Compensatory Growth of Adipose Tissue After Partial Lipectomy: Involvement of Serum Factors

Metabolic changes after surgical fat removal: A dose-response meta-analysis

BACKGROUND

Bariatric surgery averts obesity-induced insulin resistance and the metabolic syndrome. By contrast, surgical fat removal is considered merely an esthetic endeavor. The aim of this article was to establish whether surgical fat removal, similar to bariatric surgery, exerts measurable, lasting metabolic benefits.

METHODS

PubMed, Embase, and Scopus were searched using the Polyglot Search Translator to find studies examining quantitative expression of metabolic markers. Quality assessment was done using the MethodologicAl STandard for Epidemiological Research scale. The robust-error meta-regression model was employed for this synthesis.

RESULTS

Twenty-two studies with 493 participants were included. Insulin sensitivity improved gradually with a maximum reduction in fasting insulin and homeostatic model assessment for insulin resistance of 17 pmol/L and 1 point, respectively, at postoperative day 180. Peak metabolic benefits manifest as a reduction of 2 units in body mass index, 3 kg of fat mass, 5 cm of waist circumference, 15 µg/L of serum leptin, 0.75 pg/ml of tumor necrosis factor-alpha, 0.25 mmol/L of total cholesterol, and 3.5 mmHg of systolic and diastolic blood pressure that were observed at day 50 but were followed by a return to preoperative levels by day 180. Serum high-density lipoproteins peaked at 50 days post-surgery before falling below the baseline. No significant changes were observed in lean body mass, serum adiponectin, resistin, interleukin-6, C-reactive protein, triglyceride, low-density lipoproteins, free fatty acids, and fasting blood glucose.

CONCLUSION

Surgical fat removal exerts several metabolic benefits in the short term, but only improvements in insulin sensitivity last beyond 6 months.

Failure of subcutaneous lipectomy to combat metabolic dysregulations in ovariectomy-induced obesity in young female rats

PURPOSE

The deleterious effect of visceral adipose tissue accumulation is well known. However, the recent trend in liposuction is mal-directed toward easily accessible subcutaneous fat for the purpose of body shaping. The aim of the present study is to probe the metabolic effects of subcutaneous abdominal adipose tissue lipectomy in ovariectomized obese rats as well as the role of adipokines in these changes.

METHODS

The study was conducted on young female rats randomized into two main groups according to the duration of the experiment, namely, 5-week and 10-week. Both groups were subdivided as follows: sham-operated, ovariectomized, and ovariectomized lipectomized rat groups. The rats underwent measurement of body weight (BW) and determination of body mass index (BMI). Fasting blood glucose, lipid profile, liver function, plasma malondialdehyde, leptin, and adiponectin were estimated, and the content of both blood and hepatic tissue of reduced glutathione was assessed. In addition, histological study of the liver, aorta, and perirenal fat of all rat groups was performed.

RESULTS

Ovariectomy-induced obesity is marked by a significant increase in BW and BMI. Following subcutaneous lipectomy, the rats exhibited significant weight gain accompanied by fasting hyperglycemia, dyslipidemia, deterioration of synthetic function of the liver, and disturbed oxidant/antioxidant status. Histological examination revealed fatty infiltration of aortic and hepatic tissues.

CONCLUSION

Despite the immediate positive effect of subcutaneous lipectomy for weight loss and/or body shaping, multiple delayed hazards follow the procedure, which should be carefully considered.

Dynamics of the development of subcutaneous fat depots in rabbits – a gross anatomical and microscopic study

In this study, gross anatomical and microscopic features of interscapular (IsFD) and inguinal (InFD) fat depots of 24 New Zealand White rabbits were evaluated. Rabbits were equally distributed into 4 groups: 1st - newborns, 2nd - 1 month old, 3rd - 2 months old and 4th - 3 months old. The cranial subcutaneous fat pad in newborns covered dorsal and ventral cervical and interscapular regions. As age advanced, cervical lobes underwent a rapid reduction but the development of interscapular lobes continued. IsFD in rabbits from 1st and 2nd group was composed of both white and brown adipocytes, while in 3rd and 4th groups it consisted of white adipocytes only. InFD in rabbits from all tested groups occupied respective inguinal region and no age-dependent changes in shape and topography were observed. In all groups InFD was composed of white adipocytes only. The highest growth rate of interscapular and inguinal adipocytes was established in one-month-old rabbits. Differences in anatomy and histology of interscapular and inguinal fat depots in rabbits could be successfully used for comparison in other experiments in the field of adipobiology and autologous transplantation, where fat depots undergo significant morphological changes.

