Dose-response studies on the metabolic effects of a growth hormone pulse in humans

Body composition and physical fitness improve after 8 weeks of high-intensity circuit training using body weight in obese women

BACKGROUND

We examined the effects of an 8-week modified high-intensity circuit training using body weight as resistance (HICT^BW) on health-related physical fitness in sedentary obese women.

METHODS

Twenty-four sedentary obese women were allocated into the HICT^BW or a non-training control group (CG). The modified HICT^BW was performed for eight weeks (three times per week). Training consisted of a 30-second workout and 10-second rest for 12 exercise poses per one circuit (one circuit in the first week), with an increase of one circuit every two weeks. Body weight and body composition included skeletal muscle mass (SMM), body fat mass (BFM), body fat percentage (BF%), visceral fat area (VFA), and skeletal muscle mass to visceral fat area ratio (MFR) were measured. Physical fitness included flexibility of the lower back and hamstrings (Flex<inf>LH</inf>), and leg and handgrip muscle strength (Strength<inf>Leg</inf>, Strength<inf>HG</inf>). Cardiovascular endurance included the Åstrand-Rhyming heart rate (HR<inf>Åstrand</inf>), relative maximum oxygen uptake (relative V̇O<inf>2max</inf>), and workload.

RESULTS

All variables were obtained at baseline, week 4, and week 8. The HICT^BW improved Flex<inf>LH</inf>, Strength<inf>Leg</inf>, and relative V̇O<inf>2max</inf> from baseline to week 4 (All P<0.05). Improvements from baseline to week 8 were observed for SMM, BFM, BF%, VFA and MFR, Flex<inf>LH</inf>, Strength<inf>Leg</inf>, HR<inf>Åstrand</inf>, relative V̇O<inf>2max</inf>, and workload (All P<0.05). Furthermore, the HICT^BW elicited a higher change in SMM (+2.9%), BFM (-3.4%), BF% (-3.2%), MFR (+9.5%), Flex<inf>LH</inf> (+145.7%) and relative V̇O<inf>2max</inf> (+32.3%) than the CG at week-8 (All P<0.05).

CONCLUSIONS

An eight-week modified HICT^BW program thrice a week is an effective training modality to influence health-related physical fitness in sedentary obese women.

Myokines in Acromegaly: An Altered Irisin Profile

INTRODUCTION

The muscle is an endocrine organ controlling metabolic homeostasis. Irisin and myostatin are key myokines mediating this process. Acromegaly is a chronic disease with a wide spectrum of complications, including metabolic disturbances.

PURPOSE

To examine the influence of acromegaly on irisin and myostatin secretion and their contribution to metabolic profile and body composition.

MATERIALS AND METHODS

In 43 patients with acromegaly and 60 controls, serum levels of irisin, myostatin, growth hormone (GH), insulin-like growth factor 1 (IGF-1), parameters of glucose, and lipid metabolism were determined. Body composition was assessed with dual-energy x-ray absorptiometry.

RESULTS

The irisin concentration was significantly lower in patients with acromegaly compared to controls (3.91 vs. 5.09 μg/ml, p = 0.006). There were no correlations between irisin and GH/IGF-1 levels. In the study group, irisin was negatively correlated with fasting insulin (r = -0.367; p = 0.042), HOMA-IR (r = -0.510; p = 0.011), and atherogenic factors: Castelli I (r = -0.416; p = 0.005), Castelli II (r = -0.400; p = 0.001), and atherogenic coefficient (AC) (r = -0.417; p = 0.05). Irisin and myostatin concentrations were also lower in acromegalics with insulin resistance than without (2.80 vs. 4.18 μg/ml, p = 0.047; 81.46 vs. 429.58 ng/L, p = 0.018, respectively). There were no differences between study group and controls in myostatin concentration. Myostatin levels negatively correlated with GH (r = -0.306; p = 0.049), HOMA-IR (r = -0.046; p = 0.411), and insulin levels (r = -0.429; p = 0.016).

CONCLUSIONS

Decreased irisin concentrations in acromegaly may suggest impaired hormonal muscle function contributing to metabolic complications in this disorder. However, learning more about the association between myostatin and GH in acromegaly requires further studies. Nevertheless, it appears that myostatin is not critical for muscle mass regulation in acromegaly.

Short-Term Effects of Growth Hormone on Lipolysis, Glucose and Amino Acid Metabolism Assessed in Serum and Microdialysate of Healthy Young Men

OBJECTIVE

We investigated direct effects of a therapeutic growth hormone dose on lipolysis, glucose and amino acid metabolism.

METHODS

This crossover microdialysis trial involved six healthy male volunteers receiving single subcutaneous injections of both growth hormone (0.035 mg/kg) and placebo (0.9% sodium chloride). The investigation comprised three test days with standard diet. The first day served for adaptation, the second and third one for determining study data during 9 night hours with or without growth hormone. Abdominal subcutaneous microdialysate and blood were continuously collected and forwarded to a separate room next door where hourly taken samples were centrifuged and frozen until analysed.

