Studies on the Flows of Propionate Carbon to Glucose in Sheep

Abstract

In this thesis the flows of 14C to glucose from labelled propionate infused into the rumen of sheep were studied. The pattern of tracer flow does not represent the pattern of net carbon flow because of equilibration of tracer in the symmetrical dicarboxylic acid pools, recycling of tracer, tracer flows via indirect routes and metabolic crossover. The effects of these influences have not been fully appreciated and accounted for in the interpretation of data obtained from many isotope dilution experiments. In this thesis an attempt was made to correct the percentage of the carbon atoms in the glucose pool that originated in the propionate pool (i.e. the transfer quotient) for the above influences and thus, calculate the true percentage of the glucose pool being provided by propionate. ... The incorporation of 14 CO₂ into glucose was much higher than predicted by the pathways of incorporation presently accepted. Therefore, it appears that there is at least one further pathway by which CO₂ can be incorporated into glucose that has not been accounted for in the interpretation of the results. More basic research is needed to identify all forms of tracer recycling and to quantify their effects on the tracer flows. Until this is done flows calculated from the transfer of tracer from propionate to glucose can not be converted into net carbon flows.