Site-specific differences in the action of NRTI drugs on adipose tissue incubated in vitro with lymphoid cells,and their interaction with dietary lipids

Existing theories of the origin of HIV-related adipose tissue redistribution syndrome cannot adequately explain simultaneous hypertrophy of certain depots and atrophy of others, or its occasional occurrence in untreated HIV infection. These experiments explore the hypothesis that hypertrophy of lymphoid tissue-containing adipose depots arises from drug-induced disruption to local interactions between perinodal adipocytes and activated lymphoid cells. Guinea pigs were fed on plain or lipid-supplemented (10% suet, sunflower or fish oil) chow ad libitum or restricted, and the popliteal lymph nodes were activated by repeated injection of lipopolysaccharide. Explants of perinodal and other samples from popliteal, mesentery, omentum and nodeless perirenal and epididymal depots were incubated with lymphoid cells and zidovudine, didanosine, lamivudine or stavudine at physiological concentrations (0.1-1 microg/ml) or interleukin-10 and interleukin-6, and basal and maximum lipolysis was measured. All drugs increased lipolysis from perinodal adipocytes, especially mesenteric, though less than exogenous cytokines. Effects on adipocytes from non-perinodal sites and nodeless depots were minimal. The sunflower-oil diet enhanced, and the fish-oil and restricted diets reduced, these effects. We conclude that these NRTI antiretroviral drugs modulate the local interactions between perinodal adipocytes and activated lymphoid cells. Local interactions, and hence the selective hypertrophy of node-containing adipose depots, may be curtailed by dietary manipulation.     

The activation of the adipose tissue associated with lymph nodes during the early stages of an immune response

The effects of repeated local immune challenges with lipopolysaccharide (LPS) over 24 h on basal and noradrenaline-stimulated lipolysis and the development of sensitivity to interleukin-4 and tumour necrosis factor-alpha in adipocytes associated with lymph nodes were studied in adult guinea-pigs. Properties characteristic of perinodal adipocytes appeared in adipocytes at least 10 mm from the locally stimulated popliteal lymph node within 12 h, and in other node-containing depots over 24 h. All effects appeared first in perinodal adipocytes and spread as though in response to signals emanating from the enclosed lymph node. The popliteal depot was more completely activated than the mesenteric, but its maximum rate of lipolysis/100 adipocytes was lower. None of the pre-treatments in vivo, nor incubation with cytokines in vitro modulated lipolysis in adipocytes from the nodeless perirenal depot. The sensitivity of the perinodal adipocytes to cytokines changed within 3 h of immune stimulation, preceding detectable increases in lipolysis. Cytokine-stimulated and noradrenaline-stimulated lipolysis sum, suggesting separate pathways. We conclude that sustained local activation of a single popliteal lymph node recruits additional adipocytes in node-containing depots only. Signals spread from lymph nodes to surrounding adipocytes, but the time courses of activation of adipocytes and their maximum responses differ between the mesenteric and popliteal depots.     

Interactions of noradrenalin and tumour necrosis factor alpha, interleukin 4 and interleukin 6 in the control of lipolysis from adipocytes around lymph nodes.

The contributions of inflammatory and immunosuppressive cytokines and noradrenalin to the control of lipolysis in adipocytes surrounding and remote from lymph nodes were investigated in healthy adult guinea-pigs. A few hours after excision from fasting animals, spontaneous lipolysis in adipocytes from around the popliteal and mesenteric lymph nodes and omental "milky spots" was significantly lower than in those from elsewhere in the same depots, and much lower than in perirenal, epididymal or parametrial adipocytes. The perinodal adipocytes were consistently more sensitive to noradrenalin at 10(-8), 10(-7)and 10(-5) M, and their maximum rate of lipolysis was higher. They also responded more strongly to pre-incubation for 24 h with tumour necrosis factor alpha interleukin 6 and interleukin 4 than those elsewhere in the same depots. Tumour necrosis factor alpha and interleukin 6 applied alone stimulated lipolysis, but combined with interleukin 4, they suppressed glycerol release, especially in perinodal adipocytes, thereby creating large within-depot differences. These cytokines had minimal effects on lipolysis in perirenal or gonadal adipocytes.The authors conclude that adipocytes surrounding lymph nodes contribute little to whole-body energy supply during fasting, but are more sensitive than all others to cytokines and to noradrenalin, having higher maximum but lower minimum rates of lipolysis. These properties equip perinodal adipocytes for local interactions with lymphoid tissue.     

