Effect of beta-adrenergic agonists on lipolysis and lipogenesis by porcine adipose tissue in vitro

The effects of the beta-adrenergic agonists isoproterenol, cimaterol, ractopamine and clenbuterol on lipolysis (release of glycerol and free fatty acids) and lipogenesis (incorporation of 14C into fatty acids from [14C]glucose) was examined in porcine adipose tissue explants in vitro. Lipolysis was stimulated by isoproterenol, cimaterol or ractopamine but not by clenbuterol. Insulin reduced the lipolytic effects of the beta-adrenergic agonists (isoproterenol, cimaterol and ractopamine). Lipogenesis was inhibited by all beta-adrenergic agonists tested (isoproterenol, cimaterol, ractopamine and clenbuterol). The antilipogenic effect of the beta-adrenergic agonists was reduced by the presence of insulin in the incubation. Although effects of the different beta-adrenergic agonists varied, all had some direct effects that could be expected to reduce adipose accretion. Effects of beta-adrenergic agonists in the pig are due in part to direct effects on adipose tissue.     

Adipose tissue, longissimus muscle and anterior pituitary growth and function in clenbuterol-fed heifers

The present study was conducted to determine the effects of feeding clenbuterol on adipose tissue and longissimus muscle growth in heifers. For 50 d, 14 heifers were fed either a sucrose-based, clenbuterol supplement or a placebo in which the clenbuterol had been omitted. The heifers were slaughtered in two groups, based on initial weight. Adipose tissue from several anatomical sites and longissimus muscle (depending on slaughter group) were obtained fresh at slaughter. Changes in carcass characteristics elicited by clenbuterol were similar to those reported by others for steers and sheep. Subcutaneous (sc) and intramuscular (im), but not perirenal, adipocytes were smaller and there were more cells per g tissue in the adipose tissue depots of the clenbuterol-fed heifers. Clenbuterol decreased lipogenic enzyme activities, fatty acid-binding protein activity, basal lipolysis and acetate incorporation into glyceride-fatty acids (P less than .05) in sc adipose tissue, but had no effect (P greater than .05) on lipogenesis or lipolysis in im adipose tissue. Clenbuterol elicited a 20% increase in type II myofiber diameters (P less than .05) but had no effect on type I myofiber diameters. In vitro growth hormone release by perifused anterior pituitaries was not affected significantly by long-term in vivo exposure to clenbuterol. These data indicate that a depression in lipogenesis is the mechanism by which clenbuterol decreases subcutaneous fat accretion in cattle.     

肿瘤坏死因子-α在脂肪组织中的作用

作为一种由脂肪细胞产生和分泌的多功能细胞因子,肿瘤胚死因子-α(TNF-α)除了在免疫系统中发挥作用外,其在脂肪组织中也具有重要的调控作用,如促进脂肪分解、抑制脂肪合成、抑制脂肪细胞分化、诱导脂肪细胞凋亡等。综合起来看,TNF-α可抑制动物的脂肪沉积。     

Influence of the beta 2-adrenergic agonist clenbuterol on insulin-stimulated lipogenesis in mouse adipocytes

Growing mice fed the beta 2-adrenergic agonist clenbuterol (CB; 20ppm) had increased rate of growth and altered composition of gain (greater protein and less fat). Adipocytes prepared from the epididymal fat pads of treated and untreated mice were used to examine the influence of CB on lipid metabolism. Using cells from untreated mice, CB stimulated lipolysis to an equivalent maximum rate as epinephrine (EPI), but CB was far less potent (EC50 (microM); CB = 5, EPI = 0.2). Both CB and EPI inhibited insulin-stimulated lipogenesis over the physiological range of insulin concentrations. This inhibition was expressed as a dose-dependent decrease in tissue sensitivity to insulin and a decrease in maximal lipogenic capacity. Inhibition of maximal rate, but not of insulin sensitivity, could be stimulated by the addition of palmitate without EPI or CB. Adipocytes isolated from CB-treated mice did not differ from controls in sensitivity to insulin or in activity of fatty acid synthetase. Increased lipolysis and reduced lipogenesis as observed in vitro with CB are consistent with reduced fat accretion in CB-treated mice. However, the absence of detectable changes in adipocyte lipogenesis from CB-fed mice leaves open the question of the relevance of altered lipid metabolism to the observed changes in body composition.     

