Insulin and cortisol promote leptin production in cultured human fat cells.

The aim of this study was to investigate the regulation of leptin expression and production in cultured human adipocytes using the model of in vitro differentiated human adipocytes. Freshly isolated human preadipocytes did not exhibit significant leptin mRNA and protein levels as assessed by reverse transcriptase (RT)-polymerase chain reaction (PCR) and radioimmunoassay (RIA). However, during differentiation induced by a defined adipogenic serum-free medium, cellular leptin mRNA and leptin protein released into the medium increased considerably in accordance with the cellular lipid accumulation. In fully differentiated human fat cells, insulin provoked a dose-dependent rise in leptin protein. Cortisol at a near physiological concentration of 10(-8) mol/l was found to potentiate this insulin effect by almost threefold. Removal of insulin and cortisol, respectively, was followed by a rapid decrease in leptin expression, which was reversible after readdition of the hormones. These results clearly indicate that both insulin and cortisol are potent and possibly physiological regulators of leptin expression in human adipose tissue.

Testosterone substitution normalizes elevated serum leptin levels in hypogonadal men.

The ob gene product leptin (OB) is a feedback signal from the adipocyte to the hypothalamus and is involved in regulation of food intake and energy expenditure in rodents. A major determinant of serum OB levels is fat mass. Several studies suggest that men have lower OB levels than women even after adjustment for percent body fat. We, therefore, investigated the influence of testosterone (T) substitution in hypogonadal men on serum OB levels. Hypogonadal men with T levels of 3.6 nmol/L or less and off substitution therapy for at least 3 months were assigned to two treatment groups: testosterone enanthate (TE; 250 mg, i.m., every 21 days; n = 10) or a single s.c. implantation of 1200 mg crystalline T (TPEL; n = 12). Blood samples for determination of T, 5 alpha-dihydrotestosterone (DHT), sex hormone-binding globulin, and 17 beta-estradiol were obtained before therapy and then every 21 days until day 189 and at follow-up visits on days 246 and 300. Serum OB levels were assessed on days 0, 42, 84, 126, 168, and 300. OB levels were referred to a normal range for men based on the analysis of OB levels in 393 adult men. Substitution with T led to a large rise in T and DHT in both groups compared to baseline values (average T, days 21-189: TE, 14.33 +/- 2.63 nmol/L; TPEL, 24.98 +/- 1.64; average DHT, days 21-189: TE, 4.20 +/- 0.57 nmol/L; TPEL, 5.11 +/- 0.56; P < or = 0.05). Concomitantly, 17 beta-estradiol increased in both groups, and sex hormone-binding globulin levels were significantly decreased. At baseline, serum OB levels in hypogonadal men were 3-fold elevated compared to those in normal men (12.39 +/- 2.93 micrograms/L vs. 4.28 +/- 0.52; P < 0.01) and not different between groups (TE, 13.7 +/- 5.6; TPEL, 11.3 +/- 2.9 micrograms/L). This elevation was retained after adjustment for body mass index in the normal control group [TE, 1.45 +/- 0.51 SD score (P < 0.0001); TPEL, 0.98 +/- 0.35 SD score (P < 0.0008)]. During T substitution serum OB was completely normalized (trough levels: TE, 4.6 +/- 1.0 micrograms/L; TPEL 4.3 +/- 0.9 micrograms/L). In multiple regression analysis, the androgen (T plus DHT)/estrogen ratio was the only significant determinant of OB levels (r = -0.32; P < 0.01). At baseline, OB levels did not correlate with body mass index, but during substitution, the correlation was considerably improved. We conclude that hypogonadal men exhibit elevated OB levels that are normalized by substitution with T. The only determinant of OB levels was the androgen/estrogen ratio, indicating a major influence of sex steroids on OB production. The interaction of T and OB might be part of a hypothalamic-pituitary-gonadal-adipose tissue axis that is involved in body weight maintenance and reproductive function.

Levels of leptin in maternal serum, amniotic fluid, and arterial and venous cord blood: relation to neonatal and placental weight.

