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.     

Blood glucose control in healthy subject and patients receiving intravenous glucose infusion or total parenteral nutrition using glucagon-like peptide 1

AIMS: It was the aim of the study to examine whether the insulinotropic gut hormone GLP-1 is able to control or even normalise glycaemia in healthy subjects receiving intravenous glucose infusions and in severely ill patients hyperglycaemic during total parenteral nutrition. PATIENTS AND METHODS: Eight healthy subjects and nine patients were examined. The volunteers received, in six separate experiments in randomised order, intravenous glucose at doses of 0, 2 and 5mg kg(-1) min(-1), each with intravenous GLP-1 or placebo for 6 h. Patients were selected on the basis of hyperglycaemia (>150 mg/dl) during complete parenteral nutrition with glucose (3.2+/-1.4 mg kg(-1) min(-1)), amino acids (n=8; 0.9+/-0.2 mg kg(-1) min(-1)), with or without lipid emulsions. Four hours (8 a.m. to 12 a.m. on parenteral nutrition plus NaCl as placebo) were compared to 4 h (12 a.m. to 4 p.m.) with additional GLP-1 administered intravenously. The dose of GLP-1 was 1.2 pmol kg(-1) min(-1). Blood was drawn for the determination of glucose, insulin, C-peptide, GLP-1, glucagon, and free fatty acids. RESULTS: Glycaemia was raised dose-dependently by glucose infusions in healthy volunteers (p<0.0001). GLP-1 ( approximately 100-150 pmol/l) stimulated insulin and reduced glucagon secretion and reduced glucose concentrations into the normoglycaemic fasting range (all p<0.05). In hyperglycaemic patients, glucose concentrations during the placebo period averaged 211+/-24 mg/dl. This level was reduced to 159+/-25 mg/dl with GLP-1 (p<0.0001), accompanied by a rise in insulin (p=0.0002) and C-peptide (p<0.0001), and by trend towards a reduction in glucagon (p=0.08) and free fatty acids (p=0.02). GLP-1 was well tolerated. CONCLUSIONS: Hyperglycaemia during parenteral nutrition can be controlled by exogenous GLP-1, e.g. the natural peptide (available today), whereas the chronic therapy of Type 2 diabetes requires GLP-1 derivatives with longer duration of action.     

Dietary fish oil normalize dyslipidemia and glucose intolerance with unchanged insulin levels in rats fed a high sucrose diet

The aim of this study was to investigate the relationship between the lipid-lowering effects of fish oils and concomitant consequences on glucose tolerance and insulin sensitivity in an experimental animal model of hypertriglyceridemia induced by high sucrose intake. To achieve this goal, male Wistar rats were fed a semi-synthetic sucrose rich diet (SRD) (w/w: 62.3% sucrose, 8% corn oil, 17% protein) for 90 days. At the time, a well established and permanent hypertriglyceridemia accompanied by glucose intolerance was present. After that, one half of the animals continued on the SRD up to 120 days. The other half received an SRD in which the source of fat was substituted by cod liver oil (w/w 7% CLO plus 1% corn oil) from day 90 to 120 (SRD + CLO). Control rats were fed a semi-synthetic diet (CD) (w/w: 62.5% corn starch, 8% corn oil, 17% protein) throughout the 120 days experimental period. Results obtained after the experimental period show that the hypertriglyceridemia and glucose intolerance ensuing long term feeding normal rats with a sucrose-rich diet could be completely reversed mediating no change in circulating insulin levels by shifting the source of fat in the diet from corn oil to cod liver oil. These findings suggest that manipulation of dietary fats may play a role in the management of the lipid disorders associated with glucose intolerance and insulin resistance.     

