Lack of a direct role for cyclic AMP in parathyrin action on phosphate reabsorption by the kidney

Isolated chick kidney proximal tubule cells have been used in a study of the mechanism by which PTH inhibits Na+-dependent Pi transport in the kidney. Treatment with PTH inhibits Pi uptake by the cells by 13% and stimulates cyclic AMP production by 77%. Forskolin, a potent activator of adenyl cyclase, brought about an 11-fold stimulation of cyclic AMP production by the cells, but in contrast to PTH, the drug had no effect on Na+-dependent Pi uptake. These results provide evidence that PTH action on phosphate transport is not mediated by cyclic AMP.