The secretion of parathyroid hormone and its fragments from dispersed cells of adenomatous parathyroid tissue at different calcium concentrations.
The effect of varying calcium concentrations on PTH release from dispersed cells of adenomatous parathyroid tissues (n = 15) was studied. During high calcium concentrations PTH secretion was inhibited up to 62.5% as compared to low calcium concentrations. There was no correlation between iPTH secretion rate and suppressibility. Each adenoma had a different iPTH secretion rate. Three adenomas showed a high suppressibility (28.0%, 53.8%, and 62.5%). The supernates of their media were chromatographed and examined by midregion and C-terminal specific PTH-RIAs. Carboxyl-terminal PTH fragments were found to be released by two adenomas. There was no evidence for the release of midregion PTH fragments. Comparison of incubation media revealed that the adenoma with the lowest suppressibility released the highest amount of intact PTH (per 100,000 cells/ml). This adenoma exclusively secreted intact PTH, whereas PTH fragments were only released from two adenomas with higher suppressibility. In these media the ratio of PTH fragments to intact PTH increased with the calcium content of the media. The ratio was also dependent on the suppressibility of the adenomas; i.e. the ratio was greater when the suppressibility was higher. This suggests that in adenomas the intracellular hormone degradation is responsible for the degree of PTH suppression. As the suppressibility of PTH secretion is reduced in hyperfunctioning parathyroid tissue, diminished intracellular hormone degradation seems to be involved in the pathogenesis of primary hyperparathyroidism.
D000236:Adenoma / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D010281:Parathyroid Hormone / Q000378:metabolism*; D010282:Parathyroid Neoplasms / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011863:Radioimmunoassay
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D002118:Calcium