Impact of body fat mass extent on cardiac autonomic alterations in women.

BACKGROUND: Obesity has been associated with significant abnormalities of the cardiac autonomic regulation. However, the precise impact of increasing body weight on cardiac autonomic function and the metabolic and hormonal contributors to these changes are presently unclear. The aim of our study was to explore in subjects with increasing values of body mass index (BMI) the alterations of cardiac autonomic function and to establish the potential role of various metabolic and hormonal contributors to these alterations. MATERIALS AND METHODS: We investigated time and frequency domain heart rate variability (HRV) parameters taken from 24-h Holter recordings, and several anthropometric, metabolic and hormonal parameters (plasma glucose, insulin, triglycerides, free fatty acids, leptin and adiponectin) in 68 normoglycaemic and normotensive women (mean age of 40 +/- 3 years), subdivided according to their BMI into 15 normal body weight (controls), 15 overweight, 18 obese and 20 morbidly obese. RESULTS: Heart rate was increased and HRV was decreased in the morbidly obese group as compared with controls. In overall population, a negative association linked body fat mass (FM) to HRV indices. None of the metabolic and hormonal parameters were significantly related to the HRV indices, after they were adjusted for the body FM. CONCLUSIONS: Morbidly obese, normoglycaemic and normotensive young women have increased HR and low HRV, indicating an abnormal cardiac autonomic function and representing a risk factor for adverse cardiovascular events. A decrease of HRV parameters is associated with a progressive increase of body FM. Other metabolic and hormonal factors, characterising obesity, do not show an independent influence on these HRV alterations.

Persistent correlation of ghrelin plasma levels with body mass index both in stable weight conditions and during gastric-bypass-induced weight loss.

BACKGROUND: Studies done on serial changes in plasma ghrelin levels after gastric bypass (GBP) have yielded contrasting results since decreased, unchanged, or increased levels have been reported in the literature. This study investigates whether or not GBP has an inhibitory effect on fasting ghrelin levels independently of weight loss. METHODS: Fasting ghrelin levels were measured in 115 stable body weight females, classified as normal body weight (NW; body mass index (BMI)<25 kg/m2), overweight (OW; BMI 25-30 kg/m2), and obese subjects, divided in three subgroups with increasing BMI (BMI 30-40 kg/m2; BMI 40-50 kg/m2; BMI>50 kg/m2). RESULTS: Each obese subgroup showed significantly lower ghrelin levels as compared to both NW (p<0.0001) and OW subjects (p<0.05 or 0.005); however, no significant differences were observed within the three obese subgroups. Forty-nine obese patients underwent a GBP. Plasma ghrelin, measured at 3, 6, and 12 months after GBP, significantly increased from the sixth month on (p<0.0001). When patients were classified, at each postoperative time point, according to their actual BMI, ghrelin was significantly (p=0.0002) related to postoperative BMI and not significantly different from ghrelin measured in stable body weight conditions. CONCLUSIONS: Fasting ghrelin displays an inversely significant correlation with BMI in both stable body weight conditions and after GBP. No evidence was found that GBP had an effect on fasting ghrelin levels, independent of weight loss.

An anomaly of insulin removal in perfused livers of obese-hyperglycemic (ob/ob) mice.

Obese-hyperglycemic (ob/ob) mice have the interesting feature of being hyperinsulinemic, thus having some characteristics in common with human maturity-onset diabetics. As the cause of hyperinsulinemia in these mice is not established, and as the liver is known to play a role in determining the amount of hormone that reaches the periphery, it was hypothesized that an anomaly in the hepatic handling of insulin might prevail in obese-hyperglycemic mice. Immunoreactive insulin was therefore measured in the perfusate before and after a single passage through perfused livers of lean and ob/ob mice, permitting. It was found that the removal of insulin by livers of lean mice increased with increasing concentrations of the hormone in the portal vein. The removal process had a limited capacity, however, and as a consequence the percentage of hormone removed by the liver actually decreased when portal insulin concentrations increased. Insulin removal by livers of ob/ob mice had qualitatively the same characteristics but was considerably less efficient than in normal livers. Due to this, more insulin was found in the perfusate leaving the liver of ob/9b mice than in that of controls, at any insulin concentration tested. These observations suggest that in obese-hyperglycemic mice more of the hormone may reach the periphery and thus contribute to hyperinsulinemia. The present study further suggests that the anomaly of insulin removal observed in perfused livers of ob/ob mice might be secondary to hyperinsulinemia, since it was partly corrected upon artificially decreasing the circulating levels of insulin (e.g. via a fast, anti-insulin serum, or streptozotocin treatment) before perfusion. The characteristics of hepatic insulin removal reported in this study, as well as the differences observed between livers of lean and ob/ob mice, may reflect changes in membrane insulin receptors and/or in processes responsible for the degradation of the horomone.

