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Biomedical subjects

F Rohner-Jeanrenaud

Publications and source records attributed to F Rohner-Jeanrenaud.

At least 37 records · Page 2Linked to original sources

Induction of obesity and hyperleptinemia by central glucocorticoid infusion in the rat.

It has been claimed that factors favoring the development or maintenance of animal or human obesity may include increases in glucocorticoid production or hyperresponsiveness of the hypothalamic-pituitary-adrenal axis. In normal rats, glucocorticoids have been shown to be necessary for chronic intracerebroventricular infusion of neuropeptide Y to produce obesity and related abnormalities. Conversely, glucocorticoids inhibited the body weight-lowering effect of leptin. Such dual action of glucocorticoids may occur within the central nervous system, since both neuropeptide Y and leptin act within the hypothalamus. The aim of this study was to determine the effects of glucocorticoids (dexamethasone) given intracerebroventricularly to normal rats on body weight homeostasis and hypothalamic levels of neuropeptide Y and corticotropin-releasing hormone. Continuous central glucocorticoid infusion for 3 days resulted in marked sustained increases in food intake and body weight relative to saline-infused controls. The infusion abolished endogenous corticosterone output and produced hyperinsulinemia, hypertriglyceridemia, and hyperleptinemia, three salient abnormalities of obesity syndromes. Central glucocorticoid infusion also produced a marked decrease in the expression of uncoupling protein (UCP)-1 and UCP-3 in brown adipose tissue and UCP-3 in muscle. Finally, chronic central glucocorticoid administration increased the hypothalamic levels of neuropeptide Y and decreased those of corticotropin-releasing hormone. When the same dose of glucocorticoids was administered peripherally, it resulted in decreases in food intake and body weight, in keeping with the decrease in hypothalamic neuropeptide Y levels. These results suggest that glucocorticoids induce an obesity syndrome in rodents by acting centrally and not peripherally.

Animals↗

Effects of intravenous neuropeptide Y on insulin secretion and insulin sensitivity in skeletal muscle in normal rats.

Intracerebroventricular administration of neuropeptide Y to normal rats induces a syndrome characterised by obesity, hyperinsulinaemia, insulin resistance and over expression of the adipose tissue ob gene. Little is known about the effect of circulating neuropeptide Y on glucose metabolism, insulin secretion and leptin. We therefore aimed to evaluate the effect of an intravenous infusion of neuropeptide Y on glucose disposal, endogenous glucose production, whole body glycolytic flux, and glucose storage as assessed during euglycaemic hyperinsulinaemic clamp. In addition, the insulin-stimulated glucose utilisation index in individual tissues was measured by the 2-deoxy-[1-3H]-glucose technique. The effect of neuropeptide Y on insulin secretion was evaluated by hyperglycaemic clamp. Infusion did not induce any change in endogenous glucose production during basal conditions or at the end of the clamp. Glucose disposal was significantly increased in the rats given neuropeptide Y compared with controls (27.8 +/- 1.3 vs 24.3 +/- 1.6 mg x min(-1) x kg(-1); p < 0.05) as was the glycolytic flux (18.9 +/- 1.6 vs 14.4 +/- 0.8 mg x min(-1) x kg(-1); p < 0.05), while glucose storage was comparable in the two groups. In skeletal muscle, the glucose utilisation index was increased significantly in rats given neuropeptide Y. The glucose utilisation index in subcutaneous and epididimal adipose tissue was not significantly different between the two groups. Plasma leptin was significantly increased by hyperinsulinaemia, but was not affected by neuropeptide Y infusion. Both the early and late phase of the insulin response to hyperglycaemia were significantly reduced by neuropeptide Y. In conclusion neuropeptide Y infusion may increase insulin-induced glucose disposal in normal rats, accelerating its utilisation through the glycolytic pathway. Neuropeptide Y reduces both phases of the insulin response to hyperglycaemia.

Adipose Tissue↗

Chronic central leptin infusion enhances insulin-stimulated glucose metabolism and favors the expression of uncoupling proteins.

