Lack of a diurnal plasma adenosine 3',5'-monophosphate rhythm.

Plasma cAMP levels were measured using a protein-binding radioassay in nine healthy volunteer subjects over a period of 24 h under standardized conditions and also after an hour of orthostatism. No circadian variations of cAMP in plasma were observed. After orthostatism, however, there was a significant rise in cAMP concentrations.