Evidence for a role of the microtubular system in the secretion of newly synthesized albumin and other proteins by the liver.

Livers of normal mice were prefused in situ and the secretion of newly synthesized (i.e. labeled) proteins into the perfusate were measured. In control livers, the secretion of newly synthesized proteins was found to be linear with time. In marked contrast, when livers were perfused with vinblastine, vincristine, or colchicine, drugs known to interfere with the hepatic microtubular system, the release of newly synthesized proteins was either strongly inhibited or completely suppressed although total hepatic protein synthesis (estimated by the incorporation of labeled amino acids into hepatic plus perfusate proteins) remained unaltered. Chromatographic separation of the various secreted proteins showed that the release of albumin, globulins, and small polypeptides was decreased to a similar extent by vincristine or colchicine. In the particular case of albumin, it was further observed that total (i.e. liver plus perfusate) labeled amino acid incorporation into albumin was not altered by either vincristine or colchicine, whereas the incorporation of these amino acids into liver albumin was markedly increased but incorporation into perfusate albumin was decreased, suggesting that the translocation of this particular protein from the liver to the perfusate had been affected by the presence of these drugs. It is proposed that the functional integrity of microtubules is necessary for the intracellular movement and eventual release of albumin and other proteins by the liver, and suggested that microtubules might possibly be a site of regulation of hepatic protein secretion.

Lipid infusion lowers sympathetic nervous activity and leads to increased beta-cell responsiveness to glucose.

We investigated the possible involvement of the autonomic nervous system in the effect of a long-term elevation of plasma free fatty acid (FFA) concentration on glucose-induced insulin secretion (GIIS) in rats. Rats were infused with an emulsion of triglycerides (Intralipid) for 48 hours (IL rats). This resulted in a twofold increase in plasma FFA concentration. At the end of infusion, GIIS as reflected in the insulinogenic index (DeltaI/DeltaG) was 2.5-fold greater in IL rats compared with control saline-infused rats. The ratio of sympathetic to parasympathetic nervous activities was sharply decreased in IL rats relative to controls. GIIS was studied in the presence of increasing amounts of alpha- and beta-adrenoreceptor agonists and antagonists. The lowest concentrations of the alpha2A-adrenoreceptor agonist oxymetazoline, which were ineffective in control rats, reduced GIIS in IL rats. At the dose of 0.3 pmol/kg, GIIS became similar in IL and control rats. The use of beta-adrenoreceptor agonist (isoproterenol) or antagonist (propranolol) did not result in a significant alteration in GIIS in both groups. GIIS remained as high in IL vagotomized rats as in intact IL rats, indicating that changes in parasympathetic tone were of minor importance. Altogether, the data show that lipid infusion provokes beta-cell hyperresponsiveness in vivo, at least in part through changes in alpha2-adrenergic innervation.

Parallel increases in rates of fatty acid synthesis and in pyruvate dehydrogenase activity in isolated rat hepatocytes incubated with insulin.

The effect of insulin on the activity of pyruvate dehydrogenase is studied in isolated hepatocytes from fed rats. Insulin increases the 'initial' activity of pyruvate dehydrogenase by 30% without modifying the total activity of the enzyme. The maximal increase is reached 3 min after addition of the hormone and is dose-dependent. Insulin also increases the rate of fatty acid synthesis.

Long-chain fatty acids inhibit acetyl-CoA carboxylase gene expression in the pancreatic beta-cell line INS-1.