Continuous (4 days) intracerebroventricular leptin infusion (12 microg/day) was performed in lean rats, and its hormonometabolic effects were determined. Intracerebroventricular leptin administration did not result in leakage of the hormone into the peripheral circulation. Thus, its effects were elicited by its presence within the central nervous system. Intracerebroventricular leptin infusion produced marked decreases in food intake and body weight gain relative to vehicle-infused fed ad libitum rats. Because decreases in food intake alter hormonometabolic homeostasis, additional control rats pair-fed to the amount of food consumed by leptin-infused ones were included in the study. Intracerebroventricular leptin-infused and vehicle-infused pair-fed rats were characterized, relative to vehicle-infused ad libitum-fed animals, by decreases in body weight and insulinemia and by increases in insulin-stimulated overall glucose utilization and muscle and brown adipose tissue glucose utilization index. Brown adipose tissue uncoupling protein (UCP)1, UCP2, and UCP3 mRNA levels were markedly decreased in pair-fed animals relative to those of fed ad libitum control animals, as were liver and white adipose tissue UCP2 and muscle UCP3 mRNA levels. In marked contrast, intracerebroventricular leptin administration was accompanied by the maintenance of high UCP1, UCP2, and UCP3 expression in all these tissues. Thus, despite analogies between leptin's effects and those of pair-feeding with regard to glucose handling, their respective underlying mechanisms differ. While leptin maintains or favors energy-dissipating mechanisms (UCP1, UCP2, and UCP3), the latter are markedly depressed in pair-fed rats. This effect of leptin may prevent subsequent excessive storage processes, thereby maintaining normal body homeostasis.

Adipose Tissue, Brown↗

[From Claude Bernard to the regulatory system between the hypothalamus and the periphery: implications for homeostasis of body weight and obesity].

The concept of interrelationships between the central nervous system and the periphery aimed at maintaining normal body weight homeostasis has been strengthened by the discovery of hypothalamic neuropeptide Y (NPY) and adipose tissue leptin. NPY, when infused intracerebroventricularly in normal animals produces hyperphagia and hormono-metabolic changes (hyperinsulinemia, hypercorticism) channeling nutrients preferentially toward lipogenesis and storage in adipose tissue and away from their utilization by muscles (muscle insulin resistance). Storage in NPY-infused rats is further favored by the observed decrease in the expression of uncoupling proteins. NPY-induced hyperinsulinemia and hypercorticosteronemia also promote leptin over-secretion. Released leptin, acting within the hypothalamus, decreases hypothalamic NPY levels (probably those of other hypothalamic neuropeptides as well), food intake, insulinemia, insulin sensitivity of white adipose tissue, while increasing that of muscles. Leptin acting centrally additionally favors the expression of uncoupling protein 1, 2, and 3, in keeping with an eflect on energy dissipating mechanisms. The respective hormono-metabolic eflects of NPY and leptin maintain a normal body homeostasis. In most obesity syndromes, the functional relationships between NPY and leptin are altered. Due to hypothalamic leptin receptor mutations or dysfunctions, leptin cannot exert its eflects: NPY levels (possibly those of other neuropeptides) remain elevated, maintaining excess storage, insulin as well as leptin resistance.

Adipose Tissue↗

Direct effects of leptin on brown and white adipose tissue.

Leptin is thought to exert its actions on energy homeostasis through the long form of the leptin receptor (OB-Rb), which is present in the hypothalamus and in certain peripheral organs, including adipose tissue. In this study, we examined whether leptin has direct effects on the function of brown and white adipose tissue (BAT and WAT, respectively) at the metabolic and molecular levels. The chronic peripheral intravenous administration of leptin in vivo for 4 d resulted in a 1.6-fold increase in the in vivo glucose utilization index of BAT, whereas no significant change was found after intracerebroventricular administration compared with pair-fed control rats, compatible with a direct effect of leptin on BAT. The effect of leptin on WAT fat pads from lean Zucker Fa/ fa rats was assessed ex vivo, where a 9- and 16-fold increase in the rate of lipolysis was observed after 2 h of exposure to 0.1 and 10 nM leptin, respectively. In contrast, no increase in lipolysis was observed in the fat pads from obese fa/fa rats, which harbor an inactivating mutation in the OB-Rb. At the level of gene expression, leptin treatment for 24 h increased malic enzyme and lipoprotein lipase RNA 1.8+/-0.17 and 1.9+/-0.14-fold, respectively, while aP2 mRNA levels were unaltered in primary cultures of brown adipocytes from lean Fa/fa rats. Importantly, however, no significant effect of leptin was observed on these genes in brown adipocytes from obese fa/fa animals. The presence of OB-Rb receptors in adipose tissue was substantiated by the detection of its transcripts by RT-PCR, and leptin treatment in vivo and in vitro activated the specific STATs implicated in the signaling pathway of the OB-Rb. Taken together, our data strongly suggest that leptin has direct effects on BAT and WAT, resulting in the activation of the Jak/STAT pathway and the increased expression of certain target genes, which may partially account for the observed increase in glucose utilization and lipolysis in leptin-treated adipose tissue.

