Elevated leptin concentrations in growth hormone-deficient hypopituitary adults

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

Potential for NPY receptor-related therapies for polycystic ovary syndrome: an updated review

Polycystic ovary syndrome (PCOS) is a complex endocrine disease that can cause female infertility and bring economic burden to families and to society. The clinical and/or biochemical manifestations include hyperandrogenism, persistent anovulation, and polycystic ovarian changes, often accompanied by insulin resistance and obesity. Although its pathogenesis is unclear, PCOS involves the abnormal regulation of the hypothalamic-pituitary-ovarian axis and the abnormal activation of GnRH neurons. Neuropeptide Y (NPY) is widely distributed in the arcuate nucleus of the hypothalamus and functions as the physiological integrator of two neuroendocrine systems, one governing feeding and the other controlling reproduction. In recent years, an increasing number of studies have focused on the improvement of the reproductive and metabolic status of PCOS through the therapeutic application of NPY and its receptors. In this review, we summarize the central and peripheral regulation of NPY and its receptors in the development of PCOS and discuss the potential for NPY receptor-related therapies for PCOS.

Idiopathic short stature and growth hormone sensitivity in prepubertal children

OBJECTIVE

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range.

METHODS

Forty-six prepubertal children (~7.1 years) born at term were studied: ISS (n = 23; 74% boys) and NS (n = 23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05 mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5.

RESULTS

Children with idiopathic short stature were 1.90 SDS lighter (P < 0.0001) but had 4.5% more body fat (P = 0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentage IGF-I response to rhGH stimulation in univariable (r = 0.45; P = 0.002) and multivariable models (β = 24.6; P = 0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P < 0.0001). GHBP levels (P = 0.002) were suppressed in ISS children (-19%; P = 0.029) but increased among NS children (+18%; P = 0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P = 0.006).

CONCLUSIONS

A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

Relationship of serum leptin with some biochemical, anthropometric parameters and abdominal fat volumes as measured by magnetic resonance imaging

AIMS

To measure the level of leptin in volunteers and correlate it with several anthropometric, biochemical variables and abdominal fat volumes.

METHODS

The level of leptin was investigated in 167 disease-free volunteers. Serum levels of IL-6, adiponectin, and resistin, blood lipid profile (cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglyceride (TG) were determined. Waist circumference (WC) was measured using tape and magnetic resonance imaging (MRI) images.

RESULTS

All measured anthropometric (BMI, WC measured by tape and MRI) and biochemical variables (adiponectin, resistin, cholesterol, HDL, LDL and TG); and abdominal fats showed a significant (p<0.05) difference between participants with abnormal serum leptin levels and those with normal leptin levels. A higher percentage of participants with abnormal serum leptin were obese males while participants with normal leptin levels were either overweight or normal weight females. A significant (p <0.05) positive correlation was detected between serum leptin concentration and WC, BMI, subcutaneous fat, visceral fat, total abdominal fat, and resistin. A moderate association was found between serum leptin concentration and the inflammatory cytokine IL-6.

CONCLUSION

Abnormal serum leptin, was detected in obese male individuals which may be considered as an important indicator for the development of cardiovascular diseases and type 2 diabetes.

Panhypopituitarism due to Absence of the Pituitary Stalk: A Rare Aetiology of Liver Cirrhosis

Studies have established a relationship between hypothalamic-pituitary dysfunction and the onset of liver damage, which may occasionally progress to cirrhosis. Patients with hypopituitarism can develop a metabolic syndrome-like phenotype. Insulin resistance is the main pathophysiological axis of metabolic syndrome and is the causal factor in the development of nonalcoholic fatty liver disease (NAFLD). We present the case of a young patient with liver cirrhosis of unknown aetiology that was finally attributed to panhypopituitarism.

The association of leptin with dyslipidemia, arterial hypertension and obesity in Kyrgyz (Central Asian nation) population

BACKGROUND

Leptin, an adipocytokine produced by adipose tissue, along with the traditional cardiometabolic risk factors, contributes to the development of cardiovascular complications. At the same time, ethnic features of adipocytokines have been insufficiently investigated, especially among Asians, who have an increased risk of cardiovascular complications compared with Europeans. Aim of study was to investigate the relationship between leptin levels and age, gender, anthropometric parameters, lipid parameters, arterial hypertension (AH), and obesity in the adult population of ethnic Kyrgyz people living in Central Asia.

RESULTS

In total, 322 ethnic Kyrgyz (145 men, 177 women) aged ≥ 30 years were studied. Waist and hip circumference, body mass index, blood glucose, lipids, leptin, and homeostatic model assessment were measured. Patients in the upper quartile of leptin levels had high values of BMI, WC, systolic and diastolic blood pressure, glucose, and HOMA index compared with patients with lower leptin levels. The prevalence of metabolic syndrome and AH increased with higher levels of leptin. Leptin positively correlated with BMI, WC, triglycerides, and glucose concentrations in patients of both sexes. According to the multivariate logistic regression analysis, elevated leptin levels increased by 30 times the risk of obesity in men, regardless of the presence of type 2 diabetes, and 17.7 times in women.

CONCLUSION

Leptin is associated with general and abdominal obesity, dyslipidemia, and insulin resistance in Kyrgyz patients.

Serum leptin is associated with metabolic syndrome in obese and nonobese Korean populations

Leptin is mainly secreted from adipose tissue and is known to be associated with cardiovascular diseases. However, there are not many studies on the association between serum leptin and metabolic syndrome. The objective of this study was to determine the association between serum leptin and metabolic syndrome among the Korean adult population. The study population consisted of 3,272 Koreans (men: 1,915, women: 1,357) 30 to 84 years of age who had visited the Health Examination Center. Leptin levels were divided into quintiles and metabolic syndrome was defined by NCEP ATP III. The serum leptin levels increased as the number of components present for metabolic syndrome increased. Controlling for age, smoking, exercise, and LDL cholesterol, subjects with high leptin levels were more likely to have an elevated risk of metabolic syndrome than those with lower levels in both men and women. Subjects in the highest leptin quintile were found to have a higher risk of having metabolic syndrome than those in the lowest quintile (OR = 11.51 for men; OR = 4.65 for women). After further adjustment of the BMI, the risk of metabolic syndrome still increased slightly for men but not for women in increasing leptin categories. This association of leptin levels and metabolic syndrome did not change after stratification into obese and nonobese weight status. Serum leptin is associated with metabolic syndrome in Korean populations independent of body mass index. Thus, the reduction of circulating leptin may confer cardiovascular and metabolic protective effects regardless of weight status.