A Systematic Scoping Review of Surgically Manipulated Adipose Tissue and the Regulation of Energetics and Body Fat in Animals

OBJECTIVE

Surgical manipulations of adipose tissue by removal, or partial lipectomy, have demonstrated body fat compensation and recovered body weight, suggesting that the body is able to resist changes to body composition. However, the mechanisms underlying these observations are not well understood. The purpose of this scoping review is to provide an update on what is currently known about the regulation of energetics and body fat after surgical manipulations of adipose tissue in small mammals.

METHODS

PubMed and Scopus were searched to identify 64 eligible studies. Outcome measures included body fat, body weight, food intake, and circulating biomarkers.

RESULTS

Surgeries performed included lipectomy (72%) or transplantation (12%) in mice (35%), rats (35%), and other small mammals. Findings suggested that lipectomy did not have consistent long-term effects on reducing body weight and fat because regain occurred within 12 to 14 weeks post surgery. Hence, biological feedback mechanisms act to resist long-term changes of body weight or fat. Furthermore, whether this weight and fat regain occurred because of "passive" and "active" regulation under the "set point" or "settling point" theories cannot fully be discerned because of limitations in study designs and data collected.

CONCLUSIONS

The regulation of energetics and body fat are complex and dynamic processes that require further studies of the interplay of genetic, physiological, and behavioral factors.

Impaired metabolic and hepatic functions following subcutaneous lipectomy in adult obese rats

NEW FINDINGS

What is the central question of this study? What is the impact and drawbacks of subcutaneous lipectomy on body metabolism? What is the main finding and its importance? Subcutaneous lipectomy resulted in deterioration of hepatic functions, atherosclerotic lipid profile and disturbed redox state. While the results support lipectomy as an effective treatment for obesity, lipectomy induces unfavourable changes in health.

ABSTRACT

The number of obese older adults is on the rise, but data about proper treatment of obesity in the elderly is controversial. The present study was designed to investigate the effectiveness and consequences of partial subcutaneous lipectomy, as a rapid medical intervention against increased accumulation of body fat, in adult obese rats. The study was conducted on adult (9-12 months) female rats, in which obesity was induced by bilateral surgical ovariectomy. They were randomized into two main groups: short term (5 weeks) and long term (10 weeks). Both groups were subdivided into control, ovariectomized (OVX) and ovariectomized lipectomized groups. Body weight (BW) was measured and body mass index (BMI) calculated. Fasting blood glucose, lipid profile and plasma levels of total proteins, albumin, liver enzymes, malondialdehyde (MDA), leptin and adiponectin were determined. The content of both blood and hepatic tissue of reduced glutathione was estimated. In addition, histological study of the liver, aorta and peri-renal fat was performed. Compared to controls, OVX rats showed significant increase in BW, BMI and plasma levels of liver enzymes, MDA and leptin. Histological study revealed vacuolated ballooned hepatocytes and enlarged irregular visceral adipocytes with atherosclerotic changes in the wall of aorta. Following subcutaneous lipectomy, rats exhibited significant fasting hyperglycaemia, dyslipidaemia, lowered plasma albumin and disturbed redox state with aggravation of the histological changes. The findings indicate that although subcutaneous lipectomy appears to be effective in combating obesity in older females, it has unfavourable effects on both metabolic and hepatic functions.

Inhibition of adipose tissue PPARγ prevents increased adipocyte expansion after lipectomy and exacerbates a glucose-intolerant phenotype

OBJECTIVES

Adipose tissue plays a fundamental role in glucose homeostasis. For example, fat removal (lipectomy, LipX) in lean mice, resulting in a compensatory 50% increase in total fat mass, is associated with significant improvement in glucose tolerance. This study was designed to further examine the link between fat removal, adipose tissue compensation and glucose homeostasis using a peroxisome proliferator-activated receptor γ (PPAR γ; activator of adipogenesis) knockout mouse.