RESULTS

Growth hormone achieved the peak serum level after 3 h followed by a plateau-like course for the next 6 h. Glycerol in microdialysate started to rise 2 h following growth hormone injection achieving significance compared to placebo after 9 h (P<0.05). Serum glycerol increased 4 h after growth hormone administration achieving significance after 6 h (P<0.05). Glucose and amino acid concentrations showed neither in microdialysate nor in serum significant differences between growth hormone and placebo. Serum values of insulin and C-peptide revealed no significant difference between growth hormone and placebo.

SUMMARY AND CONCLUSION

As the result of a high single subcutaneous dose of GH, persistent lipolysis can be shown in continuously collected microdialysate and blood, but no indication for gluconeogenesis or protein anabolism.

Systemic Complications of Acromegaly and the Impact of the Current Treatment Landscape: An Update

Acromegaly is a chronic systemic disease with many complications and is associated with increased mortality when not adequately treated. Substantial advances in acromegaly treatment, as well as in the treatment of many of its complications, mainly diabetes mellitus, heart failure, and arterial hypertension, were achieved in the last decades. These developments allowed change in both prevalence and severity of some acromegaly complications and furthermore resulted in a reduction of mortality. Currently, mortality seems to be similar to the general population in adequately treated patients with acromegaly. In this review, we update the knowledge in complications of acromegaly and detail the effects of different acromegaly treatment options on these complications. Incidence of mortality, its correlation with GH (cumulative exposure vs last value), and IGF-I levels and the shift in the main cause of mortality in patients with acromegaly are also addressed.

Diabetes mellitus induced by somatostatin analogue therapy is not permanent in acromegalic patients

CONTEXT

Therapy with somatostatin analogues (SSAs) may have deleterious effects on glucose metabolism in patients with acromegaly, often leading to the development of diabetes mellitus (DM).

AIM

The aim of the study was to evaluate whether DM, developed during therapy with SSAs, may revert after drug withdrawal and cure of acromegaly with pituitary adenomectomy.

DESIGN

Retrospective cohort study, in a tertiary referral centre.

PATIENTS

Eighteen acromegalic patients without DM at the diagnosis of acromegaly treated with SSAs as a primary therapy, and then cured by pituitary adenomectomy.

METHODS

Endocrine status and glucose homeostasis were evaluated at diagnosis of acromegaly and at least every 6 months during SSA therapy. At each visit, patients were classified into one of the following classes: normal glucose tolerance, prediabetes, overt diabetes.

RESULTS

Median follow-up after starting SSAs therapy was 69 months (IQR 54.75-132.25). During SSA therapy, all patients had controlled acromegaly defined by normal serum IGF1 concentrations for the age. Of the 13 euglycaemic patients at diagnosis, three developed prediabetes and three diabetes, whereas, of the five prediabetic patients at diagnosis, two worsened to overt diabetes and three remained in the prediabetic range (P = 0.04). After curing acromegaly with pituitary adenomectomy and subsequent SSA withdrawal, prediabetes reverted in five of six patients, and diabetes in all five patients (three reverted to euglycaemia, while two reverted to prediabetes) (P = 0.01).

CONCLUSIONS

In acromegalic patients with controlled disease, changes in glycaemic status induced by SSAs are not permanent.

The evolution of diabetic ketoacidosis: An update of its etiology, pathogenesis and management

The prognosis of diabetic ketoacidosis has undergone incredibly remarkable evolution since the discovery of insulin nearly a century ago. The incidence and economic burden of diabetic ketoacidosis have continued to rise but its mortality has decreased to less than 1% in good centers. Improved outcome is attributable to a better understanding of the pathophysiology of the disease and widespread application of treatment guidelines. In this review, we present the changes that have occurred over the years, highlighting the evidence behind the recommendations that have improved outcome. We begin with a discussion of the precipitants and pathogenesis of DKA as a prelude to understanding the rationale for the recommendations. A brief review of ketosis-prone type 2 diabetes, an update relating to the diagnosis of DKA and a future perspective are also provided.

The exercise-induced biochemical milieu enhances collagen content and tensile strength of engineered ligaments

Exercise stimulates a dramatic change in the concentration of circulating hormones, such as growth hormone (GH), but the biological functions of this response are unclear. Pharmacological GH administration stimulates collagen synthesis; however, whether the post-exercise systemic milieu has a similar action is unknown. We aimed to determine whether the collagen content and tensile strength of tissue-engineered ligaments is enhanced by serum obtained post-exercise. Primary cells from a human anterior cruciate ligament (ACL) were used to engineer ligament constructs in vitro. Blood obtained from 12 healthy young men 15 min after resistance exercise contained GH concentrations that were ∼7-fold greater than resting serum (P < 0.001), whereas IGF-1 was not elevated at this time point (P = 0.21 vs. rest). Ligament constructs were treated for 7 days with medium supplemented with serum obtained at rest (RestTx) or 15 min post-exercise (ExTx), before tensile testing and collagen content analysis. Compared with RestTx, ExTx enhanced collagen content (+19%; 181 ± 33 vs. 215 ± 40 μg per construct P = 0.001) and ligament mechanical properties - maximal tensile load (+17%, P = 0.03 vs. RestTx) and ultimate tensile strength (+10%, P = 0.15 vs. RestTx). In a separate set of engineered ligaments, recombinant IGF-1, but not GH, enhanced collagen content and mechanics. Bioassays in 2D culture revealed that acute treatment with post-exercise serum activated mTORC1 and ERK1/2. In conclusion, the post-exercise biochemical milieu, but not recombinant GH, enhances collagen content and tensile strength of engineered ligaments, in association with mTORC1 and ERK1/2 activation.

