Plasma levels of adenosine 3',5'-monophosphate in the fetoplacental unit and maternal circulation at delivery.

Adenosine 3',5'-monophosphate (cAMP) was measured in matched samples of maternal plasma (MV) and umbilical artery (UA) and vein (UV) of 14 normal infants born following an uncomplicated vaginal delivery. There was good correlation between UA and UV cAMP levels, which seems to indicate that the fetoplacental unit maintains a constant equilibrium of the nucleotide concentration in the umbilical circulation. There was a markedly increased UA cAMP concentration at term relative to that of MV, as well as an arteriovenous gradient of plasma cAMP level (UA greater than UV) in the fetoplacental circulation, which strongly suggest that the high cAMP levels in the cord blood originate mainly from the fetus.