Sensitivity to metabolic signals in late-gestation growth-restricted fetuses from rapidly growing adolescent sheep

Fetal sensitivity to insulin and glucose was investigated during fetal hyperinsulinemic-euglycemic (HI-euG, n = 18) and hyperglycemic-euinsulinemic (HG-euI, n = 12) clamps. Singleton bearing adolescent ewes were fed high (H) or control (C) nutrient intakes to induce compromised or normal placental/fetal size, respectively. Catheters were inserted in the umbilical vein (v), fetal artery, (a) and veins, and studies were conducted between day 126 and 133 of gestation. Umbilical blood flow (UmBF) was determined by the steady-state transplacental diffusion technique using (3)H(2)O, and glucose fluxes were quantified by the Fick principle. For the HI-euG study, fetal glucose utilization was measured at spontaneously occurring fetal insulin concentrations and two additional higher levels, whereas fetal glucose was clamped at the initial baseline level. For the HG-euI study, fetal insulin was suppressed by somatostatin infusion, and fetal glucose utilization was determined at baseline (before somatostatin) glucose concentrations, and at 150 and 200% of this value. Placentome weight (219 vs. 395 g), fetal weight (2,965 vs. 4,373 g), and UmBF (519 vs. 794 ml/min) were lower (P < 0.001) in H than in C groups. Relative to control fetuses, glucose extraction (G[v - a]/G[v] x 100) in the nonperturbed state was higher (21.7 vs. 15.9%) in growth-restricted fetuses despite lower glucose (0.78 vs. 1.05 micromol/ml) and insulin (8.5 vs. 16.9 microU/ml) concentrations (all P < 0.001). During the HI-euG study, total fetal glucose utilization rate increased in response to higher insulin concentrations (65 and 64% in H and C groups). Similarly during the HG-euI study, a twofold increase in glucose supply increased fetal glucose utilization by 41 and 44% in H and C groups, respectively. Throughout both studies, absolute total fetal glucose utilization rates were reduced in H vs. C groups (P < 0.01) but were similar when expressed per kilogram fetus (HI-euG: 34.7, 49.5, and 57.5 in H vs. 34.7, 51.2, and 56.1 micromol.min(-1).kg(-1) in C, HG-euI: 28.7, 35.7, and 40.8 in H vs. 32.9, 34.5, and 43.8 micromol.min(-1).kg(-1) in C). These normal body weight-specific metabolic responses to short-term experimental increases in plasma insulin and glucose in response to chronic IUGR indicate maintained mechanisms of insulin action and glucose uptake/utilization capacity, which, if persistent, might predispose such IUGR offspring to excessive energy deposition in later life.