Hormone-sensitive lipase activity in relation to fat content of muscle in Wagyu hybrid cattle

The relationship between hormone-sensitive lipase (HSL; EC 3.1.1.3) activity from pars costalis diaphragmatis (PCD) muscle (skirt muscle of diaphragm) and the lipid content of PCD and longissimus muscle was examined in a herd of Wagyu hybrid cattle. HSL activity from subcutaneous (SC) adipose tissue was examined as control for general fattening. When assayed as a cholesterol esterase (i.e. using cholesteryl oleate as a substrate), cytosolic HSL activity from both PCD muscle and SC adipose tissue displayed similar dependence on bulk substrate concentration. Significant positive correlations were found for PCD HSL specific activity and activity per g wet weight with both the total lipid content of PCD muscle (r=0.49, P <0.01) and longissimus muscle (r=0.41, P<0.01). As well, HSL specific activity and activity per g wet weight of PCD muscle showed significant negative correlations with the Canadian marbling score (an inverse scale; r=-0.42, P<0.01 and r=0.40, P<0.05, respectively). In contrast, HSL activity of SC adipose tissue showed no significant correlation with any parameter examined including muscle lipid content and backfat depth. The results suggest HSL activity in bovine muscle is associated with the content of intramuscular (IM) fat, and may have predictive value for assessing the potential of cattle to deposit IM fat.