Relationship between growth hormone (GH) status, serum leptin and body composition in healthy and GH deficient elderly subjects

Live Probiotic Lactobacillus johnsonii BS15 Promotes Growth Performance and Lowers Fat Deposition by Improving Lipid Metabolism, Intestinal Development, and Gut Microflora in Broilers

Numerous studies have focused on the beneficial effects of probiotics in animals. Even so, additional information should be obtained about the mechanisms by which a useful probiotic strain successfully exerts such beneficial effects. In this study, we evaluated the effect of the dietary supplementation of both live and disrupted Lactobacillus johnsonii (LJ) strain BS15 in broilers at different ages. Specifically, growth performance, lipid metabolism, gut microbiota, intestinal development, and digestive ability of the broilers were assessed. A total of 180 1-day-old Cobb 500 chicks were randomly distributed into three groups. These chicks were fed diets supplemented with 1 × 10⁶ colony-forming units (cfu) LJ per gram of feed (LJ group); 1 × 10⁶ cfu disrupted LJ per gram of feed (D-LJ group); and de Man, Rogosa, and Sharpe liquid medium (control group), respectively, throughout a 42-day experimental period. The results demonstrated that LJ supplementation of feed had a positive effect on the average daily gain and starter feed conversion ratio. In addition, LJ supplementation of feed decreased serum triglyceride and low-density lipid cholesterol levels, as well as abdominal fat deposition. LJ also reduced the mRNA levels of lipoprotein lipase in adipose tissue and stearoyl-CoA desaturase-1 in the liver. LJ diminished the mRNA quantities of the sterol regulatory element binding protein-1c and fatty acid synthase, as well as increased the level of serum high-density lipid cholesterol. LJ increased the mRNA quantities of peroxisome proliferator-activated receptor α, acyl-CoA oxidase in the liver, and carnitine palmitoyltransferase-1. LJ also improved the intestinal development and digestive ability mainly by increasing the villus height/crypt depth ratio in the ileum. The probiotic increased the levels of epidermal growth factor and insulin-like growth factor-1, as well as the activities of trypsin and lipase in the jejunum and ileum. LJ exerted beneficial effects on the intestinal flora. Specifically, LJ markedly enhanced the population of Bacteroidetes and Lactobacillus spp. Moreover, the probiotic reduced the population of Enterobacteriaceae and the Firmicutes/Bacteroidetes ratio. Slight changes caused by disrupted LJ were detected. These findings indicated that live LJ supplementation may promote growth performance and lower fat deposition in broilers.

Diet-Induced Nonalcoholic Fatty Liver Disease Is Associated with Sarcopenia and Decreased Serum Insulin-Like Growth Factor-1

BACKGROUND

Decreased muscle mass or sarcopenia has been associated with nonalcoholic fatty liver disease (NAFLD). However, the functional consequences of this association and its pathogenesis remain ill-defined.

AIMS

To evaluate muscle mass and function in a diet-induced NAFLD mouse model and explore its association with changes in serum insulin-like growth factor-1 (IGF-1).

METHODS

Weight gain, visceral fat, serum biochemical parameters, liver histology, and hepatic triglyceride content (HTC) were assessed in C57/Bl6 mice fed a westernized diet during 16 weeks. In addition, we determined muscle fiber size and strength of limb skeletal muscle, myosin heavy chain (MHC) protein levels, and IGF-1 serum levels.

RESULTS

Westernized diet feeding was associated with weight gain, increased visceral fat mass (epididymal pad weight: 0.76 g ± 0.13 vs. 0.33 ± 0.27 g; p = 0.0023), hepatic steatosis (HTC: 118.2 ± 6.88 mg/g liver vs. 43.26 ± 5.63 mg/g<, p < 0.05), and necroinflammation (histological scores: 1.29 ± 0.42 vs. 4.00 ± 0.53<, p < 0.05). Also, mice fed the experimental diet had an increased proportion of low-diameter muscle fibers (0-30 μm) and a decreased proportion of high-diameter muscle fibers (60-90 μm), which correlated with decreased MHC protein levels, consistent with significant muscle atrophy. Functional studies showed that mice fed a westernized diet had reduced muscle strength and lower serum levels of IGF-1 (284.2 ± 20.04 pg/ml) compared with chow-fed mice (366.0 ± 12.42 pg/ml, p < 0.05).

CONCLUSION

Experimental NAFLD is associated with sarcopenia, decreased muscle strength, and reduced IGF-1 serum levels. IGF-1 reduction may be involved in pathogenesis of NAFLD-associated sarcopenia.

Serum leptin levels in gastric cancer patients and the relationship with insulin resistance

INTRODUCTION

Serum leptin levels have been examined in various cancers, with conflicting results. However, there is limited information regarding serum leptin levels and insulin resistance in gastric cancer patients. Therefore, we aimed to investigate serum leptin levels, performance status, insulin levels and insulin resistance in patients with gastric cancer. In addition, we examined the relationship between these measurements and leptin levels.

MATERIAL AND METHODS

Thirty-nine patients with gastric cancer and 30 control subjects were enrolled in the study. Serum leptin, total protein, albumin, growth hormone, insulin and glucose levels were measured. The homeostasis model assessment (HOMA) was used to assess insulin resistance.

RESULTS

Serum levels of insulin, glucose and growth hormone and insulin resistance were significantly lower in gastric cancer patients than controls (p < 0.05 for all). In the Pearson correlation analysis, insulin resistance was found to be significantly correlated with serum leptin levels in gastric cancer patients (r = 0.320, p = 0.047). We observed a significant negative correlation between performance status and insulin resistance in patients with cachexia (r = -0.512, p = 0.030), while no association was found in non-cachectic patients.