Adipose tissue and the immune system

Adipocytes anatomically associated with lymph nodes (and omental milky spots) have many special properties including fatty acid composition and the control of lipolysis that equip them to interact locally with lymphoid cells. Lymph node lymphocytes and tissue dendritic cells acquire their fatty acids from the contiguous adipocytes. Lymph node-derived dendritic cells suppress lipolysis in perinodal adipocytes but those that permeate the adipose tissue stimulate lipolysis, especially after minor, local immune stimulation. Inflammation alters the composition of fatty acids incorporated into dendritic cells, and that of node-containing adipose tissue, counteracting the effects of dietary lipids. Thus these specialised adipocytes partially emancipate the immune system from fluctuations in the abundance and composition of dietary lipids. Prolonged, low-level immune stimulation induces the local formation of more adipocytes, especially adjacent to the inflamed lymph node. This mechanism may contribute to hypertrophy of the mesentery and omentum in chronic inflammatory diseases such as HIV-infection, and in smokers. Paracrine interactions between adipose and lymphoid tissues are enhanced by diets rich in n-6 fatty acids and attentuated by fish oils. The latter improve immune function and body conformation in animals and people. The partitioning of adipose tissue in many depots, some specialised for local, paracrine interactions with other tissues, is a fundamental feature of mammals.     

Adipose tissue,the immune system and exercise fatigue: how activated lymphocytes compete for lipids

Adipose depots that contain lymph nodes, and probably intermuscular fat in skeletal and cardiac muscle, are specialized to provision adjacent tissue in a paracrine mode. Perinodal adipocytes respond selectively to various cytokines and incorporate proportionately more polyunsaturated fatty acids. Lipolysis in the adipocytes of node-containing depots can be stimulated via inflammation of the enclosed lymph nodes. Repeated immune stimulation elicits properties characteristic of perinodal adipocytes in those elsewhere in the same depot, and hours later in other node-containing depots, but not in nodeless depots. Such site-specific properties of adipose tissue enable partitioning of dietary and metabolic supplies of fatty acids between competing tissues. Local interactions emancipate the peripheral immune system from competing with other tissues for lipids during immune responses, and may be especially important during periods of high demand, such as strenuous exercise. Biopsies of subcutaneous adipose tissue from sites remote from lymph nodes do not adequately represent the composition of fatty acids available to the immune system in situ, and perhaps that supplied to other tissues. Intermuscular fat in skeletal and cardiac muscle may also indicate paracrine relationships between adipocytes and "end-user" tissues. The concept of paracrine interactions between certain adipocytes and "user" tissue may account for the widespread contiguity between these tissues in vivo.     

The early postnatal development of the primary immune response in TNP-KLH-stimulated popliteal lymph node in the rat

Summary The popliteal lymph nodes were removed from young rats of various ages five days after a single immunization with TNP-KLH in the hind footpads. Cryostat sections of the lymph nodes were investigated by means of enzyme and immunohistochemical techniques at the light-microscopical level.The presence and localization of anti-TNP antibody-containing cells were examined using a new technique to visualize specific antibodies. Moreover, the development of the lymph nodes following exogenous antigenic stimulation was compared with that of unstimulated lymph nodes.Specific antibody-containing cells could not be found before day 15 after birth, in rats immunized at day 10. From that time these lymphoid cells were located primarily at the border between cortex and medulla. Younger popliteal lymph nodes showed only aspecific immunoglobulin-containing lymphoid cells. With age, the number of specific antibody-containing cells tended to increase. These cells were more mature, according to morphological criteria and were located nearer the medulla.The first primary follicles were seen at day 19, as was the case in unstimulated animals. The first secondary follicles, containing germinal centers, were detected at day 23, whereas in unstimulated popliteal lymph nodes they were never found.Trapping of immune complexes could not be demonstrated before day 33 after birth. The later appearance of this phenomenon might be a consequence of the techniques applied to demonstrate specific antibody-containing cells.Abbreviations PLN popliteal lymph node - FDC follicular dendritic cell - IDC interdigitating cell - HEV high endothelial venule - TNP trinitrophenyl - KLH keyhole limpet hemocyanin - PBS phosphate-buffered saline - GCPC germinal center precursor cell - sIg surface immunoglobulin - cIg cytoplasmic immunoglobulin     