Nonalcoholic Fatty liver disease and metabolic syndrome in hypopituitary patients

BACKGROUND

Increased incidence of cardiovascular mortality and nonalcoholic fatty liver disease (NAFLD) has been reported in hypopituitarism, but previous studies did not correct for obesity in these patients. Therefore, it remained unclear if endocrine deficiency in hypopituitarism is associated with metabolic consequences independent of obesity. This study was designed to determine the burden of cardiovascular disease and NAFLD in hypopituitarism.

METHODS

We performed a retrospective case-control analysis of hypopituitary patients at Veterans Affair Medical center, Memphis, from January 1997 to June 2007. After matching for age, gender, obesity, and race, relevant data were abstracted from the subjects' records to determine the presence of hypopituitarism, cardiovascular risk factors, and fatty liver disease. Cases and controls were characterized by descriptive statistics and compared using chi(2) and Student t tests.

RESULTS

Hypopituitary patients exhibited higher prevalence of hypertension- 88% versus 78% (P < 0.03), hypertriglyceridemia-80% versus 70% (P = 0.05), low high-density lipoprotein cholesterol-84% versus 70% (P < 0.001), and metabolic syndrome-90% versus 71% (P < 0.001). Patients also had higher mean plasma glucose levels-228 +/- 152 versus 181 +/- 83 mg/dL (P < 0.01). Despite higher preponderance of cardiovascular risk factors in hypopituitary patients, prevalence of cardiovascular morbidity was similar in both groups (P > 0.3). Hypopituitary patients had higher elevations in serum aminotransferase levels and hyperbilirubinemia-24% versus 11% (P < 0.01), as well as higher international normalized ratio (INR) and hypoalbuminemia 40% versus 23% (P < 0.01).

CONCLUSIONS

There is an increased prevalence of metabolic syndrome and liver dysfunction consistent with NAFLD in hypopituitarism. Although hypopituitary patients had higher prevalence of cardiovascular risk factors than controls, they were not disproportionately affected by cardiovascular disease.

Influence of long-term growth hormone replacement on leptin and ghrelin in GH deficiency before and after glucose load

INTRODUCTION

This cross-sectional study was performed to evaluate the effect of long-term GH substitution on leptin and ghrelin in GH deficiency (GHD).

METHODS

Leptin and ghrelin were measured after glucose load for 3 h in 52 pat and 10 age- and BMI-matched healthy controls. 22 GHD pat were on GH substitution (GH-Sub) for a median of 10 yr (range 2-27 yr). 30 age- and BMI-matched GHD pat were not substituted for at least 2 yr (non-Sub).

RESULTS

Basal leptin (8 microg/l (1-130) vs. 16 microg/l (3-89), p<0.05) and AUC of leptin (p<0.05) was significantly lower in GH-Sub compared to non-Sub. In the control group, leptin was higher compared to GH-Sub and similar to non-Sub (19 microg/l (4-57)). Ghrelin (baseline: non-Sub 113 ng/l (61-270), GH-Sub 145 ng/l (83-280), controls 131 ng/l (83-274)) were slightly but not significantly lower for non-Sub. After glucose load, a significant decrease in leptin appeared in both GHD groups, but not in the control group. Ghrelin decreased significantly in all groups.

CONCLUSION

Lipolytic GH causes lower leptin in GH-Sub. The reason for similar ghrelin might be the compensating effect of acute GH suppression and stimulating low fat mass on ghrelin. Leptin regulation after glucose load is impaired in GHD, whereas ghrelin regulation seems to be not effected.

Influence of insulin-like growth factor-1 and leptin on bone mineral content in healthy premenopausal women

The aim of the present investigation was to study the influence of plasma insulin-like growth factor-1 (IGF-1) and leptin levels on bone mineral mass (BMC) and bone mineral density (BMD) in premenopausal women and the relationship between IGF-1 and leptin levels. Two hundred and four healthy women participated in this study. All participants had a body mass index (BMI) <30 kg/m(2) and were matched for their level of mean daily energy expenditure. BMC and BMD were correlated with measured body composition and blood biochemical parameters. No association was observed between BMC and BMD values with measured physical performance characteristics. Leptin had a significant association with BMC (beta = 0.840; P = 0.0001), total BMD (beta = 0.833; P = 0.0001), femoral neck BMD (beta = 0.829; P = 0.0001), and lumbar spine BMD (beta = 0.833; P = 0.0001). However, these associations were no longer independent when adjusted for body fat mass (FM) and trunk fat:leg fat ratio (P > 0.385). IGF-1 was significantly related to BMC (beta = 0.920; P = 0.0001), total BMD (beta = 0.918; P = 0.0001), femoral neck BMD (beta = 0.921; P = 0.0001), and lumbar spine BMD (beta = 0.917; P = 0.0001), but did not remain significant when adjusted for fat free mass (FFM; P > 0.062). In addition, a significant association between IGF-1 and leptin was found (beta = 0.801; P = 0.0001), and it remained significant after controlling for age, FM, FFM, insulin, and fasting insulin resistance index (FIRI), but not when adjusted for BMC and body mass values. In conclusion, it appears that fasting IGF-1 and leptin concentrations have no direct effect on BMC and BMD values. In addition, if there is an important relationship between IGF-1 and leptin, it is mediated or confounded by BMC in premenopausal women.

Correlation of apolipoprotein M with leptin and cholesterol in normal and obese subjects

Apolipoprotein M (apoM) is a recently characterized apolipoprotein that is exclusively expressed in the liver and kidney. In plasma it is present predominantly in high-density lipoprotein (HDL). The physiological function of apoM is not yet known. In the present study we investigated relationships between plasma apoM levels and leptin levels, body mass index (BMI), as well as fasting glucose and other lipid parameters in women with a wide range of BMI (18.9-57.1 kg/m(2), n = 51). In univariate analysis, apoM correlated significantly with leptin (r = 0.54, P < 0.001), BMI (r = 0,70, P < 0.001), fasting insulin (r = 0.33, P = 0.025), total cholesterol (r = -0.41, P = 0.016), and LDL-cholesterol (r = -0.39, P = 0.018). The correlations between apoM and cholesterol and between apoM and leptin remained significant after adjustment for the influence of BMI. Forward stepwise multiple regressions when leptin, BMI, insulin, and cholesterol were entered into a model as independent variables and apoM as the dependent variable, showed that cholesterol and leptin were independent predictors of circulating apoM. These two parameters yielded a value of r(2) = 0.28, thereby explaining approximately 30% of the variance in apoM. Hence, we show that apoM is positively related to leptin and negatively related to cholesterol in humans.