Effect of antecedent moderate-intensity exercise on the glycemia-increasing effect of a 30-sec maximal sprint: a sex comparison

This study investigated whether a prior bout of moderate-intensity exercise attenuates the glycemia-increasing effect of a maximal 30-sec sprint. A secondary aim was to determine whether the effect of antecedent exercise on the glucoregulatory response to sprinting is affected by sex. Participants (men n = 8; women n = 7) were tested on two occasions during which they either rested (CON) or cycled for 60-min at a moderate intensity of ~65% (EX) before performing a 30-sec maximal cycling effort 195 min later. In response to the sprint, blood glucose increased to a similar extent between EX and CON trials, peaking at 10 min of recovery, with no difference between sexes (P > 0.05). Blood glucose then declined at a faster rate in EX, and this was associated with a glucose rate of disappearance (R_d) that exceeded the glucose rate of appearance (R_a) earlier in EX compared with CON, although the overall glucose R_a and R_d profile was higher in men compared with women (P < 0.05). The response of growth hormone was attenuated during recovery from EX compared with CON (P < 0.05), with a lower absolute response in women compared with men (P < 0.05). The response of epinephrine and norepinephrine was also lower in women compared with men (P < 0.05) but similar between trials. In summary, a prior bout of moderate-intensity exercise does not affect the magnitude of the glycemia-increasing response to a 30-sec sprint; however, the subsequent decline in blood glucose is more rapid. This blood glucose response is similar between men and women, despite less pronounced changes in glucose R_a and R_d, and a lower response of plasma catecholamines and growth hormone to sprinting in women.

Relationship between serum IGF-1 and skeletal muscle IGF-1 mRNA expression to phosphocreatine recovery after exercise in obese men with reduced GH

CONTEXT

GH and IGF-1 are believed to be physiological regulators of skeletal muscle mitochondria.

OBJECTIVE

The objective of this study was to examine the relationship between GH/IGF-1 and skeletal muscle mitochondria in obese subjects with reduced GH secretion in more detail.

DESIGN

Fifteen abdominally obese men with reduced GH secretion were treated for 12 weeks with recombinant human GH. Subjects underwent (31)P-magnetic resonance spectroscopy to assess phosphocreatine (PCr) recovery as an in vivo measure of skeletal muscle mitochondrial function and percutaneous muscle biopsies to assess mRNA expression of IGF-1 and mitochondrial-related genes at baseline and 12 weeks.

RESULTS

At baseline, skeletal muscle IGF-1 mRNA expression was significantly associated with PCr recovery (r = 0.79; P = .01) and nuclear respiratory factor-1 (r = 0.87; P = .001), mitochondrial transcription factor A (r = 0.86; P = .001), peroxisome proliferator-activated receptor (PPAR)γ (r = 0.72; P = .02), and PPARα (r = 0.75; P = .01) mRNA expression, and trended to an association with PPARγ coactivator 1-α (r = 0.59; P = .07) mRNA expression. However, serum IGF-1 concentration was not associated with PCr recovery or any mitochondrial gene expression (all P > .10). Administration of recombinant human GH increased both serum IGF-1 (change, 218 ± 29 μg/L; P < .0001) and IGF-1 mRNA in muscle (fold change, 2.1 ± 0.3; P = .002). Increases in serum IGF-1 were associated with improvements in total body fat (r = -0.53; P = .04), trunk fat (r = -0.55; P = .03), and lean mass (r = 0.58; P = .02), but not with PCr recovery (P > .10). Conversely, increase in muscle IGF-1 mRNA was associated with improvements in PCr recovery (r = 0.74; P = .02), but not with body composition parameters (P > .10).

CONCLUSION

These data demonstrate a novel association of skeletal muscle mitochondria with muscle IGF-1 mRNA expression, but independent of serum IGF-1 concentrations.

Action of GH on skeletal muscle function: molecular and metabolic mechanisms

Skeletal muscle is a target tissue of GH. Based on its anabolic properties, it is widely accepted that GH enhances muscle performance in sports and muscle function in the elderly. This paper critically reviews information on the effects of GH on muscle function covering structure, protein metabolism, the role of IGF1 mediation, bioenergetics and performance drawn from molecular, cellular and physiological studies on animals and humans. GH increases muscle strength by enhancing muscle mass without affecting contractile force or fibre composition type. GH stimulates whole-body protein accretion with protein synthesis occurring in muscular and extra-muscular sites. The energy required to power muscle function is derived from a continuum of anaerobic and aerobic sources. Molecular and functional studies provide evidence that GH stimulates the anaerobic and suppresses the aerobic energy system, in turn affecting power-based functional measures in a time-dependent manner. GH exerts complex multi-system effects on skeletal muscle function in part mediated by the IGF system.

