Effects of dietary carbohydrate and phenotype on adipose cellularity in female SHR/N-cp rats.

1. Adipose mass and cellularity were studied in congenic female SHR/N-cp rats fed iosenergetic diets containing 54% carbohydrate as sucrose (SU) or cooked cornstarch (CS), 20% protein, 16% mixed dietary fat plus vitamins, minerals, and non-nutritive fiber ad libitum from 5 weeks until 8.5 months of age. Measures of adipocyte lipid content, cell number per depot, and mass of principal white (WAT) and interscapular brown (IBAT) adipoe tissue depots were determined at the end of the study. 2. Final body weights (BW) of corpulent rats were more than twice those for their lean littermates, and were greater when fed the SU than the CS diet in both phenotypes. Phenotype effects (corpulent greater than lean) were present for fat pad weight, adipocyte number, and adipocyte lipid content in the dorsal (DOR) and retroperitoneal (RP) WAT depots. Diet effects were present for depot weight, adipocyte number, and adipocyte lipid content in both WAT depots, and were of qualitatively similar magnitude in both phenotypes. 3. IBAT weights, IBAT:BW ratios, and IBAT cell number of corpulent greater than lean, and were greater than with SU than CS diet in both phenotypes. 4. These results indicate that obesity in the corpulent phenotype of the SHR/N-cp rat occurs as the result of hypertrophy and hyperplasia of white adipose tissue, and that isoenergetic substitution of simple for complex carbohydrate resulted in greater fat accretion in both phenotypes. The greater diet and phenotype-associated adiposity occurred despite greater mass and cellularity of BAT. The results also indicate that sexual dimorphism occurs regarding effects of diet and phenotype on expression of adipose tissue development in this strain.     

Effects of dietary carbohydrate and phenotype on thyroid hormones and brown adipose tissue locularity in adult LA/N-cp rats

1. Groups of lean and corpulent LA/N-cp rats were fed isoenergetic diets containing, 54% carbohydrate as maize starch (MS) or sucrose (SU), 20% protein, 16% mixed fats, plus other essential nutrients and fiber from 1.5-9 months of age. Final body weights of corpulent rats were 2-3 times those of their lean littermates, and were greater with SU than MS diet in both phenotypes. 2. Interscapular brown adipose tissue (IBAT) mass was greater in corpulent than lean and was greater with SU than MS diet in lean but not corpulent rats. IBAT cell diameters and adipocyte volumes were generally similar in both phenotypes, and were not markedly affected by dietary carbohydrate type. 3. Brown adipocyte locularity profiles were qualitatively similar in both phenotypes, and were morphologically indicative of thermogenic activity in both phenotypes. Locule profiles of corpulent animals contained a greater proportion of thermogenically less active types IV and V brown adipocytes than similarly fed lean animals, however, and locule distribution profiles were not influenced by diet. 4. Serum T3 concentrations were similar in both phenotypes, were greater in SU than MS lean rats and were not influenced by diet in the corpulent phenotype. In contrast, serum thyroxine concentrations and percent thyroxine uptake were not influenced by diet or phenotype. 5. These results are consistent with a partial impairment in BAT-mediated thermogenic activity in the corpulent phenotype and suggest that obesity in this strain may be due to factors other than biochemically defective brown adipose tissue thermogenesis.     

Non-shivering thermogenesis and obesity in adult diabetic Wistar fatty rats

1. Characteristics of resting and of norepinephrine (NE)-stimulated thermogenesis, and the glycemic response to NE were determined in adult male Wistar Fatty rats. Rats were maintained on Purina chow No. 5001 until 22 weeks of age, and fed semisynthetic diets containing 54% carbohydrate, 20% protein, 16% mixed fats, plus essential vitamins, minerals, and non-nutritive fiber from 22 until 30 weeks of age. 2. Obese rats were 50% heavier than lean throughout the study. Phenotype effects (obese greater than lean) were present for retroperitoneal (RP) and dorsal (DOR) white fat depot weight, adipocyte number per depot, and adipocyte lipid content. Epididymal mass and cellularity were similar in both phenotypes. 3. Interscapular brown adipose tissue (IBAT) mass, adipocyte size, and adipocyte number were greater in obese than in lean. Resting metabolic rates (RMR) of obese rats were lower than in lean, and increased 79% in lean but only 33% in obese animals following NE (200 micrograms/kg BW, s.c.) stimulation. 4. The glycemic response to NE occurred normally in both phenotypes, and resulted in a 3-fold increment in plasma glucose in lean rats and a 5-6-fold increase in plasma glucose in obese rats. 5. The results of this study are consistent with hyperplasia and hypertrophy of IBAT, RP and DOR depots, and indicate that the capacity for non-shivering thermogenesis is impaired in the obese phenotype of this strain in spite of peripheral sensitivity to NE and greater mass and cellularity of brown adipose tissue.     

