Postnatal decreases in cardiac muscle fractional protein synthesis rates in fed pigs measured by an intraperitoneal flooding dose of L‐[ring‐2H5]Phe

Abstract

This study was conducted to quantify postnatal changes in cardiac muscle protein fractional synthesis rates (FSR) and their correlations with serum levels of hormones (nsulin, growth hormone, and cortisol), growth factors (IGF-I and GLP-2) and free amino acids (AA) in fed pigs. Thirty six purebred Yorkshire gilts were used for sampling at d 1, 4, 6, 12, 20 and 28 (1 wk post-weaning) d of age. Piglets received ip injection of a flooding dose of Phe containing L-[ring-2H5] (40 molar%) in saline. Serum samples before the injection and plasma and heart samples at 30 min post-injection were obtained for the determinations of tracer Phe enrichment by GC-MS, free AA by HPLC, and hormones and growth factors by RIA. Tracer Phe enrichments in the plasma and cardiac muscle free AA pools were 25–27 molar%. Cardiac muscle FSR was 29.5, 28.5, 27.6, 28.9, 21.8, and 11.7 %/d at d 1, 4, 6, 12, 20, and 28 of age, respectively, with a linear decrease (P<0.05). Postnatal changes in FSR were negatively correlated (P<0.05, r=−0.41) with serum GLP-2 levels. Postnatal changes in cardiac FSR were positively correlated (P<0.05) with the plasma concentrations of Asn, citrulline, His, Leu, ornithine, Ser, taurine, Tyr and Val (r=0.33–0.57) but negatively correlated (P<0.05) with Glu and Gly (r=−0.41 or −0.36). These results indicate dramatic postnatal decreases in cardiac muscle FSR from birth to the post-weaning transition in fed pigs, which correlated well with changes in serum GLP-2 and plasma several AA levels.