SUBSTRATE METABOLISM AND INTERRELATIONSHIPS IN THE OVINE FETUS IN UTERO

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Abstract
The kinetic parameters of substrate metabolism in the ovine fetus in utero were studied using isotope dilution techniques. The irreversible disposal rates of glucose, lactate and alanine following single injection of 14C-labelled substates are 2.94 ± 0.21 (n = 15), 2.58 ± 0.18 (n = 8), and 2.02 ± 0.34 (n = 10) mgC∙min−1∙kg−1, respectively. There is a positive correlation between glucose irreversible disposal rates and blood concentrations. The extent of glucose recirculation using 3[H] and [14C] glucose is 12.6 ± 5.5% of the irreversible disposal rate. The extent of glucose irreversible rate converted to lactate is 36 ± 4%. Recycling, which represents the re-entry of the label into the fetal circulation in its original form after sojourn in some other compartment, is an important feature of glucose, lactate and alanine metabolism in the fetus, occurring to an extent of approximately 70 – 85% of their total turnover rate. Lactate radioactivity could not be detected in the maternal blood following lactate injection into the fetus. On the other hand, approximately 52% of the fetal irreversible rate of glucose is returned to the maternal circulation. The conversion of alanine to glucose and lactate occurred to an extent of 8.9 and 35%, respectively, of its irreversible disposal rate. There was no incorporation of lactate label into fetal glucose when 14C-lactate was injected into the fetus. Key words: Glucose, lactate, alanine, metabolism, isotope dilution technique, fetus-in utero-substrate interrelationship

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