Skeletal responsiveness to parathyroid hormone in healthy females: relationship to menopause and oestrogen replacement

In order to directly evaluate the role of parathyroid hormone (PTH) and its interaction with oestrogens for postmenopausal bone loss, studies were performed where synthetic human (1-38) PTH was infused s.c. over 24 h in 15 healthy females. Measurements were made of serum electrolytes, PTH and biochemical indices of bone turnover: serum osteocalcin and alkaline phosphatase and fasting urinary hydroxyproline and calcium. During the infusion of PTH there were significant increases of serum calcium (15%), fasting urinary calcium (55%) and hydroxyproline (80%) but a reduction of the serum osteocalcin concentrations (15%). There were significant relations between the calcaemic response and the increases of urinary calcium and hydroxyproline and the two latter were also closely related. There was, however, no correlation between the responses to PTH for the formative vs the resorptive indices. Postmenopausal women displayed greater increases of serum calcium and fasting urinary hydroxyproline indicating greater skeletal sensitivity to exogenous PTH. Following treatment with oestrogens the indices of skeletal responsiveness were reversed towards the premenopausal values. The findings demonstrate that during short-term infusion of PTH there is a dissociation between bone resorption and formation and, furthermore, that the menopause is associated with an enhanced skeletal sensitivity for PTH.