Hyperparathyoidism: influence of glomerular filtration rate on urinary excretion of cyclic AMP

Urinary cyclic AMP excretion per 24 h or per g creatinine in primary hyperparathyroidism (1 degrees HPT) has been evaluated by several authors with conflicting results. In 50 patients with 1 degrees HPT, 25 patients with secondary (2 degrees) HPT and 35 healthy control persons we determined urinary cyclic AMP per 24 h or per g creatinine. These parameters did not satisfactorily discriminate patients from controls, especially when glomerular filtration rate (GFR) as determined by creatinine clearance was reduced. Since urinary cyclic AMP is derived from plasma by glomerular filtration and from kidney by tubular production-the amount of tubules is reflected by GFR-the cyclic nucleotide was related to GFR. In controls urinary cyclic AMP correlated better with GFR than with creatinine excretion. Additionally, in 45 of 50 patients with 1 degrees HPT and in all with 2 degrees HPT, urinary cyclic AMP/GFR was raised. In 1 degrees HPT serum levels of parathyroid hormone correlated closer with urinary cyclic AMP/GFR than with urinary cyclic AMP/g creatinine. The ratio cyclic AMP/GFR decreased to normal or subnormal values after removal of adenomatous or hyperplastic glands in 1 degrees HPT and during infusion of calcium in 2 degrees HPT. In 50 patients with renal lithiasis caused by diseases other than 1 degrees HPT (anatomical variations, pyelonephritis, immobilization after tetraplegia) the ratio cyclic AMP/GFR was not raised. Urinary cyclic AMP/GFR, therefore, reflects parathyroid hormone excess more reliably than cyclic AMP/g creatinine.