Role of maternal glucose as a metabolic substrate for the guinea pig conceptus.

Our study in pregnant guinea pigs was designed to determine whether the modest fractional contribution of glucose to the late-pregnant uterine caloric uptake was due to inadequate uterine glucose supply or to diminished uterine glucose demand. To this end, uterine uptake of glucose, O2, and lactate was measured in 27 late-pregnant guinea pigs with a wide range of litter sizes. A group of 11 mid-pregnant guinea pigs served as a reference. The fractional uterine uptake of glucose in mid- and late-pregnancy was 90 and 45%, respectively, confirming the indirect data calculated from different studies. In late pregnancy, uteroplacental blood flow (microspheres, -40%) as well as arterial glucose concentration (-30%) had decreased relative to mid-gestation, giving rise to a 60% lower wt-specific uterine glucose supply and a 21% lower wt-specific uterine glucose uptake. Inasmuch as fetal and placental glycogen stores become rapidly depleted after the 50th day of pregnancy, the lower uterine glucose uptake in late pregnancy appears to reflect inadequate uterine glucose supply rather than diminished fetal glucose demands. In late pregnancy, uterine caloric demand per kg is about 60% more than in mid-gestation, most likely associated with accelerated fetal fat accretion. Inasmuch as the latter appears to be mostly fueled by nonglucose fat precursors, it could explain why the glucose fraction of the uterine caloric uptake in late pregnancy has decreased by 50% instead of 21% as compared to mid-gestation. The reduction in arterial glucose concentration in late pregnancy was independent of litter size suggesting this phenomenon is to be a maturational adaptation rather than a sign of inadequate maternal glucose production.