The mechanism whereby long-term exposure of the beta-cell to fatty acids alters the beta-cell response to glucose is not known. We hypothesized that fatty acids may alter beta-cell function by changing the expression level of metabolic enzymes implicated in the regulation of insulin secretion, in particular acetyl-CoA carboxylase (ACC). This enzyme catalyzes the formation of malonyl-CoA, a key regulator of fatty acid oxidation. Using the beta-cell line INS-1 as a model, the results show that the polyunsaturated fatty acid linoleate (C18:2) inhibited both basal and glucose-stimulated ACC mRNA induction. The inhibition was detected by 4-6 h, and a maximal 60% effect occurred at 12 h after cell exposure to the fatty acid. Linoleate, as glucose, did not modify the half-life of the ACC transcript. Prolonged exposure of INS-1 cells to linoleate also inhibited ACC protein accumulation at low and high glucose. The saturated fatty acids myristate (C14:0), palmitate (C16:0), and stearate (C18:0) were also effective as well as the monounsaturated oleate (C18:1) and the short-chain fatty acids butyrate (C4:0) and caproate (C6:0); long-chain omega3 fatty acids were ineffective. The threshold concentration for long-chain fatty acids was 0.05 mmol/l, and maximal inhibition occurred at 0.3 mmol/l. 2-bromopalmitate, a nonmetabolizable analog, had no effect, suggesting that fatty acids must be metabolized to change ACC gene expression. Prolonged exposure of INS-1 cells to palmitate, oleate, and linoleate markedly altered the glucose-induced insulin response, resulting in high basal insulin release and a suppression of glucose-induced insulin secretion. This was associated with an exaggerated (twofold to threefold) rate of fatty acid oxidation at all tested glucose concentrations. The data provide a possible mechanism to at least partially explain how fatty acids cause beta-cell insensitivity to glucose, i.e., by downregulating ACC with a resulting exaggerated fatty acid oxidation.

Uncoupling protein 2: a possible link between fatty acid excess and impaired glucose-induced insulin secretion?

The mechanism by which long-term exposure of the beta-cell to elevated concentrations of fatty acid alters glucose-induced insulin secretion has been examined. Exposure of INS-1 beta-cells to 0.4 mmol/l oleate for 72 h increased basal insulin secretion and decreased insulin release in response to high glucose, but not in response to agents acting at the level of the K(ATP) channel (tolbutamide) or beyond (elevated KCl). This also suppressed the glucose-induced increase in the cellular ATP-to-ADP ratio. The depolarization of the plasma membrane promoted by glucose was decreased after oleate exposure, whereas the response to KCl was unchanged. Cells exposed to free fatty acids displayed a lower mitochondrial membrane potential and a decreased glucose-induced hyperpolarization. The possible implication of uncoupling protein (UCP)-2 in the altered secretory response was examined by measuring UCP2 gene expression after chronic exposure of the cells to fatty acids. UCP2 mRNA and protein were increased twofold by oleate. Palmitate and the nonoxidizable fatty acid bromopalmitate had similar effects on UCP2 mRNA, suggesting that UCP2 gene induction by fatty acids does not require their metabolism. The data are compatible with a role of UCP2 and partial mitochondrial uncoupling in the decreased secretory response to glucose observed after chronic exposure of the beta-cell to elevated fatty acids, and suggest that the expression and/or activity of the protein may modulate insulin secretion in response to glucose.

Evidence for an anaplerotic/malonyl-CoA pathway in pancreatic beta-cell nutrient signaling.