Acute effects of beta-adrenergic agonists on porcine adipocyte metabolism in vitro

Backfat was obtained at slaughter from market weight hogs to study the acute effects of clenbuterol (CB), ractopamine (RAC) or epinephrine (EPI), in the presence and absence of theophylline (THEO) or adenosine deaminase (ADA), on rates of lipolysis and fatty acid synthesis in vitro. Only EPI increased lipolytic rate in the absence of THEO or ADA. In the presence of THEO or ADA, RAC and CB were lipolytic, although CB had a lower maximal response. With THEO present, RAC and EPI increased lipolysis with a similar potency and responsiveness. Lipolytic responses from all agonists were prevented by propranolol. Insulin stimulated glucose incorporation into fatty acids 50 to 100%; stimulated rates were not influenced by any agonist, either alone or in the presence of ADA. When THEO was present, EPI and RAC inhibited fatty acid synthesis approximately 50%. Clenbuterol was not inhibitory under any conditions. Results indicate that, under appropriate conditions, beta-adrenergic agents increase lipolysis and decrease lipogenesis in porcine adipocytes. Combined evidence suggests that lipolysis is more sensitive to beta-adrenergic stimulation than is insulin-stimulated lipogenesis. Finally, RAC and CB possess only partial agonist activity relative to EPI, CB being least active.     

Regulation of adipose tissue metabolism during pregnancy and lactation in the ewe: the role of insulin

This study was conducted to examine the effect of insulin on lipid metabolism of adipocytes during pregnancy and lactation in ewes. During the first 3 mo of pregnancy, metabolism of adipocytes from omental adipose tissue was characterized by a high rate of de novo lipogenesis (90 to 125 nmol of acetate incorporated into lipids.2 h-1.10(6) cells-1) and a 38% reduction in response to beta-lipolytic stimulus (isoproterenol 10(-6) M). Simultaneously, there was a rise in the number of high-affinity insulin receptors (Kd = .2 nM), and insulin binding characteristics showed a decrease in the negative cooperativity phenomenon. Moreover, lipogenesis stimulated by insulin (1 mU/ml) increased in comparison with observations in nonpregnant ewes. The last third of pregnancy and early lactation were characterized by a marked fall in lipogenesis and a simultaneous increase in isoproterenol-stimulated lipolysis. During lactation, the number of total insulin receptors was decreased by 62% and insulin stimulation of lipogenesis became inefficient. Results suggest that insulin plays a direct role in adipose tissue metabolism during pregnancy.     

Adipose tissue gene expression in obese dogs after weight loss

Body weight (BW) mainly depends on a balance between fat storage (lipogenesis) and fat mobilization (lipolysis) in adipocytes. BW changes play a role in insulin resistance (IR), the inability of insulin target tissue to respond to physiological levels of insulin. This results in inhibition of lipogenesis and stimulation of lipolysis. Weight gain leads to IR whereas, weight loss improves insulin sensitivity (IS). The aim of this study was to evaluate the effect of weight loss and recovery of IS on the expression of genes involved in lipogenesis and lipolysis in weight losing dogs. Gene expression was studied in both subcutaneous and visceral adipose tissue. Obese dogs received a hypoenergetic low fat high protein diet (0.6 x NRC recommendation). Before and after weight loss, IS was assessed using the euglycaemic hyperinsulinaemic clamp. Gene expression of IRS-2, SREBP, intracellular insulin effectors, ACC, FAS, FABP, ADRP, PEPCK, lipogenesis key proteins, perilipin and HSL, lipolysis key proteins were quantified using real-time RT-PCR in subcutaneous and visceral fat. BW decreased from 15.2 +/- 0.5 to 11.4 +/- 0.4 kg (p < 0.05) over 78 +/- 8 days. When obese, dogs were insulin resistant. After weight loss, IS was improved. In the subcutaneous adipose tissue, the expression of only the IRS-2 was increased. In the visceral adipose tissue, the expression of the genes involved in the lipogenesis was decreased whereas one of the genes implied in the lipolysis did not change. The expression profile of genes involved in lipid metabolism, as measured after weight loss, is indicative for a lower lipogenesis after weight loss than in obese dogs. Our results also confirm dramatic differences in the lipid metabolism of visceral and subcutaneous fat. They should be completed by comparing gene expression during weight losing and normal weight steady state.     

