Acetate as a metabolic substrate in the fetal lamb

Abstract

Fetal acetate metabolsim was studied in chronically catheterized fetal lambs of 110-141 days' gestation. Acetate concentration was measured enzymatically in whole blood drawn simultaneously from maternal and fetal pre- and postplacental vessels. The oxygen content of the fetal blood samples was also measured. Fetal umbilical venous acetate concentration was found to be proportional to the maternal arterial acetate concentration and had a mean value of 0.366 mM. Fetal blood acetate increased significantly, by a mean of 0.081 mM, during circulation through the placenta. This increase was proportional to both the maternal acetate concentration and the concentration gradient of acetate across the placenta. The mean maternal arterial acetate concentration was 1.153 mM. Maternal blood lost significant amounts of acetate, 0.112 mM, during circulation through the uterus and appeared to be the source of the acetate being gained by the fetus. It is estimated that a total of 23 mmol of acetate/kg of fetal weight is being taken up by the fetus each day, providing it with 0.560 g of carbon/kg. Comparisons of acetate uptake with fetal oxygen uptake indicate 10% of the daily fetal oxygen consumption would be required to completely oxidize the acetate being gained by the fetus.

Lactate and Pyruvate as Fetal Metabolic Substrates

“…Of the 7.69 g carbon/kg/24 hr crossing the placenta to the lamb fetus during the last one-third of gestation, the amount of carbon per kg124 hr provided by fetal glucose uptake is between 1.8 and 2.6 grams (7,12) and by acetate uptake is 0.56 g (6). Calculations based on nitrogen balance studies in the fetal lamb, using an average C to N ratio in amino acids of 3.3 (2), indicate that 3.16 g carbon/kg/24 hr reach the fetus as amino acids.…”

“…Assuming that all the glucose and acetate taken up by the fetus is oxidized, 80% of the fetal lamb's daily oxygen consumption can be accounted for by oxidation of these two substances (6,12) and catabolism of amino acids (10). The lactate/O, ratio indicates that approximately 32% of the oxygen consumption could also be used in complete oxidation of lactate.…”

“…With the use of this animal preparation glucose (7,12), fructose (17), amino acids (8, 10) ketones (13), glycerol, free fatty acids (I I, 19) and acetate (6) have been investigated as possible fetal fuels. Of these substances only glucose, amino acids, and acetate have been shown to cross the placenta in significant amounts for use in fetal metabolism.…”

Metabolic Quotients of the Gravid Uterus of the Chronically Catheterized Guinea Pig

“…The uteroplacental tissues of sheep and cattle produce lactate under aerobic conditions, which is delivered into both the uterine and umbilical circulations (2)(3)(4)(5). While the lactate production by the sheep placenta is quite large, with a uterine lactate/02 quotient of approximately -0.1 (4), the lactate production rate relative to O2 consumption is even larger in the guinea pig, where the lactate/oxygen quotient is -0.4.…”

Glucose, Acetate, and Lactate Metabolism in Perirenal Adipose Tissue of Fetal and Newborn Calves

“…A similar order of preference also exists in the adipose tissue of adult ruminants (3). That acetate traverses the placenta and is used in oxidative and synthetic reactions by the fetal lamb has been established (16). The ratios of acetate carbons:glucose carbons incorporated into fatty acids in adipose tissue of adult ruminants vary between 10-100 (3).…”