Search for biological effects of ¹³C-enrichment in developing mammalian systems

Increasing diagnostic use of stable isotopes, especially in children and pregnant women, enhances the importance of studies on the biological isotope effects in sensitive mammalian systems. Experimental data on animal systems are meager. The mouse embryos was studied at various stages and mouse limb buds were studied in organ culture. Limb bud development in vitro was unaffected by incubation with 82 mol percent ¹³C-glucose as judged by either morphological or biochemical criteria. Of 271 preimplantation embryos incubated in vitro, 95.2 percent developed normally; in ¹³C-enriched medium, 96.5 percent showed normal development. ¹³C-Enrichment of the embryos in vitro is over 60 percent. Administration of 1.2 g glucose-U-¹³C to pregnant mice during organogenesis leads to enrichment of maternal liver glycogen to over 17 mol percent ¹³C, about one-third this level in the embryo, and a lower level in maternal blood. The absolute ¹³C content of the embryo continues to increase for several days after the end of isotope administration, while the enrichment in maternal tissues falls. The lipid fraction of the fetus is most highly labeled shortly after the end of isotope administration. These studies on developing mammalian systems have not yet revealed any alteration of normal development due to stable isotope enrichment. (author)