In order to better understand the link between obesity and type 2 diabetes, lipolysis and its adrenergic regulation was investigated in various adipose depots of obese adult females SHR/N-cp rats. Serum insulin, glucose, free fatty acids (FFA), triglycerides (TG) and glycerol were measured. Adipocytes were isolated from subcutaneous (SC), parametrial (PM) and retroperitoneal (RP) fat pads. Total cell number and size, basal lipolysis or stimulated by norepinephrine (NE) and BRL 37344 were measured in each depot. Obese rats were hyperinsulinemic and hyperglycemic, suggesting high insulin resistance. They presented a marked dyslipidemia, attested by increased serum FFA and TG levels. High serum glycerol levels also suggest a strong lipolytic rate. Obese rats showed an excessive development of all fat pads although a more pronounced effect was observed in the SC one. The cellularity of this depot was increased 8 fold when compared to lean rats, but these fat cells were only 1.5 to 2-fold larger. SC adipocytes showed a marked increase in their basal lipolytic activity but a lack of change in responsiveness to NE or BRL 37344. The association between high basal lipolysis and increased cellularity yields to a marked adipose cell lipolytic rate, especially from the SC region. SHR/N-cp rats were characterized by a hyperplasic type of obesity with an excessive development of the SC depot. The dyslipidemia, attested by an altered serum lipid profile could be attributed to excessive lipolysis that contributes to increased FFA levels, and to early development of insulin resistance through a lipotoxicity effect.

Obese Zucker rat is often used as a model of genetic obesity to understand the mechanism of the development of obesity. In the present work, in order to better understand the regulation of lipolysis in the Zucker rat, the lipolytic activities of adipocytes isolated from different adipose depots of lean and obese Zucker rats, in the basal state or after catecholamine stimulation have been measured. The obese Zucker rat presents hyperinsulinemia without hyperglycemia and with elevated plasma free fatty acids, suggesting a dyslipidemia. Morphological studies of three adipose deposits show a marked hypertrophic and hyperplastic type of obesity, much pronounced in the subcutaneous depot. In the current study we show that the basal lipolytic rate is higher in adipocytes from each deposit of obese rats (when results are corrected for cell surface area). This finding, associated with the increase of all deposits, could contribute to the elevated plasma FFA observed. Investigation of the responsiveness of dibutyril cAMP (DBcAMP) points out that the defect in the NE responsiveness is essentially located at post-receptor level. Nevertheless, a receptor defect could not be excluded as suggested by a decrease of the β-ARs observed in all deposits. Our study points out that the lipolytic resistance to catecholamines in adipose tissue of obese Zucker rats appears to counteract the increase in the lipolytic rate, in order to moderate the increase in plasma FFA levels that may contribute to the hyperinsulinemia observed, characteristic of an insulino-resistant state.

Obese Zucker rat is often used as a model of genetic obesity to understand the mechanism of the development of obesity. In the present work, in order to better understand the regulation of lipolysis in the Zucker rat, the lipolytic activities of adipocytes isolated from different adipose depots of lean and obese Zucker rats, in the basal state or after catecholamine stimulation have been measured. The obese Zucker rat presents hyperinsulinemia without hyperglycemia and with elevated plasma free fatty acids, suggesting a dyslipidemia. Morphological studies of three adipose deposits show a marked hypertrophic and hyperplastic type of obesity, much pronounced in the subcutaneous depot. In the current study we show that the basal lipolytic rate is higher in adipocytes from each deposit of obese rats (when results are corrected for cell surface area). This finding, associated with the increase of all deposits, could contribute to the elevated plasma FFA observed. Investigation of the responsiveness of dibutyril cAMP (DBcAMP) points out that the defect in the NE responsiveness is essentially located at post-receptor level. Nevertheless, a receptor defect could not be excluded as suggested by a decrease of the β-ARs observed in all deposits. Our study points out that the lipolytic resistance to catecholamines in adipose tissue of obese Zucker rats appears to counteract the increase in the lipolytic rate, in order to moderate the increase in plasma FFA levels that may contribute to the hyperinsulinemia observed, characteristic of an insulino-resistant state.La rata Zucker obesa frecuentemente se uti|liza como modelo de obesidad genética para desentrañar los mecanismos de desarollo de la obesidad. El objetivo de este trabajo ha sido profundizar en el estudio de la regulación de la lipólisis en el iejido adiposo de rata Zucker. Para ello, se ha medido la actividad lipolítica de adipocitos aislados de diferente localización de tejido adiposo de ratas obesas y normoponderales tanto a nivel basal como en respuestas a catecolaminas y agonistas adrenérgicos. Asimismo, se han valorado los sitios de unión al radioligando [I]-cyanopindolol sobre membranas de células adiposas aisladas de estos mismos depósitos de grasa. Los resultados mostraron que la rata Zucker obesa presenta un cuadro de hiperinsulinemia sin hiperglucemia, pero con niveles plasmáticos elevados de ácidos grasos, indicativos de dislipidemia. Los estudios morfologicos de tres depósitos de tejido adiposo revelaron obesidad hipertrófica y hiperplásica marcada, especialmente pronunciada en el iejido adiposo subcutáneo. La lipólisis basal fue más elevada en adipocitos de ratas obesas (cuando los datos fueron corregidos por la superficie celular). Este incremento, junto a la adiposidad pronunciada de los obesos contribuye a elevar el nivel de ácidos grasos circulantes. No sólo el efecto lipolitico máximo provocado por noradrenalina sino la respuesta al DBAMPc están reducidos on ratas obesas, indicando un efecto post-receptor. Sin embargo, no puede excluirse una alteración de los receptores, ya que se observa disminución del número de receptores beta-adrenérgicos en los tres depósitos estudiados. Este trabajo pone de manifiesto una resistencia a las catecolaminas en rejido adiposo de ratas obesas Zucker que parece limitar el aumento de actividad lipolítica. Esta adaptación puede conducir a moderar el aumento de los ácidos grasos circulantes involucrados en la hiperinsulinemia, característica de la insulino-resistencia de estos rodeores obesos.

