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Pregnancy but Not Moderate Undernutrition Attenuates Insulin Suppression of Fat Mobilization in Sheep^1,2,3,

Department of Animal Science, Cornell University, Ithaca, NY 14853-4801

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. Plasma concentrations of nonesterified fatty acids (NEFA) and glycerol were measured under basal conditions and during infusion of various doses of insulin while maintaining euglycemia (hyperinsulinemic, euglycemic clamp technique). Pregnancy and undernutrition separately increased basal plasma NEFA concentration in an additive manner; plasma glycerol was increased by pregnancy but unaffected by undernutrition. The molar ratio of NEFA to glycerol was significantly greater in underfed ewes. Analysis of dose-response relations between plasma insulin and metabolites during insulin infusions showed that maximally insulin-suppressed concentrations of NEFA and glycerol were significantly greater in pregnant than in nonpregnant ewes but were unaffected by under-nutrition. Neither pregnancy nor undernutrition affected the maximally insulin-suppressed NEFA to glycerol ratio, or the plasma insulin concentration for 50% maximal responses to insulin of plasma NEFA, plasma glycerol, or the plasma NEFA to glycerol ratio. Thus, even in ewes at or close to zero energy balance, pregnancy seems to reduce adipose responsiveness but not sensitivity to the antilipolytic effect of insulin. This is another manifestation of the normal development of insulin resistance in maternal tissues during late pregnancy.

KEY WORDS: • pregnancy • lipolysis • sheep • undernutrition • insulin

¹ Presented in part at the 85th Annual Meeting of the American Society of Animal Science, July 1993, Spokane, WA [Petterson, J. A., Slepetis, R., Ehrhardt, R. A., Dunshea, F. R. & Bell, A. W. (1993). Effects of pregnancy and undernutrition on insulin-induced attenuation of lipolysis and fatty acid mobilization in sheep. J. Anim. Sci. 71 (Suppl. 1): 135 (abs.)].

² Supported by Cornell University Agricultural Experiment Station.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ Current address: Victorian Institute of Animal Science, Department of Agriculture, Werribee, VIC 3030, Australia.

⁵ To whom correspondence and reprint requests should be addressed.

Manuscript received 3 March 1994. Revision accepted 6 June 1994.

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