Paracrine interactions of mammalian adipose tissue

Adipose tissue develops in and/or around most lymphoid tissues in mammals and birds. Early reports of this widespread association and hypotheses for its functional basis were long ignored in the planning of in vitro studies and the interpretation of in vivo results. Biochemical studies on rodent tissues reveal many site-specific properties of adipocytes anatomically associated with lymph nodes and omental milky spots that equip them to interact locally with lymphoid cells. The paracrine interactions are strongest for the most readily activated lymph nodes and are modulated by dietary lipids. Perinodal adipocytes contribute less than those in the large nodeless depots to whole-body lipid supplies during fasting. Observations on wild animals show that perinodal adipose tissue is selectively conserved even in starvation but does not enlarge greatly in natural obesity. Such paracrine provisioning of peripheral immune responses improves their efficiency and emancipates activated lymphocytes from competition with other tissues for blood-borne nutrients. The relationship is found in extant protherians and metatherians, so it almost certainly arose early in the evolution of mammals, possibly as part of the metabolic reorganisation associated with homeothermy, viviparity, and lactation. Prolonged disruption to paracrine interactions between lymphoid and adipose tissue may contribute to the HIV-associated adipose redistribution syndrome, causing selective hypertrophy of the mesentery, omentum, and other adipose depots that contain much activated lymphoid tissue. Skeletal and cardiac muscle may also have paracrine relationships with anatomically associated adipose tissue, but interactions between contiguous tissues have not been demonstrated directly.     

Mature adipocytes and perivascular adipose tissue stimulate vascular smooth muscle cell proliferation: effects of aging and obesity

Adipocytes and perivascular adipose tissue are emerging as regulators of vascular function. The effects of adipocytes and perivascular adipose tissue on human smooth muscle cell (SMC) proliferation were investigated. Conditioned medium was prepared from cultured premature and differentiated 3T3-L1 adipocytes and from periaortic adipose tissue from young (3 mo) and old (24 mo) Wistar-Kyoto (WKY) rats, lean and obese Zucker rats (3 mo), and WKY rats fed normal chow or a high-fat diet for 3 mo. Conditioned medium from differentiated (but not premature) adipocytes stimulated SMC proliferation, which was abolished by charcoal and proteinase K treatment but was resistant to heat, trypsin, or phospholipase B (to hydrolyze lysophosphatidic acid). Further experiments demonstrated that the growth factor(s) are hydrosoluble and present in the fraction of molecular mass >100 kDa. Moreover, conditioned medium from periaortic adipose tissue stimulated SMC proliferation, which was significantly enhanced in aged rats and in rats fed a high-fat diet but not in obese Zucker rats deficient in functional leptin receptors. In conclusion, mature adipocytes release hydrosoluble protein growth factor(s) with a molecular mass >100 kDa for SMCs. Perivascular adipose tissue stimulates SMC proliferation, which is enhanced in aged WKY and in high-fat, diet-induced obesity but not in leptin receptor-deficient obese Zucker rats. These adipocyte-derived growth factor(s) and the effect of perivascular adipose tissue may be involved in vascular disease associated with aging and obesity.     

Effect of fat pre-feeding on bile flow and composition in the rat

Studies were conducted in rats to determine if the increase in lymph triacylglycerol output on pre-feeding a 20% glyceryltrioleate diet (Mansbach, C.M., II and Arnold, A. (1986) Am. J. Physiol. 251, G263-269) was due to an increase in phosphatidylcholine output into bile. Rats who were fed chow or pre-fed the 20% fat diet were equipped with biliary and duodenal cannulas and infused with glucose-saline while bile was collected hourly. The next day a taurocholate-glyceryltrioleate infusion was given and bile collected for 5 h. Bile flow, bile acid, phosphatidylcholine and cholesterol output were greater in the chow fed group than controls during the 6 h of the glucose saline period. Outputs were low overnight. During the taurocholate-glyceryltrioleate infusion, bile flow, bile acid, phosphatidylcholine and cholesterol output were all greater in the fat pre-fed group than the chow fed controls. We conclude that fat pre-feeding profoundly influences biliary composition and flow. The 2-fold increase in biliary phosphatidylcholine output during duodenal lipid infusion offers a potential explanation for the increased delivery of triacylglycerol into the lymph in rats on a similar fat pre-feeding program.     

