Differential Short-Term Distribution of Estrone and Oleoyl-Estrone Administered in Liposomes to Lean and Obese Zucker Rats

Thirteen-week-old female Zucker lean (Fa/Fa) and obese (fa/fa) rats were injected through a cannula inserted in the left jugular vein with 1 mL/kg of ³H-labeled oleoyl-estrone in liposomes (Merlin-2) (i.e., 670 fmol, 84 kBq). The rats were killed 10 minutes later and dissected. The presence of intact or hydrolyzed oleoyl-estrone was later determined in all samples. The pattern of distribution of estrone was quite different from that of oleoyl-estrone both in rats that were lean and in those that were obese. Estrone was better retained by white adipose tissue than oleoyl-estrone. Liver, spleen, and lungs accumulated more oleoyl-estrone and split part of it, from 4.7% (lung, obese) to 27% (liver, lean). The overall high retention of estrone by the rat tissues results in its very low circulating levels. The fast splitting of liposome-carried oleoyl-estrone by most tissues (up to more than 67% by intestine and skin of lean rats) may help explain the rise in blood free estrone. The differences between lean and obese Zucker rats are mainly quantitative in the case of estrone, the main differences being found in blood and adipose tissues. However, when we compare the data for oleoyl-estrone, the differences cannot be dismissed simply as due to differences in body size or the extent of fat deposits. A large portion of the label remained in the blood of the rats that were obese but not in those that were lean, the tissues of which took up more label. Brown adipose tissue shows a fair affinity for oleoyl-estrone in the rats that were lean but practically does not retain label in the rats that were obese, suggesting that oleoyl-estrone may have a direct effect on brown adipose tissue. The decreased uptake of oleoyl-estrone in rats that were obese shows that the mechanism regulating the turnover or disposal of this signal is altered in this type of genetic obesity.     

Changes of Islet Size and Islet Size Distribution Resulting from Protein-Malnutrition in Lean (Fa/Fa) and Obese (fa/fa) Zucker Rats

TSE, ELIZABETH O, FRANCINE M GREGOIRE, BRIGITTE REUSENS, CLAUDE REMACLE, JOSEPH J HOET, PATRICIA R JOHNSON, JUDITH S STERN. Changes of islet size and islet size distribution resulting from protein malnutrition in lean (Fa/Fa) and obese (fa/fa) Zucker rats. Potential alterations in islet size and islet size distribution resulting from protein malnutrition were studied in lean (Fa/Fa) and obese (fa/fa) Zucker rats. The purpose was to investigate whether the distribution of enlarged islets in obese rats was altered by low-protein feeding. Four-week-old, male, lean and obese Zucker rats were fed either a diet containing 20% (w/w) protein (control diet) or a diet containing 5% (w/w) protein (low-protein diet) for 3 weeks. Pancreata were dissected at autopsy and immunostained for insulin. Islet size and distribution were determined by morphometric analysis. Body-weight gain, food intake, and serum insulin and glucose were also measured. After 3 weeks on the diets, serum insulin was significantly lower in both lean (-75%) and obese (-54%) rats fed low protein compared with that in controls. However, obese rats were still hyperinsulinemic compared with lean rats. Protein malnutrition resulted in a shift in distribution of islets to smaller size both in lean and in obese rats, with an increase in the population of small islets (100 μm²) and a decrease in the population of large islets (>20,000 μ;m²). In lean and obese rats fed low protein, β-cell weight was significantly lower, B cell volume fraction tended to decrease, and islet number per section area was significantly elevated when compared with controls. Taken together, these results show that protein deficiency alters the endocrine pancreas in both lean and obese Zucker rats. Although the decrease in islet size and the shift in distribution to smaller islets most likely contribute to the decrease in serum insulin concentration, these changes appear insufficient to normalize hyperinsulinemia in the obese Zucker rat.     

