Adrenal hydroxylations in genetically obese and hypertensive rats.

The separate steps in the formation of aldosterone from cholesterol were studied in a strain of spontaneously hypertensive rats in which phenotypic obesity is inherited as a recessive trait (Koletsky rats). The obese and hypertensive state had little or no effect on side-chain cleavage of cholesterol, formation of progesterone from pregnenolone or 21-hydroxylation. Mitochondrial 18-hydroxylation of endogenous and exogenous corticosterone, however, as well as 18- and 11 beta-hydroxylation of deoxycorticosterone, were increased in obese hypertensive rats, both when compared with non-obese hypertensive siblings and when compared with healthy Sprague-Dawley rats. 18-Hydroxylation of corticosterone was increased more than 18-hydroxylation of deoxycorticosterone. In non-obese hypertensive rats, the adrenal content of mitochondrial cytochrome P-450 was lower than that in obese hypertensive rats but higher than that in rats of the conventional Sprague-Dawley strain. The results are discussed with respect to possible heterogeneity of adrenal cytochrome P-450 and to possible explanations for the changes observed.     

Ethanol-induced hypothermia and hyperglycemia in genetically obese mice

Blood glucose and rectal temperatures were monitored in two strains of genetically obese mice (C57 BL/6J ob/ob) prior to and following intragastric ethanol administration in an attempt to relate the hypothermic response to ethanol to extracellular glucose concentration. In contrast to expectation, ethanol administration was typically associated with a hyperglycemia and a hypothermic response. In the ob/ob genotype, the hypothermic response was associated with pronounced hyperglycemia which was more emphatic in older animals. The data support the conclusion that ethanol-induced hypothermia is independent of blood glucose levels. In light of the known sensitivity of ob/ob mice to insulin, it is suggested further that the observed hypothermic response was not a function of the animals' ability to transport glucose into peripheral cells. The observed hyperglycemia of the obese animals was most likely stress-related.     

Changes in gene expression foreshadow diet-induced obesity in genetically identical mice

High phenotypic variation in diet-induced obesity in male C57BL/6J inbred mice suggests a molecular model to investigate non-genetic mechanisms of obesity. Feeding mice a high-fat diet beginning at 8 wk of age resulted in a 4-fold difference in adiposity. The phenotypes of mice characteristic of high or low gainers were evident by 6 wk of age, when mice were still on a low-fat diet; they were amplified after being switched to the high-fat diet and persisted even after the obesogenic protocol was interrupted with a calorically restricted, low-fat chow diet. Accordingly, susceptibility to diet-induced obesity in genetically identical mice is a stable phenotype that can be detected in mice shortly after weaning. Chronologically, differences in adiposity preceded those of feeding efficiency and food intake, suggesting that observed difference in leptin secretion is a factor in determining phenotypes related to food intake. Gene expression analyses of adipose tissue and hypothalamus from mice with low and high weight gain, by microarray and qRT-PCR, showed major changes in the expression of genes of Wnt signaling and tissue re-modeling in adipose tissue. In particular, elevated expression of SFRP5, an inhibitor of Wnt signaling, the imprinted gene MEST and BMP3 may be causally linked to fat mass expansion, since differences in gene expression observed in biopsies of epididymal fat at 7 wk of age (before the high-fat diet) correlated with adiposity after 8 wk on a high-fat diet. We propose that C57BL/6J mice have the phenotypic characteristics suitable for a model to investigate epigenetic mechanisms within adipose tissue that underlie diet-induced obesity.     

Altered blood amino acid distribution in genetically obese mice.

The present study was undertaken to determine whether the alteration in amino acid distribution between the plasma and cellular compartment of the blood, previously described in dietary-obese rats, also occurs in genetically obese mice. The blood concentration of individual amino acids and its distribution between plasma and cells of lean and genetically obese mice (ob/ob) have been measured. The results demonstrated that genetically obese mice showed a decrease (55%, P = 0.0489) of free amino acids in the blood cells. Most amino acids were affected and among the most noteworthy characteristics was the observation that the reduction in concentration was more pronounced for the total concentration of the essential amino acids which was reduced by 76% (P = 0.0112) compared to cells of lean mice. These results suggest that an altered amino acid distribution between plasma and blood cells is a consequence of both diet-induced and genetic obesities.     

Altered liver glycogen metabolism in fed genetically obese mice.

The cyclic AMP and glycogen concentrations and the activities of phosphorylase kinase, phosphorylase a and glycogen synthase a were not different in livers from lean or ob/ob mice despite increased plasma glucose and insulin in the obese group. The liver water content was decreased by 10% in the obese mice. In hepatocytes isolated from lean mice and incubated with increasing glucose concentrations (14-112 mM), a sequential inactivation of phosphorylase and activation of glycogen synthase was observed. In hepatocytes from obese mice the inactivation of phosphorylase was not followed by an activation of synthase. The inactivation of phosphorylase occurred more rapidly and was followed by an activation of synthase in hepatocytes isolated from both groups of mice when in the incubation medium Na+ was replaced by K+ or when Ca2+ was omitted and 2.5 mM-EGTA included. The inactivation of phosphorylase and activation of synthase were not different in broken-liver-cell preparations from lean and obese animals. The re-activation of phosphorylase in liver filtrates in the presence of 0.1 microM-cyclic AMP and MgATP was inhibited by about 70% by EGTA and stimulated by Ca2+ and was always greater in preparations from ob/ob mice. The apparent paradox between the impairment of glycogen metabolism in isolated liver preparations and the situation in vivo in obese mice is discussed.     