Adipocytes↗

Chronic central neuropeptide Y infusion in normal rats: status of the hypothalamo-pituitary-adrenal axis, and vagal mediation of hyperinsulinaemia.

Neuropeptide Y in the hypothalamus is a potent physiological stimulator of feeding, and may contribute to the characteristic metabolic defects of obesity when hypothalamic levels remain chronically elevated. Since corticosterone and insulin are important regulators of fuel metabolism, the longitudinal effects of chronic (6 days) intracerebroventricular infusion of neuropeptide Y in normal rats on the hypothalamo-pituitary-adrenal axis and on insulin secretion were studied. Neuropeptide Y-infused rats were either allowed to eat ad libitum, or were pair-fed with normophagic control rats. Neuropeptide Y increased the basal plasma concentrations of adrenocorticotropic hormone and corticosterone during the first 2 days of its intracerebroventricular infusion and increased cold stress-induced plasma adrenocorticotropic hormone concentrations. After 4-6 days of central neuropeptide Y infusion, however, basal plasma adrenocorticotropic hormone and corticosterone concentrations were no different from control values (except in ad libitum-fed rats in which corticosteronaemia remained elevated), they were unaffected by the stress of cold exposure, and the hypothalamic content of corticotropin-releasing factor immunoreactivity was significantly decreased. A state of hyperinsulinaemia was present throughout the 6 days of intracerebroventricular neuropeptide Y infusion, being more marked in the ad libitum-fed than in the pair-fed group. The proportions of insulin, proinsulin, and conversion intermediates in plasma and pancreas were unchanged. Hyperinsulinaemia of the pair-fed neuropeptide Y-infused rats was accompanied by muscle insulin resistance and white adipose tissue insulin hyperresponsiveness, as assessed by the in vivo uptake of 2-deoxyglucose. Finally, bilateral subdiaphragmatic vagotomy prevented both the basal and the marked glucose-induced hyperinsulinaemia of animals chronically infused with neuropeptide Y, demonstrating that central neuropeptide Y-induced hyperinsulinaemia is mediated by the parasympathetic nervous system.

Adipose Tissue↗

Lactate infusion in anesthetized rats produces insulin resistance in heart and skeletal muscles.

Plasma lactate is elevated in many physiological and pathological conditions, such as physical exercise, obesity, and diabetes, in which a reduction of insulin sensitivity is also present. Furthermore, an increased production of lactate from muscle and adipose tissue together with increased gluconeogenic substrate flux to the liver plays a primary role in enhancing hepatic glucose production (HGP) in diabetes. It has been shown that lactate may interfere with the utilization and oxidation of other substrates such as free fatty acids (FFAs). The aim of this study was to investigate if lactate infusion affects peripheral glucose utilization in rats. Animals were acutely infused with lactate to achieve a final lactate concentration of 4 mmol/L. They were then submitted to a euglycemic-hyperinsulinemic clamp to study HGP and overall glucose metabolism (rate of disappearance [Rd]). At the end of the clamp, a bolus of 2-deoxy-[1-3H]-glucose was injected to study insulin-dependent glucose uptake in different tissues. The results show that lactate infusion did not affect HGP either in the basal state or at the end of clamp, whereas glucose utilization significantly decreased in lactate-infused rats (26.6 +/- 1.1 v 19.5 +/- 1.4 mg.kg-1.min-1, P < .01). A reduction in the tissue glucose utilization index was noted in heart (18.01 +/- 4.44 v 46.21 +/- 6.51 ng.mg-1.min-1, P < .01), diaphragm (5.56 +/- 0.74 v 9.01 +/- 0.93 ng.mg-1.min-1, P < .01), soleus (13.62 +/- 2.29 v 34.05 +/- 6.08 ng.mg-1.min-1, P < .01), and red quadricep (4.43 +/- 0.73 v 5.88 +/- 0.32 ng.mg-1.min-1, P < .05) muscle in lactate-infused animals, whereas no alterations were observed in other muscles or in adipose tissue. Therefore, we suggest that acute lactate infusion induces insulin resistance in the heart and some muscles, thus supporting a role for lactate in the regulation of peripheral glucose metabolism.