CONCLUSIONS

We concluded that serum leptin levels are significantly lower in gastric cancer patients. In addition, gastric cancer patients have decreases in insulin levels, insulin resistance and growth hormone levels. This study found a positive association between serum leptin levels and insulin resistance. Moreover, there is a negative association between serum leptin levels and growth hormone levels. Thus, low insulin and growth hormone levels may suppress the production of leptin in gastric cancer patients.

Increased adiposity and insulin correlates with the progressive suppression of pulsatile GH secretion during weight gain

Pathological changes associated with obesity are thought to contribute to GH deficiency. However, recent observations suggest that impaired GH secretion relative to excess calorie consumption contributes to progressive weight gain and thus may contribute to the development of obesity. To clarify this association between adiposity and GH secretion, we investigated the relationship between pulsatile GH secretion and body weight; epididymal fat mass; and circulating levels of leptin, insulin, non-esterified free fatty acids (NEFAs), and glucose. Data were obtained from male mice maintained on a standard or high-fat diet. We confirm the suppression of pulsatile GH secretion following dietary-induced weight gain. Correlation analyses reveal an inverse relationship between measures of pulsatile GH secretion, body weight, and epididymal fat mass. Moreover, we demonstrate an inverse relationship between measures of pulsatile GH secretion and circulating levels of leptin and insulin. The secretion of GH did not change relative to circulating levels of NEFAs or glucose. We conclude that impaired pulsatile GH secretion in the mouse occurs alongside progressive weight gain and thus precedes the development of obesity. Moreover, data illustrate key interactions between GH secretion and circulating levels of insulin and reflect the potential physiological role of GH in modulation of insulin-induced lipogenesis throughout positive energy balance.

Selective contribution of regional adiposity, skeletal muscle, and adipokines to glucose disposal in older adults

OBJECTIVES

To study the relationships between muscle mass, regional adiposity, and adipokines and glucose disposal in an older population.

DESIGN

Cross-sectional analysis.

SETTING

Community-dwelling volunteers from the Baltimore Longitudinal Study of Aging.

PARTICIPANTS

Two hundred eighty men and 259 women with a mean age of 71.1 ± 0.4 (range 55-96) and complete data on fasting plasma adiponectin and leptin, oral glucose tolerance test (OGTT) (plasma glucose available at 0, 20, 40, 60, 80, 100, and 120 minutes), thigh computed tomography (CT), physical activity levels, and anthropometric measures.

MEASUREMENTS

Participants were classified into eight groups according to the presence of global adiposity (body mass index > 27 kg/m(2)), central adiposity (waist circumference > 88 cm for women and > 102 cm for men), and low muscle mass (CT thigh, lowest sex-specific tertile (93.8 cm(2) in women and 110.7 cm(2) in men) of adjusted thigh muscle area). Linear regression models were used to estimate the contribution of these eight groups to early glucose area under the curve (AUC) (t = 0-40 minutes), late glucose AUC (t = 60-120 minutes), and total glucose AUC (t = 0-120 minutes) from the OGTT.

RESULTS

Regardless of muscle mass, individuals with a combination of central and global adiposity were more likely to have delayed glucose disposal rates (P < .05). A strong negative association was also found between circulating adiponectin levels and glucose disposal rates (early AUC, β = -0.14; late AUC, β = -0.20; and total AUC, β = -0.20; P < .05 for all three AUCs) after adjusting for regional adiposity, muscle mass, circulating leptin levels, physical activity, age, and sex.

CONCLUSION

Older individuals with global and central adiposity may be at risk of glucose intolerance unrelated to low muscle mass.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

Hypoleptinemia in gastric cancer patients: relation to body fat mass, insulin, and growth hormone

BACKGROUND

It remains elusive whether there are other causes besides body fat mass wasting contributing to decreased leptin level in cancer cachexia patients. This study attempts to explore possible factors influencing leptin levels in patients with gastric cancer.

METHODS

Hormones levels (including leptin, insulin, growth hormone (GH), insulin-like growth factor I, glucagons, and cortisol), acute phase reactant, and body composition were measured in 88 gastric cancer patients and 24 healthy controls. All patients were divided into weight-loss (48 patients) or nonweight-loss (40 patients) groups and cachexia (body mass index <18; 13 patients) or noncachexia (75 patients) groups. The detection was repeated 3 months after radical surgery in 16 patients.

RESULTS

Compared with the controls, leptin levels decreased in gastric cancer patients with and without weight loss (p < .001 and p = .003, respectively), even when the percentage of fat mass was adjusted (p = .004 and 0.018, respectively). GH and insulin levels also changed significantly. Similar results were also found in patients with and without cachexia. Multivariate regression analysis showed that the percentages of fat mass (standardized coefficient [SC] = 0.631, p < .001), GH (SC = -0.244, p = .005) and insulin (SC = 0.201, p = .020) were significantly correlated with leptin. In the 16 patients who underwent radical surgery, leptin levels remained low and no significant changes in the other hormones were detected.

CONCLUSIONS

Our results showed that low leptin levels in gastric cancer patients depended not only on the percentage of fat mass, but also on GH and insulin levels. Chronic high GH and low insulin levels may inhibit the leptin secretion.

Body mass index (BMI) and parameters of bone formation and resorption in postmenopausal women

OBJECTIVES

Aim of this study was to evaluate increased body mass index (BMI) as an anthropometric factor, predisposing to lower rates of bone turnover or changes in bone balance after menopause.