Low-carbohydrate diets affect energy balance and fuel homeostasis differentially in lean and obese rats

In parallel with increased prevalence of overweight people in affluent societies are individuals trying to lose weight, often using low-carbohydrate diets. Nevertheless, long-term metabolic consequences of those diets, usually high in (saturated) fat, remain unclear. Therefore, we investigated long-term effects of high-fat diets with different carbohydrate/protein ratios on energy balance and fuel homeostasis in obese (fa/fa) Zucker and lean Wistar rats. Animals were fed high-carbohydrate (HC), high-fat (HsF), or low-carbohydrate, high-fat, high-protein (LC-HsF-HP) diets for 60 days. Both lines fed the LC-HsF-HP diet displayed reduced energy intake compared with those fed the HsF diet (Zucker, -3.7%) or the HC diet (Wistar rats, -12.4%). This was not associated with lower weight gain relative to HC fed rats, because of increased food efficiencies in each line fed HsF and particularly LC-HsF-HP food. Zucker rats were less glucose tolerant than Wistar rats. Lowest glucose tolerances were found in HsF and particularly in LC-HsF-HP-fed animals irrespective of line, but this paralleled reduced plasma adiponectin levels, elevated plasma resistin levels, higher retroperitoneal fat masses, and reduced insulin sensitivity (indexed by insulin-induced hypoglycemia) only in Wistar rats. In Zucker rats, however, improved insulin responses during glucose tolerance testing and tendency toward increased insulin sensitivities were observed with HsF or LC-HsF-HP feeding relative to HC feeding. Thus, despite adverse consequences of LC-HsF diets on blood glucose homeostasis, principal differences exist in the underlying hormonal regulatory mechanisms, which could have benefits for B-cell functioning and insulin action in the obese state but not in the lean state.     

Effects of dietary fat content on adiposity during energy restriction in genetically obese rats.

The effects of the amount of fat provided in a restricted diet on weight loss and body composition were studied in this work. Lean male (Fa/?) Zucker rats were fed a control diet ad libitum. Obese (fa/fa) Zucker rats were divided into three groups: one group was fed a control diet ad libitum and the other two groups were fed 75% energy-restricted diets, which provided 10 or 50% of calories as fat. After 4 weeks, energy restriction normalized body weight but not body composition in the genetically obese rats. Reductions in adipose tissue weights and adipocyte size, without changes in the cellularity, were observed. Differences only reached statistical significance in subcutaneous adipose tissue. A standard fat content in the diet induced the same fat-free mass reduction as a higher amount of this macronutrient, but a greater body fat reduction. This suggests that the restriction of dietary fat, as well as energy, is necessary to achieve dietary management in obesity.     

Effects of fatty (fa) allele and high-fat diet on adipose tissue leptin and lipid metabolism.

Leptin is an adipocyte-secreted hormone that binds hypothalamic receptors and potently decreases food intake. Leptin receptor defects in homozygous mutant Zucker fatty ( fa/fa) rats lead to massive obesity, hyperphagia, decreased energy expenditure, and insulin resistance, while the phenotype of heterozygous ( Fa/fa) lean rats lies between lean ( Fa/Fa) and obese ( fa/fa) rats. Whether heterezygotes exhibit specific changes in lipid metabolism in a diet-responsive manner is not clear. Thus, the specific aim of this study was to test whether the presence of one fa allele modulates lipid metabolism and leptin, and whether these effects are exacerbated by high-fat diet. We demonstrate that the presence of one fa allele significantly increases lipogenesis in adipose tissue assessed by glycerol-3-phosphate dehydrogenase (GPDH) and fatty acid synthase (FAS) activities. FAS is more responsive to high-fat diets than GPDH in Fa/fa rats. Adipose tissue leptin levels are significantly higher in fat pads of Fa/fa compared to Fa/Fa rats. Moreover, Fa/fa rats fed high-fat diet show an additional two-fold increase in leptin levels compared to wild type rats on the same diet. Collectively, these results indicate that the presence of one fa allele increase adipocyte lipogenic enzyme activities, which results in hyperleptinemia concurrent with increased adiposity.     

