1. Foetal and maternal plasma metabolite and
catecholamine concentrations have been measured in chronically catheterized sheep, 95-145 days pregnant. 2. With increasing gestational age there was rise in foetal 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
nitrogen none of the plasma metabolites showed any correlation with foetal blood gas or pH values; alpha-amino N was inversely related to foetal blood
pH. 3.
Hypoxia in the foetuses 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. 4. In the foetus
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 foetal plasma
glucose,
free fatty acid and
ketone body concentration in response to
hypoxia were seen only between 130 and 145 days. 5. In foetuses of 130-145 days the magnitude of the
hypoxia-induced rise in plasma
glucose and
free fatty acid concentration was proportional to the plasma
catecholamine concentration. 6. The concentration of
acetate in foetal plasma was lower than and proportional to that in the maternal plasma. Neither concentration changed significantly during
hypoxia. 7. The results are discussed in relation to the ability of the foetal sheep independently to control the concentration of its plasma metabolites and to mobilize its
carbon stores at times of need. They indicate that in the sheep plasma
catecholamines are important regulators of plasma
glucose and
free fatty acid concentrations late in foetal life.