Sensitivity of lipolysis and lipogenesis to dibutyryl-cAMP and beta-adrenergic agonists in swine adipocytes in vitro

The sensitivities of lipolysis and fatty acid synthesis to dibutyryl-cAMP (dbcAMP), epinephrine, ractopamine and clenbuterol were quantified in vitro using porcine adipocytes. Insulin-stimulated lipogenesis showed a biphasic response to dbcAMP, with increased rates at low concentrations and decreased (55%) rates at higher concentrations of dbcAMP. In the absence of insulin, lipogenesis was inhibited 78% by dbcAMP. In the presence of adenosine deaminase or theophylline, all three beta-adrenergic agonists inhibited basal lipogenesis, but only epinephrine and ractopamine inhibited insulin-stimulated lipogenesis. The relationship between suppressed lipogenesis and enhanced lipolysis in response to dbcAMP and the beta-agonists revealed that 1) basal lipogenesis was more sensitive to inhibition than was the stimulation of lipolysis, 2) sensitivity differences were magnified if adenosine deaminase was present and 3) insulin decreased adipocyte sensitivity to the inhibitory effects of dbcAMP and the beta-adrenergic agonists. These results indicate that the relative sensitivities of lipogenesis and lipolysis to beta-adrenergic stimulation can be modified by adenosine and insulin. Furthermore, adenosine and insulin antagonize beta-adrenergic responses, in part, by cAMP-independent mechanisms.     

Effects of body condition score at parturition and postpartum supplemental fat on adipose tissue lipogenic activity of lactating beef cows

Three-year-old Angus x Gelbvieh beef cows nutritionally managed to achieve a BCS of 4 +/- 0.07 (479.3 +/- 36.3 kg of initial BW) or 6 +/- 0.07 (579.6 +/- 53.1 kg of initial BW) at parturition were used in a 2-yr experiment (n = 36/yr) to determine the effects of BCS at parturition and postpartum lipid supplementation on cow adipose tissue lipogenesis. Beginning 3 d postpartum, cows within each BCS were randomly assigned to be fed hay and a low-fat control supplement or supplements with either cracked high-linoleate safflower seeds or cracked high-oleate safflower seeds until d 60 of lactation. Diets were formulated to be isonitrogenous and isocaloric, and safflower seed diets provided 5% DMI as fat. Adipose tissue biopsies were collected near the tail-head region of cows on d 30 and 60 of lactation. Dietary treatment did not affect (P > or = 0.43) adipose tissue lipogenesis. Body condition score at parturition did not affect acetate incorporation into lipid (P = 0.53) or activity of acetyl CoA carboxylase (P = 0.77) or fatty acid synthase (P = 0.18). Lipoprotein lipase activity and palmitate incorporation into triacyl-glycerol tended to be greater (P = 0.06), and palmitate esterification into total acylglycerols was greater (P = 0.01) in cows with a BCS of 4 at parturition. Mean activity of acetyl-CoA carboxylase (P < 0.001), lipoprotein lipase (P = 0.01), and rate of palmitate incorporation into monoacylglycerol (P = 0.02), diacylglycerol (P = 0.001), triacylglycerol (P = 0.003), and total acylglycerols (P = 0.002) were greater at d 30 than d 60, suggesting a greater proclivity for fatty acid biosynthesis and esterification by adipose tissue at d 30 of lactation. Although dietary lipid supplementation did not affect adipose tissue lipogenesis, results suggest that cows with a BCS of 4 at parturition have a greater propensity to deliver exogenously derived fatty acids to the adipocyte surface and incorporate preformed fatty acids into acylglycerols as stored adipocyte lipid. Additionally, cows in early lactation seemed to be able to synthesize and incorporate more fatty acids into stored lipid than cows during peak lactation.     