Hyporesponsiveness to glucocorticoids in mice genetically deficient for the corticosteroid binding globulin

Corticosteroid binding globulin (CBG) is the carrier for glucocorticoids in plasma. The protein is believed to keep the steroids inactive and to regulate the amount of free hormone acting on target tissues (free hormone hypothesis). Here, we generated a mouse model genetically deficient for CBG to test the contribution of the carrier to glucocorticoid action and adrenocortical stress response. The absence of CBG resulted in a lack of corticosterone binding activity in serum and in an approximately 10-fold increase in free corticosterone levels in CBG-null mice, consistent with its role in regulation of circulating free hormone levels. Surprisingly, cbg(-/-) animals did not exhibit features seen in organisms with enhanced glucocorticoid signaling. Rather, the mice exhibited increased activity of the pituitary axis of hormonal control, normal levels of gluconeogenetic enzymes, and fatigue, as well as an aggravated response to septic shock, indicating an inability to appropriately respond to the excess free corticosterone in the absence of CBG. Thus, our data suggest an active role for CBG in bioavailability, local delivery, and/or cellular signal transduction of glucocorticoids that extends beyond a function as a mere cargo transporter.     

Membrane fluidity and adenylate cyclase activity in genetically obese mice

Adipocyte plasma membranes of genetically obese $\text{ob}\text{ob}$ mice are more fluid than their lean littermates but the fluidity was normalised in mice maintained at high environmental temperatures. The defective response of adenylate cyclase to isoproterenol was improved after normalisation of membrane fluidity. No major changes in the phospholipid composition of $\text{ob}\text{ob}$ membranes were detected.     

Dietary GABA decreases body weight of genetically obese mice

Body weight and food intake were decreased more in lean than in genetically obese (ob/ob) mice fed a low protein diet containing GABA. Young lean and obese mice, when fed a 4.5% GABA diet, lost 30% or 20% of their initial weight over periods of 10 or 32 days, respectively. When refed the control diet both groups of mice gained weight rapidly but the obese grew more over a longer period of time. With GABA at 2 or 2.5% of the diet, respectively, lean and obese mice could be maintained at constant low weights for weeks. The obese were less sensitive than the lean mice to dietary GABA. Weights increased rapidly when a high protein diet containing GABA was fed. Hepatic GABA aminotransferase activity increased in all mice fed the high protein diet.     

Zinc supplementation aggravates body fat accumulation in genetically obese mice and dietary-obese mice

A perturbation of zinc metabolism has been noted in numerous laboratory animals with diabetes and obesity. The effects of zinc supplementation on body fat deposition in two types of experimental obese mice: genetically obese (ob/ob) mice and high-fat diet-induced ICR obese (HF) mice were investigated in this study. Their lean controls were +/? mice, and ICR on basal diet, respectively. The mice in the zinc-supplemented groups were administered 200 mg/kg zinc in their diets for 6 wk. Both the ob/ob mice and the HF mice, that were fed a diet containing a marginal zinc dosage (4–6 mg/kg), had lower zinc levels in their serum and carcass, and higher body fat content than their respective lean controls (p<0.01). After zinc supplementation, ob/ob mice and the HF mice significnatly (p<0.05) increased their body fat by 49.4% and 18.9%, respectively. This study revealed that body fat deposition can be aggravated by zinc supplementation in both types of obese mice. Zinc may be associated with the energy homeostasis of obesity, via its interaction with dietary fat consumption.     

Pioglitazone administration alters ovarian gene expression in aging obese lethal yellow mice

Background  

Women with polycystic ovary syndrome (PCOS) are often treated with insulin-sensitizing agents, e.g. thiazolidinediones (TZD), which have been shown to reduce androgen levels and improved ovulatory function. Acting via peroxisome proliferator-activated receptor (PPAR) gamma, TZD alter the expression of a large variety of genes. Lethal yellow (LY; C57BL/6J Ay/a) mice, possessing a mutation (Ay) in the agouti gene locus, exhibit progressive obesity, reproductive dysfunction, and altered metabolic regulation similar to women with PCOS. The current study was designed to test the hypothesis that prolonged treatment of aging LY mice with the TZD, pioglitazone, alters the ovarian expression of genes that may impact reproduction.     

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.     

Pyruvate dehydrogenase activity in several tissues of genetically obese hyperglycemic mice

The active form (PDHa) and total activity of pyruvate dehydrogenase (PDH) were measured in homogenates from heart muscle, epididymal fat pads and liver of genetically obese hyperglycemic mice and compared with similar data derived from lean controls or Swiss albino mice. Both PDHa and total PDH activities were similar in heart muscle from all mice with a precipitous decrease in the PDHa upon fasting. Adipose tissue and liver of obese mice had a PDHa level that was almost two-fold higher than either lean control or Swiss albino mice. Fasting for 24 hours decreased the elevated activity of PDHa in adipose tissue and liver in obese mice to a value that was comparable to lean control or Swiss albino mice, fasted similarly. The elevation in both the active form and total activity of pyruvate dehydrogenase in livers from obese mice could explain the increased provision of acetyl-CoA units necessary for the accelerated hepatic lipogenesis observed with this mouse, a model for human obesity and insulin resistance.     

Fructose 2,6-bisphosphate levels are elevated in livers of genetically obese mice

Fructose 2,6-bisphosphate levels in freeze-clamped livers of $\text{C57BL}\text{6J}$$\text{ob}\text{ob}$ mice were 6-fold higher than the level in their lean (+/?) littermates. Overnight starvation reduced the hepatic level of this unique sugar diphosphate to 0.2 nmol/g in both the obese and lean mice. The elevated level in the obese mouse is consistent with the hyperinsulinemia of these animals.