Endogenous carbon monoxide formation by chorionic villi of term human placenta

Carbon monoxide (CO) is a novel messenger that is proposed to play a complementary role with nitric oxide in the regulation of placental haemodynamics. In a previous study, CO formation from exogenous haem has been measured in the microsomal fraction of chorionic villi as an index of haem oxygenase activity. The objective of the present study was to determine whether endogenous CO is formed by dissected chorionic villi of term human placenta, to which no exogenous substrate or co-factor had been added. Each sample of freshly isolated chorionic villi (approximately 0.4 g) of term human placenta from caesarean delivery was incubated in a sealed vial containing 1 ml of Krebs' solution (pH 7.4) at 37 degrees C. CO formation was determined by quantitating, using a gas-chromatographic method, the amount of CO released into the headspace gas of the incubation vial. There was time-dependent formation of endogenous CO in chorionic villi incubated at 37 degrees C during a 60-min time course. CO formation was found to be minimal in chorionic villi samples incubated at 4 degrees C and was increased relative to tissue weight. The data demonstrate that there is endogenous CO formation by chorionic villi of term human placenta.