PREGNANCY BUT NOT MODERATE UNDERNUTRITION ATTENUATES INSULIN SUPPRESSION OF FAT MOBILIZATION IN SHEEP

Nonpregnant and late-pregnant ditocous ewes were fed either to maintai n zero energy balance in maternal tissues (fed) or at 50% of this leve l (underfed) for several weeks. Plasma concentrations of nonesterified fatty acids (NEFA) and glycerol were measured under basal conditions and during infusion of various doses of insulin while maintaining eugl ycemia (hyperinsulinemic, euglycemic clamp technique). Pregnancy and u ndernutrition separately increased basal plasma NEFA concentration in an additive manner; plasma glycerol was increased by pregnancy but una ffected by undernutrition. The molar ratio of NEFA to glycerol was sig nificantly greater in underfed ewes. Analysis of dose-response relatio ns between plasma insulin and metabolites during insulin infusions sho wed that maximally insulin-suppressed concentrations of NEFA and glyce rol were significantly greater in pregnant than in nonpregnant ewes bu t were unaffected by undernutrition. Neither pregnancy nor undernutrit ion affected the maximally insulin-suppressed NEFA to glycerol ratio, or the plasma insulin concentration for 50% maximal responses to insul in of plasma NEFA, plasma glycerol, or the plasma NEFA to glycerol rat io. Thus, even in ewes at or close to zero energy balance, pregnancy s eems to reduce adipose responsiveness but not sensitivity to the antil ipolytic effect of insulin. This is another manifestation of the norma l development of insulin resistance in maternal tissues during late pr egnancy.