Both leptin and leptin-receptor are essential for apolipoprotein M expression in vivo

It was previously shown that circulating levels of leptin and apolipoprotein M (apoM) correlate to each other. In this study, we examined whether plasma leptin and leptin-receptors are of importance for apoM expression in vivo. It was found that in both liver and kidney, expression of apoM was significantly lower in leptin deficient ob/ob mice and in leptin-receptor deficient db/db mice than in control mice. Furthermore, leptin administration (0.5 or 1.5 microg/g body weight) significantly increased plasma apoM levels and apoM mRNA levels in liver and in kidney in ob/ob mice. We conclude that both leptin and leptin-receptor are essential for the apoM expression, indicating that leptin is physiologically regulating apoM synthesis in vivo.

Nonalcoholic fatty liver disease among patients with hypothalamic and pituitary dysfunction

Patients with hypopituitarism develop a phenotype similar to metabolic syndrome with central obesity and diabetes. Similarly, patients with hypothalamic damage may develop central obesity, insulin resistance, and hyperphagia. We sought to examine the clinical associations between hypopituitarism, hypothalamic dysfunction, and nonalcoholic fatty liver disease (NAFLD). A case series of patients seen at our institution with diagnoses of hypopituitarism, hypothalamic obesity, or craniopharyngioma and NAFLD was undertaken. Clinical, laboratory, and liver biopsy features were reviewed. Twenty-one patients were identified. NAFLD was diagnosed 6.4 +/- 7.5 years (median 3 years) after the diagnosis of hypothalamic/pituitary dysfunction. Mean gain in body mass index (BMI) between diagnoses of hypothalamic/pituitary disease and NAFLD was 11.3 +/- 8.9 kg/m(2) at an average yearly rate of 2.2 +/- 2.2 kg/m(2). The majority of patients developed elevated glucose levels and dyslipidemia by time of diagnosis of NAFLD. Of the 10 patients biopsied, six were cirrhotic, two had nonalcoholic steatohepatitis (NASH) with fibrosis, and two had simple steatosis. Long-term follow-up of 66 +/- 33 months (range 12-120) was available for 18 patients. Two required liver transplantation. Six patients died, two from liver related causes. In conclusion, patients with hypothalamic and/or pituitary disease are at risk of excessive weight gain, impaired glucose tolerance, and dyslipidemia with subsequent development of NAFLD. This group has a high prevalence of cirrhosis placing them at risk for liver-related death. The novel evidence that hypothalamic/pituitary dysfunction may be accompanied by progressive NAFLD has important implications for the work-up and management of patients with hypothalamic/pituitary disease.

Interactions of Leptin, GH, and Cortisol in Normal Children

Leptin is the product of the ob gene located in humans on chromosome 7q31.3. It is a 16-kDa protein named after the Greek "leptos," meaning lean, to indicate the function that this adipocyte-secreted protein was thought to have. Since its discovery, in fact, most of the research focused on the role of leptin in body-weight regulation, aiming to elucidate the pathophysiology of human obesity. However, more and more data show that leptin is not only important in the regulation of food intake and energy balance, but it also functions as a neuroendocrine hormone. It is involved in glucose metabolism, as well as in normal sexual maturation and reproduction, and interacts with the hypothalamic-pituitary-adrenal (HPA) and the growth hormone (GH) axes.

Presence of bovine leptin in edible commercial milk and infant formula

Leptin is a hormone secreted by the adipocytes that contribute to the control of energy balance, and circulating leptin levels reflect the amount of adipose tissue in the body, helping to regulate food intake and energy expenditure. Since it has been shown that human milk contains immunoreactive leptin, which is identical to intact human leptin, we decided to investigate the possible presence of immunoreactive bovine leptin in different kinds of common commercial milk. To determine the presence or absence of immunoreactive leptin in bovine milk for human consumption, 81 samples (66 commercial pasteurized milk and 15 artificial formulae for new-born babies) of the most common Spanish commercial types of milk were studied. All samples were evaluated before and after centrifugation, and leptin levels were measured by RIA. Leptin was detected in all samples and RIA standard curves were not perturbed when centrifuged and non-centrifuged milk replaced the buffer. Mean values of leptin in full-cream, semi-skimmed and skimmed samples, were: 5.7+/-0.3 ng/ml, 4.1+/-0.1 ng/ml, 3.7+/-0.1 ng/ml (significantly different). Leptin values were reduced after centrifugation. A significant correlation was observed between leptin levels and lipid content (p<0.0005, r=0.67) while no correlation was observed with respect to carbohydrate and protein levels. Interestingly, some preparations of infant formulae present very high leptin values reaching up to 18.9 ng/ml. In conclusion, leptin is present in significant and variable concentrations in edible commercial bovine milk, with higher concentrations in infant formula.

Sympathetic nerve hyperactivity is associated with increased peripheral vascular resistance in hypopituitary patients with growth hormone deficiency

OBJECTIVE

Hypopituitary patients with untreated GH deficiency have increased cardiovascular mortality. Sustained vasoconstriction is an important factor in the development of hypertension and insulin resistance. This study was designed to see whether peripheral vascular resistance was increased in subjects with GH deficiency and to examine the mechanisms involved.

METHODS

Nine patients with GH deficiency and nine matched control subjects were studied. Calf vascular resistance was measured by venous occlusion plethysmography and sympathetic vasoconstrictor nerve activity by peroneal microneurography.

RESULTS

Subjects with GH deficiency had a significantly lower blood flow (by 31%) and higher vascular resistance (by 48%) than the control group. In addition, they had a significantly higher sympathetic vasoconstrictor activity (by 67%) and this correlated with the vascular resistance (r = 0.45; P < 0.04).

CONCLUSIONS

Patients with GH deficiency have an increased peripheral vascular resistance that is contributed to by an increase in central sympathetic vasoconstrictor discharge to the peripheral vasculature. This could be important in the development of cardiovascular disease in this condition.

Resting metabolic rate, plasma leptin concentrations, leptin receptor expression, and adipose tissue measured by whole-body magnetic resonance imaging in women with Prader-Willi syndrome

BACKGROUND

Obesity in Prader-Willi syndrome (PWS) may be related to abnormalities in the adipocyte-leptin-hypothalamic pathway and may be exacerbated by reductions in the resting metabolic rate (RMR).

OBJECTIVE

We compared body composition, body-composition- adjusted RMR, and adiposity-adjusted plasma leptin between women with PWS and control women. We also examined leptin receptor expression in the PWS group.

DESIGN

We studied body composition using whole-body magnetic resonance imaging and measured plasma leptin by radioimmunoassay in 45 control women aged 18-56 y and in 13 women with PWS aged 20-38 y. RMR was measured by indirect calorimetry in 41 control women and in 8 women with PWS. Age, body composition, and regional adipose tissue (AT) depots were corrected for by multiple regression analysis. Messenger RNA expression of the leptin receptor was examined by reverse transcriptase-polymerase chain reaction in lymphocytes.