Adipose Tissue↗

Energy expenditure and substrates oxidative patterns, after glucose, fat or mixed load in normal weight subjects.

OBJECTIVES: To evaluate energy balance after three isocaloric oral loads of different composition and to establish possible relationships between the substrates oxidative patterns and the modifications of insulin and free fatty acids (FFA) plasma profiles. DESIGN: Each subject received, in a randomized order, three oral loads of 2658 +/- 45 kJ (636 +/- 11 Kcal) either as glucose, lipids (cream) or a mixture (glucose+cream). SETTING: The experiments were performed at the University Hospital of Geneva. SUBJECTS: Ten normal body-weight volunteers. METHODS: Energy expenditure (EE) and substrates oxidation were measured by indirect calorimetry during 8 h following each load. Plasma glucose, insulin and FFA were also measured. RESULTS: EE was 1776 +/- 107, 1818 +/- 125 and 1785 +/- 117 KJ over 8 h after glucose, mixed and lipids load, respectively. Glucose oxidation was the highest after oral glucose as compared to mixed and lipids load, while the highest value of lipids oxidation was measured after fat load. A significant relationship linked fat oxidation to plasma FFA (r = 0.54, P < 0.002) as well as to insulin (r = -0.40, P < 0.002). CONCLUSIONS: (a) The energetic cost of glucose and fat intake is the same; (2) after each load, the main source of energy corresponds to the substrate administered; (3) both plasma insulin and FFA influence the substrate oxidative patterns observed after each load; (4) alimentary fat may contribute to fat oxidation by maintaining elevated plasma FFA levels.

Aged↗

Adrenalectomy prevents the obesity syndrome produced by chronic central neuropeptide Y infusion in normal rats.

Neuropeptide Y (NPY) in the hypothalamus plays an important role in the regulation of food intake and body weight and seems to be implicated in the etiology of obesity. When intracerebroventricularly (ICV) infused for 6 days in normal rats, NPY resulted in hyperphagia, increased body weight gain, hyperinsulinemia, hypercorticosteronemia, and hypertriglyceridemia compared with vehicle-infused control rats. NPY infusion also resulted in an insulin-resistant state in muscles and in a state of insulin hyperresponsiveness in white adipose tissue, as assessed by the measurement of the in vivo glucose utilization index of these tissues during euglycemic-hyperinsulinemic clamps. All of these hormono-metabolic effects produced by chronic central NPY infusion were completely prevented when rats were adrenalectomized before NPY administration. Adrenalectomy per se had no effect on any of the parameters mentioned above. The levels of mRNA for the obese gene were increased in white adipose tissue after 6 days of ICV NPY infusion in normal rats, and white adipose tissue weight was also increased. These effects of ICV NPY infusion were markedly decreased by prior adrenalectomy, although NPY infusion was able to somewhat enhance the low white adipose tissue obese mRNA levels and tissue weight of adrenalectomized rats. In conclusion, intact adrenal glands, and probably circulating corticosterone in particular, are necessary for the establishment of most of the hormonal and metabolic effects induced by chronic ICV infusion of NPY in normal rats.

Adipose Tissue↗

Glucocorticoids as counterregulatory hormones of leptin: toward an understanding of leptin resistance.

