Circadian Rhythm in the Urinary Excretion of Cyclic 3′,5′-Adenosine Monophosphate in Man

Abstract

A circadian rhythm in the urinary excretion of cyclic 3′,5′-adenosine monophosphate (cAMP) was demonstrated in 8 normal volunteers throughout a 48-hr period and studied under standardized conditions. The peak excretion occurs around noon particularly 9 am–12 midday with the nadir from 6 pm–9 pm. A post midnight rise was observed in 6 of the subjects. The demonstrated fluctuations were found to be statistically significant (p < 0.05). The daytime relationship of renal phosphate handling to urinary cAMP was determined revealing a direct correlation between cAMP excretion and phosphate clearance, and an inverse relationship between cAMP/g creatinine and tubular reabsorption of phosphorus.