Glucose transport and recycling determined by means of two tracers and multicompartmental analysis
Kronfeld, D.S.
Federation Proceedings 36(2): 259-264
1977
ISSN/ISBN: 0014-9446 PMID: 557001 Document Number: 116821
Glucose labelled with 3H and 14C was injected into cows, and blood samples were taken from 1 to 720 min for measurement of plasma glucose concentration and the specific activities of each tracer. Experiments were done on 2 cows when nonlactating, lactating, and in spontaneous ketotic hypoglycaemia. Three exponential terms were required to fit the data for each of the tracers in all 6 experiments. The data were consistent with two 3-compartment models of the glucose system proposed previously on the basis of 14C data only: compartments 1 and 2 represent the glucose pool, compartment 3 represents derivatives and precursors of glucose. Constraint tests were applied to kinetics in the models to test the hypothesis that [3H]glucose does not recycle. When the parameter representing the recycling of [3H]glucose was set to zero in either model, systematic deviations were found between the predicted and observed data. When the recycling parameters for [3H]glucose and [14C]glucose were allowed to adjust independently of one another, while all other parameters in the model were constrained to be the same for both [3H]glucose and [14C]glucose, a good fit was obtained. The findings are not consistent with the hypothesis that [3H]glucose does not recycle. Recycling of [14C]glucose or [3H]glucose was estimated in terms of the return transport rate back into the glucose pool (compartments 1 or 2) divided by the transport rate from the glucose pool to compartments 3. It was 22 to 53% of [4C]glucose in the normal cows but only 12 and 13% in the ketotic hypoglycaemia cows.