Effect of growth hormone on plasminogen activator and inhibitor activity in rat

Growth retardation is one of the significant changes in chronic kidney disease (CKD) and is associated with increased morbidity and mortality. Disturbances in growth hormone (GH) are held responsible for several complications in CKD. GH is a protein based peptide hormone which directly or indirectly regulates renal functions to ensure homeostasis. We investigated the effects of growth hormone on plasminogen activators (PA) in rat kidney, PA and plasminogen activator inhibitor (PAI), glucose and fibrinogen in plasma and serum lipid profile. Rats were injected daily with 250 mU GH kg-1 body weight subcutaneously for one week. Growth hormone treatment increased PA activity significantly in rat kidneys as compared to controls. No changes were seen in PA, PAI and fibrinogen levels in the plasma of two groups of rats. There was significant decrease in plasma glucose, total cholesterol and LDL-cholesterol levels in serum of treated group resulting in the decrease of HDL/LDL and total cholesterol/cholesterol ratios. However, triglycerides and VLDL showed significant higher activity in the serum of treated group as compared to controls. Our data suggests that GH administration might improve renal function by increasing PA activity in kidney as well as by reducing the cholesterol content in blood. GH may be effective in improving growth failure as it helps to maintain the normal homeostatic balance.

Urine metabonomic profiling of a female adolescent with PIT-1 mutation before and during growth hormone therapy: insights into the metabolic effects of growth hormone

OBJECTIVE

Growth hormone (GH) is a protein hormone with important roles in growth and metabolism. The objective of this study was to investigate the metabolism of a human subject with severe GH deficiency (GHD) due to a PIT-1 gene mutation and the metabolic effects of GH therapy using Nuclear Magnetic Resonance (NMR)-based metabonomics. NMR-based metabonomics is a platform that allows the metabolic profile of biological fluids such as urine to be recorded, and any alterations in the profile modulated by GH can potentially be detected.

DESIGN

Urine samples were collected from a female subject with severe GHD before, during and after GH therapy, and from healthy age- and sex-matched controls and analysed with NMR-based metabonomics.

SETTING

The samples were collected at a hospital and the study was performed at a research facility.

PARTICIPANTS

We studied a 17 year old female adolescent with severe GHD secondary to PIT-1 gene mutation who had reached final adult height and who had ceased GH therapy for over 3 years. The subject was subsequently followed for 5 years with and without GH therapy. Twelve healthy age-matched female subjects acted as control subjects.

INTERVENTION

The GH-deficient subject re-commenced GH therapy at a dose of 1 mg/day to normalise serum IGF-1 levels.

MAIN OUTCOME MEASURES

Urine metabolic profiles were recorded using NMR spectroscopy and analysed with multivariate statistics to distinguish the profiles at different time points and identify significant metabolites affected by GH therapy.

RESULTS

NMR-based metabonomics revealed that the metabolic profile of the GH-deficient subject altered with GH therapy and that her profile was different from healthy controls before, and during withdrawal of GH therapy.

CONCLUSION

This study illustrates the potential use of NMR-based metabonomics for monitoring the effects of GH therapy on metabolism by profiling the urine of GH-deficient subjects. Further controlled studies in larger numbers of GH-deficient subjects are required to determine the clinical benefits of NMR-based metabonomics in subjects receiving GH therapy.

Effects of performing resistance exercise before versus after aerobic exercise on glycemia in type 1 diabetes

OBJECTIVE

To determine the effects of exercise order on acute glycemic responses in individuals with type 1 diabetes performing both aerobic and resistance exercise in the same session.

RESEARCH DESIGN AND METHODS

Twelve physically active individuals with type 1 diabetes (HbA(1c) 7.1 ± 1.0%) performed aerobic exercise (45 min of running at 60% V(O(2peak))) before 45 min of resistance training (three sets of eight, seven different exercises) (AR) or performed the resistance exercise before aerobic exercise (RA). Plasma glucose was measured during exercise and for 60 min after exercise. Interstitial glucose was measured by continuous glucose monitoring 24 h before, during, and 24 h after exercise.

RESULTS

Significant declines in blood glucose levels were seen in AR but not in RA throughout the first exercise modality, resulting in higher glucose levels in RA (AR = 5.5 ± 0.7, RA = 9.2 ± 1.2 mmol/L, P = 0.006 after 45 min of exercise). Glucose subsequently decreased in RA and increased in AR over the course of the second 45-min exercise bout, resulting in levels that were not significantly different by the end of exercise (AR = 7.5 ± 0.8, RA = 6.9 ± 1.0 mmol/L, P = 0.436). Although there were no differences in frequency of postexercise hypoglycemia, the duration (105 vs. 48 min) and severity (area under the curve 112 vs. 59 units ⋅ min) of hypoglycemia were nonsignificantly greater after AR compared with RA.

CONCLUSIONS

Performing resistance exercise before aerobic exercise improves glycemic stability throughout exercise and reduces the duration and severity of postexercise hypoglycemia for individuals with type 1 diabetes.

