Most (50-60%) of the cAMP in the urine comes from glomerular filtration of the plasma, with the remainder coming from the kidney ("nephrogenous" cAMP). Excretion of cAMP by the kidneys is controlled by circulating PTH, by the direct activation of adenylate cyclase in the renal tubule and release of cAMP into the luminal fluid. Thus, excretion of cAMP can be used as a measure of PTH functional activity.
