RENAL CORTICAL ADENYL CYCLASE - EFFECT OF PARATHYROID HORMONE AND CALCIUM

Adenyl cyclase activity was measured in rabbit renal cortex and the effects of parathyroid hormone and calcium ion on the enzyme studied. Basal adenyl cyclase activity (picomoles/mg protein ± S.E.) at 1, 3, and 5 minutes were 220 ± 50, 290 ± 37, and 320 ± 22, while respective values for parathyroid hormone treated samples were 330 ± 59, 660 ± 70 (p < .01) and 880 ± 78 (p < .01). A dose response curve demonstrated increasing activity at parathyroid hormone concentrations of 7.7 and 77 μg/ml. Calcium ion (3 mM) added to the assay system (containing 3 mM magnesium) decreased adenyl cyclase activity from 290 ± 28 to 170 ± 38 (p < .05). Lesser amounts of calcium (0.03, 0.3 mM) had no significant effect. The stimulatory effect of parathyroid hormone (77 μg/ml) was abolished when 3 mM calcium was present in the system. Calcium decreased but did not prevent stimulation by sodium fluoride (.01M). Parathyroid hormone had no effect on the adenyl cyclase of outer or inner medulla. These data support the hypothetical role of adenyl cyclase as a mediator of parathyroid hormone's action on kidney and further suggest an inter-relationship between the hormone and calcium ion. However, problems with the hypothesis remain, and further study is required before the exact mechanism of action of parathyroid hormone is understood. © 1969.