Abstract

The 24-hour urinary excretion of cyclic 3',5'-adenosine monophosphate (cAMP) was measured by a protein-binding assay in 55 healthy volunteers (aged 20-35 yr) and in 30 hospitalized elderly subjects (aged 70-93 yr). In the older subjects the mean 24-hour cAMP excretion was significantly lower; the correlation between cAMP excretion and age demonstrated a progressive decrease from the age of 70 to the tenth decade. Many different factors could account for the reduced urinary cAMP excretion in elderly subjects: a decline in the reactivity of the adenyl cyclase-cAMP system related to physiological ageing; reduced physical activity; a reduction in the glomerular filtration rate or decreased production of cAMP by tubular cells in the senile kidney.