A metabolic model of fuel sensing has been proposed in which malonyl-CoA and long-chain acyl-CoA esters may act as coupling factors in nutrient-induced insulin release (Prentki M, Vischer S, Glennon MC, Regazzi R, Deeney J, Corkey BE: Malonyl-CoA and long chain acyl-CoA esters as metabolic coupling factors in nutrient-induced insulin secretion. J Biol Chem 267:5802-5810, 1992). To gain further insight into the control of malonyl-CoA content in islet tissue, we have studied the short- and long-term regulation of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) in the beta-cell. These enzymes catalyze the formation of malonyl-CoA and its usage for de novo fatty acid biogenesis. ACC mRNA, protein, and enzymatic activity are present at appreciable levels in rat pancreatic islets and clonal beta-cells (HIT cells). Glucose addition to HIT cells results in a marked increase in ACC activity that precedes the initiation of insulin release. Fasting does not modify the ACC content of islets, whereas it markedly downregulates that of lipogenic tissues. This indicates differential regulation of the ACC gene in lipogenic tissues and the islets of Langerhans. FAS is very poorly expressed in islet tissue, yet ACC is abundant. This demonstrates that the primary function of malonyl-CoA in the beta-cells is to regulate fatty acid oxidation, not to serve as a substrate for fatty acid biosynthesis. The anaplerotic enzyme pyruvate carboxylase, which allows the replenishment of citric acid cycle intermediates needed for malonyl-CoA production via citrate, is abundant in islet tissue. Glucose causes an elevation in beta (HIT)-cell citrate that precedes secretion, and only those nutrients that can elevate citrate induce effective insulin release. The results provide new evidence in support of the model and explain why malonyl-CoA rises markedly and rapidly in islets upon glucose stimulation: 1) glucose elevates citrate, the precursor of malonyl-CoA; 2) glucose enhances ACC enzymatic activity; and 3) malonyl-CoA is not diverted to lipids. The data suggest that ACC is a key enzyme in metabolic signal transduction of the beta-cell and provide evidence for the concept that an anaplerotic/malonyl-CoA pathway is implicated in insulin secretion.

Increased insulin responsiveness in vivo and in vitro consequent to induced hyperinsulinemia in the rat.

The effect of constant, controlled hyperinsulinemia on in vivo and in vitro insulin responsiveness has been investigated in rats that have received insulin infusions through chronically implanted jugular vein catheters. Constant rates of insulin infusion during days 1-4 resulted in stable plasma insulin concentrations. The plasma glucose initially fell from 122 +/- 3 to 53 +/- 4 mg/dl. While the infusion rate was maintained constant, the plasma glucose continued to fall over the subsequent days so that on day 4 the plasma glucose, 40 +/- 2 mg/dl, was significantly lower than that in the same animals on day 1 (P less than 0.02). Subsequently, the rate of insulin infusion was decreased to maintain the plasma glucose level in the 35-40 mg/dl range. Plasma catecholamine levels were high in insulin-infused rats. On the eighth day an in vivo insulin tolerance test (0.5 U/kg) was performed. Insulin-infused rats responded with a hypoglycemia that was both more pronounced and longer sustained than in saline-infused controls. Insulin responsiveness in vitro has been measured in isolated adipocytes. Adipocytes from epididymal fat pads were of similar size in the two groups of animals. Glucose uptake by adipocytes from insulin-infused rats was similar to that of controls under basal (zero insulin) conditions, but showed an increase in the maximum response to insulin. Glucose incorporation into total lipid and fatty acid was greater in adipocytes from insulin-infused rats than in controls under both basal (zero insulin) and insulin-stimulated conditions. Activities of the lipogenic enzymes acetyl CoA carboxylase and fatty acid synthetase were markedly increased in epididymal fat pads of insulin-infused rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of fasting and streptozotocin in the obese-hyperglycemic (ob/ob) mouse. Apparent lack of a direct relationship between insulin binding and insulin effects.

The decrease of insulin binding to plasma membranes of liver, adipose, and muscle tissues observed in obese-hyperglycemic (ob/ob) mice was reversed towards normal by prolonged fasting or streptozotocin treatment. The extent of this reversal was related to that of the decrease in hyperinsulinemia of the obese mice. In contrast, binding of glucagon to liver plasma membranes was little influenced by fasting or streptozotocin treatment of obese animals. The relationship between insulin binding and metabolic effects of the hormone did not appear to be identical in all tissues. In muscle, insulin binding and insulin effect on glucose uptake and metabolism changed in parallel--i.e., when binding increased, tissue sensitivity to the hormone increased. In the liver, the increase in insulin binding that followed fasting or streptozotocin treatment was not accompanied by any detectable metabolic effect of insulin on hepatic metabolism. A similar situation appeared to prevail in adipose tissue. The varying relationships observed between the state of insulin binding to membranes and the target tissue responsiveness to the hormone probably reflect the multiplicity of the factors operative in these processes and help us to understand why the over-all obese-hyperglycemic syndrome of ob/ob mice cannot be improved simply by decreasing endogenous hyperinsulinemia.

Long-term exposure of beta-INS cells to high glucose concentrations increases anaplerosis, lipogenesis, and lipogenic gene expression.

