Simultaneous measurements of lactate turnover rate and umbilical lactate uptake in the fetal lamb.

Abstract

A B S T R A C T Lactic acid represents a major exogenous nutrient for the developing fetal lamb in utero. Our study was undertaken (a) to quantitate the net consumption of lactate by the fetus, (b) to quantitate the net lactate production and metabolism by the placenta, and (c) to compare the net fetal lactate consumption with fetal lactate use, measured simultaneously with radioactive tracers. 14 pregnant sheep were prepared with catheters in the maternal femoral artery and uterine vein and in the fetal aorta and umbilical vein. By simultaneous application of the Fick principle to the uterine and umbilical circulations, placental glucose consumption and placental lactate production were rapid, averaging 39.8±5.1 and 11.8±0.7 mg. min-'. Net lactate umbilical uptake averaged 1.95±0.16 mg-' kg-' min-'. During infusion of L-[14C(U)]lactate, fetal lactate turnover was much more rapid, averaging 6.5±0.8 mg* kg-' * min-1, and lactate utilization within the anatomic fetus was 5.9±0.7 mg* kg-l min-'. During infusion of tracer glucose, endogenous fetal lactate production from glucose and nonglucose substrates averaged 3.0 and 1.5 mg * kg-l * min-1, respectively. The present studies have quantitated under well oxygenated, steady-state conditions, the rapid placental metabolism and production of lactate, the net fetal consumption of lactate, and the rapid endogenous fetal lactate production from glucose and nonglucose substrates.

Concentração de lactato sérico em ovelhas e cordeiros mestiços (1/2 Suffolk) nascidos em eutocia

“…Não houve diferença estatística entre o lactato das ovelhas e o dos cordeiros, sendo os resultados do presente estudo semelhantes aos descritos por Sparks et al (1982) e Comline e Silver (1972), no que se refere à elevação do lactato materno e do neonatal, no entanto tais resultados diferiram quanto à magnitude da elevação. Segundo os autores, o aumento de lactato no plasma materno é menor quando comparado ao dos cordeiros recém-nascidos, representando apenas um terço deste.…”

Cellular Expression of the Monocarboxylate Transporter (MCT) Family in the Placenta of Mice

“…However, there is strong evidence of net lactate uptake and consumption by ovine and bovine fetuses as a whole [2,6,32,33]. Lactate and other monocarboxylates not only serve the major carbon sources for fatty acid synthesis but also are utilized as a metabolic energy source in various fetal tissues, such as the porcine heart [34], rat brain [35], and ovine liver [36].…”

“…In humans and other mammals, the concentration of lactate in the fetal circulation is known to be higher than in the maternal circulation [2][3][4][5][6]. Some researchers consider the major source of lactate in the fetal circulation of humans to be the fetus itself due to the active anaerobic metabolism of fetus-that must be discharged into the maternal circulation [3][4][5].…”

“…Some researchers consider the major source of lactate in the fetal circulation of humans to be the fetus itself due to the active anaerobic metabolism of fetus-that must be discharged into the maternal circulation [3][4][5]. On the other hand, fetal tissues of sheep effectively utilize lactate as a metabolic energy source, supplied by placental lactate production or transfer from maternal blood [2,6]. The most likely mechanism of lactate transfer through the placenta involves a specific carrier-mediated system, being coupled with proton transfer [4,7,8].…”

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

“…This study provides the first in vitro evidence for the role of lactate as an important precursor for fatty acid synthesis in adipose tissue of the bovine fetus ( dehydrogenase in both fetal and newborn calf adipose tissue appear nonlimiting and are far in excess of the sum of the rates of lactate oxidation and incorporation into triacyl glycerol (Tables 2 and 3). The importance of lactate as a major exogenous nutrient for the developing fetal lamb has been recognized (17,18). The ratios of glucose I-14C/glucose 6-I4C conversion to C02 and the calculated (see "Results") contribution of the pentose phosphate cycle to glucose metabolism indicate that metabolism of glucose via pentose phosphate cycle is increased in adipose tissue of fetal and depressed in adipose tissue of newborn calves.…”