The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. The ob protein, termed leptin, is produced by adipocytes. It is involved in the regulation of body weight by suppressing appetite and stimulating energy expenditure both in humans and rodents. In this study we examined whether leptin concentrations in the mother and the newborn correlate with birth weight, placental weight, and maternal weight at term. Leptin concentrations were measured in amniotic fluid, venous and arterial cord blood, and maternal serum at birth (n = 27) using a specific RIA employing human recombinant leptin for tracer and standard preparation. Gestational age was 38-42 weeks, maternal age was 21-42 yr, mean maternal weight at birth was 80.0 +/- 10.8 kg, and mean body mass index before pregnancy was 23.4 +/- 2.8 kg/m2. The newborns' mean weight was 3450 +/- 580 g, and mean placental weight was 616 +/- 120 g. Serum leptin levels from nonpregnant women ranged between 1.7-18.4 ng/mL, median 5.5 ng/ml (n = 30). Mean leptin concentration in maternal serum at birth was 20.0 +/- 13.2 ng/mL and was higher (P < 0.002) than in arterial cord blood (9.7 +/- 9.4 ng/mL) and venous cord blood (8.9 +/- 8.6 ng/mL). Mean amniotic fluid leptin concentration was 3.6 +/- 2.8 ng/mL. Placental weight correlated inversely with leptin levels in maternal serum at birth (r = -0.49, P < 0.01). In addition, leptin concentrations in venous cord blood correlated significantly with the levels in arterial cord blood (r = 0.98, P < 0.0001), and leptin levels in cord blood correlated positively with birth weight (r = 0.57, P = 0.03) and placental weight (r = 0.50, P < 0.01). In contrast, there was no correlation between maternal serum leptin levels and birth weight. Thus, leptin levels are high in the fetus and in the mother at term. We hypothesize that high leptin levels could represent an important feed-back modulator of substrate supply and subsequently for adipose tissue status during late gestation.

Plasma leptin levels in healthy children and adolescents: dependence on body mass index, body fat mass, gender, pubertal stage, and testosterone.

Leptin, the product of the ob gene, is thought to play a key role in the regulation of body fat mass. Beyond this function, it appears to be an integral component of various hypothalamo-pituitary-endocrine feedback loops. Because childhood and puberty are periods of major metabolic and endocrine changes, leptin levels and various hormonal parameters were investigated in a large cohort of healthy children and adolescents (312 males, 401 females, age 5.8-19.9 yr). For this purpose, a specific and sensitive RIA was developed that allowed the accurate measurement of low leptin levels in young lean children. With this assay, leptin proved to be a comparatively stable protein under common conditions of blood sampling and storage. Leptin levels increased in girls with age (r = 0.47, P < 0.0001), but decreased in boys (r = -0.34, P < 0.0001). An analysis according to pubertal stage showed a steady increase in girls between 2.51 micrograms/L (median) at Tanner stage 1 to 6.24 micrograms/L at Tanner stage 5. In boys, leptin levels were highest at Tanner stage 2 (2.19 micrograms/L) and declined thereafter to 0.71 microgram/L at Tanner stage 5. A strong exponential relationship was observed for leptin levels with body mass index (BMI) and percentage body fat as determined by bioelectric impedance measurements in a subgroup of subjects. This relationship was similar between boys and girls at Tanner stages 1 and 2. In boys, there was a significant decline of leptin at a given BMI with further progression of puberty that was much less pronounced in girls. Although the relative increase of leptin with BMI and percent body fat was the same in both genders, the absolute values at a given BMI or percent body fat were significantly lower in boys in late puberty and in adolescents. In boys, but not in girls, there was an inverse correlation with testosterone concentrations (r = -0.43, P < 0.0001), which explained 10.5% of the variation of leptin levels in a multiple regression model. Since BMI proved to be the major influencing variable, reference ranges were constructed using a best-fit regression line of the form leptin = a*e(b*BMI) and stratifying ranges according to gender and pubertal stage. In conclusion, these data suggest that 1) plasma leptin levels increase in girls and decrease in boys after Tanner stage 2 as the pubertal development proceeds; 2) they show a significant gender difference especially in late puberty and adolescence, even after adjustment for BMI or percent body fat; 3) the lower levels in males may be explained at least in part by a suppressive effect of androgens; 4) reference ranges with BMI as the independent variable should be stratified according to gender and pubertal stage.

Leptin concentrations in serum from a randomly recruited sample of 50- to 80-year-old men and women: positive association with plasma insulin-like growth factors (IGFs) and IGF-binding protein-3 in lean, but not in obese, individuals.