RESULTS

In the PWS group, fat mass was greater after correction for fat-free mass, and RMR was normal after correction for both fat-free mass and fat mass. Leptin was influenced primarily by subcutaneous AT volume in both subject groups. Leptin concentrations were not significantly different between the 2 groups after adjustment for age and AT content or distribution. Full-length leptin receptor messenger RNA was expressed in the lymphocytes of the PWS group.

CONCLUSIONS

Differences in RMR in women with PWS are explained by abnormal body composition, suggesting that energy expenditure is normal at the tissue level in PWS. There is no evidence that defective leptin production causes obesity in PWS, and leptin receptor deficiency is not a primary consequence of the gene defects leading to leptin resistance.

Leptin, cortisol, and GH secretion interactions in short normal prepubertal children

The hormonal regulation of the ob gene and leptin secretion in humans is still unclear. To investigate the interactions among leptin, cortisol, and GH, we analyzed and time-cross-correlated their spontaneous 24-h secretion in 12 short normal prepubertal children of both sexes (6 females and 6 males). Time-cross-correlation analyses demonstrated that leptin and cortisol were correlated in both a negative and positive fashion. The negative correlation, with cortisol leading leptin by 4 and 3 h for boys and girls, respectively, might reflect the stimulatory effect of CRH on the sympathetic system, which inhibits leptin secretion; the positive correlation, with leptin leading cortisol by 6 and 5 h for boys and girls, respectively, might reflect a direct effect of leptin on CRH secretion in the hypophyseal portal system. Time-cross-correlation analyses also showed a strong positive correlation between GH and leptin concentrations, with GH leading leptin by 5 and 2 h for boys and girls, respectively, suggesting a possible direct leptin-releasing effect of GH on adipocytes. We conclude that cross-correlation analyses of 24-h hormone secretions under baseline physiological conditions suggest that the hypothalamic-pituitary-adrenal axis might have a prevailing inhibitory effect on leptin secretion, whereas leptin might exert a positive effect on the hypothalamic-pituitary-adrenal axis. The relation between GH and leptin could be a direct one and characterized prevalently by a positive effect of GH on leptin secretion. Further investigations using different experimental systems are needed to ascertain the validity of these mathematically educed conclusions.

Influence of insulin-like growth factor-1 and leptin on bone mass in healthy postmenopausal women

This study examines the influence of circulating insulin-like growth factor-1 (IGF-1) and serum leptin on bone mass as well as modulation of bone mass during skeletal development. Moreover, an inverse relationship between IGF-1 and leptin is reported. To evaluate the effects of serum IGF-1 and serum leptin on bone mass in healthy postmenopausal women, and the possible role of IGF-1 in leptin production, we studied a population of 123 women, aged 39-82 years. Bone mineral density (BMD) was determined by whole-body dual-energy X ray absorptiometry, which also enables measurement of body composition. Bone metabolism was assessed by measuring serum total alkaline phosphatase (TAP) and urinary hydroxyproline/creatinine (HP/Cr) excretion. IGF-1 correlated significantly with age (r = -0.28, p < 0.01) and years since menopause (r = -0.24, p < 0.01). A negative correlation was also found with weight and body mass index (r = -0.15, p < 0.05 and r = -0.19, p < 0.05, respectively). Leptin values were strongly correlated with weight (r = 0.7, p < 0.01), BMI (r = 0.7, p < 0.01), fat mass (r = 0.77, p < 0.01), and lean mass (r = 0.39, p < 0.01); a significant correlation was found with total body BMD (r = 0.29, p < 0.01), TAP (r = 0.15, p < 0.05), and HP/Cr (r = 0.18, p < 0.05). After adjustment for BMI, the significance of these relationships disappeared, demonstrating the lack of effect of serum leptin on BMD and bone turnover independent of body weight. On the other hand, the relationship between BMD and fat mass remained statistically significant after adjusting for serum leptin (r = 0.15, p < 0.05). Controlling for BMI eliminated the significant inverse correlation between IGF-1 and leptin; significant differences in leptin levels were found among women in the lower and higher quartile of IGF-1, suggesting that leptin production may be inhibited only at high values of serum IGF-1. We conclude that serum IGF-1 and serum leptin have no direct effect on bone mass and bone turnover.

Leptin and the pituitary

Although leptin was originally viewed as an antiobesity hormone, it is now evident that it may have more pleiotropic actions. Experiments in rodents have shown that leptin activates the sympathetic nervous system, is involved in regulation of blood pressure, hematopoiesis, immune function, angiogenesis and brain, bone and pituitary development. Some biological effects expected based on observations in rodents, have so far not been seen in humans. Thus due to species differences in the role of leptin it is difficult to translate the data from rodents to human physiology. Hypothalamus is the primary brain site targeted by circulating leptin, secreted by fat cells. Leptin receptor has homology to members of class I cytokine receptor family, which may imply similarities in molecular events engaged by cytokines and leptin. In view of its cytokine-like properties it is likely that leptin produced and secreted outside of fat tissue i.e. in other tissues (CNS, pituitary, ovary, placenta, etc), is a paracrine regulator. Leptin receptor isoforms, long-signaling and short-nonsignaling, have been recently localized in human pituitaries. This opens the possibility of a direct action of leptin on the pituitary. However this appears to be quite complex and is species dependent. Leptin can be synthesized by normal and tumorous pituitary cells. Leptin protein expression in pituitary adenomas is decreased compared to that in normal pituitaries. Colocalization studies with leptin and anterior pituitary cells showed that 70% of ACTH cells are positive for leptin, 21% of GH cells, 29% of LH cells, 33% of FSH cells, 32% of TSH cells, 64% folliculo-stellate cells whereas very few PRL cells were positive (3%). Leptin is stored in secretory granules and secretory cells retain leptin in granules until stimulated. This follows a different secretory pathway than in adipocytes where upon synthesis leptin is immediately released. Question to be raised is does the pituitary contribute to the body leptin pool or is its action predominantly paracrine/autocrine? Clinically based evidence from studies performed in patients harboring different functional pituitary tumors causing a state of hormonal hypersecretion (acromegaly, prolactinomas, Cushing's disease) or hypopituitarism (due to non-functioning pituitary adenomas), are in favor of a paracrine/autocrine role of the pituitary leptin. Most of the studies have shown that the link between leptin, body composition and hormones of the pituitary is indirect. Thus changes in levels of circulating leptin are most likely due to changes in the metabolic and hormonal milieu during the chronic course of the disease or chronic treatment. Furthermore, circadian rhythm of leptin, its pulsatility and gender difference are preserved in hypopituitarism as well as in patients with functional pituitary adenomas implying that intact hypothalamic-pituitary function is not essential for leptin's circadian rhythm.