Improved n-3 fatty acid status does not modulate insulin resistance in fa/fa Zucker rats

The objective was to examine the effect of polyunsaturated fatty acid type (plant vs fish oil-derived n-3, compared to n-6 fatty acids in the presence of constant proportions of saturated, monounsaturated and polyunsaturated fatty acids) on obesity, insulin resistance and tissue fatty acid composition in genetically obese rats. Six-week-old fa/fa and lean Zucker rats were fed with a 10% (w/w) mixed fat diet containing predominantly flax-seed, menhaden or safflower oils for 9 weeks. There was no effect of dietary lipid on obesity, oral glucose tolerance (except t=60 min insulin), pancreatic function or molecular markers related to insulin, glucose and lipid metabolism, despite increased n-3 fatty acids in muscle and adipose tissue. The menhaden oil diet reduced fasting serum free fatty acids in both fa/fa and lean rats. These data suggest that n-3 composition does not alter obesity and insulin resistance in the fa/fa Zucker rat model when dietary lipid classes are balanced.     

Marked enhancement of acyl-CoA synthetase activity and mRNA, paralleled to lipoprotein lipase mRNA, in adipose tissues of Zucker obese rats (fa/fa).

To clarify the role of acyl-CoA synthetase in development of obesity, the mRNA levels and activities were studied in Zucker fatty rats (fa/fa). In Zucker fatty rats compared with their lean littermates, marked enhancement of ACS were observed in adipose tissues. Obese/lean rats ratio of ACS activity and mRNA in abdominal subcutaneous fat (3.3- and 3.9-fold, respectively) were greater than in mesenteric fat (2.0- and 2.2-fold). The enhancement of ACS activity and mRNA in the liver of fatty rats (1.2- and 1.8-fold) were less than those in the adipose tissues. There were no enhancement of ACS activities and mRNA levels in heart tissue of the obese rats. LPL mRNA levels were also enhanced in adipose tissue of fatty rats and obese/lean ratio of LPL mRNA was also higher in abdominal subcutaneous fat than mesenteric fat (6.2- vs 3.1-fold). The larger obese/lean rats ratio of LPL and ACS parameters in abdominal subcutaneous fat than mesenteric fat may be related to the observation that the increase of subcutaneous fat weight was larger than that of mesenteric fat weight in fatty rats (21.1- vs 4.9-fold). Integrated enhancement of LPL and ACS gene expression in adipose tissue may play an important role in the development of obesity.     

Interactions between effects of adrenalectomy and diet on insulin secretion in fa/fa Zucker rats

Our objective was to determine if a cafeteria-type diet with increased fat content would block the decrease in insulin secretion induced by adrenalectomy in obese rats. Five week old Zucker (fa/fa) rats were adrenalectomized. One week later, half of the adrenalectomized groups, and age-matched, sham-operated animals were given a diet of 16% fat and 44% carbohydrate. Control animals were maintained on standard rat chow (4.6% fat and 49% carbohydrate). After 4 weeks on the diets, in vivo measurements included caloric intake, weight gain, plasma corticosterone, triglyceride, free fatty acids, and oral glucose tolerance tests. In vitro measurements included glucose-stimulated insulin secretion, glucose phosphorylating activity, islet triglyceride content, and fatty acid oxidizing activity of cultured islets. Generally, the cafeteria diet did not block the effects of adrenalectomy on in vitro insulin secretion parameters, even though in sham-operated animals weight gain and insulin resistance was induced by the diet in vivo. Adrenalectomy and the diet exerted independent effects on glucose phosphorylation and fatty acid oxidation in islets. In conclusion, adrenalectomy decreased the elevated insulin secretion in fa/fa rats. The failure of a cafeteria diet enriched in fat to block the adrenalectomy-mediated changes in B-cell function indicates the importance of glucocorticoids and centrally-mediated effects on insulin secretion and other metabolic parameters.     

