Nutrient balance and obesity: an approach to control of food intake in humans

Exendin-4 antagonizes the metabolic action of acylated ghrelinergic signaling in the hypothalamic paraventricular nucleus

In the current study we investigated the interaction of hypothalamic paraventricular nucleus (PVN) glucagon-like peptide-1 (GLP-1) and ghrelin signaling in the control of metabolic function. We first demonstrated that acylated ghrelin injected directly into the PVN reliably altered the respiratory exchange ratio (RER) of adult male Sprague Dawley rats. All testing was carried out during the initial 2 h of the nocturnal cycle using an indirect open circuit calorimeter. Results indicated that acylated ghrelin induced a robust increase in RER representing a shift toward enhanced carbohydrate oxidation and reduced lipid utilization. In contrast, treatment with comparable dosing of des-acyl ghrelin failed to significantly impact metabolic activity. In separate groups of rats we subsequently investigated the ability of exendin-4 (Ex-4), a GLP-1 analogue, to alter acylated ghrelin's metabolic effects. Rodents were treated with either systemic or direct PVN Ex-4 followed by acyl ghrelin microinjection. While our results showed that both systemic and PVN administration of Ex-4 significantly reduced RER, importantly, Ex-4 pretreatment itself reliably inhibited the impact of ghrelin on RER. Overall, these findings provide increasingly compelling evidence that GLP-1 and ghrelin signaling interact in the neural control of metabolic function within the PVN.

Body Mass Index and Obesity : Tailoring "cut-off" for an Asian Indian Male Population

BACKGROUND

Obesity/overweight is a recognized risk factor for a host of disorders. The disease risk stratification is commonly based on the Quetelets Index (Body Mass Index- BMI), a surrogate measure of fatness. The currently used BMI cut-offs to classify people as overweight or obese in Armed Forces have been defined in studies on Caucasian populations. However, because of differences in body structure and composition in different ethnic, socioeconomic, cultural and regional groups the correspondence between BMI and body fat content varies between populations. We conducted this pilot study in the Indian Navy to define BMI cut-offs for overweight and obesity using body fat content derived from Skin Fold Thickness as the standard.

MATERIAL AND METHODS

The study was conducted on 121 volunteers from a naval hospital staff in the age range of 18 to 47 years. The mean age, height, weight, BMI, body fat in the study group was 26.73 years (± 5.5098), 168.56 cm (± 6.1034), 65.92 Kg (± 10.2746), 23.17 Kg/m(2) (± 3.0265) and 19.91% (± 4.831) respectively.

RESULTS

The prevalence of overweight/obesity was 20.66% by BMI and 47.11% by body fat content. Receiver operating characteristic (ROC) curve analysis defined a BMI of 23.85 kg/m(2) as the cut off for overweight with a sensitivity of 70.2% (95% CI 56.6 - 81.6) and 87.5% specificity (95% CI 76.8-94.4) and a BMI of 24.38 kg/m(2)with 90% sensitivity (95% CI 68.3-98.5) and 81.2% specificity (95% CI 72.2-88.3) for obesity.

CONCLUSION

The results of our study suggest lower BMI cut offs for overweight and obesity in Indian populations than those recommended by WHO.

Ghrelin is an orexigenic and metabolic signaling peptide in the arcuate and paraventricular nuclei

Ghrelin is a 28-amino acid acylated peptide and is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The GHS-R is expressed in hypothalamic nuclei, including the arcuate nucleus (Arc) where it is colocalized with neuropeptide Y (NPY) neurons. In the present study, we examined the effects of ghrelin on feeding and energy substrate utilization (respiratory quotient; RQ) following direct injections into either the arcuate or the paraventricular nucleus (PVN) of the hypothalamus. Ghrelin was administered at the beginning of the dark cycle at doses of 15–60 pmol to male and female rats. In feeding studies, food intake was measured 2 and 4 h postinjection. Separate groups of rats were injected with ghrelin, and the RQ (V̇co2/V̇o2) was measured using an open circuit calorimeter over a 4-h period. Both Arc and PVN injections of ghrelin increased food intake in male and female rats. Ghrelin also increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. Because these effects are similar to those observed after PVN injection of NPY, we then assessed the impact of coinjecting ghrelin with NPY into the PVN. When rats were pretreated with very low doses of ghrelin (2.5–10 pmol), NPY's (50 pmol) effects on eating and RQ were potentiated. Overall, these data are in agreement with evidence suggesting that ghrelin functions as a gut-brain endocrine hormone implicated in the regulation of food intake and energy metabolism. Our findings are also consistent with a possible interactive role of hypothalamic ghrelin and NPY systems.