Chronic exposure of pancreatic beta-cells to high glucose has pleiotropic action on beta-cell function. In particular, it induces key glycolytic genes, promotes glycogen deposition, and causes beta-cell proliferation and altered insulin secretion characterized by sensitization to low glucose. Postglycolytic events, in particular, anaplerosis and lipid signaling, are thought to be implicated in beta-cell activation by glucose. To understand the biochemical nature of the beta-cell adaptive process to hyperglycemia, we studied the regulation by glucose of lipogenic genes in the beta-cell line INS-1. A 3-day exposure of cells to elevated glucose (5-25 mmol/l) increased the enzymatic activities of fatty acid synthase 3-fold, acetyl-CoA carboxylase 30-fold, and malic enzyme 1.3-fold. Pyruvate carboxylase and citrate lyase expression remained constant. Similar observations were made at the protein and mRNA levels except for malic enzyme mRNA, which did not vary. Metabolic gene expression changes were associated with chronically elevated levels of citrate, malate, malonyl-CoA, and conversion of glucose carbon into lipids, even in cells that were subsequently exposed to low glucose. Similarly, fatty acid oxidation was suppressed and phospholipid and triglyceride synthesis was enhanced independently of the external glucose concentration in cells preexposed to high glucose. The results suggest that a coordinated induction of glycolytic and lipogenic genes in conjunction with glycogen and triglyceride deposition, as well as increased anaplerosis and altered lipid partitioning, contribute to the adaptive process to hyperglycemia and glucose sensitization of the beta-cell.

Severe hepatic and peripheral insulin resistance as evidenced by euglycemic clamps in genetically obese fa/fa rats.

The action of insulin on glucose metabolism and hepatic glucose production was studied in vivo over a wide range of insulin concentrations in lean and genetically obese (fa/fa) rats, using the euglycemic clamp technique. While total glucose metabolism was stimulated 3-fold by insulin in lean animals (half-maximal stimulation at 400 microU/ml insulin), the hormone had no significant effect on glucose metabolism in obese animals, whatever the concentration used. In lean rats, the endogenous (i.e. hepatic) glucose production was completely suppressed at a steady state insulin concentration of about 360 microU/ml. In obese rats, an insulin concentration as high as 10,000 microU/ml was needed to suppress the hepatic glucose production. These results suggest that, in obese rats 1) basal plasma insulin levels appear to maximally stimulate peripheral glucose metabolism, and the presence of postreceptor defects prevents any further stimulatory effect of the hormone on glucose metabolism; 2) grave impairments of the action of insulin on hepatic glucose production are present, despite a normal responsiveness obtained at pharmacological concentrations of the hormone. These hepatic alterations could be due to postbinding and/or intracellular defects, as well as to defects, yet to be defined, of the homeostasis of insulin counterregulatory hormones.

Vanadate treatment markedly increases glucose utilization in muscle of insulin-resistant fa/fa rats without modifying glucose transporter expression.

The present study examined the effects of chronic treatment with vanadate on in vivo insulin-stimulated glucose uptake by various tissues of obese and insulin-resistant fa/fa rats. It further determined whether the substantial improvement induced by vanadate administration was associated with altered expression of the insulin-responsive glucose transporter (GLUT4). Since oral Na3VO4 caused decreases in food intake and body weight, vanadate-treated fa/fa rats were compared with controls, fed ad libitum, and pair-fed rats. The animals in the three groups were submitted to hyperinsulinemic clamps combined with the 2-deoxyglucose method. At similar levels of imposed hyperinsulinemia, the glucose infusion rate (milligrams per kg.min-1) required to maintain euglycemia, extremely low in controls (0.8 +/- 0.3) and pair-fed rats (1.2 +/- 0.6), was strikingly improved in vanadate-treated rats (9.5 +/- 0.3). Correspondingly, the insulin-mediated glucose utilization indices were 2- to 3-fold higher in all types of muscle in treated rats: hindlimb skeletal muscle, diaphragm, and heart. Glucose utilization remained unaffected in white adipose tissue and jejunum, whereas it was increased by mere food restriction in brown adipose tissue of pair-fed rats. The amounts of GLUT4 and GLUT4 mRNA were then measured in the insulin-sensitive tissues of the three groups of animals. Vanadate treatment induced no change in GLUT4 mRNA or GLUT4 protein levels in any of the examined tissues. It even prevented the rise in GLUT4 protein expression caused by calorie restriction in brown adipose tissue of pair-fed rats. In conclusion, chronic administration of vanadate markedly increases the insulin-mediated glucose uptake in muscle of insulin-resistant fa/fa rats without altering GLUT4 number. A functional improvement of glucose transporters due to more efficient translocation and/or increased intrinsic activity or changes in the insulin signaling pathway is, thus, likely to play a major role in the beneficial effects of vanadate.