Reduced anorexic effects of insulin in obesity-prone rats fed a moderate-fat diet

Rats prone to develop diet-induced obesity (DIO) have reduced central sensitivity to many metabolic and hormonal signals involved in energy homeostasis. High-fat diets produce similar defects in diet-resistant (DR) rats. To test the hypothesis that genotype and diet exposure would similarly affect central insulin signaling, we assessed the anorectic effects of 8 mU third ventricular (iv3t) insulin before and after 4 wk intake of a 31% fat, high-energy (HE) diet intake in outbred (OutB) rats. Rats were retrospectively designated as DR or DIO by their low or high weight gains on HE diet. Before the HE diet, iv3t insulin reduced 4-h and 24-h chow intake by 53% and 69% in DR rats but by only 17% and 27% in DIO rats, respectively. Also, the anorectic response to iv3t insulin in OutB rats was inversely correlated (r = 0.72, P = 0.002) with subsequent 4-wk weight gain on the HE diet. Similarly, in selectively bred (SB) chow-fed DR rats, 8 mU iv3t insulin reduced 4-h and 24-h intake by 21% and 22%, respectively, but had no significant effect in SB DIO rats. Four-week HE diet intake reduced 4-h and 24-h insulin-induced anorexia by 45% in OutB DR rats and completely abolished it in SB DR rats. Reduced insulin responsiveness was unassociated with differences in arcuate nucleus insulin receptor mRNA expression between DIO and DR rats or between rats fed chow or HE diet. These data suggest that DIO rats have a preexisting reduction in central insulin signaling, which might contribute to their becoming obese on the HE diet. However, since the HE diet reduced central insulin sensitivity in DR rats but did not make them obese, it is likely that other brain areas are involved in insulin's anorectic action or that other pathways contribute to the development and maintenance of obesity.     

Plasma glucose and insulin responses to oral and intravenous glucose in cold-exposed humans

Although glucose tolerance and skeletal muscle glucose uptake are markedly improved by cold exposure in animals, little is known about such responses in humans. This study used two variations of a glucose tolerance test (GTT) to investigate changes in carbohydrate metabolism in healthy males during nude exposure to cold. In experiment 1, an oral GTT was performed in the cold and in the warm (3 h at 10 or 29 degrees C). To bypass the gastrointestinal tract, and to suppress hepatic glucose output, a second experiment was carried out as described above, using an intravenous GTT. Even though cold exposure raised metabolic rate greater than 2.5 times, plasma glucose and insulin responses to an oral GTT remained unaltered. In contrast, cold exposure reduced the entire plasma glucose profile as a function of time during the intravenous GTT (P less than 0.05), as plasma glucose was returned to basal levels within 1 h in comparison to a full 2 h in the warm, despite low insulin levels. The results of the intravenous GTT demonstrate that even with low insulin levels, carbohydrate metabolism is increased in cold-exposed males. This effect could be masked in the oral GTT by gastrointestinal factors and a high hepatic glucose output. Cold exposure may enhance insulin sensitivity and/or responsiveness for glucose uptake, mainly in shivering skeletal muscles.     

Neutral and polar lipid metabolism in liver microsomes of growing rats fed a calcium-deficient diet

We studied the incorporation of (14)C-labeled fatty acids and glycerol into different classes of glycerolipids in an in vitro system containing liver microsomes from growing Wistar rats fed a calcium-deficient (CaD; 0.5 g/kg) diet for a 60-day period. Desaturase activities and incorporation of the elongation-desaturation metabolites into specific neutral and polar glycerolipids were also studied and correlated with the activities of various enzymes involved in complex lipid metabolism (acyl-CoA synthase, acyl-CoA hydrolase, DAG-acyltransferase, DAG-kinase, lysophospatidate-acyl-CoA transferase, phosphatidate-phosphohydrolase and phospholipase A(2)). Low calcium condition led to a significant increase in the incorporation (relative amounts and specific activities) of both labeled fatty acids and glycerol with a preferential increase of labeling in neutral lipids rather than in phospholipids. Acyl-CoA synthetase, diacylglycerol acyltransferase and diacylglycerol-3-P acyltransferase activities were increased in low calcium microsomes while diacylglycerol kinase, phospholipase A(2) and palmitoyl-, stearoyl-, linoleyl-, alpha-linolenyl, and eicosatrienoyl-desaturases were decreased. The modifications observed in the interlipid and lipid/protein relationships, enzyme activities, and pattern of incorporation of labeled precursors into each glycerolipid class, suggest that decreased intake of calcium should be considered as a harmful risk factor for the development of cardiovascular diseases.     