MATERIAL AND METHODS

For this purpose, we calculated BMI, and measured spinal (BMD(SP)) and femoral bone mineral density (BMD(FN)) and biochemical markers of bone formation (serum osteocalcin (S-OC), serum procollagen type I C propeptide (S-PICP), serum bone-specific alkaline phosphatase (S-B-ALP)) and resorption (urine N- and C-terminal cross-linking telopeptide of type I collagen (U-NTX-I and U-CTX-I), pyridinoline (U-PYD) and deoxypyridinoline (U-DPD)) in 130 healthy postmenopausal women, aged 46-85 years. Bone balance indices were calculated by subtracting z-scores of resorption markers from z-scores of formation markers, to evaluate bone balance.

RESULTS

S-PICP ( r = -0.297, P = 0.002), S-OC ( r = -0.173, P = 0.05) and bone balance indices (zPICP-zDPD) and (zPICP-zPYD) were negatively correlated with BMI (r = -0.25, P = 0.01 and r = -0.25, P = 0.01 and r = -0.21, P = 0.037) and with BMD(SP) (r = -0.196, P = 0.032 and r = -0.275 and P = 0.022). Women were grouped according to their BMI, in normals (BMI < 25 kg/m2), overweight (BMI = 25-30 kg/m2, and obese (BMI > 30 kg/m2). Overweight and obese women had approximately 30% lower levels of S-PICP compared to normals (68.11 +/- 24.85 and 66.41 ng/ml versus 97.47 +/- 23.36 ng/ml, respectively; P = 0.0001). zPICP-zDPD, zPICP-zCTX-I and zPICP-zPYD were significantly declined in obese women compared to normals (P = 0.0072, 0.02 and 0.0028).

CONCLUSIONS

We conclude that in postmenopausal women, BMI is inversely associated with levels of collagen I formation marker, serum PICP. In obesity formation of collagen I was reduced, in favor of degradation, but since this finding is not followed by simultaneous decrease in bone mineral density, it seems that increased body weight may have different effects on mature estrogen-deficient bone and extraskeletal tissues containing collagen I.

Hormônio do crescimento ou somatotrófico: novas perspectivas na deficiência isolada de GH a partir da descrição da mutação no gene do receptor do GHRH nos indivíduos da cidade de Itabaianinha, Brasil

Além de influenciar o crescimento corpóreo, o hormônio do crescimento, ou somatotrófico, desempenha importante papel no metabolismo, composição corporal, perfil lipídico, estado cardiovascular e longevidade. Seu controle é multi-regulado por hormônios, metabólitos e peptídeos hipotalâmicos. Dados sobre a Deficiência Isolada de GH (DIGH) obtidos a partir da descrição da mutação IVS1+1G®A no gene do receptor do hormônio liberador do GH (GHRH-R) em indivíduos da cidade de Itabaianinha, SE, são revisados. São abordadas novas perspectivas sobre o modelo de resistência ao GHRH, a importância do GHRH no controle da secreção de GH, a freqüência das mutações do gene do GHRH-R, a relevância diagnóstica do IGF-I e os achados metabólicos, cardiovasculares e de qualidade de vida nestes indivíduos.

Serum leptin levels in acromegalic patients before and during somatostatin analogs therapy

GH excess is characterized by alterations of body composition such as decreased body fat mass; however, scant data are present regarding its effect on serum leptin levels. To better elucidate this topic, leptin secretion was studied in 20 acromegalic patients, before and after 6 months of treatment with somatostatin analogs (SR-lanreotide 30 mg and octreotide LAR). Basal GH, IGF-I, insulin, blood glucose and lipid levels were measured and the area under the curve (AUC) for insulin and glucose and oral glucose insulin sensitivity (OGIS) during oral glucose tolerance test (OGTT) were calculated. After 6 months of somatostatin analogs therapy, a significant reduction in GH and IGF-I plasma levels was observed (p<0.0005, both) with a significant increase of leptin levels (7.4+/-1.3 vs 13.2+/-1.6 ng/ml; p<0.05). Interestingly, the typical correlation of leptin with body mass index (BMI) was not present in active acromegaly, whereas it was restored after somatostatin analogs treatment; moreover, the gender difference in leptin secretion between men and women was preserved in active and controlled acromegaly. In conclusion, the gender-based leptin differences are preserved and leptin secretion/BMI ratio is normalized in acromegalic patients after somatostatin analogs therapy.

Gender variation in leptin circadian rhythm and pulsatility in adult growth hormone deficiency: effects of growth hormone replacement

OBJECTIVES

Adult growth hormone deficiency (AGHD) is characterized by obesity and associated with increased leptin concentration and decreased leptin pulsatility. Growth hormone replacement (GHR) results in a decrease in leptin concentration and increase in leptin pulsatility, followed by reduction in body fat mass (BFM). In both health and AGHD, women exhibit relatively higher leptin concentrations compared to men. The effect of gender on leptin rhythm and pulse parameters in AGHD is yet to be defined and the gender difference in the response of leptin secretory pattern to GHR has not been determined. Therefore the aim of this study was to evaluate the effect of gender on circadian and pulse parameters of leptin secretion in AGHD, and examine the gender variation in response of these parameters to GHR.

STUDY DESIGN

A prospective, open treatment design study to determine the effect of gender on leptin rhythm and pulse parameters in untreated and treated AGHD. GH was commenced at a daily dose of 0.5 IU, and titrated up by increments of 0.25 IU at 2-weekly intervals to achieve and maintain IGF-I SDs between the median and upper end of the age-related reference range.

