.