The negative association between serum free testosterone and leptin is dependent on insulin-like growth factor-binding protein 1 in healthy young and middle-aged men

Correlation of Serum Leptin Concentrations with Body Composition and Gender in Taiwanese Hemodialysis Patients without Diabetes

OBJECTIVE

(1) To evaluate the impact of body composition and gender on serum leptin concentration in hemodialysis patients. (2) To study which marker of adiposity is most appropriate in Taiwanese hemodialysis patients without diabetes. (3) To compare the nutrition status between nonlean and lean subjects.

PATIENTS AND METHODS

Serum leptin concentrations were measured by radioimmunoassay collected in 88 hemodialysis patients without diabetes. Bioimpedance analysis was performed to determine percent fat mass (%FM), lean body mass (LM), and total body water (TBW). Body mass index (BMI) was calculated as weight/height2. Albumin and transferrin were measured by standard laboratory methods.

RESULTS

Serum leptin levels were more correlated with percent fat mass (r = 0.697; P < 0.001) than with body fat mass (r = 0.672; P < 0.001) or with BMI (r = 0.594; P < 0.001) in the group as a whole and in each subgroup when analyzed separately by gender. The mean (+/- SD) serum leptin levels were 32.5 +/- 34.3 ng mL(-1) in women subjects and 13.6 +/- 15.5 ng mL(-1) in men subjects (P < 0.001). Multiple regression analysis in all subjects revealed that serum leptin levels were independently affected by percent fat mass and gender. Adiposity corrected serum leptin, such as leptin/BMI, leptin/percent fat mass, and leptin/body fat mass was significantly different between sexes (P < 0.001). The significantly higher serum leptin concentrations in women than in men were observed in obese subjects with BMI > 25 kg/m2 (P < 0.001) as well as nonobese subjects with BMI < 25 kg/m2 (P < 0.05). There were no differences in lean mass and albumin between nonlean and lean subjects.

CONCLUSION

Gender and adiposity had impact on serum leptin levels in hemodialysis patients without diabetes. In terms of adiposity, serum leptin levels had stronger correlation with percent fat mass than with body fat mass (FM) or BMI in Taiwanese hemodialysis patients. Steady-state serum leptin levels could serve as valuable clinical markers for the body adiposity in stable hemodialysis patients without diabetes. Protein malnutrition markers and lean mass should be checked in lean subjects for the evaluation of the protein stores of hemodialysis patients.

Leptin inhibits basal but not gonadotrophin-stimulated testosterone production in the immature mouse and sheep testis

The mechanisms whereby leptin regulates testosterone secretion are complex and are likely to involve actions at different levels of the hypothalamus–pituitary–gonadal axis. In the present study, the effect of leptin on testicular steroidogenesis at different developmental stages in mice and sheep was investigated. Testosterone data from testicular slice and Leydig cells of immature and adult mice testes demonstrated that the action of leptin in the regulation of steroidogenesis appears to be dependent on the developmental stage of the testis. Leptin biphasically modulates basal testosterone production in immature testicular slice cultures: at relatively low concentrations (6.25–12.5 ng mL–1) leptin exerts a significant inhibitory effect, but has less of an effect at very low (1.25 ng mL–1) or high concentrations (25 ng mL–1). However, leptin failed to modulate basal testosterone levels in Leydig cell preparations. In contrast with immature testes, leptin was unable to regulate either basal or human chorionic gonadotrophin (10 IU mL–1)-stimulated testosterone production in adult testicular slices or Leydig cell cultures. The age- and concentration-dependent regulation pattern was confirmed using sheep testicular slice culture. Leptin (1.56–25 ng mL–1) significantly inhibited basal testosterone production in the testis from birth to Day 21, but had no effect on Day 27 or older testes. However, the plasma and testicular concentrations of leptin and testosterone data in the ram indicate that such a regulatory effect of leptin on testis steroidogenesis in vitro is unable to efficiently influence testosterone concentrations in vivo. This does not exclude the possibility of a non-competitive mechanism of interaction between leptin and luteinising hormone to regulate testosterone production. Thus, we hypothesise that leptin is not an important independent regulator of testosterone concentration in the normal physiological state. The physiological significance and mechanism of leptin regulation of basal testosterone production are not known; further studies are required to elucidate these important issues.

Direct effects of sex steroid hormones on adipose tissues and obesity

Sex steroid hormones are involved in the metabolism, accumulation and distribution of adipose tissues. It is now known that oestrogen receptor, progesterone receptor and androgen receptor exist in adipose tissues, so their actions could be direct. Sex steroid hormones carry out their function in adipose tissues by both genomic and nongenomic mechanisms. In the genomic mechanism, the sex steroid hormone binds to its receptor and the steroid-receptor complex regulates the transcription of given genes. Leptin and lipoprotein lipase are two key proteins in adipose tissues that are regulated by transcriptional control with sex steroid hormones. In the nongenomic mechanism, the sex steroid hormone binds to its receptor in the plasma membrane, and second messengers are formed. This involves both the cAMP cascade and the phosphoinositide cascade. Activation of the cAMP cascade by sex steroid hormones would activate hormone-sensitive lipase leading to lipolysis in adipose tissues. In the phosphoinositide cascade, diacylglycerol and inositol 1,4,5-trisphosphate are formed as second messengers ultimately causing the activation of protein kinase C. Their activation appears to be involved in the control of preadipocyte proliferation and differentiation. In the presence of sex steroid hormones, a normal distribution of body fat exists, but with a decrease in sex steroid hormones, as occurs with ageing or gonadectomy, there is a tendency to increase central obesity, a major risk for cardiovascular disease, type 2 diabetes and certain cancers. Because sex steroid hormones regulate the amount and distribution of adipose tissues, they or adipose tissue-specific selective receptor modulators might be used to ameliorate obesity. In fact, hormone replacement therapy in postmenopausal women and testosterone replacement therapy in older men appear to reduce the degree of central obesity. However, these therapies have numerous side effects limiting their use, and selective receptor modulators of sex steroid hormones are needed that are more specific for adipose tissues with fewer side effects.

Diurnal variation in circulating leptin is dependent on gender, food intake and circulating insulin in mice

Leptin is an adipocyte hormone involved in the regulation of energy homeostasis. Its circulating levels show a diurnal rhythm with a nocturnal peak. We examined the influences of gender, feeding state, and plasma insulin and glucose on the diurnal rhythm in normal mice. Plasma was sampled at 4-h interval for 24 h in female (n=80) and male (n=80) mice, which were freely fed or fasted. In both genders, plasma leptin displayed a diurnal rhythm with a nadir at 8 or 10 AM and a nocturnal peak at 10 PM to 2 AM. The nocturnal increase in leptin was higher in females (+160+/-18%) than in males (61+/- 16%; P<0.001), completely abolished by fasting, and correlated significantly to the diurnal variation in plasma insulin both in females (r=0.44, P=0.003) and males (r=0.46, P<0.001). Baseline plasma leptin in non-fasted animals were not different between the genders, whereas during fasting, the reduction in leptin was more pronounced in males than in females, resulting in a higher plasma leptin after fasting in females. Plasma insulin was higher in males under non-fasted conditions (P=0.003), but not significantly different between genders in fasted animals. In conclusion, plasma leptin displays a nocturnal increase in mice, which is more pronounced in female mice than in male mice, is completely abolished by fasting and correlates to the diurnal variation in circulating insulin. It is suggested that the nocturnal rise in leptin shows gender dependency and is caused by the increase in plasma insulin caused by food intake.