The development of some metabolic responses to hypoxia in the foetal sheep.

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Abstract
Fetal and maternal plasma metabolite and catecholamine concentrations were measured in chronically catheterized sheep, 95-145 days pregnant. With increasing gestational age there was rise in fetal plasma lactate, free fatty acid and ketone body concentration and in maternal plasma in free fatty acid and ketone body concentration. With the exception of .alpha.-amino N none of the plasma metabolites showed any correlation with fetal blood gas or pH values; .alpha.-amino N was inversely related to fetal blood pH. Hypoxia in the fetuses was induced by causing the ewe to breathe 9% O2 with 3% CO2 in N2. This had a small effect on plasma metabolites in the ewe, mainly producing an increase in free fatty acid and ketone body concentration. In the fetus hypoxia was associated with a large rise in plasma lactate and a small rise in .alpha.-amino N, the magnitudes of which did not change over the gestational range studied. Consistent and large increases in fetal plasma glucose, free fatty acid and ketone body concentration in response to hypoxia were seen only between 130 and 145 days. In fetuses of 130-145 days the magnitude of the hypoxia-induced rise in plasma glucose and free fatty acid concentration was porportional to the plasma cetecholamine concentration. The concentration of acetate in fetal plasma was lower than and proportional to that in the maternal plasma. Neither concentration changed significantly during hypoxia. The results were discussed in relation to the ability of the fetal sheep independently to control the concentration of its plasma metabolites and to mobilize its carbon stores at times of need. In the sheep plasma catecholamines were important regulators of plasma glucose and free fatty acid concentrations late in fetal life.