Hypothalamic paraventricular 5-hydroxytryptamine: receptor-specific inhibition of NPY-stimulated eating and energy metabolism

The feeding effects of 5-hydroxytryptamine (5-HT)(1) and 5-HT(2) receptor agonists injected into the hypothalamic paraventricular nucleus (PVN) immediately prior to PVN administration of neuropeptide Y (NPY) were examined. The impact of these same compounds on NPY-induced alterations in energy metabolism was also assessed in an attempt to characterize further the potential interactive relationship of PVN NPY and 5-HT on feeding and whole body calorimetry. Specifically, several experiments examined the effect of various 5-HT receptor agonists on NPY-stimulated eating and alterations in energy substrate utilization [respiratory quotient (RQ)]. This included the 5-HT(1A) receptor agonist 8-OH-DPAT, the 5-HT(1B/1A) agonist RU 24969, the 5-HT(1D) agonist L-694,247, the 5-HT(2A/2C) agonist DOI, the 5-HT(2B) agonist BW 723C86 and the 5-HT(2C) agonist mCPP. In feeding tests conducted at the onset of the dark cycle, drugs were administered 5 min prior to PVN injection of NPY and food intake was measured 2 h postinjection. The metabolic effects of NPY following a similar pretreatment were monitored using an open-circuit calorimeter measuring the volume of oxygen consumed (VO(2)), carbon dioxide produced (VCO(2)) and RQ (VCO(2)/VO(2)). PVN injection of NPY (100 pmol) potentiated feeding and evoked reliable increases in RQ. Only DOI (2.5--5 nmol) pretreatment antagonized NPY-induced eating and blocked the peptide's effect on energy substrate utilization. Direct PVN pretreatment with spiperone (SPRN), a 5-HT(2A) receptor antagonist, and ketanserin (KTSN), a 5-HT(2A/2C) antagonist, but not SDZ SER 082, a 5-HT(2B/2C) antagonist, or the 5-HT(2C) antagonist RS 102221, blocked the effect of DOI in both feeding and metabolic tests providing additional evidence that activation of PVN 5-HT(2A) receptors inhibits NPY's action on feeding and substrate utilization.

Hypothalamic paraventricular nucleus injections of urocortin alter food intake and respiratory quotient

Corticotropin releasing hormone (CRH) acts on the central nervous system to alter energy balance and influence both food intake and sympathetically-mediated thermogenesis. CRH is also reported to inhibit food intake in several models of hyperphagia including neuropeptide Y (NPY)-induced eating. The recently identified CRH-related peptide, urocortin (UCN), also binds with high affinity to CRH receptor subtypes and decreases food intake in food-deprived and non-deprived rats. The present experiment characterized further the feeding and metabolic effects of UCN by examining its impact after direct injections into the paraventricular nucleus (PVN) of the hypothalamus. In feeding tests (n=8), UCN (50-200 pmol) was injected into the PVN at the onset of the dark cycle and food intake was measured 1, 2 and 4 h postinjection. In separate rats (n=8), the metabolic effects of UCN were monitored using an open circuit calorimeter which measured oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)). Respiratory quotient (RQ) was calculated as V(CO2)/V(O2). UCN suppressed feeding at all times studied and reliably decreased RQ within 30 min of infusion. Additional work examined the effect of UCN (50-100 pmol) pretreatment on the feeding and metabolic effects of NPY. NPY, injected at the start of the dark period, reliably increased 2 h food intake. This effect was blocked by PVN UCN administration. Similarly, UCN blocked the increase in RQ elicited by NPY alone. These results suggest that UCN-sensitive mechanisms within the PVN may modulate food intake and energy substrate utilization, possibly through an interaction with hypothalamic NPY.