The aim of the present study was to determine the respective roles of energy substrates and insulin on leptin secretion from white adipocytes. Cells secreted leptin in the absence of glucose or other substrates, and addition of glucose (5 mM) increased this secretion. Insulin doubled leptin secretion in the presence of glucose (5 mM), but not in its absence. High concentrations of glucose (up to 25 mM) did not significantly enhance leptin secretion over that elicited by 5 mM glucose. Similar results were obtained when glucose was replaced by pyruvate or fructose (both 5 mM). l-Glycine or l-alanine mimicked the effect of glucose on basal leptin secretion but completely prevented stimulation by insulin. On the other hand, insulin stimulated leptin secretion when glucose was replaced by l-aspartate, l-valine, l-methionine, or l-phenylalanine, but not by l-leucine (all 5 mM). Interestingly, these five amino acids potently increased basal and insulin-stimulated leptin secretion in the presence of glucose. Unexpectedly, l-glutamate acutely stimulated leptin secretion in the absence of glucose or insulin. Finally, nonmetabolizable analogs of glucose or amino acids were without effects on leptin secretion. These results suggest that 1) energy substrates are necessary to maintain basal leptin secretion constant, 2) high availability of glycolysis substrates is not sufficient to enhance leptin secretion but is necessary for its stimulation by insulin, 3) amino acid precursors of tricarboxylic acid cycle intermediates potently stimulate basal leptin secretion per se, with insulin having an additive effect, and 4) substrates need to be metabolized to increase leptin secretion.

The effects of insulin on white adipose tissue hyperplasia have been studied by quantitative radioautography in streptozotocin diabetic rats. After 1 mo of diabetes, the majority of the adipocytes were extremely small (less than 15 microM) but contained several tiny triglyceride droplets (pauciadipose cells). At this point, the diabetic animals were infused with insulin (8.5 U.kg-1.day-1) delivered via osmotic minipumps for 0-8 days. Control and diabetic rats were pulse-injected with tritiated thymidine (4 h), and samples of parametrial white adipose tissue (PWAT) were collected for quantitative analysis of mitotic frequencies. One-day insulin treatment increased PWAT weight and adipocyte size without stimulating mitoses. However, after 4 days of insulin replacement, the total tissue labeling index increased greater than 120 times over control values. This marked enhancement of mitotic activity principally occurred in interstitial cells rather than in typical adipocytes, pauciadipose cells, or endothelial cells. After 8 days of insulin infusion, the mitotic activity significantly decreased. The results demonstrate that 1) insulin is able to stimulate cell proliferation in PWAT of adult diabetic rats, 2) it transiently stimulates proliferative activity in adipose tissue after a 2- to 3-day period of induction, 3) the increase in adipocyte size precedes the enhancement of mitotic activity, and 4) the effects of insulin were specific, as in the same rats, under the same experimental conditions, insulin did not increase the cell labeling in brown adipose tissue.

