Pregnancy and undernutrition alter glucose metabolic responses to insulin in sheep

Nonpregnant and late-pregnant ditocous ewes were fed either to maintain zero energy balance in maternal tissues (fed) or at 50% of this level (underfed) for several weeks. Whole-body kinetics of glucose metabolism were measured under basal conditions, and the hyperinsulinemic, euglycemic clamp technique was used to define insulin-dose response profiles for several indices of whole-body glucose utilization, and for endogenous glucose production. Pregnancy increased and undernutrition decreased basal glucose entry rate (GER), glucose metabolic clearance rate (GMCR) and insulin-independent glucose utilization (IIGU). The consistent increment in IIGU of pregnant over nonpregnant ewes was comparable to previous estimates of uterine glucose uptake. Pregnancy resulted in higher plasma concentration for 50% maximal responses (ED50) to insulin of GER, GMCR, steady-state glucose infusion rate (SSGIR) to maintain euglycemia and insulin-dependent glucose utilization (IDGU). These changes were especially large in underfed pregnant ewes. Effects on the maximal response to insulin of these variables (Rmax) were relatively small (GMCR, IDGU) or nonsignificant (GER, SSGIR). Maximum insulin-induced suppression of endogenous glucose production was significantly lower due to undernutrition; neither Rmax nor ED50 for this response was affected by pregnancy. Insulin resistance in late-pregnant ewes is primarily due to decreased insulin sensitivity in (presumably) peripheral tissues, implying an alteration of receptor function or of early postreceptor signal transduction.