PATIENTS

Twelve patients (six men, six women) with severe AGHD following pituitary surgery, defined as peak GH response < 9 mU/l to provocative testing were studied. All patients required additional pituitary replacement hormones following pituitary surgery and were on optimal doses at recruitment.

MEASUREMENTS

Plasma leptin was measured at half-hourly intervals for 24 h, before and 1 month after initiation of GHR. Cosinor analysis was used to determine the circadian rhythm parameters: MESOR (rhythm-adjusted mean), acrophase and amplitude; and ULTRA algorithm used for pulse analysis. Body composition was measured using bioelectrical impedance.

RESULTS

BFM was higher in women than men at both visits (P < 0.05), but there was no significant change in BFM in either gender following 1 month of GHR. Women had a higher mean 24-h leptin concentration, MESOR, circadian amplitude and pulse amplitude, both before and after GHR (P < 0.05). Following treatment, mean leptin concentration and MESOR decreased significantly in both men and women (P < 0.05), with no significant difference in percentage change between the genders. Pulse frequency increased and duration decreased significantly after GHR in both groups, without any significant gender difference. IGF-I and IGF SDs were similar in both genders at baseline (P = 0.93). However, after 1 month GHR, the increase in both measurements was greater in men than women (P = 0.005) and men had significantly higher IGF-I and IGF SDs than women (P = 0.01).

CONCLUSIONS

As in healthy individuals, leptin levels were higher in women with AGHD than men, both prior to and after GHR. Decline in leptin concentrations and increase in leptin pulsatility following 1 month of GH treatment were similar in both genders. Changes in leptin secretory parameters appeared to occur without any significant decrease in BFM, suggesting a regulatory role for GH. Additionally, the action of GH on leptin secretory pattern does not appear to be mediated by IGF-I. Our data suggest that changes in leptin concentration and rhythm parameters following GHR are independent of gender.

The inhibition of growth hormone secretion presented in obesity is not mediated by the high leptin levels: a study in human leptin deficiency patients

GH secretion is regulated by hypothalamic and peripheral hormones under a very complex interplay. Superimposed on this regulation, signals of a metabolic nature connect GH secretion with the metabolic and energetic homeostasis of a given individual. GH secretion is enhanced in malnutrition and is severely impeded in obesity, but no information is available to explain why GH secretion is severely impeded or blocked in excess adiposity. Obesity is associated with high plasma levels of leptin, and leptin participates at the hypothalamic and pituitary levels in the regulation of GH secretion. Thus, it has been postulated that the inhibitory action of obesity on GH discharge may be mediated by excess leptin levels. The only situation in which obesity does not parallel leptin values is the rare case of morbid obesity due to leptin deficiency caused by missense mutation of the leptin gene. To understand the causes of GH blockade presented in obesity, patients with both homozygous and heterozygous mutations of the leptin gene and matched controls for both sex and body mass index (BMI) were studied. Three homozygous and 5 heterozygous patients with leptin gene mutations as well as 13 control subjects were studied. In all subjects basal levels of leptin and GH values stimulated by the combined administration of GHRH plus GH-releasing peptide-6 (GHRP-6) were analyzed. To analyze the effects of obesity and leptin levels, 5 groups were designed, all them matched by sex and adiposity. The number of subjects (n), leptin levels in micrograms per liter, and adiposity in BMI were as follows: nonobese subjects: n = 5, BMI = 22.1 +/- 0.9 kg/m2, leptin = 5.4 +/- 0.9; heterozygous patients: n = 5, BMI = 27.0 +/- 1.0 kg/m2, leptin = 2.3 +/- 0.1; controls for the heterozygous group: n = 5, BMI = 24.7 +/- 1.1 kg/m2, leptin = 5.7 +/- 1.2; homozygous patients: n = 3, BMI = 54.4 +/- 0.2 kg/m2, leptin = 1.0 +/- 0.2; and controls for the homozygous group: n = 3, BMI = 50.3 +/- 2.0 kg/m2, leptin = 35.0 +/- 6.6. In these matched groups, the GHRH- and GHRP-6-stimulated GH secretion (mean peak +/- SE; micrograms per liter) was: nonobese, 86.8 +/- 8.9 [significantly higher than heterozygous (28.6 +/- 4.9) and control for heterozygous (39.9 +/- 10.4)]; homozygous group, 9.4 +/- 3.0; control for homozygous, 9.3 +/- 1.0 (significantly lower than the heterozygous, control for heterozygous, and nonobese groups). Hence, it appeared that GH discharge was negatively conditioned by adiposity and was not influenced by leptin levels. To further analyze this observation, a correlation analysis showed that GH peaks were negatively correlated with BMI in the 13 control subjects as well as in the 8 leptin-deficient patients. On the contrary, the GH peaks were negatively correlated with leptin levels in controls, but showed the opposite pattern in homo- and heterozygous patients. In conclusion, the GH secretion blockade, which is characteristic of obese states, is due to adiposity or some factor linked to adiposity, but not to elevated plasma leptin levels.

Leptin measurement in urine in children and its relationship to other growth peptides in serum and urine

OBJECTIVE

Leptin has been implicated in the interaction between nutrition, energy balance and sexual maturation in humans. A non-invasive method of measuring leptin would greatly facilitate longitudinal studies of changes in leptin in normal children. The aim of this study was to evaluate the use of urinary leptin as a surrogate for serum leptin measurements.