Endothelial and vascular dysfunctions and insulin resistance in rats fed a high-fat, high-sucrose diet

This study was designed to examine the effects of a high-fat, high-sucrose (HFHS) diet on vascular and metabolic actions of insulin. Male rats were randomized to receive an HFHS or regular chow diet for 4 wk. In a first series of experiments, the rats had pulsed Doppler flow probes and intravascular catheters implanted to measure blood pressure, heart rate, and regional blood flows. Insulin sensitivity and vascular responses to insulin were assessed during a euglycemic hyperinsulinemic clamp performed in conscious rats. In a second series of experiments, new groups of rats were used to examine skeletal muscle glucose transport activity and to determine in vitro vascular reactivity, endothelial nitric oxide synthase (eNOS) protein expression in muscle and vascular tissues and endothelin content, nitrotyrosine formation, and NAD(P)H oxidase protein expression in vascular tissues. The HFHS-fed rats displayed insulin resistance, hyperinsulinemia, hypertriglyceridemia, hyperlipidemia, elevated blood pressure, and impaired insulin-mediated renal and skeletal muscle vasodilator responses. A reduction in endothelium-dependent vasorelaxation, accompanied by a decreased eNOS protein expression in muscles and blood vessel endothelium, and increased vascular endothelin-1 protein content were also noted in HFHS-fed rats compared with control rats. Furthermore, the HFHS diet induced a reduced insulin-stimulated glucose transport activity in muscles and increased levels of NAD(P)H oxidase protein and nitrotyrosine formation in vascular tissues. These findings support the importance of eNOS protein in linking metabolic and vascular disease and indicate the ability of a Westernized diet to induce endothelial dysfunction and to alter metabolic and vascular homeostasis.     

Effect of structured lipid-enriched total parenteral nutrition in rats bearing yoshida sarcoma

The efficacy of structured lipid, a triacylglycerol of medium and long chain fatty acids, as an element of nutritional support therapies in cancer cachexia was investigated. Using the Yoshida sarcoma to induce cachexia, male Sprague Dawley rats (90 g) were injected subcutaneously with tumor cells (n = 17) or sterile saline (n = 16). Seven days later, rats were randomized to two intravenous diets for 3 days at 220 kcal/kg body weight/d, including 2 g nitrogen/kg body weight/d and 39% of total calories as either structured lipid or long chain triglyceride. Nitrogen balance, tumor growth rate, energy metabolism, and plasma albumin and free fatty acid levels were measured, and whole-body protein kinetics and liver, muscle, and tumor fractional protein synthetic rates were evaluated by adding (14)C-leucine to the diet during the last 4 hours of feeding. Nitrogen balance improved (P < .05) in both tumor and control rats receiving structured lipid-enriched total parenteral nutrition, and was also greater in tumor rats compared with controls. There were no differences in tumor growth or protein kinetics between diet groups. Albumin was lower (P < .05) in tumor rats, but significantly higher in both tumor and control rats given structured lipid-enriched total parenteral nutrition. Free fatty acid was significantly higher in tumor rats versus controls. Whole-body protein kinetics were similar among the four groups. Liver weight, liver weight to body weight ratio, and liver protein synthetic rate were higher in tumor rats. Also, liver weight to body weight ratio was lower in tumor and control animals given structured lipid-enriched total parenteral nutrition. Muscle protein synthetic rate was significantly lower in tumor rats, but higher in tumor and control rats given long chain triglyceride-enriched total parenteral nutrition. The nutritional benefits of structured lipid-enriched total parenteral nutrition favor support of host tissue without promoting tumor growth.     

Impaired glucose homeostasis and mitochondrial abnormalities in offspring of rats fed a fat-rich diet in pregnancy

