Glucose metabolism and lipid mobilization by adipocytes from mice selected for growth

The impact of dietary fat withdrawal on carcass iodine value, belly characteristics, and changes in body fat over time

The inclusion of unsaturated fats in pig diets has raised issues related to pork carcass fat quality. The objective of this experiment was to understand how withdrawal from the diet of unsaturated dietary fat before slaughter impacts the composition of jowl fat during the growth cycle and at market. Fifty individually housed pigs (PIC 337 × C22/29; initial BW = 59.3 ± 0.55 kg) were allotted based on sex and initial BW to 10 treatments for an 82-d experiment as follows: 3 dietary fat withdrawal times before slaughter (21, 42, or 63 d) by 3 dietary fat unsaturation loads (DFUL), which includea high intake of unsaturated fatty acids supplied through an inclusion of 5% corn oil (HIGH), a high intake of a mixture of saturated and unsaturated fatty acids supplied through an inclusion of 5% animal-vegetable blend (MED), and a moderate intake of unsaturated fatty acids supplied through an inclusion of 2.5% corn oil (LOW). Pigs were weighed and jowl adipose samples were collected on d 0, 21, 42, and 63 and at harvest on d 82. Data were analyzed using PROC MIXED with treatment and sex as fixed effects. At market (d 82), increasing the withdrawal of dietary fat further away from market increased 18:1 (P = 0.045) and tended to increase 14:0 concentrations (P = 0.054). It also significantly decreased 18:2 (P < 0.001) and tended to decrease 18:3 concentrations (P = 0.081). A HIGH DFUL resulted in the greatest 18:2 concentrations in jowl fat followed by LOW; MED resulted in the lowest 18:2 levels (P < 0.001). Dietary fat withdrawal before market significantly reduced carcass iodine value (IV) measured at d 82 (P = 0.006). In conclusion, elevated 18:2 intake makes lowering carcass IV in the depot fat very difficult and may take as long as 61 d. The withdrawal of unsaturated dietary fat apparently altered the fat depot to be more reflective of fat synthesized de novo, resulting in a more saturated depot fat. Importantly, this alteration of deposited fat composition did not translate into improved belly firmness, depth, weight, or fat color.

Correlation of food intake in lambs with adipocyte glucose metabolism and NEFA release

1. Experiments were conducted with lambs to determine the correlation between food intake, rate of glucose incorporation into CO(2) and lipids, and rate of lipid mobilization by their isolated omental adipocytes.2. During the interval between weaning and slaughter average daily dry matter (ADDM) intakes of the individual lambs were significantly correlated with average daily gains; however, the ratio of ADDM intake to body wt.((3/4)) was similar in all individuals.3. The average size of adipocytes for each lamb, as determined by lipid: protein ratios, was not significantly correlated with food intake.4. Oxidation of glucose to CO(2) and the total measured glucose incorporation by the adipocytes were significantly and negatively correlated with lamb ADDM intakes at low levels of glucose (0.1 mg/ml.), whereas rates of lipogenesis from glucose were similar for all intake levels.5. Insulin-induced increases in glucose utilization were positively and significantly correlated with ADDM intakes to the extent that insulin had over twice the effect on the adipocytes from high-intake lambs as it had on those from low-intake lambs. The minimum effective dose of insulin necessary to significantly increase glucose utilization by the adipocytes was also positively and significantly correlated with the ADDM intakes of the lambs.6. Basal NEFA release rates were higher for adipocytes from low-intake lambs. Epinephrine significantly increased NEFA release rates, independent of lamb intakes.7. A larger number of adipocytes in the high-intake lambs means that they would have a greater total potential to lower blood glucose, particularly when they are under the effects of normal circulating levels of insulin. The amount of glucose removed from the glucose pool could be the feed-back signal which results in a high long-term food intake.