Onset of genetic obesity in the absence of hyperphagia during the first week of life in the Zucker rat (fa/fa).

The aim of this study was to discover which of three major abnormalities of the genetically obese Zucker rat (fa/fa), namely hyperphagia, excess adiposity, and hyperlipidemia, is the first to appear prior to manifest obesity, i.e., before weaning. Suckling fa/fa rats, bred from heterozygous parents, were detected by sizing fat cells obtained from an inguinal fat pad biopsy. Cell hypertrophy was observed in fa/fa rats, compared to Fa/-littermates of the same sex, as soon as 5-7 days after birth. Prediction of fa/fa genotype at this age by this method was assessed using a series of 80 pups and proved to be totally successful. The identity of the "predicted" obese pups was confirmed morphologically at 6 weeks of age. Food (milk) intake was estimated from water turnover rates determined on 86 pups aged 2-8 days using tritiated water. The results show that 7-day-old fa/fa rats had heavier inguinal fat pads with larger adipocytes and higher lipoprotein lipase activity than their lean controls. There was no genotype effect on water intake adjusted to body weight during the first week of life. Moreover weight of stomach contents and triglyceridemia were similar in all animals at 7 days. These results show that excess adiposity develops in the fa/fa rat during the first week of life, before hypertriglyceridemia and hyperphagia, and raises the question of whether this adiposity results from a defect in energy expenditure or an abnormality of fat cell storage capacity, or both.     

Tamoxifen does not prevent the mobilization of body lipids elicited by oleoyl-estrone

Oleoyl-estrone is a powerful, slimming adipose tissue-derived signal that has biological effects widely opposed to those of its estrone moiety. The present experiment was designed to determine whether oleoyl-estrone effects on body energy are mediated by the estrogen receptor, blocked with the antagonist tamoxifen. Male Wistar rats were given daily oral doses of 10 micromol/kg d of oleoyl-estrone in oil containing 0 or 0.40 mg/kg d of tamoxifen. The data were compared with controls receiving only oil or 50 nmol/kg d of free estrone. After 10 days, the rats were killed, and their body composition and plasma metabolites and hormones were analyzed. Rats receiving estrone increased their body energy and lipid content compared with controls. Both groups of oleoyl-estrone-treated rats lost body weight, energy, and lipid; the losses in the rats receiving tamoxifen alone were less marked than in those receiving oleoyl-estrone. No significant changes in plasma glucose or triacylglycerols were observed. The patterns of change of estrone sulphate, estradiol, and oleoyl-estrone were consistent with a noticeable hydrolysis of oleoyl-estrone. The lack of differences in the fat mass in oleoyl-estrone-treated rats irrespective of the presence of tamoxifen suggested that the estrogenic pathway was not responsible for the slimming effects observed. Thus, it can be concluded that oleoyl-estrone effects are not mediated through its conversion to estrone or estradiol acting through the estrogen receptor. Tamoxifen partly mimicked the slimming effects of oleoyl-estrone; this could be speculatively explained by tamoxifen acting through the oleoyl-estrone signalling pathway.     

Exercise training increases glucose transporter protein GLUT-4 in skeletal muscle of obese Zucker (fa/fa) rats

The present study examined the level of GLUT-4 glucose transporter protein in gastrocnemius muscles of 36 week old genetically obese Zucker (fa/fa) rats and their lean (Fa/-) littermates, and in obese Zucker rats following 18 or 30 weeks of treadmill exercise training. Despite skeletal muscle insulin resistance, the level of GLUT-4 glucose transporter protein was similar in lean and obese Zucker rats. In contrast, exercise training increased GLUT-4 protein levels by 1.7 and 2.3 fold above sedentary obese rats. These findings suggest endurance training stimulates expression of skeletal muscle GLUT-4 protein which may be responsible for the previously observed increase in insulin sensitivity with training.     

