In vitro effects of leptin on human adipocyte metabolism.

OBJECTIVE: Leptin receptors are expressed in adipocytes, suggesting potential autocrine/paracrine effects. Studies on the direct effects of leptin on adipose tissue metabolism in different species have yielded controversial data. To assess the in vitro effects of leptin on human adipocyte metabolism: lipolysis, the insulin-induced inhibition of lipolysis and lipogenesis were studied in adipocytes obtained from infants and adults. METHODS: Lipolysis was studied by incubating adipocytes with increasing concentrations of leptin or isoprenaline. Glycerol in the incubation medium was measured as an indicator of lipolysis. For the lipogenesis and insulin-induced inhibition of lipolysis experiments, the cells were preincubated with 0, 25, or 250 ng/ml of leptin for 2 h. RESULTS: Leptin did not stimulate lipolysis in human adipocytes, either in children or adults. Preincubation with leptin did not affect the insulin-induced inhibition of lipolysis, but decreased the insulin-induced lipogenesis (p < 0.05). CONCLUSIONS: This study shows that leptin has no direct lipolytic effect in human adipocytes. The lack of effect on the insulin-induced inhibition of lipolysis and the negative effect on lipogenesis indicates that the effect of leptin is not at the proximal insulin-signalling pathway but further downstream.

Effects of growth hormone treatment on the leptin system and body composition in obese prepubertal boys.

UNLABELLED: Leptin correlates with measures of body fat stores. Growth hormone (GH) treatment may affect leptin levels either directly or indirectly by influencing body composition and circulating insulin level. Here, the effects of GH treatment on the leptin axis and body composition of six severely obese, but otherwise healthy, prepubertal boys were studied. Fasting serum leptin was significantly reduced after only 3 wk of GH treatment. Body fat percentage, but not BMI, decreased significantly (p < 0.05) after 3 mo. The serum leptin concentration per unit fat mass decreased significantly during GH treatment (p < 0.05), suggesting that such treatment might have a direct effect on serum leptin independently of the effects on body composition. Leptin RNA expression in abdominal subcutaneous tissue was not significantly changed by treatment. CONCLUSIONS: The data indicate that GH has an early downregulatory effect on the circulating leptin level independently of the concomitant changes in body composition. Whether GH affects leptin production or metabolism needs further study.

Total parenteral nutrition after surgery rapidly increases serum leptin levels.

OBJECTIVE: In humans, leptin is regulated by long-term changes in energy intake. However, short-term regulation of serum leptin by nutrients has been difficult to show. The aim of this study was to investigate whether short periods of fasting and stress sensitise the leptin response to nutrients. SUBJECTS AND EXPERIMENTAL PROTOCOL: Fourteen patients of normal weight undergoing elective open cholecystectomy were randomised into two groups. One group received saline infusion during surgery and for 24 h postoperatively. The other group also received saline during the surgical procedure, but total parenteral nutrition (TPN) was started immediately after surgery. Blood samples were drawn before as well as 2, 4, 8, 16, and 24 h after the start of surgery to determine the serum levels of leptin and other hormones. RESULTS: Postoperative TPN induced a significant rise in serum leptin within 6 h, reaching a more than fourfold increase within 14 h (P<0.001). Serum glucose and insulin levels increased within 2 h. Growth hormone and IGF-1 serum levels also increased significantly in the group receiving TPN. Serum cortisol levels increased postoperatively in both groups, which may explain why no significant reduction in serum leptin was observed in the group receiving saline. Free tri-iodothyronine (T3) decreased in both groups, while catecholamines were similar in the groups. CONCLUSION: During fasting and surgical stress, nutrients rapidly increased the serum leptin levels in humans in a manner similar to that previously reported in rodents. This may be mediated by increases in serum glucose, insulin and cortisol.

Effects of growth hormone treatment in obese prepubertal boys.

Childhood obesity is associated with several abnormalities of the GH axis, including decreased spontaneous secretion, decreased response to exogenous secretagogues, and altered pulsatile pattern of secretion. In adults, GH treatment reduces abdominal obesity and improves insulin sensitivity, as well as blood lipid profiles. Whether GH has similar effects in obese children has not been investigated previously. In this study, seven prepubertal severely obese boys aged 10-12 yr were treated with GH for 6 months and followed for an additional 6 months. No diet or exercise modifications were initiated. Body fat percentage decreased from 51.3% to 46.1% after treatment (P = 0.03). Frequently sampled iv glucose tolerance tests revealed an increased responsivity of the acute insulin secretion (P = 0.04) and a nonsignificant trend toward improved insulin sensitivity. In isolated adipocytes, the maximum isoprenaline- and terbutaline-induced lipolysis were increased approximately 2.5-fold (P = 0.02). The sensitivity of the adipocytes to isoprenaline was unchanged, whereas the sensitivity to terbutaline was increased (P = 0.04). No effect was observed on basal or insulin-stimulated lipogenesis. In conclusion, GH treatment for 6 months of obese prepubertal boys reduces body fat, possibly, via stimulation of catecholamine-induced lipolysis, without negative effects on glucose homeostasis.

