Ionized Calcium and the in vivo Response of Normal and Hyperplastic Parathyroid Glands to Beta-Adrenergic Agents

Abstract

We compared ionized serum calcium and parathyroid hormone (PTH) responses to the β-adrenergic agents, isoproterenol and propranolol, in 14 patients with hyperparathyroidism following renal transplantation and 8 normal volunteers. Following isoproterenol, PTH rose in normal subjects concurrent with a significant (p < 0.01) fall in ionized but not total, calcium. In the hyperparathyroid patients the PTH concentration decreased (p < 0.001) coincident with a significant (p < 0.01) increase in ionized, but not total, calcium. Changes in both PTH (p < 0.05) and ionized calcium (p < 0.05) were significantly different in hyperparathyroid patients compared to normal subjects. Propranolol did not affect PTH, ionized or total calcium in either group. We conclude that β-adrenergic stimulation of PTH secretion may be mediated, in part, by antecedent changes in ionized calcium and not solely a direct effect of the agonist. Concurrent assessment of changes in ionized calcium is necessary for proper interpretation of investigations involving the sympathetic nervous system’s regulation of PTH secretion.