Effects of estrogen on mineral metabolism in postmenopausal women as evaluated by multiple assays measuring parathyrin bioactivity

Data on the effect of estrogen on immunoreactive parathyrin (iPTH) in postmenopausal women are conflicting. We administered estrogen or placebo to 21 postmenopausal women for 12 weeks and measured PTH bioactivity (bioPTH), using the renal cytochemical bioassay. Before treatment, there was a negative correlation between nephrogenous cAMP and the tubular maximum for urinary phosphate excretion and a positive correlation between values measured by a mid-region-specific PTH RIA and those measured in an immunoradiometric assay for intact PTH. Values measured by the midregion-specific RIA were also positively correlated with nephrogenous cAMP. BioPTH values were not correlated with other indices of PTH activity but were increased compared with values for younger subjects. After estrogen treatment there was no change in bioPTH activity despite an early decrease in serum osteocalcin and a later increase in nephrogenous cAMP. PTH concentrations measured by mid-region-specific or intact RIAs were unchanged, but sample size may have been insufficient to exclude the possibility of significant changes in these values. The effects of estrogen on mineral metabolism in postmenopausal women are time-dependent. Early effects are independent of PTH, and later effects are variably associated with increased PTH activity.