Endothelial cell specific molecule-1--a newly identified protein in adipocytes.

Expression of the endothelial cell-specific molecule (ESM)-1 was originally identified in lung and kidney endothelial cells, where its expression is regulated by cytokines. In vitro, ESM-1 interferes with the molecular mechanisms of immune cell migration by binding to adhesion molecules. In this study, we have explored the expression of ESM-1 in isolated human adipocytes and in rat adipose tissue depots. Human primary adipocytes were cultivated after collagenase digestion and used for in vitro incubation studies. Adipocytes were also isolated from different fat depots of Sprague-Dawley rats. Gene expression was quantified by TaqMan RT-PCR using specific human and rat ESM-1 primers. The cellular localisation of ESM-1 was determined by confocal microscopy using a specific antibody. ESM-1 expression in human adipocytes was stimulated by phorbol ester, an activator of protein kinase C, and by retinoic acid, an activator of nuclear receptors. The maximum increase in gene expression was 3.2-fold after 72 h treatment with phorbol ester and 4.6-fold after 72 h treatment with retinoic acid. The highest expression was found in subcutaneous rat adipose tissue - two-fold compared to epididymal and six-fold compared to intrascapular brown adipose tissue. As obesity is related to systemic inflammation (examplified by increased circulating levels of C-reactive protein and interleukin-6), the formation of ESM-1 in adipocytes and its activation by protein kinase C may play a role in the regulation of inflammatory processes.     

Influence of dietary macronutrient composition on adiposity and cellularity of different fat depots in Wistar rats

The aim of this study was to investigate the role of dietary macronutrient content on adiposity parameters and adipocyte hypertrophy/hyperplasia in subcutaneous and visceral fat depots from Wistar rats using combined histological and computational approaches. For this purpose, male Wistar rats were distributed into 4 groups and were assigned to different nutritional interventions: Control group (chow diet); high-fat group, HF (60% E from fat); high-fat-sucrose group, HFS (45% E from fat and 17% from sucrose); and high-sucrose group, HS (42% E from sucrose). At day 35, rats were sacrificed, blood was collected, tissues were weighed and fragments of different fat depots were kept for histological analyses with the new softwareAdiposoft. Rats fed with HF, HFS and HS diets increased significantly body weight and total body fat against Control rats, being metabolic impairments more pronounced on HS rats than in the other groups. Cellularity analyses usingAdiposoft revealed that retroperitoneal adipose tissue is histologically different than mesenteric and subcutaneous ones, in relation to bigger adipocytes. The subcutaneous fat pad was the most sensitive to the diet, presenting adipocyte hypertrophy induced by HF diet and adipocyte hyperplasia induced by HS diet. The mesenteric fat pad had a similar but attenuated response in comparison to the subcutaneous adipose tissue, while retroperitoneal fat pad only presented adipocyte hyperplasia induced by the HS diet intake after 35 days of intervention. These findings provide new insights into the role of macronutrients in the development of hyperplastic obesity, which is characterized by the severity of the clinical features. Finally, a new tool for analyzing histological adipose samples is presented.     

Effect of fish oil diet on immune response and proteinuria in mice

In this study, we examined the immune response and proteinuria caused by dietary polyunsaturated fatty acids in normal NZW/N and autoimmune NZB/NZW mice. Mice were maintained more than one year on five dietary groups: normal (5% corn oil), calorie-restricted, high fat (20% corn oil), high fat (20% fish oil), and Purina laboratory rodent chow. Normal mice fed with the fish oil diet had a more reduced anti-sheep red blood cells (SRBC) plaque-forming cell (PFC) response and less interleukin-2 (IL-2) enhancement of PFC than did the group with the restricted diet and the young control group. The corn oil (5 and 20%) diet animals also showed reduced PFC response and IL-2 utilization. NZB/NZW mice fed with the fish oil diet showed similar reduced PFC response but had a significantly lower response to IL-2 than did those on the corn oil diets and the restricted diet. The IL-2 production by macrophages from NZW/N mice was reduced in both the fish oil and corn oil diet groups. However, mice fed with the fish oil diet had less proteinuria and good survival rates, similar to the group with the restricted diet. These results suggest that the beneficial effect of the fish oil diet in these animals may be attributed in part to the immunosuppression mechanism.     

Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition.

Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. The aim of the present study was to investigate how enterocytes respond to increased dietary fats of different composition. Rabbits were fed a low fat chow diet, and chow supplemented with sunflower oil (high n-6 polyunsaturated fatty acids), fish oil (high n-3 polyunsaturated fatty acids), or an oil mixture of a composition similar to that of the typical western diet. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil > western diet lipid > fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Enterocytes are replaced rapidly (half-life 1-2 days) by cells which move from the crypts to the tips of the villi, where absorption of nutrients takes place.Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are 'turned-on' to lipid absorption. The results also show that diets of different fatty acid composition vary in their effects.     

Regulation of glucose transport and transporter 4 (GLUT-4) in muscle and adipocytes of sucrose-fed rats: effects of N-3 poly- and monounsaturated fatty acids.

The goal of this study was to compare the short-term effects of dietary n-3 polyunsaturated (fish oil) and monounsaturated (olive oil) fatty acids on glucose transport, plasma glucose and lipid controls in a dietary insulin resistance model using sucrose-fed rats. The underlying cellular and molecular mechanisms were also determined in the muscle and adipose tissue. Male Sprague-Dawley rats (5 weeks old) were randomized for diets containing 57.5 % (w/w) sucrose and 14 % lipids as either fish oil (SF), olive oil (SO) or a mixture of standard oils (SC) for 3 weeks. A fourth control group (C) was fed a diet containing 57.5 % starch and 14 % standard oils. After three weeks on the diet, body weight was comparable in the four groups. The sucrose-fed rats were hyperglycemic and hyperinsulinemic in response to glucose load. The presence of fish oil in the sucrose diet prevented sucrose-induced hyperinsulinemia and hypertriglyceridemia, but had no effect on plasma glucose levels. Insulin-stimulated glucose transport in adipocytes increased after feeding with fish oil (p < 0.005). These modifications were associated with increased Glut-4 protein (p < 0.05) and mRNA levels in adipocytes. In the muscle, no effect was found on Glut-4 protein levels. Olive oil, however, could not bring about any improvement in plasma insulin, plasma lipids or Glut-4 protein levels. We therefore conclude that the presence of fish oil, in contrast to olive oil, prevents insulin resistance and hypertriglyceridemia in rats on a sucrose diet, and restores Glut-4 protein quantity in adipocytes but not in muscle at basal levels. Dietary regulation of Glut-4 proteins appears to be tissue specific and might depend on insulin stimulation and/or duration of dietary interventions.     

In vivo NMR detection of diet-induced changes in adipose tissue composition

We introduce an in vivo spectroscopic method to assess the effects of diet on fatty acid composition of the predominant chemical constituent of adipocytes in mice. To do this, we make use of a nonlinear NMR signal that, unlike a standard NMR signal, is intrinsically insensitive to local magnetic field inhomogeneities and which naturally suppresses the large water signal from nonfatty tissues. Our method yields fat composition information from fat depots distributed over large sample volumes in a single experiment, without requiring the use of tedious shimming procedures, voxel selection, or water suppression. Our results suggest that this method can reveal clear differences in adipose tissue composition of mice fed a standard chow diet compared with mice fed a diet rich in polyunsaturated fatty acids. With further developments this method could be used to obtain information on human lipid composition noninvasively and to track changes in lipid composition induced by diet intervention, pharmaceutical drugs, and exercise.     

Influence of diet form on the hyperphagia-promoting effect of polysaccharide in rats

Adult female rats were fed chow only, or chow plus the polysaccharide Polycose presented as a solution (32% w/v), as a powder, or as a powder mixed into the chow diet. The rats fed the Polycose solution overate and gained three times as much weight as did the control rats in the 30-day test period. The rats fed the Polycose powder or mixed diet, on the other hand, did not differ from controls in food intake or weight gain. The solution-fed rats consumed more Polycose than did the powder-fed rats, but the two groups were equivalent in their chow intake. The absolute and percent body fat of the solution-fed rats exceeded that of control rats, as well as that of powder and mixed-diet animals. The percent body fat of the powder and mixed diet groups exceeded that of the control animals. The findings demonstrate that the form of diet presentation has a major impact on the rat's feeding and body weight responses to polysaccharide diets.     