OBJECTIVE: The GH/IGF axis is thought to play an important role in the regulation of body composition throughout life. Changes in body fat stores also affect the activity of the GH/IGF axis, but the mechanisms whereby body fat status is signaled to the GH/IGF axis are poorly understood. The newly discovered protein leptin is exclusively produced by adipocytes, and circulating concentrations of leptin closely reflect body fat stores. DESIGN: We here examined whether leptin might be associated with the activity of the GH/IGF axis in a population-based sample. PATIENTS AND METHODS: Circulating concentrations of leptin, IGF-I, IGF-II, and insulin-like growth factor-binding protein-3 (IGFBP-3) were measured in a population-based sample of 50- to 80-year-old men (n=217) and women (n=198) by specific RIA. RESULTS: All three IGF components were significantly positively correlated with leptin in lean women (body mass index (BMI) <25 kg/m2). IGF-II was also positively correlated with leptin in lean men, and positive correlation of leptin with IGF-I in lean men was of borderline statistical significance. In contrast, no correlation was observed in moderately overweight (BMI 25-30kg/m2) and obese individuals (BMI >30 kg/m2). CONCLUSION: Our study shows that serum leptin concentrations are significantly associated with circulating IGF components in lean elderly subjects. The precise mechanism of this interaction between leptin and the GH/IGF system remains to be determined.

Lack of effects of circulating thyroid hormone levels on serum leptin concentrations.

Leptin is the protein product of the ob gene, secreted by adipocytes. It has been suggested that it may play an important role in regulating appetite and energy expenditure. The aim of this study was to evaluate a possible interaction of thyroid hormones with the leptin system. We studied 114 adult patients (65 females and 49 males): 36 were affected with primary hypothyroidism (PH), 38 with central hypothyroidism (CH) and 40 with thyrotoxicosis (TT). Patients with CH were studied both before and after 6 months of L-thyroxine replacement therapy. Body mass index (BMI; kg/m2), thyroid function and fasting serum leptin were assessed in all patients. Since BMI has been proved to be the major influencing variable of circulating leptin levels, data were expressed as standard deviation score (SDS) calculated from 393 male and 561 female controls matched for age and BMI. No difference in SDS was recorded between males and females whatever the levels of circulating thyroid hormones. In males, no significant difference was recorded among the SDSs of PH (-0.36 +/- 1.2), TT (-0.35 +/- 1.2) and CH (0.01 +/- 1.4) patients. Females with PH had an SDSs significantly lower than TT females (-0.77 +/- 1.0 vs -0.06 +/- 1.2; P < 0.02), while no significant differences between CH (-0.34 +/- 0.7) and TT females or between CH and PH females were observed. SDS in CH patients after 6 months of L-thyroxine therapy significantly varied only in females (0.25 +/- 1.4). In conclusion, circulating thyroid hormones do not appear to play any relevant role in leptin synthesis and secretion. However, as females with either overt hypo- or hyper-thyroidism or central hypothyroidism after L-thyroxine therapy show differences in their SDSs, a subtle interaction between sex steroids and thyroid status in modulating leptin secretion, at least in women, may occur.

Increased levels but preserved diurnal variation of serum leptin in GH-deficient patients: lack of impact of different modes of GH administration.

The regulation of leptin production in humans is poorly understood but appears to depend on total body fat, changes in energy intake and insulin levels. Since growth hormone (GH) is an important regulator of both lipid metabolism and insulin secretion and action, we tested whether GH status directly or indirectly regulates leptin secretion. Circadian serum leptin concentrations were measured in GH-deficient patients in two different protocols involving different modes of acute and prolonged GH exposure. In study I, eight GH-deficient patients all underwent three 4 week study periods in random order: (1) evening (2000 h) s.c. GH injections (2 IU); (2) morning (0800 h) s.c. GH injections (2 IU); (3) no GH administration. At the end of each period the patients were admitted to hospital for 24-h measurements of hormones and metabolites. For comparison, 10 age- and sex-matched healthy untreated subjects were hospitalised under identical conditions. In study II, six GH-deficient patients were hospitalised for 44 h on three occasions, separated by at least 4 weeks without GH treatment. On each occasion they received 2 IU GH, administered i.v. as (1) two boluses (at 2000 and 0200 h), (2) eight boluses (at 3 h intervals starting at 2000 h) or (3) a continuous (2000-2000 h) infusion. In both studies, serum leptin levels peaked between midnight and early morning followed by low day-time levels (P < 0.01). The mode of GH treatment or previous discontinuation did not affect the leptin level (P > 0.05), but the patients had significantly higher leptin levels than the controls (P < 0.01). The diurnal variation in leptin was compared with changes in GH, insulin, non-esterified fatty acids, 3-hydroxybutyrate, insulin-like growth factor I and glucose, but no robust cross-correlations could be demonstrated. The following conclusions were made. (1) The circadian pattern of serum leptin is not influenced by either experimental or spontaneous changes in serum GH concentrations. (2) GH deficiency is associated with elevated leptin levels which most likely reflects increased fat mass in these patients.

