Provocative tests of parathyroid and C cell function in adrenalectomized and chemically sympathectomized rats

Recent in vitro and in vivo evidence shows that secretion of parathyroid hormone (PTH) and calcitonin (CT) is stimulated by beta-adrenergic agonists and inhibited by beta-adrenergic antagonists. To assess the possible roles of adrenal medullary or adrenergic nerve terminal catecholamines in calcium homeostasis, we have examined serum calcium (Ca), immunoreactive PTH (iPTH), and immunoreactive CT (iCT) in control, adrenalectomized (ADRX), and chemically sympathectomized [6-hydroxydopamine (6-OHDA)] rats. Animals were studied in the fed and fasted states, after ip injection of CA and after ip injection of EDTA. In comparison with fasted rats, fed control rats tended to have increased serum Ca and iCT, but decreased or unchanged iPTH. Neither adrenalectomy nor 6-OHDA treatment notably altered this pattern. Serum iCT concentrations rose markedly after ip Ca, and peak iCT responses remained normal in ADRX and 6-OHDA-treated rats. Similarly, rises of iPTH levels after EDTA-induced hypocalcemia were normal in ADRX and 6-OHDA-treated rats. The only possible abnormality concerned basal serum iCT levels after 6-OHDA treatment, which were lower than control in five of six experiments, albeit not always significantly. We conclude that deprivation of either adrenal medullary or adrenergic nerve terminal catecholamines does not interfere with plasma Ca regulation or the homeostatic responses of PTH and CT in the rat.