1. Idiopathic calcium stone-formers with hypercalciuria during fasting have significantly lower urinary cyclic AMP levels (nmol/dl of glomerular filtrate) than fasting normocalciuric stone-formers.
2. Female subjects, including both normal subjects and idiopathic calcium stone-formers, have higher urinary cyclic AMP levels than their male counterparts, and this difference is significant when urinary cyclic AMP is expressed in the units μmol/g of creatinine. Expressing urinary cyclic AMP in nmol/dl of glomerular filtrate reduces this difference but does not abolish it. Thus, in comparing urinary cyclic AMP levels in various subgroups of the calcium stone-formers and in normal subjects, both sex differences and the units of urinary cyclic AMP expression must be taken into consideration.
3. The magnitude of the change in urinary cyclic AMP in response to an oral calcium load appears to depend on the antecedent urinary cyclic AMP excretion rate, whereby those individuals (either normal subjects or calcium stone-formers) having the highest urinary cyclic AMP levels demonstrate the greatest fall in urinary cyclic AMP after a calcium load.