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The impact of excess dietary Leu was studied in two growth experimental trials with pigs (8–25 kg). In each trial, forty-eight pigs were allotted to one of six dietary groups. The dietary Leu supply increased from treatment L100 to L200 (three increments). To guarantee that interactions between the branched-chain amino acids (BCAA) were not cushioned either surpluses of isoleucine (Ile, expt 1) or valine (Val; expt 2) were avoided. In the fifth treatment, the effects of a simultaneous excess of Leu and Val (expt 1), or of Leu and Ile (expt 2) were investigated. The sixth treatment was a positive control.
An increase in dietary Leu decreased growth performance, and increased plasma Leu and serum a-keto-isocaproate levels in a linear, dose-dependent manner. Levels of plasma Ile and Val, and of serum a-keto-b-methylvalerate and a-keto-isovalerate, indicated increased catabolism. Linear increases in the activity of basal branched-chain a-keto acid dehydrogenase in the liver confirmed these findings. No major alterations occurred in the mRNA of branched-chain amino acid catabolism genes. In liver tissue from expt 2, however, the mRNA levels of growth hormone receptor, insulin-like growth factor acid labile subunit and insulin-like growth factor 1 decreased significantly (P<0.05) with increasing dietary Leu.
In conclusion, excess dietary Leu increased the catabolism of BCAA mainly through post-transcriptional mechanisms. The impact of excess Leu on the growth hormone–insulin-like growth factor-1 axis requires further investigation.
MK Wiltafsky, MW Pfaffl and FX Roth, 2010. British Journal of Nutrition, 103:964-976.