Effects of increased energy expenditure on weight gain and adiposity in the LA-corpulent rat

Groups of lean or pre-obese LA/N-cp rats were subjected to a program of vigorous exercise (less than 4 hr/day) or remained sedentary from 6 weeks until 12 weeks of age. Sedentary pre-obese rats gained weight twice as rapidly as sedentary lean rats. Exercise treatment resulted in greater decrements in body wt in obese than in lean rats, but did not result in absolute weight loss in either group. At 12 weeks of age, fat pad weights in principle depots were 10-15 times greater in corpulent than in lean rats and were significantly smaller in the exercised groups of both phenotypes, and corresponded with lower relative adiposity compared to corresponding sedentary groups. Heart weights were greater in corpulent than lean, while gastrocnemius muscle weights were similar in both phenotypes. Exercise was without effect on the weight of either muscle tissue in either phenotype. Interscapular brown adipose tissue weights and the IBAT:BW ratio were greater in obese than in lean rats. IBAT weights were lower in exercised than sedentary rats of either phenotype, but the IBAT:BW ratio was lower only in the obese exercised rats. In sedentary rats, L-alpha-glycerophosphate dehydrogenase and malic enzyme activity were greater in obese than lean, and exercise treatment resulted in increased L-alpha-glycerophosphate dehydrogenase and malic enzyme only in lean rats. These results are consistent with a redistribution of energy expenditure from energy storing to energy dissipating pathways following vigorous exercise, resulting in slowed rates of weight gain and body fat accretion in both lean and obese animals, with the most significant decrements among pre-obese rats.     

The effects of the intestinal glucosidase inhibitor acarbose on cholesterogenesis in corpulent rats.

1. Groups of lean and obese LA/N-cp and obese Type II diabetic SHR/N-cp rats were fed semisynthetic diets with or without the alpha-glucosidase inhibitor acarbose (ACB, 100 mg/kg diet, p.o.) from 8 until 15 weeks of age, and measures of fasting serum total cholesterol (TC), insulin (INS), and hepatic HMG-CoA synthase activity determined at the end of the study. 2. ACB was without marked effect on mean food intake in either strain or either phenotype, and resulted in less weight gain and decreased adipose mass in obese LA/N-cp rats. INS was greater in the obese than the lean phenotype of both strains, and ACB resulted in greater reductions in INS in obese LA/N-cp than in obese LA/N-cp rats. 3. Serum TC concentrations were greater in the obese than in the lean phenotype of both strains, and ACB resulted in decreases in TC in both strains and in lower beta:alpha lipoprotein cholesterol ratios in obese LA/N-cp rats. Liver HMG Co-A synthase activity was greater in lean than obese rats and ACB resulted in normalization of enzyme activity in obese LA/N-cp but not SHR/N-cp rats. 4. These results confirm the hypercholesterolemia which occurs in the obese phenotype of the corpulent rat strains, and indicates that ACB may bring about significant reductions in body weight and fatness, TC, and in improved beta:alpha lipoprotein ratios and HMG-CoA synthase activity in obesity.(ABSTRACT TRUNCATED AT 250 WORDS)     

The anatomy of adipose tissue in captive Macaca monkeys and its implications for human biology

In a sample of 31 sedentary, ad libitum-fed monkeys, most specimens had less than 5% adipose tissue by weight. Total fatness correlated closely with the number of adipocytes per kilogram lean body mass, but not at all with mean adipocyte volume, except in specimens below 5% fat. The total number of adipocytes per kilogram of lean body mass increased more than tenfold in the most obese specimens. These data suggest that, like humans but in contrast to laboratory rodents, adipocyte proliferation, not adipocyte enlargement, is the chief mechanism of adipose tissue expansion except in very lean monkeys. Adipose tissue was found in all the typical mammalian depots and in the superficial abdominal paunch, which enlarged disproportionately in obese specimens, forming an almost continuous layer over most of the body. Site-specific differences in the activities of some glycolytic enzymes were similar to those of other mammals. Adipocytes in the paunch depot showed biochemical properties in common with those in the groin depots. The distribution and cellularity of adipose tissue in normal humans were similar to those of exceptionally obese monkeys. Many of the interspecific and sex differences can be attributed to the much greater abundance of adipose tissue in humans, and may not be associated with hair reduction or aquatic habits. Some minor changes in the size or shape of certain adipose depots may have arisen recently under sexual selection. The relevance of laboratory rodents as animal models of human obesity is assessed from comparison of the cellular structure, anatomical distribution and enzyme profiles of adipose tissue in monkeys with those of human and other mammals.     