Leptin and leptin receptor in anterior pituitary function

Leptin is a 16 kDa protein that exerts important effects on the regulation of food intake and energy expenditure by interacting with the leptin receptor in the brain and in many other tissues. Although leptin is produced mainly by white adipose tissue, several laboratories have shown low levels of leptin production by a growing number of tissues including the anterior pituitary gland. Many studies have implicated leptin in anterior pituitary function including the observation that homozygous mutations of the leptin receptor gene led to morbid obesity, lack of pubertal development and decreased GH and TSH secretion. In addition, leptin functions as a neuroendocrine hormone and regulates many metabolic activities. Leptin also interacts with and regulates the hypothalamic-pituitary-adrenal, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-gonadal axes. All of the anterior pituitary cell types express the leptin receptor. However, leptin has been localized in specific subtypes of anterior pituitary cells indicating cell type-specific production of leptin in the anterior pituitary. Subcellular localization of leptin indicates co-storage with secretory granules and implicates hypothalamic releasing hormones in leptin secretion from anterior pituitary hormone cells. Leptin signal transduction in the anterior pituitary has been shown to involve the janus protein-tyrosine kinase (JAK)/signal transducer and activation of transcription (STAT) as well as suppressor of cytokine signalling (SOCS). These proteins are activated by tyrosine-phosphorylation in anterior pituitary cells. The various steps in pituitary leptin signal transduction remain to be elucidated.

Serum leptin levels in patients with hyperlipidemias

Leptin is a protein hormone produced by adipocytes that reflects the body fat content. The aim of our study was to compare serum leptin levels in randomly selected untreated males and females with hypercholesterolemia and combined hyperlipidemia and in healthy control subjects matched for age and body mass index and to study the relations between leptin and serum lipids and lipoproteins. No statistically significant differences in serum leptin levels were found between the male control group (5.26 +/- 2.81 ng/mL(-1)) and the male group with hypercholesterolemia (8.16 +/- 3.85 ng/mL(-1)) or combined hyperlipidemia (7.51 +/- 4.83 ng/mL(-1)) and between the female control group (13.0 +/- 8.12 ng/mL(-1)) and the female group with hypercholesterolemia (15.36 +/- 8.89 ng/mL(-1)) or combined hyperlipidemia (18.63 +/- 10.15 ng/mL(-1)). Leptin concentration in male group with hypercholesterolemia did not differ significantly from the female control group; in the other male groups, leptin levels were significantly lower than those of the other female groups. Serum leptin levels in all studied groups except for the male group with hypercholesterolemia positively correlated with body mass index. Serum leptin levels correlated negatively with high-density lipoprotein cholesterol in the female group with hypercholesterolemia (r = -0.67, P < 0.01) and the male group with combined hyperlipidemia (r = -0.56, P < 0.01). A positive correlation between serum leptin and high-density lipoprotein cholesterol (r = 0.67, P < 0.01) and between leptin and lipoprotein (a) (r = 0.71, P < 005) was found in female group with combined hyperlipidemia. No other significant relationships between leptin and serum lipids or lipoproteins were found. We conclude that serum leptin levels in patients with hyperlipidemias do not significantly differ from those healthy control subjects matched by age and body mass index.

Serum lipid and leptin concentrations in hypopituitary patients with growth hormone deficiency

OBJECTIVE

To investigate the effects of growth hormone (GH) deficiency on serum lipid and leptin concentrations in hypopituitary patients taking conventional replacement therapy and to determine the relations between leptin and gender and anthropometric and metabolic variables.

SUBJECTS

Twenty-one GH deficient adult hypopituitary patients (15 women, six men) and 21 (14 women, seven men) age, sex and body mass index (BMI) matched healthy controls.

MEASUREMENTS

After an overnight fast, anthropometric parameters were measured and body composition was determined by a bioelectrical impedance analyser. Venous blood samples were obtained for the measurements of glucose, total cholesterol, high density lipoprotein (HDL) cholesterol, triglyceride, intact insulin, insulin-like growth factor 1 (IGF-1) and leptin concentrations. Serum leptin and hormones were analysed by radioimmunoassay.

RESULTS

Hypopituitary patients with GH deficiency showed significantly higher triglyceride, total and low density lipoprotein (LDL) cholesterol and lower HDL cholesterol concentrations on conventional replacement therapy. The unfavourable lipid profile was particularly evident in women. Significantly higher leptin concentrations were found in patients compared with healthy controls with similar body fat content (23. 5+/-11.8 ng/ml vs 11.7+/-6.9 ng/ml, P=0.01). This difference remained significant even when leptin values were expressed in relation to fat mass percentage (0.79+/-0.40 vs. 0.42+/-0.17 ng/ml%, P<0.05) and fat mass kg (1.32+/-0.81 vs 0.66+/-0.30 ng/ml kg, P<0. 05). Significant positive correlations were observed between leptin concentrations and body fat percentage and age in the control group. In patients the sole significant relation between leptin and study parameters was the positive correlation observed between leptin and total cholesterol concentrations. Serum leptin concentrations were significantly higher in women than men in the control group, but not in the patients. No significant gender difference was observed when leptin concentrations were expressed in relation to fat mass (percentage and kg).

CONCLUSION

Growth hormone deficient hypopituitary patients (particularly women) on conventional replacement therapy have a more atherogenic lipid profile. Leptin concentrations are increased in GH deficient adults even after adjustment for percentage body fat and body fat mass (kg). Although the nature of our data does not allow us to draw any conclusions on the mechanism(s) of increased leptin concentrations in GH deficiency, decreased central sensitivity to leptin and increased leptin production from per unit fat mass, or alterations in leptin clearance, might be operative.

Leptin levels in Arabs with primary hyperthyroidism

BACKGROUND

The aim of this report was to study leptin status in hyperthyroid men and women (prior to and after medical treatment) and in matched controls in Arabs.

SUBJECTS AND METHODS

Twenty-nine hyperthyroid patients (19 women and 10 men) and 32 controls (20 women and 12 men) matched for age, ethnic status and body mass index (BMI) were studied. The patients were studied at the time of diagnosis and six months after antithyroid treatment with carbimazole-titrating dose, which rendered them euthyroid. On each study occasion, the subjects fasting blood was collected for the measurement of leptin, glucose, insulin and C-peptide.

RESULTS

Fasting leptin level was significantly lower in women with hyperthyroidism at baseline (mean+/-SEM, 15.8+/-2.9 microg/L, P=0.01), and after six months of antithyroid treatment (13.4+/-1.7 microg/L, P=0.004) than in control women (25.6+/-2.7 microg/L), but the difference was not significant in the men. Women in each group had significantly higher leptin concentrations than men (patients: 15.8+/-2.9 vs. 4.9+/-0.9 microg/L, P=0.009; controls: 25.67+/-2.7 vs. 7.9+/-1.4 microg/L, P=0.0005). The differences in women leptin remained significant even when expressed in relation to BMI. Baseline fasting glucose (P=0.01), insulin (P=0.007), and C-peptide (P=0.02) were significantly higher in the patients than controls. After six months of antithyroid therapy, fasting glucose, insulin and C-peptide levels were similar in the patients and controls. Within the patients, baseline leptin concentrations correlated positively with BMI (rho=0.65, P=0.02) and negatively with free T3 (rho=0.62, P=0.03). It neither demonstrated an association with baseline nor with six-month values of fasting glucose, insulin and C-peptide.

