OBJECTIVE:To study the relation between body mass index (BMI) and age on the one hand and total number of human (pre-) adipocytes and preadipocyte differentiation capacity on the other hand. SUBJECTS: In total, 189 women undergoing surgical mammary reduction, age range 16-73 y, BMI range 19.7-39.7 kg/m 2 . MEASUREMENTS: Differentiation of preadipocytes in primary culture was assessed by morphological criteria, and determination of glycerol-3-phosphate dehydrogenase after stimulation of the cells by standardized adipogenic conditions containing isobutyl-methylxanthine, troglitazone or both compounds. The total number of stromal cells (ie preadipocytes) and fat cells per gram of adipose tissue and per body as well as mature fat cell volume were calculated from isolated stromal cells and adipocytes, respectively, and anthropometric measures. RESULTS: BMI correlated positively to age, mature fat cell size and total number of adipocytes and stromal cells per body (r varying from 0.22 to 0.54, each Po0.05). In contrast, BMI correlated negatively to the number of adipocytes and stromal cells per gram of adipose tissue and the capacity of preadipocytes to differentiate (r varying from À0.20 to À0.37, each Po0.05). No significant correlation was observed between BMI and the ratio of stromal cells to adipocytes. The sample was also divided into three groups: BMI o25 kg/m 2 (lean), BMI 25-29.9 kg/m 2 (overweight) and BMI Z30 kg/m 2 (obese). The overweight group showed a larger fat cell size but no increase in total fat cell or stromal cell number when compared to the lean subjects. The obese subjects showed larger stromal and fat cell numbers when compared to the lean subjects. Age did not independently correlate to the number of stromal cells or adipocytes per gram of adipose tissue or total body, nor with the capacity of preadipocytes to undergo differentiation and the ratio of stromal cells to adipocytes. CONCLUSION: There seems to be a constant ratio between the number of adipose tissue stromal cells and adipocytes independently of BMI and age in humans. During adipose tissue expansion, there seems to be both a continuous increase in fat cell size, and in stromal cell and adipocyte number, but the increase in fat cell size apparently precedes the increase in fat cell number. The differentiation capacity of the stromal cells appears to decrease with increasing BMI.

Objective: Circulating leptin, the product of the ob gene, is known to be closely correlated with adipose tissue mass, but it is also subject to short-term regulation by a variety of hormones including catecholamines. The aim of this study was to investigate the contribution of the three b-adrenergic receptors to leptin secretion from cultured human adipocytes. Design and methods: The model of in vitro differentiated human subcutaneous adipocytes was used in this study. The presence of the b-adrenoceptor subtypes was studied by RT-PCR. The functional role of the receptor subtypes was determined by stimulation of lipolysis by selective b-adrenergic agonists and by measuring glycerol release. Leptin secretion into the medium of cultured human adipocytes from young normal-weight females was measured by radioimmunoassay. Results and conclusion: In a ®rst set of experiments, the expression of the three b-adrenergic receptor subtypes in cultured human adipocytes was demonstrated. To test their functional activity, the effect of the b-adrenoceptor agonists isoproterenol (non-selective agonist), dobutamine (b 1 -selective), fenoterol (b 2 -selective) and the b 3 -selective agonists BRL 37344 and CGP 12177 was studied. All agonists exhibited a dose-and time-dependent stimulation of glycerol release into the medium in a rather uniform manner. Isoproterenol rapidly reduced leptin secretion from cultured subcutaneous adipocytes in a dose-dependent fashion. Incubation with 10 À6 mol/l isoproterenol for 24 h resulted in a reduction of the leptin concentration by 48% (P < 0.01). A similar, but less pronounced suppressing effect was seen for dobutamine and fenoterol, whereas both BRL 37344 and CGP 12177 were not effective. These data provide evidence that catecholamines are able to suppress leptin release from differentiated human adipocytes, supporting the concept that leptin secretion is acutely regulated by surrounding hormones. This inhibition is obviously mediated via b 1 -and b 2 -adrenergic receptors.

BACKGROUND:Leptin is an adipose protein regulating food intake in the hypothalamus. Animal studies have suggested that leptin also acts in an auto-=paracrine fashion on adipose cell function. OBJECTIVE: The aim of this study was to investigate the effects of leptin on the differentiation and metabolism of cultured human adipocytes. MATERIAL: Adipose tissue from young healthy, lean women (body mass index (BMI) < 27 kg=m 2 ) undergoing elective mammary reduction surgery and young obese individuals (BMI > 40 kg=m 2 ) undergoing laparoscopic gastric banding. METHODS: Human preadipocytes in primary culture were induced to undergo differentiation by defined adipogenic factors. Mature adipocytes were isolated by collagenase digestion and kept in culture suspension. Glycero-3-phosphate dehydrogenase (GPDH) activity was used as a marker of adipose differentiation; glucose uptake, lipolysis and PAI-1 secretion were measured as parameters of fat cell function. RESULTS: Human preadipocytes and adipocytes from lean and obese subjects expressed the long leptin receptor isoform and two of the three short forms as assessed by polymerase chain reaction (PCR). Leptin at a supraphysiological concentration induced a transient increase of GPDH activity, but had no effect on glucose uptake and PAI-1 secretion from human adipocytes. In addition, basal and isoproterenol-stimulated lipolysis as well as the antilipolytic action of insulin in human adipocytes was not significantly affected by leptin exposure. CONCLUSION: In contrast to animal data, the results of our experiments do not demonstrate significant effects of leptin on main metabolic functions of human adipocytes arguing against a local auto-=paracrine action of leptin in human adipose tissue.