Effect of nutritional status on swine adipose tissue lipolytic activities

Selective mobilization of fatty acids in adipose tissue of heavy pigs

The mobilization of fatty acids during food deprivation is a selective process studied in different species (humans, rodents, birds, viverrids). The aim of this work was to study the effect of fasting on selective mobilization in commercial pigs. A total of 16 barrows (Large White×Landrace (167 kg±12.5 kg live weight) were subdivided into two homogeneous groups, one subjected to 12 h and the other to 60 h of fasting (fasting time) before slaughtering. For each pig inner and outer backfat layer were sampled at slaughter and at ham trimming 24 h later (sampling time). Increasing the fasting time and the sampling time after slaughter caused an increase in the amount of free fatty acids in both layers. Therefore it can be argued that during fasting lipolysis is stimulated and remains active also after slaughtering. The factors that stimulate lipolysis determine a greater mobilization of unsaturated fatty acids than saturated ones. Thus fasting time may influence the suitability of pork for processing and conservation, since free fatty acids are more suitable for oxidation than the esterified ones.

Increased expression of resistin and tumour necrosis factor-alpha in pig adipose tissue as well as effect of feeding treatment on resistin and cAMP pathway

AIM

Resistin, a novel hormone, is expressed in mouse, rat and human adipose tissue. Its resistance to insulin is controversial. We hypothesized that resistin has the similar roles like those of tumour necrosis factor-alpha (TNF-alpha), a putative mediator of insulin resistance, and they are in common involved in regulating lipid metabolism in vivo.

METHODS

We demonstrated TNF-alpha and resistin expression in different growth-stage adipose tissue of genetically lean and obese pigs using semiquantitative reverse transcriptase-polymerase chain reaction and Western blotting analysis. Moreover, we analysed the variations of resistin and some parameters associated with lipolysis pathway after body-weight reduction in feeding-restricted obese pigs. In addition, we localized resistin expression in the cell types from pig adipose tissue.

RESULTS

Overall, the expression of TNF-alpha and resistin in obese pigs was statistically higher than their lean counterparts, although this difference in resistin mRNA expression tailed off with age. In individual pigs, their levels increased progressively with age and degree of obesity. After feeding restriction, resistin expression was gradually decreased. Simultaneously, feeding restriction also resulted in a significant decrease of serum triglyceride and plasma cAMP, free fatty acids and insulin as well as fat adenyl cyclase and cAMP. In addition, in isolated pig adipocytes, our data showed that resistin was localized not only to adipocytes but also to other unidentified stromal vascular cells.

CONCLUSIONS

TNF-alpha and resistin are increased in obesity. Weight loss results in the decrease of resistin and lipolysis-associated parameters, suggesting the possible association between resistin and lipolysis pathway. Cell localization of resistin expression implies the possibility of other biological actions of resistin.

Dietary fat and adipose tissue metabolism in ruminants, pigs, and rodents: a review

Effects of dietary fat on dairy cows are reviewed. Dietary fat did not affect gain in BW or body condition score after peak lactation but tended to increase BW loss during early lactation and body fat deposition in growing cattle. Dietary fat decreased de novo fatty acid synthesis in adipose tissue. Basal FFA release from adipose tissue in vitro and beta-adrenergic lipolytic responses were increased by protected polyunsaturated fatty acids. Dietary fat increased body fat in growing pigs and decreased BW loss in lactating sows. Dietary fat decreased de novo fatty acid synthesis and basal glycerol release in adipose tissue and tended to increase simultaneously beta-adrenergic lipolytic responses to increased membrane fluidity. Dietary fat increased body fat in rats. Polyunsaturated fatty acids were sometimes less efficient than saturated ones in increasing body fat. Lipoprotein lipase activity in adipose tissue generally decreased. Hepatic fatty acid synthesis was decreased sharply by polyunsaturated fatty acids, and adipose tissue response was less important. beta-Adrenergic-stimulated lipolysis decreased, and fatty acid esterification increased, particularly from saturated fatty acids. A trend toward insulin resistance, which was more marked with saturated fatty acids, occurred in adipose tissue.

Duodenal rapeseed oil infusion in early and midlactation cows. 4. In vivo and in vitro adipose tissue lipolytic responses

In vitro glycerol and FFA releases from adipose tissue were studied in early (wk 3, trial 1) and midlactation (wk 19 to 26, trial 2) multiparous Holstein Friesian cows receiving a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In trial 2, in vitro basal FFA release, basal FFA: glycerol ratio, and isoproterenol-stimulated FFA and glycerol releases were higher in perirenal adipose tissue from oil-infused cows. Plasma FFA concentration also was higher in oil-infused cows before and after intravenous isoproterenol injection. In trail 1, basal and stimulated glycerol and FFA releases from perirenal (but not subcutaneous) adipose tissue tended to be lower in oil-infused cows. This was probably linked to a lower milk production potential of oil-infused than of control cows which introduced a bias in energy balance. The basal FFA:glycerol ratio tended to be higher in oil-infused cows in both adipose tissues, suggesting a lower rate of reesterification inducted by oil, as was the case in trial 2. The alpha 2-agonist clonidine decreased perirenal adipose tissue glycerol release in cows and treatments in which the responses to 4 x 10(-7) M isoproterenol were higher. In vivo and in vitro lipolytic responses were lower in trial 2 than in trial 1, except the in vitro maximally stimulated lipolytic rate, which probably reflected a long lasting teleophoretic adaptation to ensure energy needs of lactation. This study indicated that oil infusion affected both beta- and alpha 2-adrenergic responses and that postpartum lipid mobilization did not seem to be reduced by the exogenous unsaturated fatty acid supply.

Effects of dietary fat and adipose tissue location on insulin action in young boar adipocytes

1. Regulation of lipogenesis and lipolysis by insulin was studied on adipocytes isolated from 100 kg Large white male pigs. Two adipose tissues were studied: subcutaneous and perirenal. Animals were fed either a control low fat diet or a diet containing 14.7% sunflower seed oil. 2. The cell diameter was higher in the group fed the sunflower diet. 3. De novo lipogenesis was decreased for each adipose tissue in the group fed the sunflower diet. The perirenal site had a higher lipogenic activity than subcutaneous site whatever the diet. 4. Insulin did not significantly stimulate lipogenesis but had an important antilipolytic effect on stimulated lipolysis by isoproterenol. 5. The antilipolytic action of insulin was higher in perirenal adipocytes with the control diet. With the sunflower diet, the decrease was about 54.4% for subcutaneous adipocytes, whereas the inhibition was decreased in perirenal adipocytes. Addition of theophylline reversed the antilipolytic action of insulin. 6. Insulin binding was not affected neither by the dietary fat nor by the adipose tissue location. 7. Absence of de novo lipogenesis stimulation by insulin was not due to an impairment in insulin binding. 8. The different effects of dietary fat and adipose tissue location on the antilipolytic action of insulin could not be explained by a modification of insulin binding but rather by a latter event, probably at a post-insulin binding stage.