Comparison of Fat Storage between Fischer 344 and Obesity‐Resistant Lou/C Rats Fed Different Diets**

Objective: We aimed to characterize further the Lou/C (LOU) and Fischer 344 (F344) rat strains for nutritional traits to validate their use as contrasting strains for molecular genetic studies. Research Methods and Procedures: Five batches of LOU and F344 rats were used to measure caloric intake, weight gain, and body composition when fed a chow diet, a self‐selection diet (together with the study of preferences for macronutrients), hypercaloric diets, and a chow diet in a cold environment. Results: Despite a higher caloric intake when fed a chow diet, LOU rats showed a lower weight gain, final body weight, and percentage of fat tissue, together with a higher percentage of carcass weight, than F344 rats. When fed a self‐selection diet, LOU males ingested less protein and more fat than F344 males, and the reverse was observed for females. In this condition, feed efficiency was reduced in LOU but increased in F344 rats compared with the chow diet. Diet‐induced obesity was observed in F344 rats but not in LOU rats fed hypercaloric diets. In a cold environment, both LOU and F344 rats displayed an increased percentage of brown adipose tissue compared with control groups, together with a higher caloric intake. Discussion: The study shows robust nutritional differences between the LOU rat, a lean strain with a low feed efficiency and resistant to diet‐induced obesity, and the contrasting F344 rat strain. It also shows the interest in these strains for studying the genetic components of resistance to obesity.     

Obesity Impairs Lymphatic Fluid Transport and Dendritic Cell Migration to Lymph Nodes

Introduction

Obesity is a major cause of morbidity and mortality resulting in pathologic changes in virtually every organ system. Although the cardiovascular system has been a focus of intense study, the effects of obesity on the lymphatic system remain essentially unknown. The purpose of this study was to identify the pathologic consequences of diet induced obesity (DIO) on the lymphatic system.

Methods

Adult male wild-type or RAG C57B6-6J mice were fed a high fat (60%) or normal chow diet for 8–10 weeks followed by analysis of lymphatic transport capacity. In addition, we assessed migration of dendritic cells (DCs) to local lymph nodes, lymph node architecture, and lymph node cellular make up.

Results

High fat diet resulted in obesity in both wild-type and RAG mice and significantly impaired lymphatic fluid transport and lymph node uptake; interestingly, obese wild-type but not obese RAG mice had significantly impaired migration of DCs to the peripheral lymph nodes. Obesity also resulted in significant changes in the macro and microscopic anatomy of lymph nodes as reflected by a marked decrease in size of inguinal lymph nodes (3.4-fold), decreased number of lymph node lymphatics (1.6-fold), loss of follicular pattern of B cells, and dysregulation of CCL21 expression gradients. Finally, obesity resulted in a significant decrease in the number of lymph node T cells and increased number of B cells and macrophages.

Conclusions

Obesity has significant negative effects on lymphatic transport, DC cell migration, and lymph node architecture. Loss of T and B cell inflammatory reactions does not protect from impaired lymphatic fluid transport but preserves DC migration capacity. Future studies are needed to determine how the interplay between diet, obesity, and the lymphatic system modulate systemic complications of obesity.     

Effects of a new hypoglycemic agent A-4166 on glucose metabolism in rat adipocytes and muscle tissues

The effects of the oral administration of a non-sulfonylurea hypoglycemic agent, the phenylalanine derivative A-4166, on serum insulin and glucose levels and glucose metabolism in isolated rat adipocytes and slices of muscle tissues were studied. An increase in serum insulin and a decrease in glucose levels were observed 30 minutes after A-4166 administration to rats fed basal or high fat diet. No changes in basal glucose transport in isolated fat cells were observed after the administration of A-4166. The effect of in vitro added insulin was, however, stronger in rats fed basal diet and treated with A-4166. An elevation of the membrane glucose transporter GLUT 4 was observed in rats treated with A-4166. An increase of basal lipogenesis, measured by incorporation of radiocarbon labeled glucose into lipids, was noted in adipocytes from rats fed high fat diet. The addition of insulin was followed by stimulation of lipogenesis in rats fed basal diet, however, this hormone had no effect in rats fed high fat diet. The administration of A-4166 did not affect the basal or insulin stimulated lipogenesis. Basal glucose oxidation in the diaphragm was not influenced by high fat diet or by A-4166 treatment. In the soleus muscle, basal glucose oxidation was decreased in rats fed high fat diet, and treatment with A-4166 increased the glucose oxidation up to values observed in the control basal diet fed rats. These results indicate that the administration of A-4166 can affect glucose metabolism in muscle tissue and the sensitivity of adipocytes to insulin.