Parathyroid hormone modulates angiotensin II-induced aldosterone secretion from the adrenal glomerulosa cell

The effect of PTH on aldosterone secretion from isolated bovine adrenal glomerulosa cells was examined. PTH binding was autoradiographically localized to the adrenal cortex, suggesting a specific effect. This binding of PTH was displaceable by cold PTH, but not by ACTH. No binding was observed in the adrenal medulla. In addition, PTH was shown to stimulate aldosterone secretion in a dose-dependent manner and to potentiate aldosterone secretion in response to angiotensin-II, such that PTH (10^-9 M) elevated the secretory rate from 58.6 ± 6.8 to 110.9 ± 19 pg/min·million cells in the presence of 10 nM angiotensin-II. The magnitude of the synergism between the two hormones depended on the concentrations of PTH and angiotensin-II as well as the time during which aldosterone secretion was measured. Within the first 15 min of stimulation, PTH increased the sensitivity to angiotensin-II, shifting the K_a for activation from 1.0 to 0.3 nM. In contrast, between 30-45 rain of angiotensin-II stimulation, PTH elevated the maximal secretory response to angiotensin-II from 109 ± 3.4 to 219 ± 13.3 pg/min·million cells. By itself PTH elicited only a small increase in the intracellular Ca²⁺ concentration, as measured by aequorin luminescence in glomerulosa cells. In cells pretreated with angiotensin-II or 15 mM potassium, the intracellular calcium response to PTH was markedly potentiated. PTH was also found to cause a small increase in the cellular cAMP content. Thus, PTH stimulates aldosterone secretion from adrenal glomerulosa cells, both alone and in combination with angiotensin-II.