Serum leptin levels in children and adolescents with insulin-dependent diabetes mellitus in relation to metabolic control and body mass index.

The ob protein, termed leptin, is produced by adipocytes and is thought to act as an afferent satiety signal regulating weight through suppressing appetite and stimulating energy expenditure in humans and/or rodents. Insulin has been found to be a potent stimulator of leptin expression in rodents. It is unclear at present whether this insulin action is a direct or an indirect effect. To investigate whether leptin concentrations in children and adolescents with type 1 diabetes (IDDM) were related to metabolic status, body weight, body mass index and insulin treatment, we have measured leptin concentrations in serum from 13 newly diagnosed IDDM patients before the beginning of insulin treatment (8 girls, 5 boys, aged 4.7-17.5 years) and in 134 patients with IDDM during treatment (64 girls, 70 boys, aged 2.6-20.1 years) using a specific radioimmunoassay. The data from patients with diabetes were compared with normative data that were derived from a large cohort of healthy children and adolescents. Serum from children with newly diagnosed diabetes had significantly lower levels of leptin (mean 1.28+/-1.60 ng/ml, range 0.14-6.13 ng/ml) compared with healthy children (n=710) (mean 2.2 ng/ml, range 0.26-14.4ng/ml) and compared with insulin-treated children and adolescents (mean 5.18+/-5.48 ng/ml, range 0.26-29.77 ng/ml) (P<0.0001) even after adjustment for gender and body mass index (BMI). Serum leptin levels in patients with IDDM were significantly correlated with BMI (r=0.42, P<0.0001). Multiple regression analysis showed that age and BMI were significantly correlated with leptin levels, while duration of diabetes, mean HbA1c levels, insulin dose and plasma glucose, triglyceride and cholesterol levels were not. Females had higher serum leptin concentrations than males even when adjusted for BMI (P<0.0001). Surprisingly and most importantly, leptin levels in insulin-treated young adult (Tanner stage 5) patients were significantly higher than values found in the healthy nondiabetic reference population when adjusted for sex, Tanner stage and BMI. These findings suggest that leptin levels in IDDM patients show a similar dependency on adipose tissue and age as in healthy, normal children. The data provide evidence that insulin may be of importance as a regulator of serum leptin levels in vivo not only in rodents but also in humans. It is hypothesized that the elevated BMI-adjusted leptin levels in adolescents with IDDM could indicate either that these patients may be oversubstituted by the intensified insulin therapy that they are receiving or that their body composition and body fat content may differ from that of healthy adolescents in the sense that they have a relative increase in fat mass.

Chronic administration of leptin into the lateral ventricle induces sexual maturation in severely food-restricted female rats.

In many species, delayed sexual maturation occurs when metabolic conditions are not satisfactory. Recently, leptin was shown to be involved in the regulation of food intake and body mass. Furthermore, leptin administration was shown to advance sexual maturation in mice and to rescue sexual function in adverse metabolic conditions. We examined plasma leptin levels in female rats during development and evaluated the role of leptin on sexual maturation in rats subjected to food restriction. In normal rats, plasma leptin levels were low at day 24 of life, then steadily increased during the juvenile period, reaching 740+/-56 pg/ml at 40 days at time of vaginal opening (VO) and further increasing by day 60 (957+/-73 pg/ml). Food restriction initiated at day 25 strongly impaired this increase, in proportion to the severity of the restriction. With a daily food intake reduced to 7-8 g/day, that permanently prevented VO, plasma leptin levels were very low at day 53 (169+/-67 pg/ml). Following switch to ad libitum feeding, plasma leptin reached high levels within 2 days (1577+/-123 pg/ml), and VO occurred 4 days later. If the severe food restriction was maintained and a central infusion of leptin (10 microg/day) was initiated, a significant decrease in body weight compared with vehicle-infused controls was observed. In these conditions, VO occurred in eight out of the nine leptin-treated rats, representing induction of the process of sexual maturation confirmed by increases in ovarian and uterine weights. This induction of sexual maturation exclusively results from a central effect of leptin because no leak of the i.c.v. administered leptin to the general circulation was observed. These data suggest that the rising plasma levels of leptin in the prepubertal period represent a signal to the brain indicating that the young animal is metabolically ready to go through the process of sexual maturation.