Genotype and diet effects in lean and obese Zucker rats fed either safflower or coconut oil diets

Previously we reported that suckling lean heterozygous (FA/fa) Zucker rats had a number of adipose tissue measurements intermediate between those of homozygous lean (FA/FA) and obese (fa/fa) rats. However, in young adult male rats maintained on a low-fat diet, these differences were no longer apparent (i.e., values for the two lean genotypes were similar). In the present study we determined whether the heterozygous effect of the "fa" gene was dependent on the consumption of a high-fat diet. Mother rats were fed high-fat diets containing either safflower (SOD) or coconut (COD) oil throughout mating and lactation. Homozygous lean male and female rats were bred, as well as obese male and lean heterozygous female rats. Suckling rats were studied at 17 days of age. Additional male rats were maintained on the same diet as their mothers until 11-12 weeks of age. Obese suckling rats had higher body weights than lean pups. Inguinal fat pad weights and pad-to-body weight ratios followed the pattern of obese greater than lean (FA/fa) pups that were greater than lean (FA/FA) pups. A similar relationship was found for adipose tissue lipogenic enzyme activities. At 11-12 weeks of age, measurements followed the general pattern of obese rats having greater values than lean rats (i.e., FA/fa = FA/FA). SOD-fa/fa rats had higher hepatic lipogenic enzyme activities than COD-fa/fa rats. In addition, SOD rats had higher fat cell numbers than COD rats. These results suggest that specific fatty acids can alter adipocyte proliferation and/or differentiation in vivo. In addition, there appears to be a defect of fatty acid regulation in livers of genetically obese rats. The heterozygous effect of the "fa" gene in suckling Zucker rats was confirmed. However, high-fat feeding did not result in a heterozygous effect in young adult lean male rats. We will next evaluate the role of sex on this effect.     

Management of dietary essential metals (iron,copper, zinc,chromium and manganese) by Wistar and Zucker obese rats fed a self-selected high-energy diet

The balances and content of essential elements (iron, copper, zinc, chromium and manganese) in the body of Wistar, Zucker lean and Zucker obese rats fed a reference or cafeteria diet from day 30 to 60 after birth have been studied. Intestinal iron absorption compensated for low iron content of the cafeteria diet and the extra needs of growth and fat deposition. It can be assumed that the altered energy regulation processes that afflict the genetically obese rat are not directly related to altered iron metabolism. Obese Zucker rats had lower copper tissue concentrations than lean rats, but when fed a cafeteria diet the differences between Zucker rats strains disappear. This cannot be traced to large differences in diet copper concentration. A low diet availability of zinc—such as that of cafeteria-fed fa/fa rats—is easily compensated for by increasing absorption. So, as a consequence, we can conclude that genetic obesity did not impair zinc absorption. There was no deficit of zinc in any of the groups studied; the rats have enough capacity to extract zinc within a wide range of dietary concentrations. The absorption of dietary chromium was inversely proportional to its concentration. The ability to extract chromium from the diet and the very low urinary losses are a consequence of its scarcity in most dietary items. Despite wide variations in the manganese of the diets, the absorption rates were practically unchanged except for obese rats fed the cafeteria diet. It seems that this low absorptive capacity is enough to supply the rat with the manganese it needs, since a sizeable—but subjected to 8-fold-span variations-proportion is lost in the urine. This alone points towards a considerable excess of manganese in both diets studied. Obesity does not have a significant effect on the abilities to absorb and retain minerals, since these processes were more related to dietary availability. Management of essential metals by obese rats depends whether this condition is genetic or induced by diet. Most of the differences observed can be related to differences in diet concentration, to the excess fat content or different metabolic attitude to use substrates of obese animals. The data presented show that the cafeteria diet used adequately serves the mineral needs of the rat, since the rat adapts its absorbing and retaining strategies to match the dietary availability of these minerals.     

