Muscle metabolism in two rabbit lines divergently selected for intramuscular fat

Abstract

[EN] A divergent selection experiment for intramuscular fat (IMF) of Longissismus dorsi muscle at 9 wk of age was performed in rabbits. The objective of this work was to compare the lipid metabolism in muscles and fat tissues of the high-IMF and low-IMF lines. Lipogenic, catabolic and lipolytic activities were studied in two muscles with different oxidative patterns (Longissimus dorsi and Semimembranosus proprius) and in perirenal fat depot at two ages, 9 wk and 13 wk. In addition, adipocytes were characterized in perirenal fat. In the fifth generation, direct response to selection was 0.26 g of IMF/ 100 g of muscle. Lines showed differences in their lipogenic activities of muscles and fat tissues at 13 wk, but not at 9 wk. High-IMF line showed greater glucose-6-P dehydrogenase (G6PDH), malic enzyme (EM) and fatty acid synthase (FAS) activities in Longissimus dorsi than low- IMF line with probabilities P0 = 1.00, 0.93 and 0.90, respectively. Differences between lines were particularly great for G6PDH activity, representing 1.13 SD. High-IMF line also showed greater G6PDH and FAS activities in Semimembranosus proprius (P0 = 0.98 for G6PDH and 0.95 for FAS) and perirenal fat (P0 = 0.91 for G6PDH and 0.96 for FAS). However, in perirenal fat, EM activity was greater in the low-IMF line (P0 = 0.90). No differences between lines were found almost in any catabolic or lipolytic activities of muscles. Regarding adipocyte characteristics, high-IMF line showed larger adipocytes in perirenal fat depot (P0 = 0.97) tissue compared to the low-IMF line, but no differences between lines were observed in the number of adipocytes. This study cast light on the metabolic activities involved in the genetic differentiation on lipid deposition in rabbits. This study shows that lipogenic activities in muscles and fat tissues, in particular G6PDH in Longissimus dorsi, are involved in the lipid accumulation in muscle and adipose tissues.