The production of 14CO following the administration of 2-[14C] glycine in normal subjects determined by an oxygen washout technique.

The endogenous production of 14CO during the first week after administration of 2-[14C]glycine, i.e. the early peak of 14CO derived mainly from erythropoietic and hepatic haem turnover, was measured in six normal subjects. Samples from the body CO store were collected by washout of CO with oxygen breathing, CO concentration of expired gas was determined with an infrared CO-meter and, for determination of 14C activity, CO washed out was oxidized to CO2 in a trapping system and absorbed in ethanolamine. The endogenous production of CO was measured with a rebreathing technique and the production of 14CO was calculated. The specific activity and total amount of circulating red cell haemoglobin haem was determined to calculate the potential late peak of 14CO production. The method for determination of 14CO expired was demonstrated to be specific and reproducible and no haemolysis induced by the sampling procedure was detected. The average production of 14CO was 6.94 nCi/24 h the day after injection of 100 muCi of labelled glycine and decreased gradually to 1.08 nCi/24 h on day 8. The early labelled peak was 32.9 +/0 8.1 nCi (mean +/- SD) and the potential late labelled peak 221 +/- 30 nCi. The early peak represented 13.0 +/- 2.9% of the calculated total production of labelled CO, a figure significantly lower than erythropoietic and hepatic haem turnover calculated from total bilirubin or CO production and red cell life span, probably due to the hepatic component being underestimated by the radiolabelled precursor method.