DESIGN

We have modified and validated a serum immunoradiometric assay (IRMA) kit for the measurement of leptin in urine, and subsequently investigated the relationship between urinary leptin and other growth-related proteins.

METHODS

Cross-sectional study: urinary leptin, measured in the first morning urine voided and expressed as ng excreted overnight, and serum concentrations of leptin, IGF-I, IGF-II, IGFBP-3 and IGFBP-1 were determined in a cohort of 188 healthy schoolchildren aged 5-19 years (88 males, 100 females). Height, weight and pubertal status were assessed in all children. Longitudinal study: urinary levels of leptin, IGF-I and GH were measured daily in two adults (one male, one female) over a period of 6 weeks.

RESULTS

The detection limit of this modified assay was 0.59 ng/L. The intra- and interassay coefficients of variation range was 4-8% and 4-9%, respectively. The recovery of recombinant leptin added to urine was 98-108%, and the assay had a recovery rate for serial dilution in the range of 106-112%. Urinary leptin correlated significantly with serum leptin (r = +0.65, P < 0.01). Urinary leptin showed similar changes through puberty to those of serum leptin, with levels rising in females throughout puberty, whereas in males levels peaked at G2/G3 then decreased. BMI SDS was the main determinant of urinary leptin, as it was for serum leptin. In the cross-sectional study urinary leptin correlated significantly with serum IGF-I (r = +0.41, P = 0.001), IGF-II (r = +0.19, P = 0.05), IGFBP-3 (r = +0.29, P = 0.001) and IGFBP-1 (r = -0.25, P = 0.001). In the adult study, leptin was also detected in urine with similar night-to-night variability to that found for IGF-I and GH.

CONCLUSION

Urinary leptin is a valid marker of serum leptin concentrations, and therefore this non-invasive assay would be a useful tool for longitudinal assessment of changes in leptin in children.

Serum leptin levels are not influenced by arginine and insulin infusion and by acute changes of GH

The aim of this study was to evaluate the relationship between GH and leptin in a group of short children and adolescents. Leptin and GH serum levels were measured before and during pharmacological stimulation tests (arginine and insulin) in a group of 45 children (30 male, 15 female), mean age 8.6+/-3.9 yr, affected by idiopathic isolated GH deficiency (GHD), and in a group of 27 children (15 male, 12 female), age 10.9+/-3.3 yr, with constitutional growth delay. Results showed that basal and peak leptin levels as well as the AUC were significantly higher in GHD patients compared to controls (p<0.05) and correlated with BMI SDS (p<0.0001) in GHD patients. No change in leptin serum levels was observed during either stimulation test. No correlation was found, however, between basal leptin serum levels and basal, peak and the AUC of GH during the tests. Moreover, no correlation was found between the acute changes of serum GH concentration during both stimulation tests and leptin serum levels. The results suggest that leptin and GH secretion is not correlated and that leptin serum levels mainly reflect the amount of fat tissue, which is higher in GHD patients.

Overweight, waist circumference, age, gender, and insulin resistance as risk factors for hyperleptinemia

OBJECTIVE

To evaluate the influence of overweight, waist circumference, age, gender, and insulin resistance as risk factors for hyperleptinemia.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study was carried out in a population of 197 subjects: 59 men (21 aged < 60 years and 38 aged > or =60 years) and 138 women (37 aged < 60 years and 101 aged > or =60 years). The groups were stratified by overweight and normal weight. After a 12-hour fasting period, we measured serum leptin and insulin levels with radioimmunoassay methods. We also measured serum glucose and lipid profile. The data were analyzed by means of comparative tests. A variance-stabilizing transformation (natural logarithmic) was used to meet multiple linear regression, analysis of covariance, and logistic regression models.

RESULTS

The leptin serum levels were higher and statistically significant in young and older women than they were in men. We observed an interaction between gender and body mass index to explain the difference in leptin levels (p < 0.0001). Our study demonstrated an inverse relationship between leptin with age and high-density lipoprotein cholesterol. In logistic regression analysis, the overweight x gender interaction and waist circumference have a statistically significant influence as independent variables on hyperleptinemia (overweight x gender odds ratio = 6.81; 95% confidence interval, 1.10 to 46.86; p < 0.05 and waist circumference odds ratio = 4.34; 95% confidence interval, 1.47 to 12.83; p = 0.001).

DISCUSSION

Women who were overweight or had a higher waist circumference (women > or = 88 cm and men > or = 102 cm) have a significantly higher risk of having hyperleptinemia. The increase in age as an isolated variable is not a risk factor for hyperleptinemia.

Leptin in anorexia nervosa and bulimia nervosa: importance of assay technique and method of interpretation

Studies of the role of leptin in patients with anorexia nervosa and bulimia nervosa have conflicted in their data and interpretation. Such differences may be a result of the assay methods used or the way results are compared with those from normal controls. To investigate these possibilities, we analyzed serum leptin levels in anorexic, bulimic, obese, and control individuals, thereby spanning the full range of human body weights, using three frequently employed commercial kits. Kits from Linco (St Louis, MO) and DSL (Webster, TX) employ a radioimmunoassay method, and the R&D Systems kit (Minneapolis, MN) uses an enzyme-linked immunosorbent assay. We found that the three kits provide results that are highly linearly correlated with each other and remarkably linearly related to percent ideal body weight (%IBW) over more than three orders of magnitude (Linco, r = 0.90; R&D, r = 0.87; DSL, r = 0.86). For very low leptin levels, the more sensitive kits from R&D and Linco appeared to give more reliable results. Measurement method does not appear to explain the literature conflicts. We found that patients with anorexia nervosa have serum leptin values that lie above the line extrapolated from the %IBW/leptin curve generated from analysis of all non-anorexic patients. Therefore, in anorexia nervosa, inappropriately high leptin levels for %IBW may contribute to a blunted physiologic response to underweight and consequent resistance to dietary treatment. By contrast, most bulimic patients have leptin levels significantly below those predicted from the same %IBW/leptin curve. The relative leptin deficiency in bulimic subjects may contribute to food-craving behavior. We propose that using the %IBW/ leptin curve can facilitate identification of true pathophysiologic abnormalities in eating-disordered individuals and provide a basis for the design of therapeutic interventions or monitoring of response to treatment.