5-Hydroxytryptaminergic receptor agonists: effects on neuropeptide Y potentiation of feeding and respiratory quotient

The objective of the present report was to characterize further the potential interactive effects of NPY and 5-HT on feeding and whole-body calorimetry. Specifically, several experiments examined the impact of various 5-HT receptor agonists on NPY stimulated eating and alterations in respiratory quotient (RQ). This included the 5-HT1A/1B receptor agonist RU 24969, the 5-HT1B/2C agonist TFMPP and the 5-HT2A/2C agonist DOI. In feeding tests conducted at the onset of the dark cycle, RU 24969, TFMPP and DOI were administered 5 min prior to PVN injection of NPY and food intake was measured 1 h postinjection. The metabolic effects of NPY following similar pretreatment were monitored using an open-circuit calorimeter measuring the volume of oxygen consumed (VO2), carbon dioxide produced (VCO2) and RQ (VCO2/VO2). PVN injection of NPY (50-100 pmol) potentiated feeding and evoked reliable increases in RQ. DOI (5-20 nmol), but not RU 24969 (5-20 nmol) or TFMPP (10-40 nmol), antagonized NPY induced eating and blocked the peptide's effects on RQ. These findings suggest that 5-HT2A receptors within the PVN modulate NPY's effect on feeding and energy substrate utilization at the start of the nocturnal period.

Association of altered whole-body metabolism with locomotor sensitization induced by quinpirole

Repeated exposure to drugs classed as psychostimulants can produce behavioral sensitization, defined as augmented motor responses to fixed doses of such compounds. For example, chronic treatment of rats with the dopamine D2/D3 agonist quinpirole increases the locomotor response to this drug to levels that are several times higher than after acute treatment. To determine if such enhanced activity is associated with changes in energy metabolism, one group of rats (n = 16) received 11 injections of quinpirole (0.5 mg/kg every second day) while a second received equal numbers of saline injections. Immediately after each injection, rats were placed in individual metabolic chambers where oxygen (O2) consumption, carbon dioxide (CO2) output, and motor activity were measured every 5 min for the next 2 h. Locomotor responses to quinpirole doubled during the course of treatment, thereby confirming the establishment of behavioral sensitization. The magnitude of energy metabolism and motor activity were positively correlated in control rats but not in quinpirole-treated rats. However, quinpirole reliably reduced respiratory quotient (CO2/O2). This suggests that enhanced utilization of body lipids could be a separate physiological consequence of quinpirole that might support in part the heightened locomotor activity characteristic of the behavioral sensitization it induces.

Control of food intake. A physiologically complex, motivated behavioral system

This article has examined the control of food intake as a physiologically complex, motivated behavioral system. During the past four decades, considerable progress has been made in understanding putative signals for hunger, satiation, and satiety, although hunger signals have proven to be more difficult to identify. The putative physiologic controls of food intake include positive and negative sensory feedback; gastric and intestinal distension; the effects of nutrients, nutrient reserves, and metabolism in producing signals to the liver or brain; and peptides and hormones released in the gastrointestinal tract or the brain. However, food intake is not influenced solely by physiologic signals for hunger, satiation, and satiety. To comprehend feeding behavior more thoroughly, current physiologic models must be extended to include modulating factors such as feeding-associated responses adapted through learning processes and the influence of circadian rhythms, which can be dominating over hunger, satiation, and satiety signals.

Regional hypothalamic differences in neuropeptide Y-induced feeding and energy substrate utilization

Previous research has shown that both the paraventricular nucleus (PVN) of the hypothalamus and the perifornical hypothalamus (PFH) are sites at which microinjection of neuropeptide Y (NPY) can induce eating. The PVN has also been shown to be responsive to the effects of exogenous NPY on energy substrate utilization. Therefore, the objective of the present study was to further characterize and compare the effects of NPY on whole-body calorimetry and feeding after microinjection into either the PVN or the PFH. The metabolic effects of NPY (19.5-78 pmol) were determined using an open-circuit calorimeter by measuring the volumes of oxygen consumed and carbon dioxide expired in order to compute respiratory quotients (RQs). Following NPY injection into the PVN (n = 10) or PFH (n = 10), RQs and locomotor activity were monitored over three hours. Additional groups of rats with PVN (n = 10) or PFH (n = 10) cannulae were tested for their feeding responses to these same doses of peptide. While NPY injections into the PVN evoked dose-dependent increases in RQ within 30-40 min of treatment, PFH NPY did not alter RQ at any of the doses tested. Locomotor activity was unaffected by NPY in either site. NPY administration into both the PVN and PFH stimulated eating, although the PFH was found to be the more sensitive in terms of absolute amount of food consumed. These findings support the hypothesis that the PVN may regulate metabolic processes that either produce or coincide with NPY-induced feeding. This contrasts with the PFH, which appears to mediate only the feeding-stimulatory actions of NPY.

