The Importance of Glucose in the Oxidative Metabolism of the Pregnant Uterus and Its Contents in Conscious Sheep With Some Preliminary Observations on the Oxidation of Fructose and Glucose by Fetal Sheep

Abstract

The day after implantation of catheters under general anaesthesia, u-[14C] glucose was infused intravenously into four conscious ewes about 130 days pregnant, and into two fetuses about 130 days old. u-[14C] fructose was infused into three other similar fetuses.It could be calculated that the pregnant uterus with its contents derived about 40% of its CO2 from blood glucose and oxidized directly about 45% of the glucose utilized. The total uptake of glucose by the uterus and contents accounted for about 70% of the glucose metabolism of the pregnant ewes, but the proportion of C02 derived by the pregnant ewes from glucose was no higher than for non-pregnant ewes or rams. The total oxygen consumption of uterus and contents was comparable to the extra oxygen used by a ewe when pregnant, as measured by calorimetry. The specific radioactivity of fetal blood fructose was still only about 60% of that of maternal blood glucose after 5 hours infusion which suggests that there are other precursors for fetal fructose besides maternal glucose.[14C] from fructose and glucose infused into the fetus was converted into C02 and glycogen and [14C] from fructose was converted to glucose by the fetus or placenta. The degree of incorporation of both sugars into C02 and glycogen was similar but neither sugar could account for more than a fraction of the CO2 production.It has been stated [Kronfeld, 1958;Reid, 1968] that the pregnant uterus is a major user of glucose in the body and that most of its oxidative metabolism depends on blood glucose. In the present experiments an attempt has been made to put these deductions on a quantitative basis in conscious animals.In addition, some preliminary experiments are reported in which we measured the rate of fetal utilization of fructose in conscious animals. The high concentration of fructose in the blood of fetal lambs was demonstrated many years ago [Bacon and Bell, 1946;Cole and Hitchcock, 1946] and fetal fructose is formed in the placenta from glucose [Huggett, Warren and Warren, 1951;Alexander, Huggett and Widdas, 1951;Alexander, Andrews, Huggett, Nixon and Widdas, 1955;Britton, Huggett and Nixon, 1967]. All the evidence to date suggests that this sugar is not metabolized to any great extent by the lamb [Huggett, 1961;Alexander, Britton and Nixon, 1966;Alexander, Britton, Cohen and Nixon, 1969]. Alexander, Britton and Nixon [1970] have shown that in the isolated perfused fetus only about 3% of the CO2 production came from fructose, and they suggested that glucose was probably the major fetal metabolite. However, we have shown that [14C] from

Fructose Disposal and Oxidation Rates in the Ovine Fetus

“…Alexander, Britton & Nixon (1970) demonstrated that in an artificially perfused fetal sheep preparation the rate of oxidation of fructose was much less than that of glucose. By contrast, Setchell, Bassett, Hinks & Graham (1972) inferred from a limited number of observations in intact pregnant ewes that there is little difference in the contribution of fetal glucose and fructose carbon to fetal CO2 turnover.…”

Partitioning of Nutrients in Merino Ewes. I. Contribution of Skeletal Muscle, the Pregnant Uterus and the Lactating Mammary Gland to total Energy Expenditure

“…These techniques have proved invaluable for studying metabolism in specific tissues, as exemplified by the studies of the mammary gland by Linzell (1974), and similar work on the liver and gut (Bergman and Wolff 1971), a defined muscle mass in the leg (Domanski et al 1974), the pregnant uterus (Setchell et al 1972) and the fetus and placenta (Battaglia and Meschia 1978).…”

Influence on Fetal Carbohydrate and Fat Metabolism and on Acid-Base Balance of Glucose Administration to the Mother during Labour

“…The metabolic conse quences for the human fetus of such a treatment are not fully known, having been studied mainly by single-point determinations of biochemical param eters in fetal blood [Paterson et al, 1967a;A n d erson et al, 1970], The opin ion has recently been expressed that glucose load to parturients may adverse ly increase the acidosis in the oxygen-deprived fetus owing to a rise of plasma lactate [Shelley, 1973]. Furthermore, the role of glucose as the predominant source of energy for fetal metabolism [Sabata et al, 1968;A lexander et al, 1969] has recently been challenged [Setchell et al, 1972;Battaglia and M eschia, 1973] but the alternatives of metabolic fuel are not yet completely defined. The metabolic effects of glucose administration prenatally are thus of great physiological and clinical importance.…”