Secretory and biosynthetic responses of adenomatous, carcinomatous, and hyperplastic parathyroid tissues to variable concentrations of extracellular calcium were assessed in vitro. Tissues, obtained at the time of parathyroidectomy, were incubated for 4 h in media containing radioactive amino acids and varying (0.5-5.0 mM) concentrations of calcium. Amounts of newly synthesized and total parathyroid hormone and proparathyroid hormone in extracts of tissues and media were measured by polyacrylamide gel electrophoresis and by radioimmunoassay, respectively. All tissues studied (six adenomas, two specimens of chief-cell hyperplasia, one carcinoma, and normal bovine and human glands) responded to changes in calcium concentrations; decreasing concentrations of calcium stimulated release and decreased tissue storage of hormone. Six of the abnormal tissues required greater than normal concentrations of calcium (1.8-2.4 mM for 50% of effect) to elicit secretory responses comparable with those of normal glands (1.4 mM). Maximum effects of calcium on release of hormone varied from 2- to 10-fold among different tissues. Release of some hormone persisted even in concentrations of calcium as high as 5.0 mM. Relative amounts of hormone released from and retained in the tissues varied greatly among the tissues, as did the absolute amounts of hormone produced; newly synthesized, labeled hormone ranged between 0.6 and 12% of total labeled protein, and immunoreactive hormone ranged between 0.015 and 0.9% of total tissue protein. Effects of calcium on hormone biosynthesis, as determined by analyses of amounts of proparathyroid hormone in the tissues, were variable among tissues and in many cases were negligible. These results indicate that neoplastic and hyperplastic parathyroid tissues retain secretory responsiveness to changes in extracellular concentrations of calcium. Responses, however, are highly variable among different tissues, and in many instances are abnormal, inasmuch as greater than normal concentrations of calcium are required to alter release and synthesis of hormone. A combination of both increased mass of glandular tissue and abnormal regulations of hormone secretion appear to contribute to the hypersecretion of hyperparathyroidism.
J F Habener
Usage data is cumulative from April 2023 through April 2024.
Usage | JCI | PMC |
---|---|---|
Text version | 86 | 0 |
58 | 11 | |
Scanned page | 230 | 0 |
Citation downloads | 12 | 0 |
Totals | 386 | 11 |
Total Views | 397 |
Usage information is collected from two different sources: this site (JCI) and Pubmed Central (PMC). JCI information (compiled daily) shows human readership based on methods we employ to screen out robotic usage. PMC information (aggregated monthly) is also similarly screened of robotic usage.
Various methods are used to distinguish robotic usage. For example, Google automatically scans articles to add to its search index and identifies itself as robotic; other services might not clearly identify themselves as robotic, or they are new or unknown as robotic. Because this activity can be misinterpreted as human readership, data may be re-processed periodically to reflect an improved understanding of robotic activity. Because of these factors, readers should consider usage information illustrative but subject to change.