Differential effects of fat and sucrose on the development of obesity and diabetes in C57BL/6J and A/J mice

We have previously demonstrated that the C57BL/6J (B/6J) mouse will develop severe obesity, hyperglycemia, and hyperinsulinemia if weaned onto a high-fat, high-sucrose (HH) diet. In the present study, we compared the effects of fat and sucrose separately and in combination on diabetes- and obesity-prone B/6J and diabetes- and obesity-resistant A/J mice. After 4 months, the feed efficiency ([FE] weight gained divided by calories consumed) did not differ across diets in A/J mice, but B/6J mice showed a significantly increased FE for fat. That is, B/6J mice gained more weight on high-fat diets without consuming more calories than A/J mice. The increase in FE was related to adipocyte hyperplasia in B/6J mice on high-fat diets. Fat-induced obesity in B/6J mice was unrelated to adrenal cortical activity. In the absence of fat, sucrose produced a decreased in FE in both strains. Animals fed a low-fat, high-sucrose (LH) diet were actually leaner than animals fed a high-complex-carbohydrate diet. Fat was also found to be the critical stimulus for hyperglycemia and hyperinsulinemia in B/6J mice. In the absence of fat, sucrose had no effect on plasma glucose or insulin. These data clearly show that across these two strains of mice, genetic differences in the metabolic response to fat are more important in the development of obesity and diabetes than the increased caloric content of a high-fat diet.

Somatostatin and the paraventricular hypothalamus: modulation of energy balance

The effects of somatostatin injections (0.1, 1 and 5 micrograms) into the paraventricular nucleus of the hypothalamus (PVN) were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. The 0.1 and 1 microgram doses produced large and long-lasting decreases in respiratory quotient, which indicates the preferential utilization of fats as an energy substrate. The 5 micrograms dose produced a brief decrease in energy expenditure. Locomotor activity was not affected by any treatment which indicates that the effects on respiratory quotient and energy expenditure are not secondary to changes in activity. These findings demonstrate that somatostatin in the PVN inhibits thermogenesis and induces the preferential utilization of fats while sparing carbohydrate reserves. However, it is significant that the effects on energy expenditure and energy substrate utilisation occurred at different doses. These data constitute the first evidence that somatostatin in the PVN produces a primary modulation of the metabolic parameters central to energy balance. In separate experiments, all three doses of somatostatin increased blood glucose concentration over a one hour period, and the 5 micrograms dose decreased body weight over a 24 h period. Food and water intake were not affected by the somatostatin injections. Taken together, these findings are interpreted in a model in which somatostatin is a signal to the PVN of increased body fat. This mobilizes sympathetic mechanisms which increase fat utilization and blood glucose levels.

Glucagon and the paraventricular hypothalamus: modulation of energy balance

The effects of glucagon injections (25, 100 and 200 ng) into the paraventricular nucleus of the hypothalamus (PVN) were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. High doses of glucagon (100 and 200 ng) produced small and short-lasting increases in energy expenditure. The independence of these changes from changes in locomotor activity suggests that the thermogenesis represents a primary modulation and is not secondary to increased locomotion. All three doses of glucagon produced long-lasting and dose-related increases in respiratory quotient which were unrelated to any changes in locomotor activity. As with the changes in energy expenditure, this dissociation indicates that the effects are not secondary to changes in locomotor activity. These data constitute the first evidence that glucagon in the PVN modulates the metabolic parameters central to energy balance. In separate experiments, the three doses of glucagon increased blood glucose concentration over a one hour period, but they did not affect food and water intake and body weight over 24 h. These findings suggest that glucagon normally acts on the PVN in conditions of increased body fat to initiate autonomic mechanisms which increase glycemic levels, thermogenesis and carbohydrate utilization. These data constitute the first direct evidence for the involvement of the PVN in the regulation of energy balance by glucagon. The main effect of glucagon in the PVN is anabolic in that it increases dependence on carbohydrates as an energy substrate which results in a sparing of fat reserves.