Lipogenesis from glucose and lipoprotein lipase activity were investigated in humans. The reliability of measurements was quantified and correlations with fat cell weight were assessed. Twenty-four subjects (7 women, 17 men) were studied twice within a 2-week period, along with 17 additional male subjects who were studied once and used only in the correlation analyses. All subjects were not regularly involved in an exercise-training program and were between 18 and 30 years of age. Following an overnight fast, adipose tissue specimens were obtained by suprailiac biopsy and fat cells were collagenase isolated. Mean fat cell weight was obtained from 400 to 500 cell diameter determinations per subject. Basal and insulin-stimulated fat cell lipogenesis from glucose were determined using D-[U-14C]glucose and were reported in nanomoles of glucose per hour per 10(6) cells. Adipose tissue heparin-releasable lipoprotein lipase activity was also determined and expressed in micromoles of free fatty acids per hour per gram of tissue and per 10(6) cells. Fat cell weight, basal and insulin-stimulated lipogenesis and lipoprotein lipase activity per gram showed high reliability of measurement, interclass and intraclass coefficients being 0.83 and over. Lipoprotein lipase activity per 10(6) cells showed a somewhat lower degree of reliability, interclass and intraclass coefficients being, respectively, 0.69 and 0.81. On the other hand, fat cell weight was positively correlated with lipoprotein lipase activity (r = 0.80), while no significant correlation was observed between basal lipogenesis and fat cell weight. Moreover, basal lipogenesis presented no significant correlation with lipoprotein lipase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

In order to study the effects of heredity and of physical training on adipose tissue morphology and metabolism, 15 pairs of monozygotic twins (MZ) (six males and nine females), aged from 16 to 24 years, weighing 56.2 +/- 9.1 kg and with 13.9 +/- 8.2 percent body fat, were submitted to a biopsy of adipose tissue in the suprailiac region. In addition, eight pairs of twins (four male and four female) took part in a 20-week ergocycle training program, five days a week, 40 min a day, at 80 percent of their maximal heart rate. Adipocyte diameter (AD) was assessed on collagenase isolated fat cells. Basal (BL), epinephrine submaximal (10(-5) M) (ESML) and epinephrine maximal stimulated lipolysis (10(-4) M) (EML) were determined on isolated fat cells. Intraclass correlation coefficients indicated significant intrapair resemblance before training for all fat morphological and metabolic indicators (0.78 less than or equal to ri less than or equal to 0.93). Training significantly increased VO2 max (pre: 44.7 +/- 7.6 (ml/kg) vs post: 50.8 +/- 5.0; P less than or equal to 0.001). No training effect was found in percent body fat and AD. Training significantly increased BL, ESML, and EML (P less than or equal to 0.01). Moreover, twins of the same MZ pair yielded identical responses in ESML and EML with training. Intraclass coefficients for the magnitude of change in activity over pretraining values reached 0.84 and 0.90 respectively. Apparently a genetically determined response to training could not be found for BL. These results show that training per se has an effect on adipose tissue lipolysis beyond variation in fatness. Furthermore, sensitivity of stimulated lipolysis to training appears to have a genetic basis.

Twenty-three male subjects, 31.7 (mean) +/- 7.4 (s.d.) yr of age, weight 70.7 +/- 9.0 kg and with 13.4 +/- 4.7 percent body fat were submitted twice within a week to biopsies of subcutaneous adipose tissue in the suprailiac region. Two biopsies (sample A and B) were obtained on day 1 and two others (sample C and D) in the contralateral region on day 2. Average fat cell diameter (ACD) was assessed by measuring at least 500 cells per subject. There was no significant difference between day 1 and day 2 for ACD (means 1 = 62.6 +/- 12.2 micron; means 2 = 63.2 +/- 12.3 micron). Intra-class reliability coefficient reached 0.97. ANOVA-RBFD showed no day or sample effects (P greater than 0.05) on ACD. Basal (BL), epinephrine submaximal (10(-5) M) (ESML) and epinephrine maximal (10(-4) M) (EML) stimulated lipolysis have been determined for 18 of these subjects. Intra-class reliabilities were moderately high, reaching 0.71 for BL, 0.83 for ESML and 0.72 for EML, respectively. Controlling the level of activity for 36 h prior to the biopsies resulted, however, in increased coefficients. In this case, intra-class coefficients computed with 11 subjects were 0.99 for BL, 0.88 for ESML and 0.85 for EML. The data demonstrate that ACD and lipolytic capacity can be reliably measured, particularly when activity of subjects is controlled during the 36-h period preceding the biopsies.

