Serum Leptin Levels and Adiposity in Chinese.

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Serum Leptin Levels and Adiposity in Chinese*

*This work was financially supported by the Rockefeller Foundation of the United States and Natural Science Fund of Shanghai Secondary Medical University

98-11-25


SUMMARY

     Objective: To establish normal serum leptin levels in Chinese and to investigate the relationships between serum leptin levels and body fat, gender, age and androgen. Methods: Serum leptin levels were measured in 77 lean (BMI<25) and 28 overweight or obese(BMI≥25) subjects by a RIA method. Results: The serum leptin levels in lean Chinese were 2.15±1.46ng/ml in male and 7.85±3.60ng/ml in female, which are similar to those of Caucasians, while in overweight or obese ones, the levels were 4.87±3.47ng/ml and 16.59±6.92ng/ml respectively, lower than those in Caucasians. A 2-3 times higher leptin concentrations were found in women than in men in both conditions. Even when the number of lean males were expanded to 79 subjects aged from 17-80, no significant leptin-age relationship was found. Despite 25% of obese subjects manifested a relative deficiency of leptin, as a whole, leptin levels in both men and women were significantly correlated with BMI (r=0.69, P<0.001 in male and r=0.63, P<0.001 in female).  Conclusion: Serum leptin levels in Chinese lean people are similar to those in Caucasians and in both lean and obese groups, the leptin levels are correlated with BMI, suggesting that the great majority of the obese patients are resistant to endogenous leptin. Those who are relatively deficient of leptin may become a group of good candidates for leptin treatment in the future.

[Key words] Leptin  Obesity  BMI


INTRODUCTION

     Obesity, with its complications which cause major human morbidity and mortality, has become a common concern in western society and its prevalence is also increasing rapidly even in developing countries. Leptin, the protein product of the ob gene, is produced mainly in white adipose tissue. As a messenger of fat tissue, with 16KD molecular weight, it crosses the blood-brain barrier by virtue of a special transporting receptor, reaches central nervous system, then alters eating behavior and adjusts the activity of autonomous system. Finally , by feed-back from adipose tissue to the hypothalamus, leptin maintains a homeostasis of the fat volume and body weight. In fact, in the obese animal model resulting from the ob gene mutation (ob/ob mouse), leptin administration reduced their body weight and fat mass, while correcting their hyperinsulinemia and hyperglycemia[1-3]. It seemed to be a reasonable and efficient cure for the obese patient and clinical trial is on-going in the United States. However, except several cases reported, mutations in the leptin gene have not been linked to obesity in most humans[4]. On the contrary, both the ob mRNA expression in adipocytes and serum leptin concentrations are elevated in obese subjects[5-7]. This elevation of leptin levels is associated with the increasing of body mass index(BMI), fat mass or percentage body fat. As it is the case in insulin resistance, the high circulating leptin level in obese patients indicates a leptin resistance. To our knowledge, no Chinese serum leptin levels which were determined with a method comparable with those of western countries have been reported so far. In this study, by using internationally recognized and conventionally used method, we intended to establish normal leptin levels in Chinese and to investigate the relationships between leptin and body fat, gender, age, fat distribution and androgen.


   

SUBJECTS AND METHODS

Subjects

        One hundred and five subjects(53 men and 52 women) without any detectable medical or surgical illnesses, were recruited from the physical examination station of the local district and the Outpatient Department of Rui Jin Hospital. The mean ages were 33±11.8 and 37±13.0 yr respectively. The blood samples were drawn at 07-08h after overnight fast, and the sera were separated and stored at –200C until hormone assay. In order to study age-leptin relationship, an additional 46 male sera, which were collected previously and stored in deep-freezer as normal controls in a hypertension survey, were used, which expanded the age of male subjects to a range from 17 to 80 yr.

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Measurements and assays:

     Body weight was measured to the nearest 0.1Kg and height was measured without cap and shoes to the nearest 0.1cm. Waist and hip circumferences were determined to the nearest 0.1cm. The former was taken to the smallest standing horizontal circumference between the ribs and the iliac crest, while the latter was measured as the largest standing horizontal circumference of the buttocks. BMI calculation was weight(kilograms)/height(m)2, BMI>25 being considered as overweight or obese.

      Serum leptin levels were determined by RIA with an internationally conventionally used leptin RIA Kit (Linco Research, St. Charles, ...

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