Substrate utilization and dose response to insulin by subcutaneous adipose tissue of Angus steers fed corn- or hay-based diets.

We hypothesized that, at a common age endpoint, adipose tissue from corn-fed steers would be less sensitive to insulin than adipose tissue from hay-fed steers. Angus steers were assigned to either a corn-based diet (n = 6) or hay-based diet (n = 6) and fed to common days on feed. Steers fed the corn-based diet had 2.44 cm of fat thickness over the 12th thoracic rib, whereas hay-fed steers had 1.04 cm of fat thickness. At slaughter, subcutaneous adipose samples were collected and portions of subcutaneous adipose tissue were incubated with [U-(14)C]acetate to quantify fatty acid synthesis or with [U-(14)C]glucose to assess glucose utilization in the presence of 0, 100, or 500 ng/mL of insulin. Additional subcutaneous samples were used to evaluate glycolytic intermediate concentrations as indicators of glycolytic flux. Data were analyzed as a split-plot with diet in the main plot and insulin concentration and its interaction with diet in the sub-plot. Within diet, linear and quadratic contrasts of insulin concentration were tested. Diet had no effect (P > or = 0.31) on glucose metabolism or acetate carbon incorporation into total lipids (P = 0.32). Insulin had no effect (P > 0.21) on glucose conversion to CO(2), lactate, or total lipids, nor did it affect (P = 0.28) acetate conversion to total lipids. No diet x insulin interaction (P > 0.36) was observed for any measure of subcutaneous metabolism in vitro. Steers fed the corn-based diet exhibited neither a linear (P > 0.22) nor a quadratic (P > 0.24) effect to increasing insulin concentration. However, when steers were fed the hay-based diet, there was a positive linear (P = 0.06) effect for glucose oxidation. These results suggest that subcutaneous adipose tissue may become resistant to stimulation by insulin in steers fed to a fat thickness above the average feedlot steer, but this is independent of diet.

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

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.

Lipid characteristics of subcutaneous adipose tissue and M. longissimus thoracis of Angus and Wagyu steers fed to US and Japanese endpoints.

We hypothesized that the concentrations of monounsaturated fatty acids (MUFA) and cholesterol of adipose tissue and M. longissimus thoracis would not differ between Angus and American Wagyu steers when fed to a typical US live weight, but would diverge when fed to a Japanese live weight. To test this, 8 steers of each breed type were assigned to a high-energy, corn-based diet, and another 8 steers of each breed type were fed coastal bermuda grass hay diet, supplemented with the corn-based diet to achieve a daily gain of 0.9kg/d. Targeted final body weights were 525kg for steers fed for 8 or 12mo the corn- or hay-based diets, respectively, and were 650kg for steers fed for 16 or 20mo the corn- or hay-based diets. Digesta concentrations of stearic (18:0) and trans-vaccenic acid decreased, whereas linoleic acid (18:2n-6) increased between the US and Japanese endpoints (all P⩽0.03). α-Linolenic acid (18:3n-3) increased in digesta only in the hay-fed steers during this time. Plasma concentrations of palmitic (16:0) and palmitoleic acid (16:1n-7), and the 16:1:18:0 ratio, were higher in Angus steers than in Wagyu steers. Also, the plasma 16:1:18:0 ratio was decreased by hay feeding in Angus steers, but increased in Wagyu steers, when fed to the Japanese endpoint. Concentrations of oleic (18:1n-9), linoleic, α-linolenic, and 18:2trans-10,cis-12 conjugated linoleic acid all were higher in Wagyu than in Angus subcutaneous (s.c.) adipose tissue, whereas myristic (14:0) and palmitic acid were higher in Angus s.c. adipose tissue (P⩽0.05). All MUFA increased, and saturated fatty acids decreased, between the US and Japanese endpoints. Slip points of lipids in s.c. adipose tissue were over 10°C lower (P=0.01) in Japanese-endpoint steers than in US endpoint steers, consistent with the overall increase in MUFA with time on feed. The concentration of cholesterol in the M. longissimus thoracis increased with time, which may have been related to the increase in oleic acid. Because the breed×endpoint interaction was not significant for cholesterol or any of the adipose tissue fatty acids, we conclude that our original hypothesis was incorrect. Of the three factors tested (breed type, diet, and slaughter age endpoint), endpoint had the greatest effect on adipose tissue lipid composition.

Positional distribution of fatty acids in triacylglycerols from subcutaneous adipose tissue of pigs fed diets enriched with conjugated linoleic acid, corn oil, or beef tallow.

This study was conducted to determine the effects of dietary beef tallow, corn oil, and conjugated linoleic acid (CLA) on the distribution of fatty acids among positions within triacylglycerols. Crossbred barrows (n=6 per treatment group) received diets containing 1.5% beef tallow, 1.5% corn oil, or 1.5% CLA for 5 weeks. Subcutaneous adipose tissue samples were obtained immediately postmortem. The fatty acid composition was determined for the sn-2 positions of the triacylglycerols by digestion with Rhizopus arrhizus lipase. Fatty acids in the sn-1/3 position were calculated from these data. Feeding CLA increased (P<0.05) the concentration of total saturated fatty acids (SFA, especially 16:0) and isomers of CLA in adipose tissue lipids, but reduced (P<0.05) the concentration of total monounsaturated fatty acids (MUFA, especially 18:1n-9). Dietary CLA caused an accumulation of total SFA in the sn-1/3 position, with a proportional decrease in total MUFA and 18:2n-6 in the outer positions. Correspondingly, lipids extracted from CLA-fed pigs had slip points that were 10 °C higher (P<0.05) than those from corn oil- or tallow-fed pigs. These data suggest that dietary CLA increases the melting point of lipids in porcine adipose tissue by increasing the proportion of SFA at the sn-1/3 position of lipids.

African American female physicians in South Carolina: role models and career satisfaction.

BACKGROUND: This study examined the factors that influenced African American women to select medicine as a career and their satisfaction with their career choice. METHODS: Of 132 African American female physicians in South Carolina, 62 responded to a survey of open-ended questions about why they chose medicine, what they liked and disliked about their career, and who influenced their decision to become a physician. RESULTS: The majority chose medicine for altruistic reasons and found that medicine provided challenge and the opportunity to make a positive difference. Family members, teachers, and physicians served as the common external influences in their decision to become a physician. Managed care, paper work, and time demands constituted the most disliked aspects of medicine. CONCLUSION: Altruistic reasons and/or an interest in science motivated most of these African American female physicians to study medicine. Family members most often were their principal role models.