Relation of leptin and neuropeptide Y in human blood and cerebrospinal fluid.

Leptin and neuropeptide Y (NPY) are involved in the regulation of food intake and body weight. Both hormones act through specific receptors in the central nervous system. The objective of this study was to investigate the relation of leptin and NPY in human plasma and cerebrospinal fluid (CSF). Leptin and NPY in CSF and in serum/plasma were measured by radioimmunoassays in 35 patients. Leptin concentrations in serum were 100-200 fold higher than in CSF. There was a significant correlation between leptin levels in CSF and in serum (r=0.88, P<0.0001). Female patients had significantly higher leptin serum concentrations than males (16.6+/-10.9 microg/l vs. 6.5+/-7.3 microg/l, P=0.002). In contrast, NPY levels were only twofold higher in CSF than in plasma. There was no relation between leptin and NPY in CSF and serum/plasma, respectively. The ratio of CSF and peripheral leptin levels did not correlate with the respective albumin ratio, indicating that leptin did not merely leak into the CSF via a defective blood-CSF barrier. It is concluded that leptin uptake from the circulation into CSF is a regulated process. The NPY concentration in CSF is not directly related to leptin CSF levels.

Leptin concentrations in maternal serum and amniotic fluid during the second trimenon: differential relation to fetal gender and maternal morphometry.

Leptin, a hormone produced by adipocytes, provides information on the availability of fat stores to the hypothalamus and acts as an afferent satiety signal regulating appetite and energy expenditure in both rodents and humans [Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature 1994;372:425-432; Sinha MK. Human leptin: the hormone of adipose tissue. Eur J Endocrinol 1997;136:461-4; Campfield LA, Smith FJ, Guisez Y, Devos R, Burn P. Recombinant mouse ob protein: evidence for a peripheral signal linking adiposity and central neural networks. Science 1995;269:546-9; Halaas JL, Gajiwala KS, Maffei M, Cohen SL, Chait BT, Rabinowitz D, Lallone RL, Burley SK, Friedman JM. Weight-reducing effects of the plasma protein encoded by the obese gene. Science 1995;269:543-6; Saladin R, De Vos P, Guerre-Millo M, Leturque A, Girard J, Staels B, Auwern J. Transient increase in obese gene expression after food intake or insulin administration. Nature 1995;377:527-9; Campfield LA, Smith FJ, Burn P. The OB protein (leptin) pathway - a link between adipose tissue mass and central neural networks. Horm Metab Res 1996;28:619-632; Blum WF, Kiess W, Rascher W, editors. Leptin - the voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997]. In addition, leptin is thought to play an important role for reproduction and during gestation [Kiess W, Blum WF, Aubert ML. Leptin, puberty and reproductive function: lessons from animal studies and observations in humans. Eur J Endocrinol 1997;138:1-4; Barash IA, Cheung CC, Wigle DS, Ren H, Kabitting EB, Kuijer JL, Clifton DK, Steiner RA. Leptin is a metabolic signal to the reproductive system. Endocrinology 1996;133:3144-47; Chehab F, Lim M, Lu R. Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin. Nature Genetics 1996;12:318-20; Kiess W, Schubring C, Prohaska F, Englaro P, Rascher W, Attanasio A, Blum WF. Leptin in amniotic fluid at term and at midgestation. In: Blum WF, Kiess W, Rascher W, editors. Leptin - the voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997]. The purpose of this study was to gain more insight into a putative role of leptin during midgestation. Therefore we have measured leptin concentrations in maternal serum and amniotic fluid using a specific radioimmunoassay (RIA) employing human recombinant leptin for tracer and standard preparation [Blum WF, Kiess W, Rascher W, editors, Leptin - The voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997; Blum WF, Englaro P, Heiman M, Attanasio Am, Kiess W, Rascher W. Clinical studies of serum leptin. In: Blum WF, Kiess W, Rascher W. Leptin - The voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997; Blum WF, Englaro P, Heiman M, Attanasio AM, Kiess W, Rascher W. Plasma leptin levels in healthy children and adolescents: dependence on body mass index, body fat mass, gender, pubertal stage and testosterone. J Clin Endocrinol Metab 1997;82:2904-2910]. In addition, estriol, hCG and alphafetoprotein were measured in maternal serum. (ABSTRACT TRUNCATED)

Leptin as a metabolic regulator during fetal and neonatal life and in childhood and adolescence.