Metabolic modulation by amino acid stimulation of the paraventricular nucleus of the hypothalamus

The role of the paraventricular nucleus of the hypothalamus (PVN) in the regulation of energy expenditure and energy substrate utilization was investigated after the injection of the excitatory amino acid D,L-homocysteic acid (DLH) or its vehicle. Male Wistar rats with chronic PVN cannulae were tested for 1 h with no food available in an open-circuit calorimeter. Whereas low (0.5 nmol), excitatory doses of DLH increased energy expenditure, the thermogenic effect became smaller and then vanished as the DLH dose was increased to inhibitory levels (7 and 50 nmol). None of these doses affected motor activity, indicating a primary thermogenic effect. The highest dose (100 nmol) increased energy expenditure, but this appeared to be secondary to increased locomotor activity. The increased locomotor activity produced by the highest dose of DLH constitutes the first demonstration of an activity effect induced by stimulating the PVN. However, this effect likely reflects the activation of neighboring areas. Only the 50 nmol dose of DLH increased respiratory quotient, indicating a shift toward the preferential utilization of carbohydrates as an energy substrate. These data complement our findings with neuropeptide Y and insulin in showing that different doses of the same substance injected into the PVN may produce qualitatively different effects. Furthermore, the present study demonstrates that exciting PVN neurons activates catabolic forces, whereas inhibiting them activates anabolic forces.

Metabolic effects of galanin injections into the paraventricular nucleus of the hypothalamus

The metabolic effects of single injections of galanin into the paraventricular nucleus of the hypothalamus (PVN) were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. In the dose range of 0.03-0.3 nmol, galanin produced a very short-latency (approximately 2 minutes) and short-lasting (approximately 15 minutes) reduction in energy expenditure. Since the same doses had no effect on respiratory quotient or locomotor activity, the metabolic effect is not secondary to changes in energy substrate utilization or locomotor activity. This antithermogenic effect complements the eating stimulatory action of PVN galanin, and together these phenomena suggest a role for galanin as an anabolic neuropeptide. The similarity of galanin's effects to those of norepinephrine, with which it coexists in PVN nerve endings, further suggests the involvement of this amine and the PVN alpha2-noradrenergic system in galanin's mechanism of action.

Molecular mapping of obesity genes

Advances in molecular genetics have made it possible to clone mutant genes from mammals. This capability should facilitate efforts to determine the genetic factors that control food intake and body composition. In order to identify these genetic factors, we have been making use of mouse mutations that cause obesity. The basic premise of this approach is to take advantage of the mouse as a genetic system for the analysis of genetically complex disorders and to then apply that information to the study of human disease. This paper reviews: (1) current concepts concerning the control of body weight in man and other mammals; (2) the biologic characteristics of the mouse obesity mutations; (3) our progress in the use of positional cloning techniques to clone the mouse obese (ob) and diabetes (db) genes; (4) an approach to polygenic obesity in mice; and (5) the possible relevance of the mouse obesity mutations to human obesity.

Insulin and the paraventricular hypothalamus: modulation of energy balance

The effects of insulin injections (0.1, 1, 10 and 40 mU) into the paraventricular hypothalamus (PVN) were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. The 0.1 and 1 mU doses had no effects on either respiratory quotient or energy expenditure. The 10 mU dose increased respiratory quotient which indicates increased dependency on carbohydrates as an energy substrate. The same dose had no effects on thermogenesis. In contrast, the 40 mU dose decreased respiratory quotient which indicates increased dependency on fats as an energy substrate. The higher dose also increased thermogenesis. Since neither dose significantly affected locomotor activity, the metabolic data are not confounded with activity effects. These data indicate that insulin in the PVN produces a primary modulation of the metabolic parameters central to maintaining energy balance. In separate experiments, the 4 doses of insulin reduced food intake and body weight over a 24 h period. They also produced a dose-related increase in blood glucose concentration over a one hour period. Taken together, these findings are interpreted in a model in which insulin in the PVN acts as a signal indicating increased body fat. This increases thermogenesis, fat utilization and glycemic levels, and inhibits feeding. The net effect of this integrated metabolic-behavioural response is a regulatory reduction in body fat.