Differential effects of GH replacement on the components of the leptin system in GH-deficient individuals

GH therapy is associated with a reduction in fat mass and an increase in lean mass in subjects with GH deficiency (GHD). Leptin, like GH, plays an important role in the regulation of body composition. GH treatment has been shown to reduce serum leptin; however, the physiological interactions between the leptin system (free leptin, bound leptin, and soluble leptin receptor) and the GH/IGF-I system largely remain unknown. Twenty-five patients with childhood (n = 10) and adult-onset (n = 15) GHD were studied. GH status had previously been determined using an insulin tolerance test and/or an arginine stimulation test. The following parameters were recorded at baseline (V1) and then after 3 months (V2) and 6 months (V3) on GH treatment: fat mass, body mass index (BMI), and waist/hip ratio (WHR); blood samples were taken after an overnight fast for free leptin, bound leptin, soluble leptin receptor, insulin, and IGF-I. At V2 and V3, respectively, a fall in free leptin (P < 0.001 for each), and at V3 a fall in in percent fat mass (P < 0.001) were observed. There were no significant changes in BMI or WHR. Simultaneously, there was a rise in insulin (P = 0.068 and P < 0.001), IGF-I (P < 0.001 and P < 0.001), bound leptin (P = 0.005 and P < 0.001), and soluble leptin receptor (P = 0.61 and P < 0.001). A positive relationship was noted between free leptin and BMI (P < 0.001) and between free leptin and fat mass (P < 0.001), and a negative relationship was found between free leptin and IGF-I (P < 0.001) and, within patient, between free leptin and insulin (P < 0.001). There was no significant correlation between free leptin and WHR. Bound leptin had a positive association with IGF-I (P < 0.001) and insulin (P = 0.002) and a negative relationship with percent fat mass (P = 0.023). Soluble leptin receptor was also positively related to IGF-I (P < 0.001). In conclusion, our data suggest that the reduction in serum leptin with GH treatment, as noted by others, is mediated through a fall in free leptin. The fall in free leptin and in part the rise in bound leptin are most likely through a reduction in percent fat mass. However, the observed changes in free leptin and bound leptin and, more importantly, the rise in soluble leptin receptor, are not explained entirely by modifications in body composition and may be a direct result of GH/IGF-I.

Body composition, fasting leptin, and sex steroid administration determine GH sensitivity in peripubertal short children

Serum IGF-I levels in GH-treated subjects demonstrate a wide range of responsiveness to GH. However, the factors influencing GH sensitivity are not well known. The aim of this work was 1) to test whether body composition (determined by dual energy x-ray absorptiometry) or factors related to body composition (fasting blood glucose, FFA, C-peptide, leptin, and insulin sensitivity determined by an insulin tolerance test) influence GH sensitivity; and 2) to study the effect of sex steroid priming on GH sensitivity. We measured serum IGF-I at baseline and 24 h after a single administration of GH (2 mg/m(2)) in 60 healthy prepubertal and early pubertal children (height, -2.1 +/- 1.0 SD score). GH sensitivity, as estimated by the increase in serum IGF-I after GH administration (difference between stimulated and baseline serum IGF-I = delta IGF-I), was also determined after a short-term administration of oral ethinyl E2 in girls and im T in boys. The serum IGF-I concentration was 297 +/- 114 microg/liter at baseline and increased to 429 +/- 160 microg/liter, corresponding to a 46 +/- 29% increase over the baseline value (P < 0.0001, stimulated vs. baseline serum IGF-I). delta IGF-I was not different between gender or pubertal stage. There were positive correlations (P < 0.001) between delta IGF-I and adiposity (total body fat, r = 0.62; trunk fat, r = 0.62), fasting leptin (r = 0.64), and C-peptide (r = 0.54), and a negative correlation with fasting FFA (r = -0.33; P < 0.05) even after adjustment for age, gender, and pubertal stage. These factors remained significant independent predictors of the absolute as well as the percent increase in serum IGF-I in multiple regression analyses. Priming with T and ethinyl E2 had a similar stimulating effect on the serum GH peak in response to the insulin tolerance test. In boys, serum baseline IGF-I increased by 60%, and delta IGF-I was similar after vs. before T administration. By contrast, in girls, serum baseline IGF-I was similar, and delta IGF-I was 60% less after vs. before ethinyl E2 administration. This study indicates that 1) GH sensitivity is determined by fat mass, serum fasting leptin, C-peptide, and FFA; and 2) oral ethinyl E2 and im T have divergent effects on the IGF-I response to a single administration of GH.