Acute and chronic hormone and metabolite changes in lambs fed the beta-agonist, cimaterol

The objective of this study was to determine if acute and chronic changes in circulating metabolic hormone and metabolite concentrations are associated with β-agonist-induced nutrient repartitioning in young growing lambs. Two groups of 12 Dorset and Dorset-Finn cross ram lambs weighing 36 or 33 kg live weight were assigned to 3- or 6-week treatment intervals, respectively, to achieve similar slaughter weights. Six lambs within each treatment interval were fed ad libitum a complete mixed high-concentrate diet containing either 0 or 10 ppm cimaterol. During the first 12 hr of cimaterol administration plasma somatotropin (ST), thyroxine (T₄), and triiodothyronine (T₃) concentrations were not altered by treatment, but plasma insulin, glucose, non-esterified fatty acids (NEFA) and glycerol concentrations were elevated 2 hr after ingestion. These acute responses suggest direct stimulation of glycogenolysis and lipolysis by cimaterol, which is characteristic of β-adrenergic alteration of carbohydrate and lipid metabolism. Chronic administration of cimaterol significantly decreased insulin concentrations by 36% and 52% at 3 and 6 weeks, respectively, while glucose concentrations remained unchanged. Serum IGF-I concentrations were not significantly altered by cimaterol. T₄ levels were reduced 22.1% after 3 weeks of cimaterol treatment. Although plasma NEFA concentrations were chronically elevated 56% to 65% in lambs fed cimaterol, plasma glycerol concentrations remained at baseline levels. The relative changes in plasma NEFA and glycerol concentrations are consistent with a decreased rate of lipogenesis, rather than an increase in lipolysis.     

Regulation of porcine adipocyte metabolism by insulin and adenosine

The acute effects of insulin and adenosine on rates of lipolysis and lipogenesis in pig adipocytes were investigated to determine what limits the expression of the insulin response in vitro. Adenosine and insulin independently inhibited isoproterenol-stimulated lipolysis. Adenosine, acting through the pertussis toxin-sensitive G-protein Gi, was more effective than insulin and could completely inhibit lipolysis. Fatty acid synthesis from glucose was increased by both adenosine and insulin. Neutralization of endogenous adenosine with adenosine deaminase decreased basal rates of lipogenesis and increased the insulin response from 30 to 60% above basal. Neutralization of Gi with pertussis toxin further decreased the basal rate and increased the insulin response to 160% above basal. These data indicate that Gi, and the ligands that signal through Gi, stimulate glucose incorporation into fatty acids and can attenuate the insulin response. It seems likely that an exaggerated rate of glucose metabolism in the absence of insulin contributes to the inconsistent insulin responses exhibited in pig adipose tissue in vitro. These data also demonstrate that insulin and adenosine have major roles in regulating pig adipose tissue metabolism.     

A species comparison of liver slice synthesis and secretion of triacylglycerol from nonesterified fatty acids in media

The ability of liver slices from eight species to synthesize and secrete triacylglycerol from nonesterified fatty acids contained in media was investigated. Species were grouped according to the relative proportion of lipogenesis occurring in the liver. The rate of liver triacylglycerol synthesis from nonesterified fatty acids in media was similar among species studied. Liver slices from species in which the liver contribution to lipogenesis is minor (sheep, cattle, pig and guinea pig) secreted less triacylglycerol synthesized from nonesterified fatty acids than did liver slices from species in which lipogenesis occurs predominantly in the liver (chicken and fish) or in liver and adipose tissue (rat and rabbit). The results suggest that the ability of liver to secrete triacylglycerol in very low density lipoproteins is proportional to the liver's lipogenic capacity.     

Carcass composition and adipose tissue metabolism in growing sheep

Experiments were conducted to investigate biological variables that influence fat accretion in growing ram lambs. Carcass composition and adipose tissue development were measured in Columbia-sired ram lambs from 32.0 to 73.9 kg body weight. Five or six ram lambs were slaughtered every 2 mo, from 4 to 10 mo of age. The percentage of carcass fat-free dry matter decreased with age from 30.9 to 27.5% (P less than .05), while the percentage of carcass fat increased from 17.7 to 33.4%. Similarly, offal fat-free dry matter decreased with age (from 24.5 to 21.5), and there was nearly a threefold increase in the percentage of offal fat (P less than .05 for both measures). Subcutaneous adipocyte diameter and lipogenesis in vitro increased from 4 to 6 mo of age, and did not increase further with age. A bimodal distribution of adipocytes was apparent in the 4-mo-old lambs, but was not observed in any other age group. The presence of glucose in incubation media stimulated acetate incorporation into fatty acids in vitro in adipose tissue from 8- and 10-mo-old lambs. However, glucose did not affect the rate of lipogenesis from lactate. The data indicate early, rapid increases in carcass fat accretion, which corresponded to similar increases in lipogenesis and lipogenic enzyme activities.     