Changes in the phosphorylation state of the inhibitory guanine-nucleotide-binding protein Gi-2 in hepatocytes from lean (Fa/Fa) and obese (fa/fa) Zucker rats

Treatment of intact, 32Pi-labelled hepatocytes from lean Zucker rats with a range of agents including 12-O-tetradecanoyl-phorbol 13-acetate (TPA), vasopressin, and angiotensin II elicited substantial increases in the phosphorylation of the alpha-subunit of the inhibitory G protein of adenylate cyclase (alpha Gi-2). These agonist-induced phosphorylations of alpha Gi-2 were associated with loss of Gi function as assessed by the ability of low concentrations of guanylyl 5'-[beta,gamma imido]triphosphate (p[NH]ppG) to inhibit forskolin-stimulated adenylate cyclase activity. Hepatocytes from obese Zucker rats displayed a resistance to both agonist-induced phosphorylation of alpha Gi-2 and to p[NH]ppG-mediated inhibition of adenylate cyclase. The basal level of alpha Gi-2 phosphorylation in hepatocytes from obese Zucker rats was considerably greater at 1.06 +/- 0.09 mol phosphate/mol alpha Gi-2 than in hepatocytes from lean animals which gave 0.54 +/- 0.09 mol phosphate/mol alpha Gi-2. Incubation with TPA (10 ng/ml, 15 min) approximately doubled the level of phosphorylation of alpha Gi-2 in the hepatocytes from lean animals but had little effect on the phosphorylation of alpha Gi-2 in hepatocytes from obese animals. Incubation of hepatocytes from lean animals with ligands which lead to the phosphorylation of alpha Gi-2 abolished the ability of low concentrations of p[NH]ppG to inhibit adenylate cyclase expressed in isolated membranes. Treatment of hepatocyte plasma membranes from lean but not obese Zucker rats with pure protein kinase C led to the phosphorylation of alpha Gi-2. The resistance to protein-kinase-C-mediated phosphorylation in hepatocyte membranes from obese animals could be overcome by treatment of the membranes with alkaline phosphatase. These results indicate that the defect in guanine-nucleotide-mediated 'Gi function' seen in obese Zucker rats may be due to an inactivating phosphorylation of alpha Gi-2.     

Plasma B-cell tropin (ACTH22-39) concentration in lean and obese (ob/ob) mice and lean and obese (fa/fa) Zucker rats

A method has been developed for the measurement of plasma concentrations of Beta-cell tropin (BCT), which is a potent insulinotropic and lipogenic peptide secreted by the pituitary. The method was employed to compare plasma Beta-cell tropin concentrations between lean and genetically obese (ob/ob) mice and between lean and genetically obese (fa/fa) Zucker rats. The plasma concentration in lean mice was 0.17 +/- 0.02 (5)nmole/l (mean +/- SEM, n = 5), while that in obese (ob/ob) mice was significantly higher, being 2.88 +/- 1.13 (5)nmole/l. The plasma BCT concentration in Zucker rats was 0.14 +/- 0.02 (15)nmole/l, while that in obese Zucker (fa/fa) rats was significantly higher, being 1.69 +/- 0.72 (16)nmole/l. These results explain previously observed differences in the Beta-cell tropin-like biological activity in plasma from lean and obese animals, and support the hypothesis that the peptide has a role in the development of hyperinsulinaemia and obesity.     

