cAMP Radioimmunoassay

Radio immunoassay for the in-vitro diagnostic quantitative determination of cAMP in human plasma and urine. The test can also be used for non-clinical applications in other biological material. Cyclic adenosin-3',5'-monophosphate (cAMP) serves as a second messenger in signal transduction of various hormones, like adrenaline, ACTH, LH, FSH, glucagon and calcitonin. The hormone itself is the first messenger, binding to specific membrane receptors of hormone-responsive cells. This leads to the activation of an enzyme located at the inner side of the cell membrane, called adenylate cyclase, which catalyses the synthesis of cAMP from ATP. The increased cellular level of cAMP initiates the activation of protein kinases. The determination of cAMP in urine (or plasma) has become more and more important in the clinical assessment of parathyroid functions. The parathyroid hormone (PTH) stimulates the synthesis of cAMP in the renal cortex and an increased secretion of cAMP. The nephrogenic cAMP is a specific marker of circulating PTH: 90 % of patients with hyperparathyroidism show increased levels of nephrogenic cAMP. The determination of nephrogenic cAMP is also significant for the differential diagnosis of hypercalcemia. Urinary levels of cAMP support the diagnosis of hypoparathyroidism and pseudohypoparathyroidism: The administration of PTH to patients with pseudohypoparathyroidism does not lead to an increased cAMP secretion, which is indicative of a defective adenylate cyclase in the renal cortex. Total urinary cAMP levels comprise the nephrogenic cAMP and the plasma cAMP which is not resorbed in the kidneys. In most cases the determination of total urinary cAMP is sufficient, because the concentration of plasmatic cAMP is more or less constant.