Free fatty acids inhibit growth hormone/signal transducer and activator of transcription-5 signaling in human muscle: a potential feedback mechanism

CONTEXT

Stimulation of lipolysis, leading to increased blood concentrations of free fatty acids (FFAs), is a primary effect of GH and phosphorylation of intracellular signal transducer and activator of transcription (STAT)-5 is a primary mediator of the effects of GH.

OBJECTIVE

Based on preliminary results, we intended to test whether FFAs exert a negative feedback inhibition of STAT5 phosphorylation in skeletal muscle.

DESIGN AND PARTICIPANTS

Eight healthy young men were investigated for 8 h on four occasions at four different FFA levels in a single blind, randomized manner. Acipimox was used to suppress FFA levels and Intralipid was infused to obtain appropriate FFA concentrations. Somatostatin was infused to control GH levels and GH, insulin, and glucagon were replaced. Muscle biopsies were taken after 8 h and compared with a fifth biopsy taken under normal basal conditions.

SETTING

The study was conducted at a university clinical research unit.

RESULTS

GH concentrations remained steady and comparable in all studies and FFA concentrations varied between 0.01 and 1.71 mmol/liter on the four occasions (P < 0.05). We observed a dose-dependent 40% decrease of STAT5 phosphorylation in skeletal muscle with increasing concentrations of FFAs.

CONCLUSIONS

Our results strongly suggest the existence of a negative feedback loop, whereby effects of GH may be dampened by FFA inhibition of GH-dependent STAT5 phosphorylation. The mechanisms behind and biological consequences of this finding awaits additional studies.

Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects

In evolutionary terms, GH and intracellular STAT 5 signaling is a very old regulatory system. Whereas insulin dominates periprandially, GH may be viewed as the primary anabolic hormone during stress and fasting. GH exerts anabolic effects directly and through stimulation of IGF-I, insulin, and free fatty acids (FFA). When subjects are well nourished, the GH-induced stimulation of IGF-I and insulin is important for anabolic storage and growth of lean body mass (LBM), adipose tissue, and glycogen reserves. During fasting and other catabolic states, GH predominantly stimulates the release and oxidation of FFA, which leads to decreased glucose and protein oxidation and preservation of LBM and glycogen stores. The most prominent metabolic effect of GH is a marked increase in lipolysis and FFA levels. In the basal state, the effects of GH on protein metabolism are modest and include increased protein synthesis and decreased breakdown at the whole body level and in muscle together with decreased amino acid degradation/oxidation and decreased hepatic urea formation. During fasting and stress, the effects of GH on protein metabolism become more pronounced; lack of GH during fasting increases protein loss and urea production rates by approximately 50%, with a similar increase in muscle protein breakdown. GH is a counterregulatory hormone that antagonizes the hepatic and peripheral effects of insulin on glucose metabolism via mechanisms involving the concomitant increase in FFA flux and uptake. This ability of GH to induce insulin resistance is significant for the defense against hypoglycemia, for the development of "stress" diabetes during fasting and inflammatory illness, and perhaps for the "Dawn" phenomenon (the increase in insulin requirements in the early morning hours). Adult patients with GH deficiency are insulin resistant-probably related to increased adiposity, reduced LBM, and impaired physical performance-which temporarily worsens when GH treatment is initiated. Conversely, despite increased LBM and decreased fat mass, patients with acromegaly are consistently insulin resistant and become more sensitive after appropriate treatment.

IGF-I improved bone mineral density and body composition of weaver mutant mice

Our recent report on a parallel decrease in the body weights and serum IGF-I levels of weaver mice suggests that IGF-I's endocrine function may be impaired in neurodegenerative diseases. To further understand the overall effects of IGF-I deficiency on the postnatal growth, we measured bone mineral density (BMD), bone mineral content (BMC), lean body mass (LBM) and fat mass in male and female weaver mice and wild-type littermates on D21 (prepuberty), D45 (puberty), and D60 (postpuberty) using dual-energy X-ray absorptiometry (DEXA). In both male and female weaver mice, we found that the levels of circulating IGF-I paralleled those of BMD, BMC, and LBM, but not the fat mass. Male weaver mice have normal fat mass at all three ages studied, whereas female weaver mice showed a trend to increase their fat mass as they mature. To determine whether circulating IGF-I is a determinant of body composition, we crossbred IGF-I transgenic mice with homozygous weaver mice, which resulted in a significant increase in circulating IGF-I levels in both male and female weaver mice and normalization of their BMD, BMC and body weights. In summary, our results demonstrated that normal circulating IGF-I levels are important in maintaining BMD, BMC, and body composition in neurodegenerative diseases, such as hereditary cerebellar ataxia.

Motivations and methods for analyzing pulsatile hormone secretion

Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses.