This study examined the role of heating on oxidative stress and muscle mass in immobilized limbs. Rats were divided into three groups (n = 9/group): a control group (Con), an immobilized group (Im), and an immobilized and heated group (ImH). Rats were immobilized in the plantarflexed position for 8 days. The core temperature of the ImH group was elevated to 41-41.5 degrees C on alternating days and maintained for 30 min before cooling. On day 8, both heat shock protein 25 (HSP25) and HSP72 were markedly elevated in the ImH compared with the Im group, whereas results in the Im group were not different from Con. Most notably, the ImH group had significantly larger solei compared with the Im group, which were less than those shown in the Con group. Furthermore, immobilization alone caused a significant increase in oxidative damage, and the addition of heating to immobilization significantly reduced oxidative damage. In an effort to further identify the cause of this protective effect, antioxidant enzyme activities were assessed. CuZnSOD was sharply elevated in Im compared (P < 0.025) with that in the Con and reduced in the ImH group compared with that in the Im group (P < 0.025). Catalase was elevated 8% (P < 0.025) in the Im group compared with the Con group and was similar to the ImH group. Glutathione peroxidase, glutathione reductase, and MnSOD did not differ between groups. These data indicate that heating provides protection against oxidative stress and preserves muscle mass during disuse atrophy. These data also suggest that antioxidant protection is not conferred via antioxidant enzymes, and HSPs may play an important role.     

Pancreatic hydrolases in cold-induced hyperphagia of rats fed a low or high-fat diet

Rats fed either a low (2p. 100) or high (40 p. 100)-fat diet were exposed to 22 or 5 degrees C. The resulting hyperphagia adequately compensated energy losses as judged from body weight. The cold-induced hyperphagia was accompanied by a non-parallel increase in pancreatic hydrolases. Amylase and lipase were not increased above the adaptive levels they had respectively reached in the heat with a high-starch or high-lipid diet. Chymotrypsinogen, on the contrary, responded to increased intake of both diets. It also responded to the higher protein concentration in the high-fat diet caused by isocaloric replacement of starch by fat. Colipase varied independently of lipase and was increased additively by fat and protein intakes. Consequently, although limiting for lipase in the warm, colipase rose to a 1:1 ratio in the cold. Increased intake had a consistent pleiotropic effect evidenced by an increase of amylase with the high-fat diet and of lipase with the low-fat diet. The net effect was a significant increase in the lipid-digesting potential of the organism of lipid-fed animals upon exposure to cold, while the starch-digesting potential remained unaffected in starch-fed animals.     

Neuronal-glial interactions in rats fed a ketogenic diet

Glucose is the preferred energy substrate for the adult brain. However, during periods of fasting and consumption of a high fat, low carbohydrate (ketogenic) diet, ketone bodies become major brain fuels. The present study was conducted to investigate how the ketogenic diet influences neuronal-glial interactions in amino acid neurotransmitter metabolism. Rats were kept on a standard or ketogenic diet. After 21 days all animals received an injection of [1-(13)C]glucose plus [1,2-(13)C]acetate, the preferential substrates of neurons and astrocytes, respectively. Extracts from cerebral cortex and plasma were analyzed by (13)C and (1)H nuclear magnetic resonance spectroscopy and HPLC. Increased amounts of valine, leucine and isoleucine and a decreased amount of glutamate were found in the brains of rats receiving the ketogenic diet. Glycolysis was decreased in ketotic rats compared with controls, evidenced by the reduced amounts of [3-(13)C]alanine and [3-(13)C]lactate. Additionally, neuronal oxidative metabolism of [1-(13)C]glucose was decreased in ketotic rats compared with controls, since amounts of [4-(13)C]glutamate and [4-(13)C]glutamine were lower than those of controls. Although the amount of glutamate from [1-(13)C]glucose was decreased, this was not the case for GABA, indicating that relatively more [4-(13)C]glutamate is converted to GABA. Astrocytic metabolism was increased in response to ketosis, shown by increased amounts of [4,5-(13)C]glutamine, [4,5-(13)C]glutamate, [1,2-(13)C]GABA and [3,4-(13)C]-/[1,2-(13)C]aspartate derived from [1,2-(13)C]acetate. The pyruvate carboxylation over dehydrogenation ratio for glutamine was increased in the ketotic animals compared to controls, giving further indication of increased astrocytic metabolism. Interestingly, pyruvate recycling was higher in glutamine than in glutamate in both groups of animals. An increase in this pathway was detected in glutamate in response to ketosis. The decreased glycolysis and oxidative metabolism of glucose as well as the increased astrocytic metabolism, may reflect adaptation of the brain to ketone bodies as major source of fuel.     

