Effect of fasting neonatal piglets on blood hormone and metabolite profiles and on skeletal muscle metabolism.
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 less than .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 greater than .05), but glucose and triacylglycerol serum levels were lower (P less than .01, P less than .05, respectively) in the non-suckled group. The biceps femoris muscle of the non-suckled group weighed less (P less than .05) and contained less RNA (P less than .01) and protein (P less than .07), but DNA and dry matter were similar between groups. Rates of glucose oxidation to CO2 (with [1-14C] glucose tracer, P less than .01; with [6,14C] glucose tracer, P less than .09) and incorporation into glycogen (P less than .01) and of palmitate esterification into triacylglycerol (P less than .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 less than .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.
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D005215:Fasting; D005947:Glucose / Q000378:metabolism; D013006:Growth Hormone / Q000097:blood; D006728:Hormones / Q000097:blood*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000097:blood; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism; D013552:Swine / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D006728:Hormones; D007328:Insulin; D010168:Palmitates; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D005947:Glucose; D013974:Thyroxine