Aging and parathyroid hormone secretion.

Influence of age on parathyroid hormone secretion and release was studied in vitro using rat parathyroid glands in culture and in vivo by EDTA injection. Parathyroid hormone was measured by radioimmunoassay using guinea pig antibody for bovine parathyroid hormone and 125I-labeled synthetic N-terminal peptide of bovine parathyroid hormone. Significantly less PTH was released from parathyroid glands of 18-mo-old rats than from those of 1 mo of age at various calcium concentrations of the medium in vitro. Secretion of parathyroid hormone in response to EDTA-induced hypocalcemia in vivo was also less in older rats than in younger ones, giving lower deltaPTH/deltaCa values in the older animal. Secretion of parathyroid hormone therefore appears to decrease along with aging in rats.