Observations on the effect of parathyroid hormone on environmental blood lead concentrations in humans.

The effect of parathyroid hormone (PTH) on blood lead (Pb) concentrations was observed preliminarily in three different situations. Of 342 healthy bus drivers with no unusual exposure to Pb, 25 drivers with the highest and 25 with the lowest blood Pb were compared for serum PTH concentrations. There was no association between blood Pb and serum PTH concentrations. Eight women with postmenopausal osteoporosis enrolled in an experimental protocol to increase bone mass received daily PTH (1-34 fragment) for 1 week, calcitonin for the next 2 weeks, and oral calcium for the subsequent 10 weeks. This cycle was repeated four times during the year. Initial blood Pb concentrations averaged 6.0 micrograms/dl (range 2.1-8.9). Mean blood Pb concentrations decreased by 1.7 micrograms/dl over 1 year of therapy. The confidence interval for this change excluded zero, the mean change was significantly different from the mean change for comparative population (P less than 0.050), and paired changes were statistically significant (P = 0.045). Lastly, a single subject with hyperparathyroid disease and no unusual exposures to lead demonstrated stabilized blood Pb concentrations that were 50% lower after removal of his hyperplastic parathyroid glands. These observations suggest that the effect of PTH on increasing bone turnover and releasing Pb into blood is not easily detected at low physiologic amounts of PTH, but that with pathologic increases of PTH in hyperparathyroid disease, elevation of blood Pb from bone or increased gastrointestinal absorption may be possible. Likewise, either bone building therapies (PTH + calcitonin + calcium) may move Pb from blood into bone or supplemental calcium may decrease Pb gastrointestinal absorption, thereby explaining the observed lower blood Pb concentrations.