Morphological alteration of gut-associated lymphoid tissue after long-term total parenteral nutrition in rats

Summary The morphological alteration of gut-associated lymphoid tissue (GALT) induced by long-term absence of dietary stimulation was investigated. Male Wistar rats weighing 230 g were maintained with total parenteral nutrition (TPN). Control rats were allowed to have the same amount of the solution orally. After two weeks, the morphological alteration of GALT was examined. Although no significant difference in weight gain was noted between the two groups, the area comprised by Peyer's patches was decreased in TPN rats. The number of transported lymphocytes and the ratio of helper T (T_h) cells to suppressor/cytotoxic T (T_s/c) cells in intestinal lymph were lowered after TPN treatment. In an immunohistochemical study of the rat ileum, the number of T cells and the T_h/T_s/c ratio were decreased both in the intraepithelial spaces and in the lamina propria of TPN rats. The percentage of interleukin-2 receptor-positive cells and the number of IgA-containing cells in the lamina propria were significantly reduced in TPN rats. These results suggest that dietary stimulation might play a role in the maintenance of GALT function and morphology.     

Oxyntomodulin ameliorates glucose intolerance in mice fed a high-fat diet

We evaluated the acute effects of OXM on glucose metabolism in diet-induced insulin-resistant male C57Bl/6 mice. To determine the effects on glucose tolerance, mice were intraperitoneally injected with OXM (0.75, 2.5, or 7.5 nmol) or vehicle prior to an ip glucose tolerance test. OXM (0.75 nmol/h) or vehicle was infused during a hyperinsulinemic euglycemic clamp to quantify insulin action on glucose production and disposal. OXM dose-dependently improved glucose tolerance as estimated by AUC for glucose (OXM: 7.5 nmol, 1,564 +/- 460, P < 0.01; 2.5 nmol, 1,828 +/- 684, P < 0.01; 0.75 nmol, 2,322 +/- 303, P < 0.05; control: 2,790 +/- 222 mmol.l(-1).120 min). Insulin levels in response to glucose administration were higher in 7.5 nmol OXM-treated animals compared with controls. In basal clamp conditions, OXM increased EGP (82.2 +/- 14.7 vs. 39.9 +/- 5.7 micromol.min(-1).kg(-1), P < 0.001). During insulin infusion, insulin levels were twice as high in OXM-treated mice compared with controls (10.6 +/- 2.8 vs. 4.4 +/- 2.2 ng/ml, P < 0.01). Consequently, glucose infusion rate (118.6 +/- 30.8 vs. 38.8 +/- 26.4 microl/h, P < 0.001) and glucose disposal (88.1 +/- 13.0 vs. 45.2 +/- 6.9 micromol.min(-1).kg(-1), P < 0.001) were enhanced in mice that received OXM. In addition, glucose production was more suppressed during OXM infusion (35.7 +/- 15.5 vs. 15.8 +/- 11.4% inhibition, P < 0.05). However, if these data were expressed per unit concentration of circulating insulin, OXM did not affect insulin action on glucose disposal and production. These results indicate that OXM beneficially affects glucose metabolism in diet-induced insulin-resistant C57Bl/6 mice. It ameliorates glucose intolerance, most likely because it elevates glucose-induced plasma insulin concentrations. OXM does not appear to impact on insulin action.     

Responses to dietary starch or sucrose on protein and glucose kinetics in goats fed a high-concentrate diet

Abstract

Responses of whole body protein synthesis (WBPS) and glucose irreversible loss rate (ILR) were compared between dietary starch and sucrose in four male goats. Diets were fed at 1.2 times maintenance requirements of ME and CP with 30% of the ME as starch, starch plus sucrose or sucrose, twice daily. The diets consisted of 33, 32, 11 and 24% of alfalfa hay, corn, soybean meal and the carbohydrates, respectively. The WBPS and glucose ILR during 5 – 7 h after feeding were determined by an isotope dilution method of [²H₅]phenylalanine, [²H₂]tyrosine, [²H₄]tyrosine and [¹³C₆]glucose. Sucrose elevated ammonia nitrogen and lowered acetate concentrations in the rumen, but did not differ from starch in nitrogen retention. Glucose ILR and WBPS were similar between the carbohydrates. It was concluded that dietary sucrose would have effects similar to starch on WBPS and glucose kinetics in the absorptive state in goats fed a high-concentrate diet.