Body weight is regulated by a feedback loop in which peripheral signals report nutritional information to an integratory center in the brain. The cloning of the ob gene is consistent with this concept and suggests that body fat content in adult rodents is regulated by a negative feedback loop centered in the hypothalamus/1-8/. In a recent report, two severely obese children with congenital leptin deficiency due to a homozygous frame-shift mutation involving the deletion of a single guanine nucleotide in codon 133 of the ob gene have been described. This discovery provides the first genetic evidence that leptin is an important regulator of energy balance in humans. However, it has become increasingly clear that apart from leptin's function in the central nervous system and in regulation of energy balance, leptin also acts in the periphery and might be important as a hormone modulating processes in regard to reproduction, glucose metabolism and insulin resistance, as well as growth and development of many tissues and organs either directly or indirectly. This report reviews some of the topics of leptin research that are of particular importance and relevance for pediatric and adolescent medicine and for pediatric endocrinology in particular.

Dexamethasone induces an acute and sustained rise in circulating leptin levels in normal human subjects.

Leptin, the protein product of the ob gene, is thought to have a role in signalling satiety through hypothalamic pathways. Glucocorticoids are potent stimulators of both ob gene expression and circulating leptin levels in the rat, yet are powerful appetite stimulants in humans. We have investigated circulating leptin responses to intermediate term and acute administration of dexamethasone. Dexamethasone 2 mg twice daily resulted in a rapid and sustained rise in 08.00 h leptin levels from basal values of 1.36 +/- 0.25 to 3.58 +/- 1.72 microg/l after 24 hours of treatment. Following placebo administration 24 h profiles confirmed a nocturnal rise in leptin levels with an increase of 73 +/- 37% at midnight compared with 0.9.00 h. After dexamethasone mean leptin levels increased by 123 +/- 51% (p = 0.0016), with an accentuation in the diurnal variation and associated hyperinsulinemia. The study confirms a nocturnal rise in leptin in humans, and demonstrates increases in leptin in response to glucocorticoid administration as previously demonstrated in the rodent. The divergence between appetite stimulating effects of glucocorticoids despite induction of a proposed satiety factor suggests that regulation of leptin levels and regulation of appetite is multifactorial, and other neurotransmitter pathways are presumably involved.

Serum leptin is suppressed by growth hormone therapy in growth hormone-deficient children.

Leptin is a hormone which is exclusively synthesized and secreted by adipocytes. As of yet, little is known about the complex interplay of hormones in the modulation of circulating leptin levels. To investigate the effect of growth hormone (GH) therapy on leptin, leptin serum concentrations were measured by a specific radioimmunoassay in 29 children with GH deficiency (21 boys, 8 girls; age range 3-14 years) before and after 1, 3 and 6 months of treatment with recombinant human GH. At baseline, serum leptin levels were identical to those of healthy children. Serum leptin correlated with body mass index (BMI; r=0.60, p < 0.001) and weight (r=0.48, p=0.004), but not with height, age, insulinlike growth factor 1, or insulinlike growth factor-binding protein 3, and there was no sex difference (p > 0.05). After 1 month of treatment, the leptin levels had decreased to 73+/-(SEM) 13% of individual pretreatment levels (p=0.002) and remained constant thereafter. While the correlation between leptin, BMI, and weight persisted throughout the study period, the changes in leptin concentrations during treatment were not associated with changes in BMI, weight, height, insulinlike growth factor 1, and insulinlike growth factor binding protein 3. In conclusion, this preliminary study demonstrates that serum leptin decreases during GH treatment in children with GH deficiency.

High leptin concentrations in serum of very obese children are further stimulated by dexamethasone.

