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Effect of Fasting Neonatal Piglets on Blood Hormone and Metabolite Profiles and on Skeletal Muscle Metabolism^1,2,

U. S. Department of Agriculture, Athens, GA 30613

Abstract

A pair of weight-matched piglets was identified at birth in each of six litters. One member of the pair was allowed to suckle for 24 h while the other was fasted. Serum concentrations of insulin, thyroxine (T₄), somatomedin-C (RIA) and somatomedin-like activity (bioassay) were non-detectable or lower in non-suckled piglets when compared with suckled piglets. The converse situation was found for serum growth hormone (GH) levels, i.e., GH levels were higher (P<.01) in non-suckled piglets. Triiodothyronine (T₃) concentration was not influenced by nutritional status. Serum concentrations of fructose and of free fatty acids were not influenced by fasting (P>.05), but glucose and triacylglycerol serum levels were lower (P<.01, P<.05, respectively) in the non-suckled group. The biceps femoris muscle of the non-suckled group weighed less (P<.05) and contained less RNA (P<.01) and protein (P<.07), but DNA and dry matter were similar between groups. Rates of glucose oxidation to CO₂ (with [1-¹⁴C] glucose tracer, P<.01; with [6, ¹⁴ C] glucose tracer, P<.09) and incorporation into glycogen (P<.01) and of palmitate esterification into triacylglycerol (P<.01) were reduced by fasting. However, the rates of glycolytic flux and of palmitate oxidation to CO₂ (expressed per mg protein) were not affected by fasting. The rate of glucose incorporated into glycogen was reduced (P<.05) by the presence of palmitate in the muscle of suckled piglets. A dose-dependent decrease in somatomedin-like activity with increased concentration of serum from non-suckled piglets in the cartilage disc bioassay suggested that the production of growth inhibitors accompanied the loss of nutrient availability. The biceps femoris muscle responded to the fast by conserving fatty acid for oxidation as an energy source rather than for incorporation into triacylglycerol or phospholipid. The reduction in glucose oxidation to CO₂, but maintenance of glycolytic flux rates, may be important to production of lactate, which can be used by the brain and heart as an energy source. It was suggested that the metabolic adaptations of pig skeletal muscle to the fasted state may be critical to survival.

¹ Mention of a trade name, propiertary products, or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may be suitable.

² The authors thank Dr. R. W. Seerley, Dept. of Anim. Sci., Univ. of Georgia and the personnel of the Univ. of Georgia Swine Farm for providing animal facilities and for maintaining the animals used in this study.

³ Agr. Res. Serv., Richard B. Russell Agr. Res. Center.

⁴ Present address: Univ. of North Carolina, Clinical Research Unit, Box 501, North Carolina Memorial Hospital, Chapel Hill, NC 27514.

⁵ Monsanto Co., Chesterfield Village, MO 63198.

⁶ Dept. of Foods and Nutrition, Univ. of Georgia, Athens, GA 30613.