Triiodothyronine (T3) neogenesis in lean and obese LA/N-cp rats

Pre-obese LA/N-cp rats consumed more food and gained weight more rapidly than their lean littermates, and measures of adipose tissue depots indicated that the excess weight was deposited principally as carcass fat. Serum T3 concentrations and resting metabolic rates were lower in corpulent than in lean animals, consistent with a greater efficiency of weight gain in those animals. In vitro measures of T3 neogenesis from T4 were lower in corpulent than in lean animals in liver, kidney, and skeletal muscle and greater in interscapular brown adipose tissue. The intracellular generation of T3 from T4 is a fundamental component of the normal adaptive response to alterations in diet and environment, and is an essential prerequisite for the expression of non-shivering thermogenesis. These results are consistent with a functional impairment in the activity of the enzyme T4-5'-deiodinase in peripheral tissues, and suggest that this impairment is contributory if not causative of obesity in this strain of rat.     

The effect of experimental overnutrition on nonshivering thermogenesis and obesity in LA/N-cp rats.

1. Groups of congenic adult male lean and obese LA/N-cp rats were fed stock chow or the chow diet plus a cafeteria diet supplement from 4 until 6 months of age. 2. Weight gain, adipose cellularity, and adiposity were greater in obese than in lean rats and all three parameters increased more rapidly in obese than in lean rats when fed the cafeteria-supplemented diet. 3. Resting metabolic rates and basal urinary vanilylmandelic acid excretion were greater in lean than in obese rats, while serum triiodothyronine concentrations were similar in both phenotypes. The cafeteria diet was associated with significant increases in all three metabolic parameters in lean but not in obese rats. 4. The results of this study indicate that the obese phenotype of this strain has an impaired capacity for non-shivering thermogenesis (NST), in association with an enhanced propensity for development of obesity when fed stock or cafeteria diets. Moreover, the impairment in NST involves both sympathetic and thyroidal components, and is likely to be contributory if not causative of obesity in this strain.     

The effects of low-dose Bay-m-1099 (Miglitol) on serum lipids and liver enzyme activity of obese and obese-diabetic corpulent rats.

1. Groups of lean, obese, and obese-non-insulin-dependent diabetic LA/N-cp and SHR/N-cp rats were administered the a-glucosidase inhibitor Miglitol (150 mg/kg diet, ad libitum) from 8 until 15 weeks of age. 2. Phenotype effects (obese greater than lean) were present for weight gain, adiposity, serum glycemic and lipid parameters, and for liver glucokinase, glucose-6-phosphate dehydrogenase, and malic enzyme activity. Miglitol treatment was associated with improvements in glucokinase and malic enzyme in both strains, and in improvements in glycemic parameters in obese rats. 3. These results are consistent with variable improvements in glycemic control and insulin action following low dose Miglitol treatment, and indicate that indirect effects of the drug on insulin sensitivity in peripheral tissues and on glucoregulatory enzymes may contribute to the glycemic improvements observed with this drug, while greater dosages or longer treatment may be required to observe comparable improvements in adiposity or plasma lipid profiles.     

Cellularity of adipose depots in six strains of genetically obese mice

Adipocyte cell size and number of three adipose depots, gonadal, subcutaneous, and retroperitoneal, were determined in several strains (aA(y), aA(iy), dbdb, obob, and NZO) of adult genetically obese mice, male and female, and in male gold thioglucose-treated mice. Epididymal pad cellularity was determined during development in yellow and viable yellow obese mice and their lean littermates, as well as in the NCS/R mouse. Cell number in the mouse epididymal pad in both lean and genetically obese animals is determined early in development, i.e., before weaning. Cell enlargement is the consistent and usually dominant morphological explanation for adipose depot enlargement in genetic and in gold thioglucose-induced mouse obesity. In some instances, hyperplasia accompanied the hypertrophy, occurring most often in the subcutaneous depot. Cell number in the subcutaneous pad of the obese-hyperglycemic female is four times that of the lean control and represents the most extreme case of hyperplasia observed. In fact, hyperplasia was consistently seen in the obob mouse. A classification for genetic obesity based primarily upon the cellularity characteristics of the adipose depots is proposed.     