Serum leptin concentrations and the levels of ob mRNA in adipocytes in obese humans are elevated. Hyperphagia and obesity are characteristics of hypercortisolism. We have therefore asked whether or not leptin levels were elevated in very obese children, and whether or not dexamethasone would increase leptin levels in obese children. A single dose dexamethasone suppression test was performed in ten obese children (5 girls, 5 boys; age 6 to 16 yrs, mean 12 +/- 1, median 12 yrs) to rule out hypercortisolism. Body mass index (BMI) in the ten children was calculated to be 27-45 kg/m2. Venous blood was sampled before dexamethasone was given in the evening and at 9.00 a.m. the following morning. Endogenous cortisol production was suppressed in all patients. Leptin levels, as measured by a newly developed specific radioimmunoassay, were 31.6 +/- 12.9 microg/l, range 19.2-59.9 microg/l before dexamethasone and 39.9 +/- 16.5 microg/l, range 26.3-80.3 microg/l after dexamethasone in the obese children (ANOVA, p = 0.01). Simple regression analysis revealed that serum levels correlated significantly with body mass index (r = 0.82, p < 0.001). Non-obese children (BMI < 27 kg/m2) had leptin levels between 0.1 and 33.3 microg/l, median 2.2 microg/l (N = 713). Girls (5.5 +/- 4.6 microg/l) (N = 401) had significantly higher leptin levels than boys (1.7 +/- 2.1 microg/l (N = 312) (p < 0.0001). We conclude that 1) high serum leptin concentrations are present in obese children. 2) A single dose of dexamethasone significantly increases the high leptin serum levels in these children. We hypothesize that glucocorticosteroids up-regulate leptin levels in the human.

Insulin induces rapid changes of plasma leptin in lean but not in genetically obese (fa/fa) rats.

OBJECTIVES: To evaluate the plasma leptin concentration in lean and genetically obese fa/fa rats and to assess the response to 2 h hyperinsulinaemia. BACKGROUND: The recently discovered peptide leptin is a putative link between the size of the adipose mass and the hypothalamic centres controlling feeding behaviour. Several genetic models of animal obesity have been characterized as carriers of mutations of either the ob gene or leptin receptor. EXPERIMENTAL DESIGN: Lean (+/?) and obese (fa/fa) Zucker rats were studied under pentobarbital anaesthesia and underwent a 2 h euglycaemic hyperinsulinaemic clamp. Plasma leptin was measured in basal condition and at the end of the clamp study. Glucose rate of disappearance was evaluated by means of the isotope dilution technique using 3-3H-glucose as tracer. RESULTS: fa/fa rats showed a 40 fold higher leptin concentration compared to lean littermates (0.47 +/- 0.10 vs 19.55 +/- 1.50 ng/ml, P < 0.0001). Euglycaemic hyperinsulinaemia increased plasma leptin in lean but not in genetically obese rats. CONCLUSIONS: Our results suggest that insulin may be a regulator of in vivo leptin secretion by adipose tissue of lean rates whereas it is ineffective in increasing plasma leptin in obese Zucker rats.

Leptin serum concentrations in healthy neonates within the first week of life: relation to insulin and growth hormone levels, skinfold thickness, body mass index and weight.

BACKGROUND AND AIMS: Leptin, the ob gene product, plays a key role in the regulation of body fat mass and weight in adult life. The mechanisms by which maternal and fetal/neonatal weight are regulated during human pregnancy and in early postnatal life are poorly understood. High leptin levels are observed in women during gestation and in cord blood at term. We have hypothesized that high leptin levels at term could represent an important feed-back indicator of nutrient supply. Subsequently, leptin could signal adipose tissue status during late gestation and during early neonatal life. SUBJECTS AND METHODS: 51 healthy newborns were studied. Clinical and auxological data (birth length, weight, and iliac, subscapular, biceps and triceps skinfold thickness) were recorded using a standardized data sheet. Venous cord blood was obtained immediately after birth in all neonates. Subsequently, capillary blood was obtained from the heel from some of the newborns when blood had to be obtained because of signs or symptoms of particular problems such as hypoglycaemia or hyperbilirubinaemia, at the following time points: two to four hours after birth in 51 infants, 56-79 h after birth in 47 infants and 99-128 h after birth in 23 of the newborns. The ratio between the sexes (girls/boys) was similar at all time points. The infants that were included in the study were subsequently found to be normal and healthy after analysis of the clinical and biochemical data. A specific ultrasensitive radioimmunoassay was used to measure leptin, while growth hormone and insulin were measured using commercially available immunoassays. RESULTS: Gestational age was 38-42 weeks, maternal age was 21-42 years. Birth weights ranged from 2480 to 4400 g. All newborns and mothers were subsequently found to be healthy. Leptin levels in venous cord blood was 0.16-6.80 microg/l, median 3. 47 microg/l and in capillary blood shortly after birth 0.26-7.03 microg/l, median 3.89 microg/l. 56-79 h after birth leptin levels had fallen dramatically, range 0.02-1.69 microg/l, median 0.26 microg/l, while 99-128 h after birth, leptin concentrations in capillary blood (0.05-2.61 microg/l, median 0.59 microg/l) had significantly increased when compared to the levels at 56-79 h (P < 0.001). There was a significant correlation between leptin levels in umbilical vein and birth weight of the neonates (r = 0.57, P < 0.03). Multistep regression analysis revealed that weight and skinfold thickness accounted for approximately 35-70% of the variation of leptin levels. Insulin and growth hormone, and glucose and bilirubin however, had no major impact on leptin levels. CONCLUSION: High leptin levels are present in cord blood at birth and in capillary blood shortly after birth. Since leptin levels in cord blood correlate with birth weight it is tempting to speculate that in the fetus as in later life leptin is signalling expansion of fat stores. Most importantly, we now report that leptin levels are high in the fetus but decline rapidly and dramatically after birth in healthy neonates. This may be important for the stimulation of feeding behaviour and the acquisition of energy homeostasis in the neonate.

