Transplacental xylose transfer in bovine pregnancy

Abstract

A substantial portion of placental function is committed to the regulation of nutrient transfer from the dam to the fetus, with glucose being the major substrate for conceptus metabolism. Due to its homomorphism with glucose, xylose can be used as tracer for the assessment of placental nutrient transfer capacity. This study was designed to evaluate transplacental permeability to xylose in bovine pregnancies on Days 90 and 180 of gestation. In Experiment 1, pregnant and nonpregnant females were infused into the jugular vein or into the allantoic sac with a 10% xylose solution to evaluate the maternal plasma xylose disappearance and the existence of feto-maternal xylose transfer, respectively. Glucose and xylose concentrations were determined in venous blood samples collected at 0, 15, 30, 60, 90, 120, 150, and 180 min. A materno-fetal but not a feto-maternal xylose transport was observed in both gestational periods. In Experiment 2, pregnant animals were slaughtered on Days 90 or 180 of gestation. A 10% xylose solution was infused intravenously into each female 60 min before slaughter to measure the materno-fetal transfer of xylose. Fetal and maternal blood samples and amniotic and allantoic fluids were collected for the determination of glucose and xylose concentrations. An increase in xylose accumulation in the uterine subcompartments was observed toward the end of the second trimester of pregnancy, demonstrating an increase in materno-fetal placental sugar transport as pregnancy advances. In conclusion, xylose can be a valid tracer for studies on transplacental transport with potential implications to conceptus growth in cattle.