Ephedrine is a potential slimming drug that stimulates thermogenesis in man and laboratory animals. Considering that brown adipose tissue is an important site of catecholamine-induced thermogenesis in homeotherms, we tested the thermogenic efficiency of several ephedrine stereoisomers on adipocytes isolated from rat interscapular brown adipose tissue. Addition of (-)-ephedrine (0.1 mM) to brown adipocyte suspensions rapidly stimulated cellular respiration eight times above basal values. A stable Vmax of 335 nmol O2/min/10(6) cells was reached less than 5 min after the onset of respiratory stimulation. This value represents 85 percent of the maximal respiration observed with norepinephrine, the physiological effector of thermogenesis. The (-)isomer of ephedrine (1/2 Vmax = 20 microM) was more potent that other stereoisomers (+)-psi-ephedrine, (-)-psi-ephedrine (racephedrine) in enhancing brown adipocyte respiration. Beta-Adrenergic antagonists (alprenolol and propranolol) were much more effective than alpha-adrenergic antagonists (phentolamine and phenoxybenzamine) in inhibiting the respiratory effects of ephedrine. It is concluded that (-)-ephedrine mimics the calorigenic action of norepinephrine by directly stimulating brown adipocyte respiration via beta-adrenoreceptors.

Cold acclimation (4 degrees C) and "cafeteria diets" increased the thermic response of rats to catecholamines. This phenomenon was accompanied by six- to eightfold increases of interscapular brown adipose tissue (IBAT) weight, total tissue cytochrome oxidase activity, and total number of brown adipocytes. Quantitative radioautographic experiments using [3H]thymidine disclosed that cold exposure markedly enhanced the mitotic activity in blood capillaries and small-venule endothelial cells, adipose tissue interstitial cells, and preadipocytes rather than in fully differentiated brown adipocytes. IBAT mitotic index increased 70 times over control values after only 2 days of cold exposure. Thereafter, the proliferative activity progressively decreased. IBAT cell composition was modified during cold acclimation as the percentage of interstitial cells and preadipocytes increased over the other cellular types. Because brown adipose tissue is the principal site of norepinephrine-induced thermogenesis in homeothermal animals, it is suggested that brown adipocyte proliferation from precursor cells represents the fundamental phenomenon explaining the increased capacity of cold-acclimated animals to respond calorigenically to catecholamines.

In order to study human fat cell morphology and metabolism in both sexes, with different levels of fatness and physical training, 53 subjects (14 women and 39 men), 25.9 +/- 7.6 (mean +/- SD) years of age, weighing 64.8 +/- 10.8 kg and with 14.8 +/- 4.7% body fat were submitted to a biopsy of subcutaneous adipose tissue in the supra-iliac region. Average fat cell diameter (ACD) was assessed by measuring at least 500 cells per subject. Basal (BL), epinephrine sub-maximal (10(-5) M) (ESML) and epinephrine maximal (10(-4) M) (EML) stimulated lipolysis have been determined on collagenase isolated fat cells. Female subjects have larger ACD (83.4 +/- 12.3 micrometer vs. 62.5 +/- 11.9 micrometer) (P less than or equal to 0.001) and lower BL, ESML, and EML than men (P less than or equal to 0.05). After control over age and sex of subjects, there were significant and negative correlations between all fatness indicators (ACD, fat mass in kg, percent body fat, sum of 9 skinfolds) and BL, ESML and EML. A completely randomized factorial ANOVA design revealed a significant effect of fatness level on BL, ESML and EML, but a non-significant trend for the effect of physical training on the same variables. It is concluded that lipolytic activity is more related to body fatness than to the training status. However, training tends to accentuate lipolytic activity as shown by values of BL, ESML and EML found in the lean highly trained subjects of the study.

In order to study human fat cell morphology and metabolism in both sexes, with different levels of fatness and physical training, 53 subjects (14 women and 39 men), 25.9 +/- 7.6 (mean +/- SD) years of age, weighing 64.8 +/- 10.8 kg and with 14.8 +/- 4.7% body fat were submitted to a biopsy of subcutaneous adipose tissue in the supra-iliac region. Average fat cell diameter (ACD) was assessed by measuring at least 500 cells per subject. Basal (BL), epinephrine sub-maximal (10(-5) M) (ESML) and epinephrine maximal (10(-4) M) (EML) stimulated lipolysis have been determined on collagenase isolated fat cells. Female subjects have larger ACD (83.4 +/- 12.3 micrometer vs. 62.5 +/- 11.9 micrometer) (P less than or equal to 0.001) and lower BL, ESML, and EML than men (P less than or equal to 0.05). After control over age and sex of subjects, there were significant and negative correlations between all fatness indicators (ACD, fat mass in kg, percent body fat, sum of 9 skinfolds) and BL, ESML and EML. A completely randomized factorial ANOVA design revealed a significant effect of fatness level on BL, ESML and EML, but a non-significant trend for the effect of physical training on the same variables. It is concluded that lipolytic activity is more related to body fatness than to the training status. However, training tends to accentuate lipolytic activity as shown by values of BL, ESML and EML found in the lean highly trained subjects of the study.