Exercise-induced lipid mobilization in subcutaneous adipose tissue is mainly related to natriuretic peptides in overweight men

Involvement of sympathetic nervous system and natriuretic peptides in the control of exercise-induced lipid mobilization was compared in overweight and lean men. Lipid mobilization was determined using local microdialysis during exercise. Subjects performed 35-min exercise bouts at 60% of their maximal oxygen consumption under placebo or after oral tertatolol [a beta-adrenergic receptor (AR) antagonist]. Under placebo, exercise increased dialysate glycerol concentration (DGC) in both groups. Phentolamine (alpha-AR antagonist) potentiated exercise-induced lipolysis in overweight but not in lean subjects; the alpha(2)-antilipolytic effect was only functional in overweight men. After tertatolol administration, the DGC increased similarly during exercise no matter which was used probe in both groups. Compared with the control probe under placebo, lipolysis was reduced in lean but not in overweight men treated with the beta-AR blocker. Tertatolol reduced plasma nonesterified fatty acids and insulin concentration in both groups at rest. Under placebo or tertatolol, the exercise-induced changes in plasma nonesterified fatty acids, glycerol, and insulin concentrations were similar in both groups. Exercise promoted a higher increase in catecholamine and ANP plasma levels after tertatolol administration. In conclusion, the major finding of our study is that in overweight men, in addition to an increased alpha(2)-antilipolytic effect, the lipid mobilization in subcutaneous adipose tissue that persists during exercise under beta-blockade is not dependent on catecholamine action. On the basis of correlation findings, it seems to be related to a concomitant exercise-induced rise in plasma ANP when exercise is performed under tertatolol intake and a decrease in plasma insulin.

Metabolic implications of GH treatment in small for gestational age

Fetal growth retardation is associated with decreased postnatal growth, resulting in a lower adult height. In addition, a low birth weight is associated with an increased risk of developing diseases during adulthood, such as insulin resistance, type 2 diabetes mellitus, hypertension, dyslipidemia, and cardiovascular diseases. Children with persistent postnatal growth retardation, i.e., incomplete catch-up growth, can be treated with human GH. The GH/IGF-I axis is involved in the regulation of carbohydrate and lipid metabolism. The question of whether treatment with GH in children born small for gestational age (SGA) has long-term implications with respect to glucose/insulin and lipid metabolism has not been answered yet. In this article, the available data are reviewed.

Somatotropic and gonadotropic axes linkages in infancy, childhood, and the puberty-adult transition

Integrative neuroendocrine control of the gonadotropic and somatotropic axes in childhood, puberty, and young adulthood proceeds via multiple convergent and divergent pathways in the human and experimental animal. Emerging ensemble concepts are required to embody independent, parallel, and interacting mechanisms that subserve physiological adaptations and pathological disruption of reproduction and growth. Significant advances in systems biology will be needed to address these challenges.

The 10-s maximal sprint: a novel approach to counter an exercise-mediated fall in glycemia in individuals with type 1 diabetes

OBJECTIVE

To investigate whether a short maximal sprint can provide another means to counter the rapid fall in glycemia associated with moderate-intensity exercise in individuals with type 1 diabetes and therefore decrease the risk of early postexercise hypoglycemia.

RESEARCH DESIGN AND METHODS

In the study, seven male subjects with type 1 diabetes injected their normal insulin dose and ate their usual breakfast. When their postprandial glycemia fell to approximately 11 mmol/l, they pedaled at 40% Vo(2peak) for 20 min on a cycle ergometer then immediately engaged in a maximal 10-s cycling sprint (sprint trial) or rested (control trial); the sprint and rest trials were administered in a counterbalanced order.

RESULTS

Moderate-intensity exercise resulted in a significant fall (P < 0.05) in glycemia in both trials (means +/- SE: 3.6 +/- 0.5 vs. 3.1 +/- 0.5 mmol/l for sprint and control, respectively). The subsequent short cycling sprint opposed a further fall in glycemia for 120 min, whereas in the absence of a sprint, glycemia decreased further (3.6 +/- 1.22 mmol/l; P < 0.05) after exercise. The stabilization of glycemia in the sprint trial was associated with elevated levels of catecholamines, growth hormone, and cortisol. In contrast, these hormones remained at stable or near-stable levels in the control trial. Changes in insulin and free fatty acid levels were similar in the sprint and control trials.

CONCLUSIONS

These results suggest that after moderate-intensity exercise, it is preferable for young individuals with insulin-treated, complication-free type 1 diabetes to engage in a 10-s maximal sprint to acutely oppose a further fall in glycemia than to only rest. The addition of the sprint after moderate-intensity exercise provides another means to reduce the risk of hypoglycemia in active individuals with type 1 diabetes.

GH secretion in acute exercise may result in post-exercise lipolysis

Exercise is a potent stimulator of growth hormone (GH) secretion. We hypothesised that after a short bout of intense exercise GH may increase lipolysis during recovery. In 7 moderately trained young male subjects (21.8 +/- 0.5 years) and 7 moderately trained older male subjects (56.0 +/- 1.0 years) [(2)H(5)] glycerol was infused for 370min to measure glycerol production rate (R(a)), a measure of lipolysis. At 130 min subjects exercised on a cycle ergonometer for 20 min at 70% V(O2 max), followed by rest for 220 min. On a separate occasion the study was repeated in the young subjects with a 1h GH infusion (4microgkg(-1)h(-1)) at 130 min instead of exercise. In response to exercise, catecholamines (p < 0.02) and glycerol R(a) (p < 0.01) increased, peaking during exercise. GH concentration increased in response to exercise (p < 0.01), peaking after exercise (150-160 min) in both groups with no significant difference in peak response between groups. A post-exercise rise in glycerol R(a) was demonstrated in both groups peaking at 265-295 min in the older group (p < 0.002, peak vs. basal) and continuing to rise until 370 min in the young group (p < 0.01, peak vs. basal). The timing and magnitude of this was reproduced with the GH infusion. There was a significant correlation between the peak GH response to exercise and the post-exercise rise in glycerol R(a) measured as area under the curve (r=0.57, p < 0.04). In conclusion, this study provides evidence that the GH response to acute exercise may increase lipolysis during recovery.

