Heavy water effects on the 13C/12C ratio of exhaled CO2 in rats

It is known that heavy water has multiple effects in biological systems but these are still far from being fully understood especially those concerning perturbations in basal metabolism. It was shown that there exist isotopic effects which affect the 13C/12C ratio of exhaled CO2 in the case of intermediary metabolism variations induced, for instance, by starvation or hormone injections. It was then interesting to study how heavy water affects this metabolism by the way of modifications at the level of the 13C content of CO2. For this purpose, rats, receiving heavy water in such a way that their blood reaches a 27% content in D2O, were observed and the 13C/12C of their CO2 was measured daily. An important 13C variation was detected following the increase as well as the decrease of the 2H content variations. Unfortunately, it was shown that this effect was mainly related to a variation in 17O content of the CO2 from which the mass is affected in the same way as from a 13C variation. This 17O enrichment comes from the fact (apparently usually neglected) that deuterium enriched waters have not exactly the same content in oxygen isotopes as natural waters. Despite the necessity of this important correction for 17O, a residual effect of 13C variation is still observed