M. Arnal

Contribution of liver, skin and skeletal muscle to whole-body protein synthesis in the young lamb

1. Protein fractional synthesis rate (FSR) was measured in some major tissues and in the whole body of six 1-week-old sucking lambs by a large injection of L-[3H]valine. 2. Upper estimates of tissue protein FSR (%/d), assuming that the tissue-homogenate free-valine specific radioactivity defined that of valyl tRNA, were 115.0 in liver, 24.1 in skin, 22.9 in the white M. tensor fasciae latae, 21.6 in the red M. diaphragma and 19.6 in the remainder (exsanguinated whole body without liver and gastrointestinal tract) of lambs. 3. Absolute synthesis rates (ASR) of tissue protein were 17, 19 and 42 g/d in the liver, skin and skeletal muscle respectively, and 112 g/d in the remainder. The ASR of whole-body protein, derived from the tissue values, was 146 g/d, i.e. 33 g/d per kg body-weight. The calculated whole-body protein FSR was 23.9%/d. 4. The relative percentage contribution of liver, skin and skeletal muscle to whole-body protein synthesis was 11.7, 13.1, and 29.0. 5. We concluded that tissue protein FSR in lambs were in exactly the same decreasing order, from visceral tissues to skeletal muscles, as observed in rats. The ovine FSR estimates and the partitioning of protein synthesis between tissues were in the same range as values recently obtained by flooding-dose experiments in immature rats, piglets, and even in chicks. These findings suggest that inter-species differences are rather limited.

Lack of an effect of a high leucine test meal on plasma insulin in preruminant lambs

Abstract The experiment was performed to determine the effects of dietary leucine excess on plasma insulin, glucagon and cortisol levels in preruminant lambs. The animals received either a control test meal or a high leucine test meal. High leucine meal resulted in an about 5 fold increase in plasma leucine and α-ketoisocaproate on 1–2h period after meal feeding when compared to the respective period in controls. Postprandial plasma glucose was unmodified by leucine excess when compared to control meal. In contrast, postprandial levels in free valine, lysine, tyrosine, phenylalanine and methionine decreased. Surprisingly postprandial levels of insulin, glucagon and cortisol were not significantly modified by dietary leucine excess.