MATERIAL AND METHODS

The study involved PPARγ knockout (FKOγ) or control mice (CON), subdivided into groups that received LipX or Sham surgery. We reasoned that as the ability of adipose tissue to expand in response to LipX would be compromised in FKOγ mice, so would improvements in glucose homeostasis.

RESULTS

In CON mice, LipX increased total adipose depot mass (~60%), adipocyte number (~45%) and changed adipocyte distribution to smaller cells. Glucose tolerance was improved (~30%) in LipX CON mice compared to Shams. In FKOγ mice, LipX did not result in any significant changes in adipose depot mass, adipocyte number or distribution. LipX FKOγ mice were also characterized by reduction of glucose tolerance (~30%) compared to shams.

CONCLUSIONS

Inhibition of adipose tissue PPARγ prevented LipX-induced increases in adipocyte expansion and produced a glucose-intolerant phenotype. These data support the notion that adipose tissue expansion is critical to maintain and/or improvement in glucose homeostasis.

[Metabolic and cardiovascular consequences of suction-assisted lipectomy: Systematic review]

BACKGROUND

Suction-assisted lipectomy is one of the most frequent procedures in plastic surgery. The aim of this study was to investigate whether suction-assisted lipectomy causes changes in the carbohydrates and lipid metabolism and the potential effects on cardiovascular risk factors.

METHODS

We interrogated five databases: Medline, American College of Physicians Journal Club Database, Cochrane central register of controlled trials, Cochrane database of systematic reviews, Database of abstracts of reviews of effects. A systematic review of the literature was performed in order to compare results of randomized controlled trials and observational studies concerning changes in weight, metabolism, endocrinology, inflammatory markers and cardiovascular risk factors after suction-assisted lipectomy. All articles were assessed by criteria from Oxford Center For Evidence Based Medicine (OCEBM).

RESULTS

The search resulted in 40 articles: 12 experimental animal studies and 28 human studies.

CONCLUSION

Different metabolic parameters are affected by suction-assited lipectomy. First, all articles point out a decrease of body weight after suction-assisted lipectomy. Weight lost only affects fat mass without any change of lean mass. The potential compensatory growth of visceral fat seems to be counteracted by physical activity. Then, resting energy expenditure seems to be stable or decrease after the surgery. This reduction is significantly related to the decrease of leptin levels and also seems to be counteracted by physical activity. About adipocytokines, leptin level decreases after suction-assisted lipectomy while results are contradictory about adiponectin and resistin levels. However adiponectin seems to tend to increase after surgery. Inflammatory markers seem to increase within first hours after surgery. Then they seem to decrease or remain at the preoperative levels. Fasting insulin level decreases and is linked to the aspirated volume. So insulin sensitivity seems to be improved. Concerning lipid profil, it tends to remain the same or to be improved by suction-assisted lipectomy. In conclusion, regarding all the literature, there is still debate about metabolic effect of suction-assisted lipectomy. Prospective clinical studies are needed to confirm or invalidate some hypotheses. These studies must consider some potential biases as physical activity, diet and medical treatment modifications (statins).

Short and long-term impact of lipectomy on expression profile of hepatic anabolic genes in rats: a high fat and high cholesterol diet-induced obese model

Objective

To understand the molecular basis of the short and long-term effects of an immediate shortage of energy storage caused by lipectomy on expression profile of genes involved in lipid and carbohydrate metabolism in high fat and high cholesterol diet-induced obese rats.

Methods

The hepatic mRNA levels of enzymes, regulator and transcription factors involved in glucose and lipid metabolism were analyzed by quantitative real time polymerase chain reaction (RT-qPCR) ten days and eight weeks after lipectomy in obese rats. Body and liver weights and serum biochemical parameters, adiponectin, leptin and insulin were determined.