The acute leptin response to GH

The effect of an acute bolus of GH on serum leptin in normal individuals and the factors affecting this response have not previously been studied. Seventeen healthy volunteers with normal body mass index, with ages ranging from 20.5-78.2 yr were studied. Each subject received three single doses of GH in random order at least 4 wk apart. Bioimpedence analysis was performed to provide estimates of fat and lean masses. Serum samples for leptin, insulin, and IGF-I were taken 0, 18, 24, 48, 72, and 120 h after each dose of GH. Leptin levels changed significantly after the 0.67- and 7-mg doses of GH, but not after the 0.27-mg dose. Compared with baseline, there was a significant elevation (P < 0.001) in serum leptin levels at 24 h, followed by a significant decrease (P < 0.01) at 72 h. Baseline and peak leptin levels were significantly determined by gender, fat mass, and log(10) insulin. Nadir leptin levels were significantly determined by gender and fat mass. In contrast, the increment in leptin levels was significantly determined by age, although this only accounted for 24% of the variability in the increment in leptin levels. We have demonstrated that administration of a single bolus dose of GH significantly increases serum leptin levels, followed by a significant nadir. This occurs not only after a supraphysiological dose of GH, but also after 0.67 mg, a dose within the physiological replacement range. The increment in leptin increases with advancing age, suggesting that at the level of the adipocyte, aging increases responsiveness to GH. However, this only partially explains the changes seen, and it is likely that another factor(s) is involved in the acute impact of GH on circulating leptin levels. The presence of a significant nadir after the peak in leptin levels supports the existence of a negative feedback loop, linking circulating leptin to its own biosynthesis in adipose tissue, mediated by peripheral leptin receptors. These data provide unequivocal evidence that GH can affect serum leptin levels in the absence of a change in body composition.

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.

Thyroid hormones influence serum leptin levels in patients with Graves' disease during suppression of beta-adrenergic receptors

Leptin is a protein product of the ob gene, mainly produced by adipocytes. Leptin is thought to play an important role in the homeostasis of body weight by suppressing appetite and increasing energy consumption. The aim of this study was to investigate the possible effect of thyroid hormone on the regulation of the leptin system during suppression of beta-adrenergic receptors in Graves' patients. We studied 15 adult female patients with Graves' disease. Thyroid function, serum levels of leptin, and percent body fat (%BF) were examined at four different clinical conditions during therapy (A, untreated; B, beta-adrenergic antagonist only [A, B; hyperthyroid], C, beta-adrenergic antagonist and antithyroid drug; D, antithyroid drug only [C, D; euthyroid]). The use of beta-adrenergic antagonist significantly reduced heart rate in spite of hyperthyroid state, indicating sufficient suppression of beta-adrenergic receptors. During treatment with beta-adrenergic antagonist, leptin percentage of body fat (%BF) ratio significantly decreased in euthyroid state compared to that in hyperthyroid state (from 38.7 +/- 21.3 to 18.1 +/- 19.3, p = 0.003). Moreover, there was a significantly positive correlation between delta leptin/%BF and delta free thyroxine (FT4) (r = 0.51, p = 0.008). Under a euthyroid state induced by antithyroid drug treatment, leptin/%BF did not change in spite of withdrawal of beta-adrenergic antagonist. Our data indicate that thyroid hormones could increase serum leptin level during suppression of beta-adrenergic receptors in Graves' patients. Our data also suggest that the beta-adrenergic action of thyroid hormones might be partly mediated by regulation of leptin.

Growth hormone responses during strenuous exercise: the role of GH-releasing hormone and GH-releasing peptide-2

PURPOSE AND METHODS

This study was designed to investigate the role of two effective releasers of growth hormone (GH): GHRH and GHRP-2 during exercise (EX). Eight healthy male subjects (ages: 22 +/- 1.2 (mean +/- SD) yr, BMI: 22.5 +/- 2.2 kg x m(-2)) were exposed to maximally stimulating dose of 100 microg GHRH iv, and 200 microg GHRP-2 iv, during incremental EX on a cycle ergometer to exhaustion. GH responses after EX alone were compared with the responses after the combined administration of the same EX plus GHRH, EX plus GHRP-2, and EX plus GHRH plus GHRP-2. Blood samples were obtained in the fasted state at intervals for 2 h postexercise and the area under the GH response curve (AUC) was calculated by trapezoidal integration.

RESULTS

Significant differences (P < 0.003) were observed between the AUCs after administration of EX alone (mean +/- SEM): 2,324 +/- 312 microg x L(-1) 120 min, after EX plus GHRH: 6,952 +/- 1,083, after EX plus GHRP-2: 14,674 +/- 2,210, and after the combination EX plus GHRH plus GHRP-2: 17,673 +/- 1,670. However, AUCs after each combination did not differ significantly from those after arithmetical addition of each separate stimulus, indicating that the mechanisms of the respective stimuli do not interact. Linear regression analysis on mean GH responses between 20 and 30 min after the start of EX showed that EX alone and GHRH alone explain about 59% (adj. R2) of the GH response to the combination EX plus GHRH. The ratio of the respective regression coefficients (GHRH vs EX) was about 2:1 (instead of 1:1), indicating that EX seems to potentiate the activity of GHRH. GHRH alone and EX alone also explained about 74% of the response to the combination EX plus GHRP-2. In the latter response, a synergistic action of GHRP-2 on GHRH could be observed.

CONCLUSIONS

The data indicate that under strenuous EX conditions, endogenous GHRH activity causes a further increase of GH release. A GHRP-2 mediated mechanism in the central neuroendocrine regulation acts as a "booster," possibly by stimulating the effects of GHRH and/or an unknown hypothalamic factor, as well as by stimulating the pituitary GH release directly.

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 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.

