Effect of dietary energy source on in vitro substrate utilization and insulin sensitivity of muscle and adipose tissues of Angus and Wagyu steers

Abstract

Angus (n = 8; 210 kg of BW) and 7/8 Wagyu (n = 8; 174 kg of BW) steers were used to evaluate the effects of dietary energy source on muscle and adipose tissue metabolism and insulin sensitivity. Steers were assigned to either a grain-based (corn) or hay-based (hay) diet and fed to similar final BW. At slaughter, LM and s.c. and i.m. adipose tissue samples were collected. Portions of the LM and adipose tissues were placed immediately in liquid N for later measurement of glycolytic intermediates. Fresh LM and s.c. and i.m. adipose tissues were incubated with [U-(14)C]glucose to assess glucose metabolism in vitro. All in vitro measures were in the presence of 0 or 500 ng/mL of insulin. Also, s.c. and i.m. adipose tissues were incubated with [1-(14)C]acetate to quantify lipid synthesis in vitro. Glucose-6-phosphate and fructose-6-phosphate concentrations were 12.6- and 2.4-fold greater in muscle than in s.c. and i.m. adipose tissues, respectively. Diet did not affect acetate incorporation into fatty acids (P = 0.86). Insulin did not increase conversion of glucose to CO(2), lactate, or total lipid in steers fed hay but caused an increase (per cell) of 97 to 110% in glucose conversion to CO(2), 46 to 54% in glucose conversion to lactate, and 65 to 160% in glucose conversion to total lipid content in adipose tissue from steers fed corn. On a per-cell basis, s.c. adipose tissue had 37% greater glucose oxidation than i.m. adipose (P = 0.04) and 290% greater acetate incorporation into fatty acids than i.m. adipose (P = 0.04). Insulin addition to s.c. adipose tissue from corn-fed steers failed to stimulate glucose incorporation into fatty acids, but exposing i.m. adipose tissue from corn-fed steers to insulin resulted in a 165% increase in glucose incorporation into fatty acids. These results suggest that feeding hay limited both glucose supply and tissue capacity to increase glucose utilization in response to insulin without altering acetate conversion to fatty acids. Because s.c. adipose tissue consistently utilized more acetate and oxidized more glucose than did i.m. adipose, these results suggest that hay-based diets may alter i.m. adipose tissue metabolism with less effect on s.c. adipose tissue.

Postweaning substitution of grazed forage with a high-energy concentrate has variable long-term effects on subcutaneous fat and marbling in Bos taurus genotypes1

“…It has been suggested that different fat depots have preferences for different substrates to support lipogenesis and/ or adipogenesis, although empirical evidence for effects on carcass characteristics independent of the amount of NE supplied is lacking (Pethick et al, 2004;Hocquette et al, 2010). Acetate is the major carbon source for fatty acid synthesis in ruminants' fat depots (Bauman, 1976); however, it has been suggested that IMF (as opposed to other depots) preferentially utilizes glucose/lactate for fatty acid synthesis (Smith and Crouse, 1984;Rhoades et al, 2007;Smith et al, 2009;Hocquette et al, 2010). Diets based on cereal grain would potentially generate additional glucose either via gluconeogenesis from propionate or via direct absorption of glucose from the small intestine (Rowe et al, 1999).…”

Intramuscular fat content in meat-producing animals: development, genetic and nutritional control, and identification of putative markers

“…Then, a higher level of GLUT4 expression and higher activities of metabolic enzymes involved in the conversion of glucose into long-chain fatty acids (namely phosphofructokinase and ATP-citrate lyase) were detected in intramuscular adipose tissue compared to subcutaneous fat in these species . More recently, it was shown that the rate of glucose incorporation into fatty acid was more than twice as high as the rate of acetate incorporation in IMF adipocytes, whereas they are similar in subcutaneous adipose tissue (Rhoades et al, 2007). Thus, when fat synthesis is limited (such as within IMF adipocytes), glucose provides a greater proportion of acetyl units for lipogenesis than acetate (for review, see Smith et al, 2009).…”

“…For instance, it should be proposed that feeding a hay-based diet (providing mainly acetate) may alter intramuscular adipose tissue metabolism with less effect on subcutaneous adipose tissue accretion in ruminants. A recent experiment indicated that feeding a corn-based diet (providing a great amount of propionate, a glucogenic precursor) enhances glucose uptake in IMF depot, whereas feeding a hay-based diet reduces insulin action without altering acetate incorporation in fatty acids (Rhoades et al, 2007). Because subcutaneous fat used acetate more effectively than intramuscular adipose tissue, feeding a hay-based diet would then promote subcutaneous fat deposition over intramuscular adipose tissue accretion.…”

Comparison of the adipogenesis in intramuscular and subcutaneous adipocytes from Bamei and Landrace pigs

“…May et al (1994) showed that pre-adipocytes of Wagyu steer proliferate more actively than the cells of Angus steer. It has been demonstrated that IM adipocytes prefer to use glucose, while SC adipocytes prefer to use acetate as primary substrates for fatty acid synthesis in bovine in vitro (Smith and Crouse 1984;Rhoades et al 2007), and triacylglycerol biosynthesis is less sensitive to starvation in IM than in SC adipose tissue (Smith et al 1998). Diets greater in starch promote IM fat deposition relative to SC deposition (Choat et al 2003).…”