Effects of fasting on uterine blood flow and substrate uptake in sheep.

Twelve chronically instrumented late-gestation ewes fasted for 5 days were found to have a 25% decrease in total uterine blood flow and a 20% decrease in placental blood flow. Cardiac output was unchanged but was redistributed, as measured by radiolabeled microspheres, in a pattern similar to that produced by catecholamines. Fasting also was associated with hypoglycemia and altered whole blood amino acid concentrations. Uterine uptakes of glucose, oxygen, essential amino acids and glutamine, an important uterine and fetal nutrient, were decreased significantly during fasting. The increased hepatic blood flow and decreased arterial concentrations of glucogenic amino acids observed during fasting are consistent with a redistribution of maternal cardiac output to support maternal hepatic gluconeogenesis at the expense of nutrient supply to the gravid uterus.