Arginine infusion and/or acute changes of growth hormone levels do not acutely alter leptin serum levels

Leptin, the ob gene product, is produced by differentiated adipocytes. It functions as an afferent signal to the central nervous system indicating satiety and fat mass status. It acts upon the hypothalamic-pituitary axis. Growth hormone (GH) secretion is thought to be stimulated by leptin. Conversely, leptin secretion and ob gene expression are regulated by classical neuroendocrine networks. Whether or not acute changes of GH concentrations directly alter leptin serum levels in vivo is still debated. We investigated whether or not acute changes in GH serum concentrations during arginine infusion (0.5 g/kg b. wt.) alter leptin serum levels in 45 children and adolescents (33 M, 12 F). GH and leptin serum levels were determined at -30, 0, 30, 60, 90, 120 min after arginine infusion using specific radioimmunoassays. Leptin serum concentrations remained unaltered throughout the arginine infusion in all children and adolescents whether or not GH secretion was normal.

IN CONCLUSION

(1) Acute changes of GH levels do not alter leptin serum levels during acute arginine infusions over 120 min. (2) Arginine does not acutely modulate leptin secretion.

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.

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.

Insulin regulation of leptin synthesis and secretion in humans: the model of myotonic dystrophy

OBJECTIVE

Myotonic dystrophy (MyD) is a systemic disorder in which insulin resistance is well recognized. In the present study we have characterized plasma leptin levels in patients with MyD and in age, sex and body mass index (BMI) matched controls and assessed the influence of leptin on the clinical manifestations of MyD.

DESIGN AND PATIENTS

Body composition, plasma leptin, fasting and post-oral glucose tolerance test insulin, IGF-I and IGFBP3 were studied in 34 MyD patients and 33 controls.

MEASUREMENTS

Body composition was measured using a bioelectrical impedance analyzer, and circulating levels of insulin, leptin, IGF-I, IGFBP3 were measured by IRMA or RIA. Insulin sensitivity was modelled according to a homeostasis model assessment (HOMA) computer-solved model.

RESULTS

Percentage body fat was higher in patients than in controls (25.6 +/- 2.28% vs 18.8 +/- 1.53%, P = 0.013). Insulin levels, both fasting and after oral glucose were higher in patients than in controls, and insulin sensitivity was lower in patients than in controls. Serum leptin was higher in patients than in controls (20.98 +/- 3.11 micrograms/l vs 10.4 +/- 1.31 micrograms/l, P = 0.004), and higher in women than in men, both in patients and in controls. In patients, leptin levels were correlated with age, BMI, fasting insulin, insulin area under curve and lower insulin sensitivity, whereas leptin levels were not correlated with body fat or other parameters of body composition. In controls, leptin levels were correlated with BMI and body fat. The results were evaluated using logistic regression models for each of the 2 populations. In the model of MyD, insulin resistance and age correctly identified higher leptin levels in relation to controls out of 87.88% of patients, and in the model of controls male sex with a negative correlation and BMI correctly identified their leptin levels out of 84.33% cases.

CONCLUSIONS

These findings show that MyD provides a different model of leptin regulation in humans, and suggest that in MyD patients there are correlations between leptin and insulin resistance and age, irrespective of body fat. In contrast, leptin levels in controls, correlate with sex and BMI. The data on leptin in this population of patients can not be related aetiologically to the muscle disease itself.

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.

The effect of body composition on hexarelin-induced growth hormone release in normal elderly subjects

OBJECTIVE

Growth hormone (GH) release is influenced by several factors including age, gender, physical exercise, nutritional status, sex steroids and body composition. The relationship with body composition is complex. Obesity is accompanied by suppression of spontaneous and stimulated GH release. As increasing body fat reduces stimulated GH secretion following a standard provocative test, the potential clinical uses of GH-releasing peptides (GHRPs), therapeutically or diagnostically, may be dependent on the relationship between body fat and GHRP-stimulated GH release. We have therefore assessed the effect of body composition and gender on the GH releasing capacity of hexarelin.

DESIGN

A single bolus of subcutaneous hexarelin at a dose of 1.5 micrograms per kg of body weight was administered at time 0. Blood samples were taken at -10, 0, 10, 20, 30, 40, 50, 60, 90, 120, 170 and 180 min.

SUBJECTS

Twenty-one (eight male) healthy elderly subjects with a median (range) age of 68 (60-81) years and BMI of 26 (19-30) kg/m2 were studied.

METHODS

Dual-energy X-ray absorptiometry (DEXA) was used to assess body composition.

RESULTS

Peak GH response correlated negatively with fat mass, BMI, percentage body fat, and weight [r = -0.72, P = 0.0001; r = -0.56, P = 0.009; r = -0.63, P = 0.002 and r = -0.48, P = 0.029, respectively,]. AUC GH correlated negatively with fat mass, BMI and percentage fat mass [r = -0.58, P = 0.006; r = -0.51, P = 0.019 and r = -0.66, P = 0.001 respectively]. Using multiple linear regression, fat mass was the most useful predictor for both peak GH response [R2 = 0.61, P < 0.0001] and AUC GH [R2 = 0.38, P = 0.003]. Gender was not a significant variable.

CONCLUSIONS

Increasing total fat mass results in a blunted GH response following subcutaneous hexarelin. Total fat mass appears to be a useful predictor of peak GH response even in normal individuals as none of the subjects in the present study was morbidly obese. This indicates that there is a continuum of effect of fat mass on hexarelin-stimulated GH release. Any impact of gender on the GH response to hexarelin is almost certainly indirect and mediated via differences in body composition. This observation will have an impact on the potential diagnostic and therapeutic uses of hexarelin and related GH secretagogues.

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.