CONCLUSION

Leptin concentration is decreased in Arab women with hyperthyroidism. Six months of antithyroid therapy is not associated with alterations in leptin levels.

Leptin concentrations in Prader-Willi syndrome before and after growth hormone replacement

OBJECTIVE

This study explored leptin concentrations in Prader-Willi syndrome (PWS), a genetic disorder characterized by significant obesity and presumed hypothalamic dysfunction. The potential interaction of leptin metabolism with the growth hormone (GH) axis was also studied.

STUDY DESIGN

Plasma leptin concentrations and percent body fat were determined by radioimmunoassay and dual energy x-ray absorptionmetry, respectively, in 23 children with Prader-Willi syndrome and 23 children with exogenous obesity.

RESULTS

Log plasma leptin concentrations were positively correlated with percentage body fat in PWS (r = 0.844) and exogenous obesity (r = 0.869). When the regression lines for the two groups were compared, there were no differences in their slopes (P = 0.737) or intercepts (P = 0.701). Administration of recombinant human growth hormone to PWS children for 12 months significantly reduced both percentage body fat and plasma leptin concentrations, but the relationship of log plasma leptin to percentage body fat was unchanged.

CONCLUSION

Prader-Willi syndrome is not accompanied by deranged leptin concentrations and there was no evidence of an interaction of the GH axis with leptin metabolism in these GH-deficient children.

Serum leptin and body composition in children with familial GH deficiency (GHD) due to a mutation in the growth hormone-releasing hormone (GHRH) receptor

OBJECTIVE

The relationship between GH, body composition and leptin in children remains ill-defined. We have therefore examined the impact of severe GH deficiency (GHD) due to a mutation in the GHRH receptor on serum leptin concentrations and body composition in childhood.

PATIENTS

12 affected children and young people (GHD) (4 M:8F, age 5.4-20.1 years, 8 Tanner stage (TS) 1-2, 4 TS 3-5) and 40 healthy controls (C) from the same region (13 M:27F, age 5.3-18.4 years, 20 TS 1-2, 20 TS 3-5).

METHODS

Percent body fat was determined by infra-red interactance, from which the amounts of fat mass (FM, kg) and fat free mass (FFM, kg) were derived. Serum leptin concentrations were measured in a single fasted, morning serum sample and results expressed as a concentration and as leptin per unit fat mass (L/FM, ng/ml/kg). To control for differences in sex and pubertal maturation, leptin standard deviation scores (leptin SDS) were calculated using normative data from UK children.

RESULTS

FFM was significantly lower in GHD children than in controls (TS 1-2 P < 0.05, TS 3-5 P < 0.001). FM did not differ significantly between the two groups. Serum leptin concentrations, leptin per unit fat mass and leptin SDS were significantly elevated in GHD children both peripubertal and pubertal compared with controls. Using all subjects, stepwise multiple linear regression with FM, FFM, age, puberty and sex as explanatory variables and leptin concentration as the dependent variable indicated that 59% of the variability in leptin could be accounted for by FM (+, 45%), FFM (-, 9%) and sex (+, 5%) (P < 0.001). However on inclusion of GH deficiency (coded GHD = 1, control = 2) as an explanatory variable 73% of the variability in leptin was explained by FM (+, 45%), GHD (-, 22%) and sex (+, 6%) (P < 0.001).

CONCLUSIONS

These data indicate that severe GH deficiency in children is associated with elevated leptin concentrations, irrespective of sex or pubertal stage. This increase is not associated with differences in fat mass but is related to reduced fat free mass in GH deficiency. Furthermore in this population there may be an additional effect of GH deficiency on leptin, independent of the influences of sex and body composition.

Neuroendocrine regulation and actions of leptin

The discovery of the adipocyte-produced hormone leptin has greatly changed the field of obesity research and our understanding of energy homeostasis. It is now accepted that leptin is the afferent loop informing the hypothalamus about the state of fat stores, with hypothalamic efferents regulating appetite and energy expenditure. In addition, leptin has a role as a metabolic adaptator in overweight and fasting states. New and previously unsuspected neuroendocrine roles have emerged for leptin. In reproduction, leptin is implicated in fertility regulation, and it is a permissive factor for puberty. Relevant gender-based differences in leptin levels exist, with higher levels in women at birth, which persist throughout life. In adult life, there is experimental evidence that leptin is a permissive factor for the ovarian cycle, with a regulatory role exerted at the hypothalamic, pituitary, and gonadal levels, and with unexplained changes in pregnancy and postpartum. Leptin is present in human milk and may play a role in the adaptive responses of the newborn. Leptin plays a role in the neuroendocrine control of GH secretion, through a complex interaction at hypothalamic levels with GHRH and somatostatin. Leptin participates in the expression of CRH in the hypothalamus, interacts at the adrenal level with ACTH, and is regulated by glucocorticoids. Since leptin and cortisol show an inverse circadian rhythm, it has been suggested that a regulatory feedback is present. Finally, regulatory actions on TRH-TSH and PRL secretion have been found. Thus leptin reports the state of fat stores to the hypothalamus and other neuroendocrine areas, and the neuroendocrine systems adapt their function to the current status of energy homeostasis and fat stores.

Normal growth despite GH, IGF-I and IGF-II deficiency

A 6.5-year-old male with normal linear growth, despite septo-optic dysplasia, panhypopituitarism and a deficient GH/IGF axis, is presented. In addition to measuring IGF-I, IGF-II and IGFBP-3, serum IGFBP-1, -2, -4 and -5 were measured. A human osteosarcoma cell line was used to assess growth-promoting activity in the patient's serum. The role of leptin in linear growth in this case was investigated. There was no evidence for hyperinsulinism or hyperandrogenism. GH was undetectable upon multiple stimulation. GHBP was elevated. Serum IGF-I (25 microg/l), IGF-II (194 microg/l), IGFBP-3 (0.4 mg/l), and IGFBP-5 (87 microg/l) levels were low compared to age-matched prepubertal children. Serum IGFBP-4 level was normal. Molecular size of IGF-II in the patient's serum was normal, suggesting normal IGF-II bioavailability. Human osteosarcoma cell proliferation in response to the patient's serum was similar to sera from age-matched normal controls. Leptin levels were markedly elevated. Osteoblast cell proliferation was not stimulated by leptin. The data demonstrate that normal growth and osteoblast cell proliferation in this patient is not mediated by GH, total IGFs, insulin, or leptin, and suggest the presence of a yet unidentified growth factor or mechanism. The case offers a detailed picture of binding proteins in a case of growth without GH. It introduces osteoblast cell proliferation as a method of assessing serum growth-promoting activity in such cases. It adds IGF-II and leptin to the list of excluded growth-promoting candidates in GH-independent growth, and further demonstrates our incomplete understanding of the phenomenon of growth.

