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

Abstract

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 re breathing 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 μCi of labeled glycine and decreased gradually to 1.08 nCi/24h on day 8. The early labeled peak was 32.9 ± 8.1 nCi (mean ± SD) and the potential late labeled peak 221 ± 30 nCi. The early peak represented 13.0 ± 2.9% of the calculated total production of labeled 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 radio labeled precursor method.

Key Words:

• CO extraction system
• endogenous CO production
• haem turnover
• Hopcalite
• infrared CO analysis