Results

No significant difference was observed on the food intake between the lipectomized and sham-operated groups during the experimental period. Ten days after the operation, the lipectomized animals showed significant higher triacylglycerol, glucose and insulin levels, a lower adiponectin concentration than the sham-operated rats, along with significant higher hepatic mRNA levels of hepatocyte nuclear factor 4α (HNF4α) and the enzymes involved in lipogenesis, sterol biosynthesis and gluconeogenesis. The results of immunohistochemical (IHC) analysis also confirmed increased levels of lipogenic enzymes in the liver of lipectomized versus sham-operated animals. The lipectomized group had a significantly lower adiponectin/leptin ratio that was positively correlated to the level of LDL (r = 0.823, P<0.05) and negatively to glucose and insulin (r = −0.821 and −0.892 respectively, P<0.05). Eight weeks after the operation, the lipectomized animals revealed significant higher body and liver weights, weight gain, liver to body weight ratio, hepatic triacylglycerol and serum insulin level.

Conclusions

In response to lipectomy a short term enhancement of the expression of hepatic anabolic genes involved in lipid and carbohydrate metabolism was triggered that might eventually lead to the final extra weight gain. These metabolic changes could be the results of reduced circulating adiponectin that further influences the functions of insulin and hepatic HNF4α.

The effects of glucose and lipids in steatotic and non-steatotic livers in conditions of partial hepatectomy under ischaemia-reperfusion

BACKGROUND

Steatosis is a risk factor in partial hepatectomy (PH) under ischaemia-reperfusion (I/R), which is commonly applied in clinical practice to reduce bleeding. Nutritional support strategies, as well as the role of peripheral adipose tissue as energy source for liver regeneration, remain poorly investigated.

AIMS

To investigate whether the administration of either glucose or a lipid emulsion could protect steatotic and non-steatotic livers against damage and regenerative failure in an experimental model of PH under I/R. The relevance of peripheral adipose tissue in liver regeneration following surgery is studied.

METHODS

Steatotic and non-steatotic rat livers were subjected to surgery and the effects of either glucose or lipid treatment on damage and regeneration, and part of the underlying mechanisms, were investigated.

RESULTS

In non-steatotic livers, treatment with lipids or glucose provided the same protection against damage, regeneration failure and ATP drop. Adipose tissue was not required to regenerate non-steatotic livers. In the presence of hepatic steatosis, lipid treatment, but not glucose, protected against damage and regenerative failure by induction of cell cycle, maintenance of ATP levels and elevation of sphingosine-1-phosphate/ceramide ratio and phospholipid levels. Peripheral adipose tissue was required for regenerating the steatotic liver but it was not used as an energy source.

CONCLUSION

Lipid treatment in non-steatotic livers provides the same protection as that afforded by glucose in conditions of PH under I/R, whereas the treatment with lipids is preferable to reduce the injurious effects of liver surgery in the presence of steatosis.

Metabolic alterations following visceral fat removal and expansion: Beyond anatomic location

Increased visceral adiposity is a risk factor for metabolic disorders such as dyslipidemia, hypertension, insulin resistance and type 2 diabetes, whereas peripheral (subcutaneous) obesity is not. Though the specific mechanisms which contribute to these adipose depot differences are unknown, visceral fat accumulation is proposed to result in metabolic dysregulation because of increased effluent, e.g., fatty acids and/or adipokines/cytokines, to the liver via the hepatic portal vein. Pathological significance of visceral fat accumulation is also attributed to adipose depot/adipocyte-specific characteristics, specifically differences in structural, physiologic and metabolic characteristics compared with subcutaneous fat. Fat manipulations, such as removal or transplantation, have been utilized to identify location dependent or independent factors that play a role in metabolic dysregulation. Obesity-induced alterations in adipose tissue function/intrinsic characteristics, but not mass, appear to be responsible for obesity-induced metabolic dysregulation, thus “quality” is more important than “quantity.” This review summarizes the implications of obesity-induced metabolic dysfunction as it relates to anatomic site and inherent adipocyte characteristics.