Effects of 2 wk of GH administration on 24-h indirect calorimetry in young, healthy, lean men

The present study was designed as a randomized, double-blind placebo (Plc)-controlled study to determine the effect of 2 wk of growth hormone administration (GH-adm.) on energy expenditure (EE) and substrate oxidation in healthy humans. Sixteen young healthy men were divided into two groups. The study consisted of two 24-h measurements (indirect calorimetry), separated by 2 wk of either Plc or GH injections (6 IU/day). At baseline, no significant differences were observed between the two groups in any of the measured anthropometric, hormonal, or metabolic parameters, neither did the parameters change over time in the Plc group. GH-adm. resulted in a 4.4% increase in 24-h EE (P < 0.05) and an increase in fat oxidation by 29% (P < 0.05). However, a decrease in the respiratory quotient was only observed in the postabsorptive phase after an overnight fast (0.84 +/- 0.1 to 0.79 +/- 0.1, P < 0.05). Furthermore, lean body mass (LBM) was increased by GH-adm. only [62.8 +/- 2.5 kg (baseline) vs. 64.7 +/- 2.4 kg (after), P < 0.001]. In conclusion, GH-adm. increases 24-h EE, which may be partly explained by increased LBM. Furthermore, GH-adm. stimulates fat combustion, especially in the postabsorptive state.

Maximizing acute fat utilization: effects of exercise, food, and individual characteristics

In discussion of the physiological mechanisms that regulate fat metabolism, and with consideration of the metabolic stimuli that modulate substrate metabolism, the issue of how an acute state of negative lipid balance can be maximized is addressed. The regulation of lipolysis by catecholamines and insulin is reviewed, and the mechanisms of fatty acid mobilization and uptake by muscle are also briefly discussed. The implications of substrate availability and the hormonal response during physiological states such as fasting, exercise, and after food intake are also addressed, with particular regard to the influences on fatty acid mobilization and/or oxidation from eliciting these stimuli conjointly. Finally, a brief discussion is given of both the nature of exercise and the exercising individual, and how these factors influence fat metabolism during exercise. It is also a primary thrust of this paper to underline gaps in the existing literature with regard to exercise timing concerning food ingestion for maximizing acute lipid utilization.

No effect of growth hormone administration on substrate oxidation during exercise in young, lean men

The purpose of this study was to examine the effects of increased fat availability induced by growth hormone (GH) administration on the oxidative metabolism during exercise. Seven well-trained males (age 25 +/- 2 years (mean +/- S.E.M.); peak oxygen consumption : 62 +/- 1 ml min(-1) kg(-1) (completed four randomised trials: 120 min bicycling at 55% 4 h after receiving either 7.5 IU (2.5 mg) GH or placebo (Plc), and during rest after receiving either GH or Plc. In all studies a standardized meal was given 2 h after GH or Plc injection. GH administration resulted in an approximately 60-fold increase in serum GH concentration at rest (P < 0.0001) and during exercise (P < 0.0001). The increase in serum GH was followed by an increase in circulating glycerol at rest (8%, P < 0.0001). When combined with exercise the increase in plasma glycerol was more pronounced (GH: 716% of baseline versus Plc: 328%, P < 0.0001). However, this increase in fat mobilization did not increase fat oxidation during exercise (indirect calorimetry). In conclusion, GH administration combined with aerobic exercise increased lipolytic parameters substantially more than exercise alone, but did not further augment whole body fat oxidation.

Endocrine control of body composition in infancy, childhood, and puberty

Body composition exhibits marked variations across the early human lifetime. The precise physiological mechanisms that drive such developmental adaptations are difficult to establish. This clinical challenge reflects an array of potentially confounding factors, such as marked intersubject differences in tissue compartments; the incremental nature of longitudinal intrasubject variations in body composition; technical limitations in quantitating the unobserved mass of mineral, fat, water, and muscle ad seriatim; and the multifold contributions of genetic, dietary, environmental, hormonal, nutritional, and behavioral signals to physical and sexual maturation. From an endocrine perspective (reviewed here), gonadal sex steroids and GH/IGF-I constitute prime determinants of evolving body composition. The present critical review examines hormonal regulation of body composition in infancy, childhood, and puberty.