Growth hormone treatment downregulates serum leptin levels in children independent of changes in body mass index.

The changes in serum leptin levels during growth hormone (GH) treatment were studied in 27 children, 17 with GH deficiency (GHD), 10 with idiopathic short stature (ISS), and 9 with Prader-Willi syndrome (PWS). Within 1 month of GH treatment, serum leptin levels decreased by 40% in the GHD children (p < 0.01). There was no significant change in serum leptin level in the children with ISS. In children with PWS, the mean serum leptin level decreased by almost 60% after 3 months of treatment (p < 0.001). Thereafter, no further decline was observed in any of the 3 groups. Changes in body composition became evident first after the 3 months of treatment. In the GHD children, the BMI was unchanged while the mean body fat percentage was 2.7% lower after 1 year of GH treatment (p < 0.05). In the ISS children, neither BMI nor body fat percentage were significantly changed during treatment. The PWS children exhibited a significant decrease in BMI after 6 months of GH treatment without any further change during the remaining period of treatment. In this group, the mean body fat percentage decreased from 42 +/- 2.4 to 28 +/- 2.2% after treatment (p < 0.001). The finding that the fall in leptin occurs before changes in body composition become detectable suggests a direct effect of GH on leptin production, metabolism, or clearance.

Variations in glucocorticoid levels within the physiological range affect plasma leptin levels.

OBJECTIVE: Leptin, the obese gene product, is thought to regulate body fat through its action on hypothalamic receptors that influence satiety. The hormonal regulation of leptin is important, since it might affect adiposity. Leptin regulation in man is poorly understood. We studied the relation between endogenous cortisol and leptin levels as well as the acute and chronic effects of a low dose of dexamethasone (DEX) on plasma leptin levels in healthy male volunteers. SUBJECTS AND EXPERIMENTAL PROTOCOL: The correlation between basal plasma levels of leptin and cortisol and the chronic effect of DEX treatment were studied in 12 subjects. Plasma leptin and cortisol levels were determined every other hour for 24 h, before and after 2 weeks of oral administration of 0.1 mg DEX twice daily. The acute effect was studied in 20 subjects, who received 1 mg DEX at 2300 h. Fasting blood samples were taken at 0800 h on the same day (i.e. before DEX) and on the day after. RESULTS: Under basal conditions, we found a correlation between mean plasma levels of leptin and cortisol (r = 0.7, P<0.02). Mean plasma leptin levels had increased by 50% after 2 weeks of DEX treatment (P<0.05). The circadian rhythm of leptin was preserved, but the night peak occurred 2.5 h earlier (P<0.05). Fasting plasma leptin levels were 20% higher 9 h after 1 mg DEX orally than at the same time on the day before (P<0.002). CONCLUSION: Physiological variations in cortisol are involved in the regulation of leptin.

Increased leptin messenger RNA and serum leptin levels in children with Prader-Willi syndrome and nonsyndromal obesity.

To study the potential role of the ob gene pathway in childhood obesity, we have investigated leptin mRNA levels in s.c. adipose tissue obtained from nonobese prepubertal children (n = 20), obese nonsyndromal children (n = 6), and children with Prader-Willi syndrome (n = 6) by in situ hybridization histochemistry. We have also investigated the fasting serum leptin levels in such children. Compared with nonobese children, leptin mRNA expression was higher both in children with Prader-Willi syndrome and in children with nonsyndromal obesity (p < 0.01). Furthermore, the serum leptin levels were also significantly higher in both children with Prader-Willi syndrome and nonsyndromal obesity compared with the nonobese children (p < 0.001). However, no significant differences in adipose tissue leptin mRNA or serum leptin levels were observed between children with Prader-Willi syndrome and nonsyndromal obese children. As expected both fasting serum leptin levels and leptin mRNA expression levels correlated to body mass index (rs = 0.80 and 0.73, respectively, p < 0.005). No difference in leptin expression between Prader-Willi syndrome and nonsyndromal childhood obesity could be revealed in the present study. However, differences in the hypothalamic response to leptin between the two forms of obesity cannot be excluded.

Diagnosis of hypoglycaemia: effects of blood sample handling and evaluation of a glucose photometer in the low glucose range.

Hypoglycaemia is a dangerous condition. Rapid and reliable blood glucose measurements are necessary for the initiation of treatment to reduce the risk of neurological sequelae. The aim of this study was to compare a bedside glucose photometer (HemoCue) with three methods of handling blood glucose measurements in a routine chemistry laboratory and to estimate the reliability of glucose measurements in the low glucose range during controlled hypoglycaemia. Nine children underwent an arginine-insulin tolerance test as part of a growth hormone deficiency investigation. Only blood samples below 4.0 mmol l-1 were included (n = 35). Significant (0.3-1.0 mmol l-1) differences in blood glucose measurements were found, depending on the handling of the blood sample. The differences seem primarily to be due to glycolysis which occurred in spite of the addition of the glycolysis inhibitor NaF to the blood samples. Immediate centrifugation and analysis of the supernatant or immediate analysis with the HemoCue results in higher, and presumably more correct, values than routine procedures and permits a more accurate diagnosis of hypoglycaemia.