Relationship between serum leptin and the insulin-like growth factor-I system in humans

The growth hormone (GH)/insulin-like growth factor-I (IGF-I) system and leptin both play an important role in the regulation of body composition. Although the regulation of these two hormonal systems by insulin has been under intense investigation, the physiologic interactions between leptin and the GH/IGF-I system remain unknown. In this study, we examined the relationships among circulating leptin and key elements of the IGF-I system in 60 subjects (27 nondiabetic lean, 21 nondiabetic obese, and 12 type 1 diabetic subjects) with a wide range of insulin secretory capacity. Leptin, glucose, insulin, free IGF-I, total IGF-I, IGF-binding protein-1 (IGFBP-1), and IGFBP-3 levels were measured in the basal state after an overnight fast, and the acute insulin response to glucose (AIRG) was determined after intravenous glucose injection. AIRG was significantly higher (P < .01) in the obese (3,365+/-562 pmol/L x min) versus lean subjects (1,624+/-155 pmol/L x min). In simple regression analysis, the serum leptin concentration was positively correlated with the body mass index ([BMI] men, r = .51, P = .005; women, r = .71, P < .001), IGFBP-3 (men, r = .20, P = nonsignificant; women, r = .41, P < .025), and AIRG (men, r = .73, P < .001; women, r = .62, P < .01). There was a nonlinear correlation between leptin and IGFBP-1, but there was no correlation between leptin and free or total IGF-I. In multiple regression analysis with leptin as the dependent variable, gender, BMI, and IGFBP-3 entered the equations at a statistically significant level. The correlation of leptin with IGFBP-3 was independent of obesity and persisted after correction for AIRG, suggesting a link between leptin and GH action.

Alcohol, slow wave sleep, and the somatotropic axis

When alcohol is a large proportion of daily nutrient energy, the network of signals for energy homeostasis appears to adapt with abnormal patterns of sleep and growth hormone (GH) release along with gradual acquisition of an addictive physical dependency on alcohol. Early relapse during treatment of alcoholism is associated with a lower GH response to challenge, perhaps reflecting an altered balance of somatostatin (SS) to somatropin releasing hormone (GHRH) that also affects slow wave sleep (SWS) in dependent patients. Normal patterns of sleep have progressively shorter SWS episodes and longer rapid eye movement (REM) episodes during the overall sleep period, but the early sleep cycles of alcoholics have truncated or non-existent SWS episodes, and the longer REM episodes occur in early cycles. During SWS delta wave activity, the hypothalamus releases GHRH, which causes the pituitary to release GH. Alcohol-dependent patients have lower levels of SWS power and GH release than normal subjects, and efforts to understand the molecular basis for this maladaptation and its relation to continued alcohol dependence merit encouragement. More needs to be learned about the possibility of decreasing alcohol dependency by increasing SWS or enhancing GHRH action.

Serum leptin response to the acute and chronic administration of growth hormone (GH) to elderly subjects with GH deficiency

In human studies, the principal determinant of serum leptin concentrations is fat mass (FM), but lean mass (LM) also has a significant negative influence. GH treatment in GH deficiency (GHD) alters body composition, increasing LM and decreasing FM, and thus would be expected to alter leptin concentrations. We have therefore examined the acute and chronic effects of GH on serum leptin in 12 elderly GHD subjects (ages 62-85 yr; 3 women and 9 men). FM (kilograms) and LM (kilograms) were determined by dual energy x-ray absortiometry. Leptin, insulin, insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 were measured by specific immunoassays. Leptin, insulin, and IGFBP-1 concentrations were log10 transformed, and data were expressed as the geometric mean (-1, +1 tolerance factor). All other data are presented as the mean +/- SD. In the acute study, patients received a single bolus dose of GH (0.1 mg/kg BW) at time zero, with blood samples drawn at 0, 12, 24, 48, and 72 h and 1 and 2 weeks. There was a significant rise in leptin, insulin, and IGF-I at a median time of 24 h, followed by a significant fall, and nadir concentrations were reached at a median time of 1.5 weeks (leptin) or 2 weeks (insulin and IGF-I). IGFBP-3 concentrations were also significantly increased, but peak concentrations were not achieved until 48 h. IGF-II, IGFBP-1, and IGFBP-2 exhibited transient decreases before returning to baseline levels. There was no relationship between increased leptin concentrations and either insulin or IGF-I concentrations. In the chronic study, patients received daily GH treatment at doses of 0.17, 0.33, and 0.5 mg/day, each for 3 months (total time on GH, 9 months), and were then followed off GH for a further 3 months. Dual energy x-ray absortiometry was undertaken at 0, 3, 6, 9, and 12 months, and blood samples were drawn at these time points. Over 9 months on GH there was a significant fall in FM and a significant rise in LM, but no change in leptin. There were also significant increments in insulin, IGF-I, and IGFBP-3, whereas IGF-II, IGFBP-1, and IGFBP-2 did not change over 9 months of GH treatment. After 3 months off GH, there was a significant rise in FM and leptin. High dose single bolus GH led to an increase in serum leptin within 24 h apparently independent of changes in insulin or IGF-I. Despite the changes in body composition during chronic GH treatment, there was no change in leptin. However, discontinuation of GH led to a rapid reversal of the favorable body composition and a rise in serum leptin.

Hyperleptinaemia in young adults following cranial irradiation in childhood: growth hormone deficiency or leptin insensitivity?

OBJECTIVE

In order to explore the mechanism of obesity in long-term survivors of childhood leukaemia, fat mass, lean body mass and serum leptin were assessed in a cohort of 32 (17 males) adults who had received cranial irradiation (XRT) in childhood as part of their treatment for acute lymphobiastic leukaemia (ALL), and compared with 35 age and body mass index (BMI) matched young adults (18 male).

DESIGN

Thirty-one patients and 18 controls had fat mass and lean body mass assessed by dual x-ray absorptiometry (DEXA), using a lunar DPX-L scanner. Serum leptin concentrations were also measured in 27 patients and all controls. Growth hormone status had previously been determined using an insulin tolerance test and arginine stimulation test. Nine patients were classified as severe growth hormone (GH) deficient (group 1), 12 patients as GH insufficient (group 2) and 11 patients as normal (group 3).