Effects of ovine growth hormone and other anterior pituitary hormones on lipolysis of rat and ovine adipose tissue in vitro

Ovine growth hormone ( oGH ) was tested for its effects on lipolysis of rat and ovine adipose tissue in vitro. Ovine growth hormone at 1, 5 and 25 micrograms/ml stimulated lipolysis (P less than .05) of chopped rat adipose tissue and isolated rat adipocytes incubated in the presence of 100 mU/ml adenosine deaminase and .2 micrograms/ml dexamethasone, but had no effect on lipolysis of chopped ovine adipose tissue or isolated ovine adipocytes. Isoproterenol, a beta-adrenergic agonist, stimulated lipolysis (P less than .05) of both rat and ovine adipose tissue. Contaminants of the oGH preparation used were examined for lipolytic effects. Thyroid-stimulating hormone (TSH), luteinizing hormone (LH) and adrenocorticotropic hormone (ACTH) content in oGH were measured by radioimmunoassay. When quantities of these hormones contaminating 5 and 25 micrograms oGH were tested for lipolysis in rat adipose tissue, the TSH contamination could account for some (30%) of the lipolysis observed with oGH , while the other hormones had no effect. Also, preincubation of oGH with anti-GH, but not with anti-TSH or anti-LH, removed the principle in oGH responsible for the lipolytic effect on rat adipose tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of beta agonists on muscle cells in culture

Increases in protein synthesis of 12% were found with two myogenic cell lines (L6 and G8-1) on treatment for 6 hr with the beta-adrenergic agonist cimaterol. In L6 cells, propranolol blocked the effect. Protein breakdown measured over 18–24 hr was unchanged. The K_d for cimaterol binding to the L6 beta-receptor was 26 nM which was compatible with its EC₅₀ for the stimulation of protein synthesis (approx 5 nM). Evidence provided with muscle cell lines indicatesa direct effect of cimaterol on protein synthesis, which may contribute to muscle accretion in cimaterol-fed animals.     

Estradiol-17 beta effects on lipid metabolism of adipose tissue in nutritionally induced lean and obese ovariectomized ewes.

Nutritionally manipulated lean (68 kg) and obese (87 kg) ovariectomized ewes were administered estradiol-17 beta (E2) or sham implants. Ewes individually had ad libitum access to corn silage. Rates of de novo lipogenesis, palmitate esterification, and glycerol and fatty acid release were determined with slices of subcutaneous adipose tissue at 0, 5, and 30 d after implantation. Condition and E2 interacted over time (linear, P less than .12; quadratic, P less than .05) to affect intake. Lean ewes implanted with E2 decreased intake initially after implantation, whereas obese ewes implanted with E2 decreased intake later after implantation. The linear effect of time x condition x E2 interacted (P less than .02) for lipogenesis. Lipogenesis was inhibited in both the lean and obese ewes implanted with E2. Lean compared with obese ewes without E2 had increased lipogenesis at a faster rate over time. Esterification increased (linear, P less than .01) in the lean ewes and decreased (quadratic, P less than .01) in the obese ewes over time. A time x E2 interaction occurred for esterification (P less than .02). Glycerol and fatty acid release were variable over time within condition and E2. A 48-h adipose tissue culture determined the effect of E2 on lipid metabolism. Estradiol-17 beta decreased (P less than .05) lipogenesis, decreased (P less than .08) esterification, and maintained fatty acid and glycerol release. Data in vivo and in culture indicated that E2 acted to decrease de novo lipogenesis and palmitate esterification and had little or no effect on lipolysis.     