Quantitative dynamics of adipose cells

Adipose cells are unique in the dynamism of their sizes, a requisite for their main function of storing and releasing lipid. Lipid metabolism is crucial for energy homeostasis. However, the regulation of lipid storage capacity in conditions of energy excess and scarcity is still not clear. It is not technically feasible to monitor every process affecting storage capacity such as recruitment, growth/shrinkage and death of individual adipose cells in real time for a sufficiently long period. However, recent computational approaches have allowed an examination of the detailed dynamics of adipose cells using statistical information in the form of precise measurements of adipose cell-size probability distributions. One interesting finding is that the growth/shrinkage of adipose cells (> 50 μm diameter) under positive/negative energy balance is proportional to the surface area of cells, limiting efficient lipid absorption/release from larger adipose cells. In addition to the physical characteristics of adipose cells, quantitative modeling integrates dynamics of adipose cells, providing the mechanism of cell turnover under normal and drug-treated conditions. Thus, further use of mathematical modeling applied to experimental measurements of adipose cell-size probability distributions in conjunction with physiological measurements of metabolic state may help unravel the intricate network of interactions underlying metabolic syndromes in obesity.

Effects of reduction mammoplasty on metabolic profile and body weight

BACKGROUND

Advanced studies on adipose tissue have established that subcutaneous adipose tissue acts as an endocrine organ to help maintain homeostasis. Based on this information, many plastic surgeons have evaluated the metabolic effects of liposuction because liposuction is the most common surgical procedure in plastic surgery. Liposuction removes a substantial amount of subcutaneous fat from a specific area of the body. Mammoplasty is another procedure that removes a large amount of subcutaneous fat. In this study, the metabolic effects of reduction mammoplasty were evaluated with hemogram, blood glucose, lipid profile, insulin, and insulin resistance tests before and after surgery.

METHODS

The study involved 35 patients who underwent reduction mammoplasty between January 2006 and June 2009. All the patients were evaluated with physical examination and their history, height, and weight were obtained. Venous blood samples were collected before, 4 h after, and 3 months after the surgical procedure to evaluate hemogram, blood glucose, insulin, and lipid profiles. The HOMA scores of the patients were calculated. Inferiorly based dermal pedicle, central pedicle, and free nipple graft techniques were used in the operations and all excision materials were sent for histopathological examination.

RESULTS

The mean age of the patients was 39.6 ± 11.6 years. The mean excision volume was 2249 ± 1001 g. Body mass indexes were not significantly different before and 3 months after the surgery (p > 0.05). Blood glucose, LDL, HDL, triglyceride, total cholesterol, hemoglobin, and hematocrit values before and 4 h after the surgery were also different (p < 0.05). However, comparisons with the 3-month postoperative test results revealed no statistically significant differences (p > 0.05) and comparisons of all the measurements showed that insulin levels and HOMA scores were not significantly different (p > 0.05).

CONCLUSION

The results of the present study showed that reduction mammoplasty operations do not have any positive effects on blood insulin, glucose profile, lipid profile, and body mass index 3 months after the surgery.

White adipose tissue re-growth after partial lipectomy in high fat diet induced obese wistar rats

The effects of partial removal of epididymal (EPI) and retroperitoneal (RET) adipose tissues (partial lipectomy) on the triacylglycerol deposition of high fat diet induced obese rats were analyzed, aiming to challenge the hypothesized body fat regulatory system. Male 28-day-old wistar rats received a diet enriched with peanuts, milk chocolate and sweet biscuits during the experimental period. At the 90th day of life, rats were submitted to either lipectomy (L) or sham surgery. After 7 or 30 days, RET, EPI, liver, brown adipose tissue (BAT), blood and carcass were obtained and analyzed. Seven days following surgery, liver lipogenesis rate and EPI relative weight were increased in L. After 30 days, L, RET and EPI presented increased lipogenesis, lipolysis and percentage of small area adipocytes. L rats also presented increased liver malic enzyme activity, BAT lipogenesis, and triacylglycerol and corticosterone serum levels. The partial removal of visceral fat pads affected the metabolism of high fat diet obese rats, which leads to excised tissue re-growth and possibly compensatory growth of non-excised depots at a later time.