RESULTS

BMI and absolute fat mass were not significantly different between the patients and controls regardless of their gender (P = 0.1 and P = 0.14 respectively). In contrast, absolute lean mass was significantly reduced (P < 0.01) and leptin concentrations were significantly increased (P < 0.001) in patients compared with controls. BMI, fat mass and leptin concentrations but not lean mass were significantly different between the three GH status groups (P < 0.01, P < 0.01, P = 0.004, and P = 0.67 respectively). When leptin concentrations were expressed per unit of fat mass, they were increased in the patients compared with the controls (P = 0.03) with significant differences between the GH status groups (P = 0.004), being significantly higher in the severe GH deficient group.

CONCLUSIONS

Young adults who receive cranial irradiation in childhood are prone to GH deficiency and hyperleptinaemia. The pathophysiological significance of the hyperleptinaemia remains to be established but it has occurred either as a consequence of radiation induced hypothalamic damage or GH deficiency.

Serum leptin levels and leptin expression in growth hormone (GH)-deficient and healthy adults: influence of GH treatment, gender, and fasting

Growth hormone (GH) treatment is associated with a reduction in fat mass in healthy and GH-deficient (GHD) subjects. This is mainly mediated via a direct GH action on adipose cells and stimulation of lipolysis. Leptin is secreted from adipose tissue and may be involved in signaling information about adipose tissue stores to the brain. Hormonal regulation of leptin is still not fully elucidated, and in the present study, we investigated both the long-term (4-month) and short-term (28-hour) GH effects on serum leptin and leptin gene expression in subcutaneous adipose tissue. In GHD adults (n = 24), leptin correlated with most estimates of adiposity (r = .62 to .86), as previously found in healthy subjects. However, no correlation was observed with intraabdominal fat determined by computed tomographic (CT) scan (INTRA-CT). GH treatment for 4 months had no independent effect on either serum leptin or leptin gene expression. In a short-term study, we found that fasting gradually reduced leptin levels in both healthy men and GHD adults, with a maximum reduction of 58% to 60% (P < .01) after 31 hours. No independent effect of GH suppression or GH substitution on serum leptin was found during fasting. Adipose tissue leptin mRNA correlated with serum leptin (r = .51, P < .01) and the body mass index ([BMI] r = .55, P < .05). Serum leptin levels and gene expression were significantly higher in women compared with men (26.6 +/- 5.8 v 10.0 +/- 1.30 ng/mL, P < .05). However, in regression analysis accounting for the gender differences in subcutaneous femoral adipose tissue (FEM-CT), the difference in serum leptin disappeared, indicating that subcutaneous femoral fat or factors closely related to femoral fat (eg, sex hormones) may be causal factors for the gender difference in leptin.

Serum leptin in obese patients with Laron syndrome before and during IGF-I treatment

Fifteen patients with primary GH resistance (Laron syndrome, LS) were studied before and during 6 months of daily replacement treatment with IGF-I. The main findings were that patients with LS and normal or high serum GH binding protein (GHBP) were less obese than those with a negative GHBP, and that serum leptin levels varied with body mass as in other types of obesity.

Interaction between body composition, leptin and growth hormone status

Administration of growth hormone (GH) induces changes in body composition, namely, increases in both bone and lean mass and a decrease in fatty tissue. However, the contrary issue, i.e. the way in which body composition affects the secretion of GH, is highly controversial. Disease states such as obesity and chronic hypercortisolism are associated with increased adiposity and/or the central distribution of fat. Ageing, characterized by excess adiposity, is also associated with impaired secretion of GH. In these states, both spontaneous and stimulated secretion of GH is severely impeded. At the other extreme, malnutrition and fasting are both associated with increased secretion of GH when confronted with most, if not all, stimuli. As the common factor in all of these situations is the increased or decreased adiposity, or the changes in energy homeostasis, it has been postulated that adipose tissue exerts a relevant role in the control of GH secretion in man. The link between adipose tissue and GH seems to be exerted through at least two signals produced by adipocytes: free fatty acids (FFA) and the recently cloned protein, leptin. An increase in FFA blocks secretion of GH, while a decrease in FFA enhances secretion. Leptin, a hormone whose main role is to regulate the intake of food and energy expenditure, seems to regulate GH secretion by acting at the hypothalamic level. In summary, body composition affects GH secretion by way of the degree of adiposity, and free fatty acids and leptin would appear to be the messages through which adipocytes participate in the regulation of GH secretion. This framework clarifies the metabolic control of GH, a hormone with profound metabolic activities.

The circadian rhythm of leptin is preserved in growth hormone deficient hypopituitary adults

OBJECTIVE

Leptin acts as a satiety factor in regulating food intake and body homeostasis, but its regulation is not well defined. Specific leptin receptors have been found in the brain and it has been hypothesized that leptin production by adipose tissue is under neuroendocrine control. A circadian rhythm has been demonstrated with highest leptin levels between midnight and early morning hours. The possibility that hypopituitarism (or pituitary surgery +/- radiotherapy) abolishes this leptin rhythm was investigated by measuring serum leptin levels during a 24-h period in patients with impaired pituitary function.

PATIENTS AND DESIGN

Circulating leptin levels were measured hourly over 24-h in 14 hypopituitary patients (8 women and 6 men) using a sensitive and specific radioimmunoassay. Hypopituitarism was the consequence of pituitary tumors treated surgically and/or with radiotherapy. All patients were GH deficient and were receiving conventional replacement with cortisol (n = 13), thyroxine (n = 12) and desmopressin (n = 4) but not with GH.

RESULTS

A significant diurnal variation in circulating leptin concentrations was observed in 13 of the 14 patients. The mean (+/- SEM) leptin levels for 8 women were 51.9 (+/- 10.7) ng/ml and for 6 men 11.0 (+/- 2.0) micrograms/l. The overall lowest leptin levels (29.3 +/- 7.9 ng/ml) were observed at 0830 h after overnight fasting, rising gradually to maximum levels (43.0 +/- 9.8 ng/ml) at 0200 h declining thereafter towards fasting values. The mean (+/- SEM) magnitude of circadian variation in absolute leptin levels from the calculated mean level for each patient was 5.6 (+/- 1.2) ng/ml (8.4 +/- 1.4 for women and 1.9 +/- 0.3 for men). The mean (+/- SEM) of the ratio of the amplitude versus mean leptin levels over 24 h for each individual patient was 0.18 (+/- 0.02) (0.19 +/- 0.03 for women and 0.18 +/- 0.02 for men).

CONCLUSIONS

A circadian rhythm for leptin is generally present in hypopituitary patients who had undergone pituitary surgery and/or radiotherapy, with the highest serum leptin levels being obtained between midnight and early morning hours. Although some patients had some residual pituitary activity, intact hypothalamic-pituitary function is not essential for leptin's circadian rhythm.