The product of the ob gene, leptin, is a hormone secreted by adipose tissue that acts in the hypothalamus to regulate the size of the body fat depot. Its central administration has been shown to decrease food intake and body weight, while favoring energy dissipation. As glucocorticoids are known to play a permissive role in the establishment and maintenance of obesity syndromes in rodents, it was hypothesized that they do so by restraining the effect of leptin. Leptin injected intracerebroventricularly as a bolus of 3 microg in normal rats induced modest reductions in body weight and food intake. In marked contrast, the same dose of leptin had very potent and long-lasting effects in decreasing both body weight and food intake when administered to adrenalectomized rats. Further, glucocorticoid supplementation of adrenalectomized rats dose-dependently inhibited these potent effects of leptin. These data suggest that glucocorticoids play a key inhibitory role in the action of leptin. Under normal conditions, this inhibitory influence of glucocorticoids may prevent lasting hypophagia. In obesity with degrees of hypercorticism, it may contribute to "leptin resistance," whose etiology is still little understood.

Adrenalectomy↗

Intracerebroventricular administration of neuropeptide Y to normal rats increases obese gene expression in white adipose tissue.

The aim of this work was to determine the possible inter-relationship between neuropeptide Y (NPY, a hypothalamic stimulator of feeding) and adipose tissue expression of the ob protein (a novel potent inhibitor of feeding). Such a relationship could be of importance in the maintenance of normal body weight. To this end, normal rats were intracerebroventricularly (i.c.v.) infused for 6 days with NPY. NPY infusion resulted in hyperphagia and a marked increase in adipose tissue ob mRNA levels. The effect of NPY on ob expression persisted when hyperphagia was prevented by pair-feeding, and was reversed following cessation of NPY infusion. Basal and glucose-stimulated insulinaemia were increased by i.c.v. NPY infusion compared to control values, regardless of whether animals were ad libitum-fed or pair-fed. Cessation of NPY infusion was accompanied by normalisation of insulinaemia. These changes in insulinaemia produced by i.c.v. NPY infusion paralleled the observed changes in ob expression. When normal rats were made hyperinsulinaemic-euglycaemic for 24 h, such hyperinsulinaemia also resulted in increased ob mRNA levels in white adipose tissue. This suggested that NPY-induced hyperinsulinaemia could be responsible for the upregulation of ob mRNA levels of NPY-infused rats. It is concluded that central (i.c.v.) NPY infusion increases adipose tissue ob expression, a functional relationship that is linked, at least in part, via NPY-induced hyperinsulinaemia.

Adipose Tissue↗

The loop system between neuropeptide Y and leptin in normal and obese rodents.

Over the years, the work of research laboratories in Baton Rouge (USA), Seattle (USA) and Geneva (Switzerland) have reached analogous conclusions regarding the main etiology of obesity as studied in animals: it largely lies within the brain, notably within the hypothalamus. The hypothalamus is indeed known to modulate food intake and energy partitioning, while the periphery has also been proposed to feed-back on the central nervous system (CNS) to provide information on the state of body energy stores, the two together constituting a loop system connecting the brain to the periphery (1,2,3). This etiologic viewpoint of a pivotal role of the hypothalamus in obesity syndromes has been strengthened by the discovery of one hypothalamic neuropeptide and one peripheral (adipose tissue) hormone, respectively neuropeptide Y (4), and quite particularly, leptin (5). As neuropeptide Y produces hyperphagia (6, 7) and as leptin produces hypophagia in normal animals (8,9,10), the loop system just mentioned was thought to comprise functional relationships, at least between these two factors. Other evidence also suggested that such a loop system was altered in obese animals.

Animals↗

Acute intracerebroventricular administration of neuropeptide Y stimulates corticosterone output and feeding but not insulin output in normal rats.

The effect of acute intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) on basal and glucose- or arginine-stimulated insulinemia was studied in anesthetized and conscious rats. Basal insulinemia was not significantly increased relative to control values after NPY injection. The insulinemic response to an intravenous bolus of glucose or arginine was unaffected by prior NPY injection, glycemic profiles being identical in control and NPY-injected rats. Plasma NPY concentrations were double the corresponding control values at 20 min after i.c.v. NPY injection, but this difference was not statistically significant. Although peripheral NPY inhibits insulin secretion, these elevated plasma NPY concentrations occurred too late to explain the lack of effect of i.c.v. NPY on substrate-induced insulin secretion. Compared to control rats, marked increases in corticosteronemia were observed after i.c.v. NPY injection in conscious animals. When allowed to eat ad libitum at the end of each experiment, NPY-injected rats consumed significantly more chow in 20 min than controls. We conclude that although acute i.c.v. injection of a maximum dose of NPY had definite effects on plasma corticosterone concentrations and feeding, it favored neither the basal nor the substrate-induced insulin output.