Comparative hormonal profile of two newly developed obese congenic rat strains

1. The effect of feeding diets containing either 54% sucrose or cooked corn starch for 12 weeks on levels of fasting plasma insulin, corticosterone, growth hormone and glucagon were compared in two newly developed genetically obese rat strains--the normoglycemic LA/N-cp and the diabetic SHR/N-cp. 2. In corpulent rats of either strain, levels of plasma insulin and corticosterone were greater when compared to the lean littermates. Corpulent LA/N-cp rats had lower levels of plasma glucagon and higher levels of plasma growth hormone than did lean LA/N-cp rats. 3. SHR/N-cp rats fed sucrose had greater levels of corticosterone and glucagon than did SHR/N-cp rats fed starch.     

Adipose triglyceride lipase expression and fasting regulation are differently affected by cold exposure in adipose tissues of lean and obese Zucker rats

Adipose triglyceride lipase (ATGL) hydrolyzes triacylglycerols to diacylglycerols in the first step of lipolysis, providing substrates for hormone-sensitive lipase (HSL). Here we studied whether ATGL messenger RNA (mRNA) and protein levels were affected by 24-h cold exposure in different white adipose tissue depots and in interscapular brown adipose tissue of lean and obese Zucker rats submitted to feeding and 14-h fasting conditions. HSL mRNA expression was also studied in selected depots. In both lean and obese rats, as a general trend, cold exposure increased ATGL mRNA and protein levels in the different adipose depots, except in the brown adipose tissue of lean animals, where a decrease was observed. In lean rats, cold exposure strongly improved fasting up-regulation of ATGL expression in all the adipose depots. Moreover, in response to fasting, in cold-exposed lean rats, there was a stronger positive correlation between circulating nonesterified fatty acids (NEFA) and ATGL mRNA levels in the adipose depots and a higher percentage increase of circulating NEFA in comparison with control animals not exposed to cold. In obese rats, fasting-induced up-regulation of ATGL was impaired and was not improved by cold. The effects of obesity and cold exposure on HSL mRNA expression were similar to those observed for ATGL, suggesting common regulatory mechanisms for both proteins. Thus, cold exposure increases ATGL expression and improves its fasting-up-regulation in adipose tissue of lean rats. In obese rats, cold exposure also increases ATGL expression but fails to improve its regulation by fasting, which could contribute to the increased difficulty for mobilizing lipids in these animals.     

Desaturation of stearic acid by liver and adipose tissue from obese-hyperglycaemic mice (ob/ob).

Stearic acid desaturase activity was assayed in preparations from perigenital adipose tissue and liver from lean and genetically obese female mice (ob/ob). The total activity in the perigenital adipose tissue from obese mice was threefold greater than in the tissue from lean mice, but per g of adipose tissue the activity was twofold greater in tissue from lean mice. In liver, the activity in obese mice was elevated at 8 weeks of age, remained elevated up to 24 weeks and then decreased by half at 48 weeks, but at all ages was higher than that in lean mice. The decrease in desaturase activity of liver from obese mice at 48 weeks corresponded to a change in the fatty acid composition of liver lipids toward that found in lean mice. Whereas in adipose tissue much of the increased enzyme activity may be due to tissue hyperplasia, in liver it is mainly an increased activity per cell.     

Effects of soybean isoflavones, probiotics, and their interactions on lipid metabolism and endocrine system in an animal model of obesity and diabetes

The effects of soybean isoflavones with or without probiotics on tissue fat deposition, plasma cholesterol, and steroid and thyroid hormones were studied in SHR/N-cp rats, an animal model of obesity, and were compared to lean phenotype. We tested the hypothesis that probiotics by promoting the conversion of isoflavone glycosides to their metabolically active aglycone form will have a synergistic effect on body fat, cholesterol metabolism, and the endocrine system. Obese and lean SHR/N-cp rats were fed AIN-93 diets containing 0.1% soy isoflavone mixture, 0.1% probiotic mixture, or both together. Different fat tissues were teased and weighed. Plasma was analyzed for cholesterol and steroid and thyroid hormones. In both phenotypes, isoflavones lowered fat deposition in several fat depots. Probiotics alone had no significant effect on fat depots. Isoflavones lowered total, LDL, and HDL cholesterol in lean rats, but in obese rats isoflavones lowered only total and LDL cholesterol. Isoflavones also lowered many of the steroid hormones involved in lipid metabolism but had no significant effect on thyroid hormones. Probiotics had no significant effect on cholesterol or hormones. Thus, our data show that soy isoflavones also lower plasma cholesterol and that this hypocholesterolemic effect appears to be due in part to the modulation of steroid hormones. Probiotics do not seem to enhance the effect of isoflavones.     

Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats

This study was designed to monitor the developmental changes in insulinemia and lipogenic enzyme activities in both inguinal adipose tissue and liver during suckling (7, 9, 14, and 17 days of age) and weaning (22 and 30 days of age) on to either a low-fat or a high-fat diet in lean (Fa/fa) and obese (fa/fa) rats. Tissues were removed through surgery and genotypes were retrospectively determined. During suckling, there was no difference in liver enzyme activities between the two groups. In contrast, adipose tissue fatty acid synthetase was increased by 50% and citrate cleavage enzyme and malic enzyme by 30% by 9 days of age. By 17 days of age, there was a threefold elevation in these enzyme activities and 6-phosphogluconic dehydrogenase and a twofold increase in glucose-6-phosphate dehydrogenase per inguinal fat pad in fa/fa versus Fa/fa. Consistent with these results, fat pad weight was increased by 20%, 50%, and 100% at 9, 14, and 17 days of age, respectively, in obese as compared to lean pups. However only by 17 days of age could a slight but significant increase in insulin level be detected in obese pups. Enlargement of inguinal fat pad accelerated after weaning on to a low-fat diet and still more after weaning on to a high-fat diet. Weaning on to a low-fat diet elicited an induction of hepatic lipogenic enzymes two or three times greater in fa/fa than in lean pups, while weaning on to a high-fat diet blunted the differences between genotypes. The lipogenic enzyme activities displayed per total inguinal fat were three to ten times greater in obese than in lean pups, regardless of the diet. However, adipose tissue lipogenic enzyme activities were much lower after weaning on to a high-fat than on to a low-fat diet in obese pups. The high-fat diet was as effective as the low-fat diet in triggering hyperinsulinemia in obese pups. The increased adipose tissue capacity for lipogenesis, starting during the suckling period, could play an important etiologic role in the development and maintenance of obesity in the Zucker rat.-Bazin, R., and M. Lavau. Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats.     

Reduced norepinephrine turnover in brown adipose tissue of pre-obese mice treated with monosodium-L-glutamate

Norepinephrine (NE) turnover, an index of sympathetic nervous system (SNS) activity, was measured in interscapular brown adipose tissue (IBAT), heart and pancreas of 3-weeks-old pre-obese monosodium-L-glutamate (MSG) mice and at 6-weeks-old mildly obese MSG mice. In IBAT, rates of NE turnover were slower not only in 3-weeks-old MSG mice but also in older obese MSG mice than in their saline controls. In heart, rates of NE turnover were slower in 6-weeks-old mildly obese MSG mice, but not in pre-obese MSG mice. No significant difference in NE turnover in pancreas was observed at either age. The low NE turnover in IBAT of MSG-treated mice prior to the onset of gross obesity suggests that low SNS activity may be an initial contributor to their high energy efficiency and resultant obesity.     

Diazoxide down-regulates leptin and lipid metabolizing enzymes in adipose tissue of Zucker rats.

We have previously reported that attenuation of hyperinsulinemia by diazoxide (DZ), an inhibitor of glucose-mediated insulin secretion, increased insulin sensitivity and reduced body weight in obese Zucker rats. These findings prompted us to investigate the effects of DZ on key insulin-sensitive enzymes regulating adipose tissue metabolism, fatty acid synthase (FAS), and lipoprotein lipase (LPL), as well as on circulating levels of leptin. We also determined the direct effects of diazoxide on FAS in 3T3-L1 adipocytes. Seven-week-old female obese and lean Zucker rats were treated with DZ (150 mg/kg/d) or vehicle (C, control) for a period of 6 wk. Changes in plasma parameters by DZ include significant decreases in triglycerides, free fatty acids, glucose, and insulin, consistent with our previous reports. DZ obese rats exhibited lower plasma leptin levels (P<0.03) compared to their C animals. DZ significantly reduced adipose tissue FAS activity in both lean (P<0.0001) and obese (P<0.01) animals. LPL mRNA content was also decreased significantly in DZ-treated obese animals (P<0.009) as compared to their respective controls without a significant effect on lean animals. The possibility that DZ exerted a direct effect on adipocytes was further tested in cultured 3T3-L1 adipocytes. Although diazoxide (5 microM) alone did not change FAS activity in cultured 3T3-L1 adipocytes, it significantly attenuated insulin's effect on FAS activity (P<0.001). We demonstrate that DZ regulates key insulin-sensitive enzymes involved in regulation of adipose tissue metabolism. These findings suggest that modification of insulin-sensitive pathways can be therapeutically beneficial in obesity management.