Alterations of brown adipose tissue in genetically obese (ob/ob) mice. I. Demonstration of loss of metabolic response to nerve stimulation and catecholamines and its partial recovery after fasting or cold adaptation.

Metabolic responses to electrical nerve stimulation or norepinephrine of isolated interscapular brown adipose tissue (BAT) from lean and ob/ob mice were studied using either continuous monitoring of the NAD(P)H/NAD(P) redox state or direct microcalorimetry. The responses to these sympathetic stimuli were not significantly different from zero in BAT of ob/ob mice kept at 22 C and fed ad libitum. The metabolic rate of BAT of lean mice was stimulated 3-fold by norepinephrine. ob/ob mice are hyperglycemic and hyperinsulinemic; cold adaptation further increased their plasma glucose, and fasting decreased the levels of both glucose and insulin to normal values. Both fasting and cold adaptation at 5 C partially restored the tissue metabolic response of ob/ob mice, whereas a decreased sensitivity was observed in the tissue of lean mice. The results of these experiments are compatible with the hypothesis that the impaired capacity of BAT of ob/ob mice to produce heat could be one of the causes of their high food efficiency and their inability to withstand acute cold exposure.

Alterations of brown adipose tissue in genetically obese (ob/ob) mice. II. Studies of beta-adrenergic receptors and fatty acid degradation.

beta-Receptor number, norepinephrine-stimulated adenylate cyclase activity and lipolysis, octanoate-induced NAD(P) redox changes, and heat production were studied in brown adipose tissue (BAT) of lean and obese (ob/ob) mice. beta-Receptor number was increased 1.54-fold in purified brown adipocyte plasma membrane of ob/ob mice compared to that in lean controls. This increase was reversed by cold adaptation (5 C). Basal and norepinephrine-stimulated adenylate cyclase values were not different in the two groups. Norepinephrine stimulated lipolysis at 10 nM in BAT of lean mice, but only at 10 microM in BAT ob/ob mice. Octanoate produced an increase in the NAD(P) redox state in BAT of lean mice, but it did not modify the NAD(P) redox state in BAT of ob/ob mice. Concomitantly, octanoate increased heat production 3-fold in BAT of lean mice, but did not promote any significant increase in heat production in BAT of ob/ob mice. These two parameters were restored toward values observed in lean mice when the ob/ob mice were adapted to a cold environment. The data indicate that BAT of ob/ob mice exhibits three alterations; one at the level of the beta-receptor, one at the level of the lipolytic response to norepinephrine, and one at the level of fatty acid activation and/or beta-oxidation.

Hyperinsulinemia increases the amount of GLUT4 mRNA in white adipose tissue and decreases that of muscles: a clue for increased fat depot and insulin resistance.

To mimick a state of hyperinsulinemia, normal rats were infused with insulin for 4 days via minipumps, and compared to saline infused rats. At the end of the experimental period, the abundance of mRNA was increased in white adipose tissue (WAT) and decreased in muscles of "insulinized" rats compared to controls. These findings were accompanied, in all tissues considered, except the diaphragm, by parallel changes in the amount of the glucose transporter protein and by parallel changes in the in vivo glucose utilization index. Hyperinsulinemia is thus a driving force in stimulating adipose tissue metabolic activity, while bringing about incipient muscle insulin resistance.

Effects of beta-adrenoceptor subtype stimulation on obese gene messenger ribonucleic acid and on leptin secretion in mouse brown adipocytes differentiated in culture.