Calcitonin mRNA activity in young obese (fa/fa) Zucker rats

Alterations in both calcitonin (CT) secretion and plasma calcium were recently described in adult obese Zucker rats. We have investigated the CT biosynthetic activity of thyroid glands in 30-day-old obese Zucker rats (fa/fa), and their controls (Lean). Plasma calcium level was significantly increased (+0.6 mg/dl) in obese animals, but plasma phosphate was unchanged. Plasma CT levels measured by radioimmunoassay (RIA) were significantly decreased in fatty (0.50 +/- 0.03 vs 0.68 +/- 0.03 ng/ml in Leans; P less than 0.001), but thyroidal hormone content was not different between Lean and fatty rats (68.7 +/- 5.1 in Leans vs 60.5 +/- 3.6 ng/gland in fatty rats). mRNA was extracted from 10 thyroids, and translated in a rabbit reticulocyte lysate (NEN) in the presence of [35S]methionine. After polyacrylamide gel electrophoresis, specific immunoprecipitates were autoradiographed and quantified by integration. A 50% decrease in translatable CT mRNA was observed in fatty rats. In basal conditions, the biosynthetic activity of C cells in obese rats correlates with the secretion rate of the hormone in the face of unchanged thyroidal CT contents.     

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

Objective: The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function. Methods and Procedures: Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO). Results: Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n ?3 polyunsaturated fatty acids (PUFA), and lower n ?6 PUFA and n ?6‐to‐n ?3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF‐α and IL‐1β (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)‐stimulated IL‐2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05). Discussion: The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T‐cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.     

Acute effects of exercise on circulating leptin in lean and genetically obese fa/fa rats

Mechanisms of regulation of plasma leptin in lean and genetically obese animals are not completely understood. In particular a relation has been proposed between energy metabolism and leptin. However, it is not clear how energy expenditure and leptin are related under exercise in lean and obese animals. To clarify these aspects we investigated lean and genetically obese (fa/fa) Zucker rats undergoing a single bout (30 min) of swimming and measured several biochemical and hormonal parameters of energy metabolism and leptin changes throughout the study. Moreover ob-gene expression in adipose tissue was also measured. Our results showed that plasma leptin is decreased by 30% at the end of exercise in lean animals while resulting unaffected in obese animals. Leptin changes in lean rats are concomitant with the peak of NEFA and glycerol release from adipose tissue rather than with the reduction of plasma insulin. Ob-gene expression in adipose tissue was markedly increased in fa/fa compared to lean rats, but was not modified by exercise both in lean and obese animals. In conclusion our data show that leptin changes during exercise are related to lipolytic events in adipose tissue and support a link between leptin and energy expenditure.     

Insulin receptor exon 11+/- is expressed in Zucker (fa/fa) rats, and chlorogenic acid modifies their plasma insulin and liver protein and DNA

In vivo studies confirmed that chlorogenic acid (CGA) improved glucose tolerance and mineral pool distribution in obese Zucker (fa/fa) rats. We found a significant decrease (P<.05) in postprandial blood glucose concentrations, which may have been due to an improved sensitivity to insulin. Impaired glucose tolerance and insulin resistance have been associated with differences in the hepatic mRNA expression of the spliced variants of the insulin receptor at exon 11. Spliced variants of the insulin receptor have not been studied in obese Zucker (fa/fa) rats, and no information exists about the effects of CGA in vivo as a possible insulin sensitizer. Thus, we studied the in vivo effect of CGA on plasma insulin concentrations during a glucose tolerance test, liver protein and DNA concentrations, the hepatic activity of glucose-6-phosphatase (G-6-PASE) and the mRNA expression of the two variants of the insulin receptor at exon 11. Zucker (fa/fa) rats were implanted with jugular vein catheters. Chlorogenic acid was administered (5 mg/kg body weight per day) for 3 weeks via intravenous infusion. In the CGA-treated group, areas under the curve (AUC) for blood glucose and plasma insulin improved (P<.005), and the protein and DNA concentrations in the liver increased (P<.05). No significant differences (P>.05) were found between groups for the hepatic G-6-PASE activity. The insulin receptor exon 11(+) and the exon 11(-) variants were expressed in the liver of Zucker (fa/fa) rats without significant changes (P>.05). Chlorogenic acid improved some cellular mechanisms that are stimulated by insulin.