Acute and long-term lipogenic response to insulin and clenbuterol in bovine intramuscular and subcutaneous adipose tissues

The present study was conducted to determine whether insulin and clenbuterol affected either short-term (2-h) incubations or long-term (48-h) tissue cultures of i.m. and s.c. adipose tissue explants. Samples were taken from control steers and steers fed 7 mg.head-1.d-1 clenbuterol for 50 d, after which time the drug was withdrawn from the diet for 90 d prior to slaughter. Neither short-term incubations nor long-term explant cultures contained bovine serum albumin (BSA). Insulin (6.67 x 10(-9) M) had no effect (P greater than .05) on lipogenesis in s.c. and i.m. adipose tissue in 2-h tissue incubations of fresh adipose tissue. There was a substantial decrease in activity during the culture period, which was ameliorated somewhat in s.c. adipose tissue by the presence of insulin in the culture media. Clenbuterol exposure for 48 h in vitro decreased the production of lipids from acetate in both adipose tissue depots but had no effect in short-term adipose tissue incubations. Results from the present study confirm that omitting BSA from incubation media does not enhance the responsiveness of bovine s.c. adipose tissue or the less mature i.m. adipose tissue to insulin. Insulin may maintain greater cell viability in 48-h explant cultures.     

Acetyl-CoA carboxylase and fatty acid synthase activity and immunodetectable protein in adipose tissues of ruminants: effect of temperature and feeding level

To gain insights into the regulation of fat synthesis, we have investigated the effect of cold environmental exposure and feed restriction of sheep on activity and immunodetectable protein content of acetyl-CoA carboxylase (ACC) and fatty acid synthase in adipose tissue. Subcutaneous and mesenteric adipose tissues were collected at slaughter from sheep exposed to either cold (0+/-2 degrees C) or warm (23+/-2 degrees C) environment, and given either ad libitum or restricted access to feed for three 5-wk periods. Acetyl-CoA carboxylase was isolated from frozen adipose tissue samples and activity determined as the rate of incorporation of H14CO3- into acid stable malonyl-CoA. Cold exposure and feed restriction reduced (P < .05) ACC activity in the two adipose tissue depots. Western blot analysis with peroxidase-conjugated streptavidin showed that both adipose tissue depots express a single isoform of ACC. In s.c. adipose tissue, cold exposure increased (P < .05) ACC protein abundance, which is opposite to the change in activity. However, feed restriction reduced immunodetectable ACC protein. There was no significant effect of environment or feeding level on ACC protein abundance in mesenteric tissue. Fatty acid synthase activity determined in ammonium sulfate extract by measuring the malonyl-CoA- and acetyl-CoA-dependent oxidation of NADPH was decreased (P < .05) by feed restriction in both s.c. and mesenteric tissues. Cold exposure reduced fatty acid synthase activity in s.c. but not in mesenteric tissue. There was no effect of environment on fatty acid synthase protein abundance in either adipose tissue depot. However, feed restriction significantly reduced fatty acid synthase protein abundance in the two depots. The data suggest that feed restriction and exposure of ruminants to cold environmental conditions may significantly down-regulate the activity of key lipogenic enzymes.     

Effects of different roughage sources and feeding levels on adipogenesis of ovine adipocytes

The objective of the present study was to conduct an adipogenic evaluation of different roughage sources and feeding levels during ruminant adipocyte differentiation in vitro. Six wether sheep were divided into a timothy hay feeding group (TFG, n = 3) and an Italian ryegrass straw feeding group (IFG, n = 3). The sheep were fed high‐roughage (HR), medium roughage (MR) and low‐roughage (LR) diets in a one‐way layout design each over a 6‐day period. Sheep serum samples collected on the last day of each dietary treatment were added to an adipogenic induction medium for differentiation of preadipocytes derived from sheep subcutaneous adipose tissue. The cytoplasmic lipid accumulations in the TFG serum‐treated preadipocytes were significantly higher than those of the IFG‐serum treated preadipocytes on day 12. Messenger RNA expression of CCAAT/enhancer‐binding protein (C/EBP)‐α, C/EBP‐β, C/EBP‐δ, fatty‐acid‐binding protein (aP2) and stearoyl‐coenzyme A desaturase (SCD) were regulated by each serum treatment. This study shows that different roughage source diets and roughage‐to‐concentrate ratio diets can regulate adipocyte differentiation via ruminant blood composition.