Longitudinal analysis of maternal serum leptin levels during pregnancy, at birth and up to six weeks after birth: relation to body mass index, skinfolds, sex steroids and umbilical cord blood leptin levels.

Leptin is an important regulator of body fat mass and energy expenditure during adult life. The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. In order to gain more insight into a potential role of leptin during gestation, a prospective, longitudinal study was carried out to measure leptin concentrations in maternal serum of 29 healthy women during pregnancy up to 6 weeks after birth and also in umbilical cord blood of their newborns. Leptin concentrations were measured using a specific RIA. In addition, estradiol, testosterone, and sex hormone binding globulin were determined using commercially available RIAs. The mothers' skinfolds were determined at four sites using a Holtain caliper. Leptin levels increased continuously during pregnancy and reached 25.8 +/- 14.7 ng/ml at 38-40 weeks. At birth, leptin concentrations were 23.5 +/- 15.4 ng/ml. Three days after delivery a significant decrease of leptin levels to 10.6 +/- 6.0 ng/ml was observed. Six weeks after birth the leptin concentration in maternal serum was 13.8 +/- 8.6 ng/ml. At birth, maternal serum levels were significantly higher than levels in cord blood and did not correlate with leptin levels in cord blood or neonatal weight. Furthermore, leptin levels did not correlate with maternal sex steroids and sex hormone binding globulin levels. At 6-8 weeks of pregnancy, maternal leptin serum levels correlated significantly with BMI (r = 0.81). The correlation coefficients (leptin vs. BMI) dropped with increasing gestational age and at birth only a poor correlation persisted (r = 0.50). Six weeks after birth there was again a high correlation between leptin levels in maternal serum and BMI (r = 0.76). Subscapular skinfold thickness was correlated to leptin concentrations in maternal serum during the whole period of the investigation. In conclusion, maternal leptin levels continuously increased from 6-8 weeks up to 38-40 weeks of pregnancy. Maternal leptin levels decreased dramatically after birth. Six weeks after delivery, leptin levels were comparable to the values measured at the beginning of pregnancy. We hypothesize that leptin might play an important role during pregnancy and fetal development.

Plasma concentrations of leptin in a bulimic patient.

Recently, the obese gene in the ob/ob mouse was cloned, along with its human homologue. The gene product leptin is important in the regulation of body weight. Excessive food intake during a binge might affect leptin synthesis. Alternatively, fluctuations in leptin synthesis might induce binge eating. Therefore, plasma leptin levels of a patient with bulimia nervosa were determined over a period of 48 hr in a natural setting. Amount, type, time of food intake, and binging and purging episodes were concomitantly assessed. Although binging and purging episodes were quite frequent, leptin levels remained stable and were neither related to food intake nor to binge episodes.

Plasma leptin in depressed patients and healthy controls.

Leptin is known to regulate food intake and energy expenditure. Since loss of appetite and bodyweight are important signs and symptoms of major depression we studied leptin plasma concentrations in both depressed patients (n = 24) suffering from loss of appetite and a healthy control group (n = 33). To rule out the possibility of inferences with other endocrine parameters known to be changed in depression or suspected to be related to leptin, we also studied cortisol, insulin, growth hormone (GH) and GH-binding protein (GHBP). We found that leptin plasma concentrations did not differ between depressed patients and healthy controls. However, leptin was positively associated with female gender, body mass index (BMI) and morning insulin. 24-hour mean cortisol was not related to leptin. Also, GH and GHBP were not related to leptin when controlled for BMI in an ANCOVA model. We conclude that leptin plasma concentrations are unchanged in depression and that there is no evidence for leptin playing a major role in loss of appetite and body weight in depressed patients.