The ob gene product is known to control food intake and energy expenditure. To determine whether thermogenic agents directly control ob gene expression, the effects of beta-adrenoceptor agonists on the level of the ob gene messenger RNA (mRNA) and on leptin secretion have been studied in mouse brown adipocytes differentiated in culture. These cells highly expressed the beta 3-adrenoceptor, the uncoupling protein, and the ob gene mRNAs. The ob gene was expressed in mouse brown adipocytes earlier than in mouse white adipocytes under the same culture conditions and to a similar level. The beta 3-, beta L-, and beta 2-adrenoceptor agonists BRL 37344, dobutamine, and terbutaline inhibited ob gene expression in mouse brown adipocytes differentiated in culture with EC50 values of 0.3, 1.0, and 85 nM, respectively. Leptin secretion by the cells under basal conditions was 78 +/- 10 pg/microgram DNA-4 h and was decreased by exposure to the beta-adrenoceptor agonists. The ob gene mRNA half-life was 9.4 h and was decreased to 2.4 h by 1 nM BRL 37344, indicating that the inhibitory effect of the beta 3-agonist might be due to destabilization of ob gene mRNA. (Bu)2cAMP (10-100 microM) and forskolin (20 microM) mimicked the effect of the beta-adrenoceptor agonists. FFA (150-800 microM) had only a small inhibitory effect on ob gene mRNA expression. The results suggest the existence in brown adipose tissue of a retroregulatory pathway by which leptin production in inhibited when the sympathetic nervous system is stimulated.

Brown adipose tissue metabolism in streptozotocin-diabetic rats.

Defects of both diet-induced thermogenesis and cold tolerance have been reported for streptozotocin-diabetic rats. Since brown adipose tissue (BAT) is a major effector of both diet- and cold-induced thermogenesis in the rat, the possible cause of these defects was investigated by comparing BAT metabolism under basal conditions and during activation by nerve stimulation, norepinephrine (NE), or octanoate addition in both streptozotocin-diabetic rats and in controls. The following metabolic indices were measured in rat interscapular BAT (IBAT): 1) tissue composition, 2) heat production rate as measured by direct microcalorimetry, 3) redox state of flavoproteins linked to the acyl-coenzyme A dehydrogenase pathway as measured by reflection spectrometry, 4) redox state of NAD(P) as measured by surface-emitted fluorescence, and 5) fatty acid activation and beta-oxidation activities in IBAT homogenate. In streptozotocin-diabetic rats, IBAT was atrophied (DNA content unmodified, protein and lipid content decreased). The basal and NE-stimulated total heat production rates showed a 75% and 56% decrease, respectively. The specific activity of fatty acid beta-oxidation as measured by flavoprotein redox state or enzymatically was decreased by 52% and 59%, respectively. The basal redox level of NAD(P) was about 3 times higher than in the controls and NE stimulation resulted in oxidation in contrast to the reduction observed in control tissues. These results show that the metabolic capacity of IBAT from streptozotocin-diabetic rats is decreased and further suggest that the reduced capacity for beta-oxidation contributes significantly to the metabolic alteration.

Energy economy hampers body weight loss after gastric bypass.

The impact of energy economy on body weight loss was investigated in 20 obese women, submitted to Roux-en-Y gastric bypass. Resting energy expenditure (REE), substrate oxidation rates, plasma glucose, free fatty acid, and insulin and leptin levels were measured before and 3, 6, and 12 months after surgery. Predicted REE was obtained from linear regression analysis of REE and fat free mass, in a group of 85 women, whose body mass index ranged between 20 and 60 kg/m(2). The deviation from predicted REE, calculated as area under the curve (AUC) over the 12-month period for each patient, was considered as the expression of energy economy. Energy economy AUC was significantly (P: < 0.005) negatively related to the weight lost during 12 months after surgery. Energy intake, calculated from self-reported food consumption, was also expressed as AUC. Energy intake AUC showed a significant (P: < 0.002) positive correlation with weight loss. Lipid oxidation rate, also calculated as AUC, significantly correlated, negatively, with energy economy (P: < 0. 001) and, positively, with energy intake (P: < 0.002). Preoperative leptin values were significantly (P: < 0.01) linked to individual energy economy capacity. In conclusion, after Roux-en-Y gastric bypass, energy economy hampers the weight loss process, probably through a low fat oxidation rate.