ENHANCEMENT OF THE STIMULATORY EFFECT OF CALCIUM ON ALDOSTERONE SECRETION BY PARATHYROID-HORMONE

In previous clinical investigations on uremic patients we found a stim ulatory effect of the presence of hyperparathyroidism on the Ca2+-indu ced secretion of various hormones, i.e. aldosterone and vasopressin. T he present investigation, therefore, examined the possible effect of P TH on the calcium-mediated aldosterone secretion from isolated, purifi ed zona glomerulosa cells obtained from the rat. After washing the cel ls and after 30 min of preincubation Ca2+ was added to the preparation s at concentrations from 0.5 to 2.0 mmol and PTH(1-84) or PTH(1-34) we re added at concentrations from 10(-7) to 10(-10) M. The cells were th en incubated for 120 min and aldosterone measured in the supernatant. The aldosterone response to Ca2+ stimulation - without PTH added - ser ved as baseline controls, while cell preparations with ACTH 10(-6) M a dded secured the viability and responsiveness of the cells. In all cel l preparations with PTH(1-84) as well as PTH(1-34) added the aldostero ne responses to a certain Ca2+ concentration increased significantly b y up to 200% (p < 0.001) above baseline values. It is suggested that P TH may have a Ca2+ ionophore-like effect on endocrine glands, which ar e not normally related to PTH and thus enhance the calcium-stimulated hormone secretion. The hypothesis is raised that this phenomenon may t ake place in uremia during the state of secondary hyperparathyroidism.