Strategies for reducing body fat mass: effects of liposuction and exercise on cardiovascular risk factors and adiposity

Liposuction is the most popular aesthetic surgery performed in Brazil and worldwide. Evidence showing that adipose tissue is a metabolically active tissue has led to the suggestion that liposuction could be a viable method for improving metabolic profile through the immediate loss of adipose tissue. However, the immediate liposuction-induced increase in the proportion of visceral to subcutaneous adipose tissue could be detrimental to metabolism, because a high proportion of visceral to subcutaneous adipose tissue is associated with risk factors for cardiovascular disease. The results of studies investigating the effects of liposuction on the metabolic profile are inconsistent, however, with most studies reporting either no change or improvements in one or more cardiovascular risk factors. In addition, animal studies have demonstrated a compensatory growth of intact adipose tissue in response to lipectomy, although studies with humans have reported inconsistent results. Exercise training improves insulin sensitivity, inflammatory balance, lipid oxidation, and adipose tissue distribution; increases or preserves the fat-free mass; and increases total energy expenditure. Thus, liposuction and exercise appear to directly affect metabolism in similar ways, which suggests a possible interaction between these two strategies. To our knowledge, no studies have reported the associated effects of liposuction and exercise in humans. Nonetheless, one could suggest that exercise training associated with liposuction could attenuate or even block the possible compensatory fat deposition in intact depots or regrowth of the fat mass and exert an additive or even a synergistic effect to liposuction on improving insulin sensitivity and the inflammatory balance, resulting in an improvement of cardiovascular risk factors. Consequently, one could suggest that liposuction and exercise appear to be safe and effective strategies for either the treatment of metabolic disorders or aesthetic purposes.

Laser lipolysis with pulsed 1064 nm Nd:YAG laser for the treatment of gynecomastia

BACKGROUND

Lipolysis using laser is currently widely used for reducing localized fat. A 1064 nm neodynium-doped yttrium aluminum garnet (Nd:YAG) laser lipolysis was investigated in this study to evaluate its efficacy and safety in the treatment of gynecomastia.

METHODS

Five male patients diagnosed with gynecomastia were enrolled in this study, which was designed as a controlled split-breast trial. One breast of each patient was subjected to laser lipolysis and was then compared with a contralateral breast. Photographs and clinical assessments were obtained before the lipolysis, and at the fourth and eighth weeks thereafter. Computed tomography (CT) scan and ultrasound (US) imaging were used to evaluate the changes in the breasts' thicknesses.

RESULTS

The mean chest circumference was found to have been significantly reduced 8 weeks after the laser lipolysis. The clinical outcomes of the laser lipolysis were considered favorable by both the patients and clinicians. The CT and US scans showed that the thicknesses of the treated right breasts reduced more than those of the left breasts were 8 weeks after the laser lipolysis. The side effects (pain, edema, and ecchymosis) were minimal and disappeared shortly after they first manifested. Limitations The limitations of this study are that it employed small treatment groups and short-term follow-up.

CONCLUSION

This study demonstrated that gynecomastia can be treated effectively and safely through 1064 nm Nd:YAG laser lipolysis.

Waves of adipose tissue growth in the genetically obese Zucker fatty rat

Background

In mammals, calories ingested in excess of those used are stored primarily as fat in adipose tissue; consistent ingestion of excess calories requires an enlargement of the adipose tissue mass. Thus, a dysfunction in adipose tissue growth may be a key factor in insulin resistance due to imbalanced fat storage and disrupted insulin action. Adipose tissue growth requires the recruitment and then the development of adipose precursor cells, but little is known about these processes in vivo.

Methodology

In this study, adipose cell-size probability distributions were measured in two Zucker fa/fa rats over a period of 151 and 163 days, from four weeks of age, using micro-biopsies to obtain subcutaneous (inguinal) fat tissue from the animals. These longitudinal probability distributions were analyzed to assess the probability of periodic phenomena.

Conclusions

Adipose tissue growth in this strain of rat exhibits a striking temporal periodicity of approximately days. A simple model is proposed for the periodicity, with PPAR signaling driven by a deficit in lipid uptake capacity leading to the periodic recruitment of new adipocytes. This model predicts that the observed period will be diet-dependent.