Prefrontal cortex alpha 2 adrenoceptors and energy balance

The sulcal prefrontal cortex (SPC) influences thermogenesis, energy substrate utilization and feeding behaviour. The present study examined the role of SPC alpha noradrenergic receptors in these effects. Fifty nmol norepinephrine (NE) injected into the SPC produced a large and long-lasting increase in respiratory quotient (RQ), indicating enhanced carbohydrate utilization and fat synthesis. This dose also reduced energy expenditure without corresponding decreases in locomotor activity, suggesting an inhibition of thermogenesis. Neither a lower dose of NE (25 nmol) injected into the SPC, nor injections of NE (50 nmol) into a variety of sites adjacent to the SPC affected energy balance. The alpha 2 agonist clonidine (20 nmol) injected into the SPC produced similar effects to 50 nmol NE, with a large increase in RQ and a decrease in thermogenesis. Forty nmol clonidine, however, decreased RQ and reduced both energy expenditure and activity. The alpha 1 agonist L-phenylephrine (20 and 40 nmol) injected into the SPC had no clear effect on energy balance. Finally, it was shown that clonidine or NE injected into the SPC promotes food intake. These results implicate alpha 2 adrenoceptors in the sulcal prefrontal cortex in the control of food intake, thermogenesis and metabolic substrate utilization.

Metabolic effects of neuropeptide Y injections into the paraventricular nucleus of the hypothalamus

The metabolic effects of single injections of neuropeptide Y (NPY) into the paraventricular hypothalamus were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. Over the dose range of 10-156 pmol NPY had large effects on respiratory quotient (RQ) while having no effect on energy expenditure or locomotor activity. The effects of NPY on RQ were unusual both in respect to their dose-response and time-dose-response characteristics. The lowest dose (10 pmol) produced a very low latency reduction in RQ which indicates a decreased utilization of carbohydrates as an energy substrate. The next higher dose (20 pmol) had no effect, whereas the next three doses (39, 78 and 156 pmol) produced increases in RQ which indicate an increased utilization of carbohydrates as an energy substrate. Surprisingly, the latencies of the increased RQs were dose-dependent over the range of 30 min to 20 h with the highest dose producing the longest latency effect. The finding of a positive relation of dose to response latency over a time range of from a few minutes to 20 h is unprecedented and appears to represent a neuromodulatory effect of NPY that acts in concert with its neurotransmitter effects. These data highlight the central role of NPY in modulating energy substrate utilization and indicate the importance of elucidating time-dose-response relationships when investigating the effects of NPY.

The effects of weight loss on the activity and expression of adipose-tissue lipoprotein lipase in very obese humans

Lipoprotein lipase is an enzyme in adipose tissue that hydrolyzes circulating triglycerides and thereby generates the fatty acids used in the synthesis of triglyceride in fat cells. To determine whether the activity and expression of lipoprotein lipase are affected by weight loss, we studied lipoprotein lipase in the adipose tissue of nine very obese subjects before and after a program of weight reduction. The subjects' mean (+/- SEM) initial weight was 136 +/- 7.3 kg, and the body-mass index (weight in kilograms divided by the square of the height in meters) ranged from 33.3 to 52.8 (mean, 43.0 +/- 2.5). Biopsies of adipose tissue were performed before weight loss and after it, when weight had been stable for three months. The weight reduction was achieved by a very-low-calorie diet (mean weight loss, 42.5 +/- 6.8 kg). After weight loss, the level of heparin-releasable lipoprotein lipase activity increased in all patients, from 3.8 +/- 1.1 to 7.1 +/- 1.6 neq of free fatty acid released per minute per 10(6) cells (P less than 0.05). In addition, the amount of lipoprotein lipase immunoreactive protein increased from 6.3 +/- 1.7 to 24.4 +/- 6.9 ng per 10(6) cells (P less than 0.05), and there was also an increase in the level of lipoprotein lipase messenger RNA as measured by Northern blotting. There was a strongly positive correlation between the initial body-mass index and the magnitude of the increase in lipoprotein lipase activity (r = 0.80, P less than 0.01) and immunoreactive protein (r = 0.92, P less than 0.01). We conclude that weight loss in very obese subjects leads to the increased activity and expression of lipoprotein lipase, thereby potentially enhancing lipid storage and making further weight loss more difficult.