Anesthesia, General↗

The weight-reducing effect of an intracerebroventricular bolus injection of leptin in genetically obese fa/fa rats. Reduced sensitivity compared with lean animals.

The effect of different doses of leptin, given as an intracerebroventricular (ICV) bolus, on body weight gain and food intake was investigated during refeeding, following a 24-h fast in lean (FA/fa) rats. It was observed that ICV leptin resulted in a dose-dependent decrease in body weight gain, compared with vehicle injection, a difference that persisted for at least 6 days. This was associated with a transient reduction in food intake over the first 2 days after leptin injection. More importantly, the effect of leptin was also observed in genetically obese fa/fa rats but at the expense of two to ten times higher leptin concentrations, indicating the presence of decreased leptin sensitivity. Furthermore, ICV leptin injections were able to decrease neuropeptide Y (NPY) levels in the arcuate and paraventricular hypothalamic nuclei in both lean and genetically obese fa/fa rats, although a higher leptin dose was again needed in the obese group. These observations provide further evidence for the implication of NPY and leptin in a regulatory loop controlling body homeostasis. This loop is functional in lean and genetically obese fa/fa rats, provided that leptin levels in the central nervous system are high enough in the obese group, in particular. Since human obesity is frequently associated with elevated circulating leptin levels, a state of decreased leptin sensitivity (i.e., leptin resistance), similar to that described here in fa/fa rats, could possibly occur in human syndromes as well.

Animals↗

Four-day hyperinsulinemia in euglycemic conditions alters local cerebral glucose utilization in specific brain nuclei of freely moving rats.

Although insulin is a well known regulator of peripheral tissue glucose metabolism, there is little agreement over its effects on brain glucose metabolism. Several investigators report that peripheral insulin may enter the brain via several routes. The presence of insulin receptors specific to brain, coupled to diverse reports of the effect of acute insulin administration on brain glucose use, led us to carry out a 4-day hyperinsulinemic euglycemic clamp in freely moving rats with subsequent labelled 2-deoxyglucose metabolic mapping studies. It was found that after 4 days of peripheral insulin infusion, several brain regions (Anterior Hypothalamic area, Suprachiasmatic nucleus, Basolateral Amygdaloid nucleus, Supramammillary bodies, Medial Geniculate nucleus and Locus Coeruleus) had an altered local cerebral glucose utilization. Upon subsequent analysis of their anatomical and functional connections it is proposed that insulin may regulate an integrated circuit of pathways within the central nervous system.

Animals↗

Effect of sustained physiological hyperinsulinaemia on hypothalamic neuropeptide Y and NPY mRNA levels in the rat.

Neuropeptide Y (NPY) synthesized in the arcuato-paraventricular projection in the rat hypothalamus is thought to play an important role in controlling energy homeostasis. The factors that regulate hypothalamic NPY are not known but, amongst others, insulin has been postulated as an inhibitory modulatory agent. To test this hypothesis, normal male rats were given either insulin (2 units/day) or saline via subcutaneous osmotic minipumps for 3 days. Euglycaemia was maintained by a concomitant glucose infusion in insulin-infused rats which had peripheral insulin levels 5-8 times higher than saline-infused controls. Hyperinsulinaemic rats ate 42% less than controls, but their total energy intake (food intake plus glucose infusion) was higher than that of controls, and they gained more weight than controls during the experimental period. Hyperinsulinaemia had no significant effect on hypothalamic NPY mRNA or NPY levels in the arcuate nucleus. NPY concentrations in the paraventricular nucleus were, however, significantly increased by 73% in hyperinsulinaemic rats, but were closely similar to controls in all other areas. Insulin may act as a satiety factor in that hyperinsulinaemic rats ate less, but the fact that these animals had increased total energy intake and gained excessive weight suggests that insulin may not function as an overall regulator of energy balance. In addition, physiological hyperinsulinaemia does not apparently inhibit NPY gene expression in the arcuate nucleus. Due to the lack of effect of hyperinsulinaemia on NPY synthesis in the arcuate nucleus, the elevated NPY concentrations in the paraventricular nucleus could result from a reduction of its release, which would be in keeping with the reduction in food intake.

Analysis of Variance↗