Hypertrophy and/or Hyperplasia: Dynamics of Adipose Tissue Growth

Adipose tissue grows by two mechanisms: hyperplasia (cell number increase) and hypertrophy (cell size increase). Genetics and diet affect the relative contributions of these two mechanisms to the growth of adipose tissue in obesity. In this study, the size distributions of epididymal adipose cells from two mouse strains, obesity-resistant FVB/N and obesity-prone C57BL/6, were measured after 2, 4, and 12 weeks under regular and high-fat feeding conditions. The total cell number in the epididymal fat pad was estimated from the fat pad mass and the normalized cell-size distribution. The cell number and volume-weighted mean cell size increase as a function of fat pad mass. To address adipose tissue growth precisely, we developed a mathematical model describing the evolution of the adipose cell-size distributions as a function of the increasing fat pad mass, instead of the increasing chronological time. Our model describes the recruitment of new adipose cells and their subsequent development in different strains, and with different diet regimens, with common mechanisms, but with diet- and genetics-dependent model parameters. Compared to the FVB/N strain, the C57BL/6 strain has greater recruitment of small adipose cells. Hyperplasia is enhanced by high-fat diet in a strain-dependent way, suggesting a synergistic interaction between genetics and diet. Moreover, high-fat feeding increases the rate of adipose cell size growth, independent of strain, reflecting the increase in calories requiring storage. Additionally, high-fat diet leads to a dramatic spreading of the size distribution of adipose cells in both strains; this implies an increase in size fluctuations of adipose cells through lipid turnover.

Sexually dimorphic responses to fat loss after caloric restriction or surgical lipectomy

White adipose tissue is the principal site for lipid accumulation. Males and females maintain distinctive white adipose tissue distribution patterns. Specifically, males tend to accumulate relatively more visceral fat, whereas females accumulate relatively more subcutaneous fat. The phenomenon of maintaining typical sex-specific fat distributions suggests sex-specific mechanisms that regulate energy balance and adiposity. We used two distinct approaches to reduce fat mass, caloric restriction (CR), and surgical fat removal (termed lipectomy) and assessed parameters involved in the regulation of energy balance. We found that male and female mice responded differentially to CR- and to lipectomy-induced fat loss. Females decreased energy expenditure during CR or after lipectomy. In contrast, males responded by eating more food during food return after CR or after lipectomy. Female CR mice conserved subcutaneous fat, whereas male CR mice lost adiposity equally in the subcutaneous and visceral depots. In addition, female mice had a reduced capability to restore visceral fat after fat loss. After CR, plasma leptin levels decreased in male but not in female mice. The failure to increase food intake after returning to ad libitum intake in females could be due to the relatively stable levels of leptin. In summary, we have found sexual dimorphisms in the response to fat loss that point to important underlying differences in the strategies by which male and female mice regulate body weight.

Thematic review series: adipocyte biology. Sympathetic and sensory innervation of white adipose tissue

During our study of the reversal of seasonal obesity in Siberian hamsters, we found an interaction between receptors for the pineal hormone melatonin and the sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT). This ultimately led us and others to conclude that the SNS innervation of WAT is the primary initiator of lipid mobilization in these as well as other animals, including humans. There is strong neurochemical (norepinephrine turnover), neuroanatomical (viral tract tracing), and functional (sympathetic denervation-induced blockade of lipolysis) evidence for the role of the SNS in lipid mobilization. Recent findings suggest the presence of WAT sensory innervation based on strong neuroanatomical (viral tract tracing, immunohistochemical markers of sensory nerves) and suggestive functional (capsaicin sensory denervation-induced WAT growth) evidence, the latter implying a role in conveying adiposity information to the brain. By contrast, parasympathetic nervous system innervation of WAT is characterized by largely negative neuroanatomical evidence (viral tract tracing, immunohistochemical and biochemical markers of parasympathetic nerves). Functional evidence (intraneural stimulation and in situ microdialysis) for the role of the SNS innervation in lipid mobilization in human WAT is convincing, with some controversy regarding the level of sympathetic nerve activity in human obesity.