Fat metabolism in exercise - with special reference to training and growth hormone administration

Despite abundance of fat, exclusive dependency on fat oxidation can only sustain a metabolic rate corresponding to 50-60% of VO(2max) in humans. This puzzling finding has been subject to intense research for many years. Lately, it has gained renewed interest as a consequence of increased obesity and physical inactivity imposed by Western lifestyle. Why are humans so poor at metabolizing fat? Can fat metabolism be manipulated by exercise, training, diet and hormones? And why is fat stored in specialized adipose tissue and not just as lipid droplets inside muscle cells? In the present review, human fat metabolism is discussed in relation to how human fat metabolism is designed. Limitations in this design are explored and examples of different designs for fat metabolism from animal physiology are included to illustrate these limitations. Various means of manipulating fat metabolism are discussed with special emphasis on exercise, training, growth hormone (GH) physiology and GH administration. It is concluded that fat stores, non-esterified fatty acids (NEFAs) availability and enzymes for fat oxidation can be increased substantially. However, it is almost impossible to increase fat oxidation during endurance exercise at higher intensities. It seems that, for some reason, the human being is far from optimally designed for fat oxidation during exercise. Acute GH administration has several unexpected effects on fat and carbohydrate metabolism during aerobic exercise, and future research in this area is likely to provide valuable information with respect to GH physiology and the regulation of fat and carbohydrate metabolism during aerobic exercise.

Atrial natriuretic peptide contributes to physiological control of lipid mobilization in humans

In humans, lipid mobilization is considered to depend mainly on sympathetic nervous system activation and catecholamine action. A contribution of ANP was hypothesized because we have previously shown that atrial natriuretic peptide (ANP) is a lipolytic agent on isolated human fat cells. Control of lipid-mobilizing mechanisms was investigated using in situ microdialysis in subcutaneous adipose tissue (SCAT) in healthy young men during two successive exercise bouts performed at 35% and 60% peak oxygen consumption (VO2max) after placebo or acute oral tertatolol (nonselective beta-antagonist) treatment. In placebo-treated subjects, infusion of propranolol in the probe (100 micromol/l) only partially reduced (40%) the increment in extracellular glycerol concentration (EGC) promoted by exercise. Moreover, oral beta-adrenergic receptor blockade did not prevent exercise-induced lipid mobilization in SCAT while exerting fat cell beta-adrenergic receptor blockade. Exercise-induced increase in plasma ANP was potently amplified by oral tertatolol. A positive correlation was found between EGC and plasma ANP levels but also between extracellular cGMP (i.e., index of ANP-mediated lipolysis) and EGC. Thus, we demonstrate that exercise-induced lipid mobilization resistant to local propranolol and lipid-mobilizing action observed under oral beta-blockade is related to the action of ANP. Oral beta-adrenergic receptor blockade, which potentiates exercise-induced ANP release by the heart, may contribute to lipid mobilization in SCAT. The potential relevance of an ANP-related lipid-mobilizing pathway is discussed.

Additive effects of cortisol and growth hormone on regional and systemic lipolysis in humans

Growth hormone (GH) and cortisol are important to ensure energy supplies during fasting and stress. In vitro experiments have raised the question whether GH and cortisol mutually potentiate lipolysis. In the present study, combined in vivo effects of GH and cortisol on adipose and muscle tissue were explored. Seven lean males were examined four times over 510 min. Microdialysis catheters were inserted in the vastus lateralis muscle and in the subcutaneous adipose tissue of the thigh and abdomen. A pancreatic-pituitary clamp was maintained with somatostatin infusion and replacement of GH, insulin, and glucagon at baseline levels. At t = 150 min, administration was performed of NaCl (I), a 2 microg.kg(-1).min(-1) hydrocortisone infusion (II), a 200-microg bolus of GH (III), or a combination of II and III (IV). Systemic free fatty acid (FFA) turnover was estimated by [9,10-3H]palmitate appearance. Circulating levels of glucose, insulin, and glucagon were comparable in I-IV. GH levels were similar in I and II (0.50 +/- 0.08 microg/l, mean +/- SE). Peak levels during III and IV were approximately 9 microg/l. Cortisol levels rose to approximately 900 nmol/l in II and IV. Systemic (i.e., palmitate fluxes, s-FFA, s-glycerol) and regional (interstitial adipose tissue and skeletal muscle) markers of lipolysis increased in response to both II and III. In IV, they were higher and equal to the isolated additive effects of the two hormones. In conclusion, we find that GH and cortisol stimulate systemic and regional lipolysis independently and in an additive manner when coadministered. On the basis of previous studies, we speculate that the mode of action is mediated though different pathways.

Effects of growth hormone (GH) on ghrelin, leptin, and adiponectin in GH-deficient patients

Ghrelin is a recently discovered gastric peptide that increases appetite, glucose oxidation, and lipogenesis and stimulates the secretion of GH. In contrast to ghrelin, GH promotes lipolysis, glucose production, and insulin secretion. Both ghrelin and GH are suppressed by intake of nutrients, especially glucose. The role of GH in the regulation of ghrelin has not yet been established. We investigated the effect of GH on circulating levels of ghrelin in relation to its effects on glucose, insulin, body composition, and the adipocyte-derived peptides leptin and adiponectin. Thirty-six patients with adult-onset GH deficiency received recombinant human GH for 9 months in a placebo-controlled study. Body composition and fasting serum analytes were assessed at baseline and at the end of the study. The GH treatment was accompanied by increased serum levels of IGF-I, reduced body weight (-2%) and body fat (-27%), and increased serum concentrations of glucose (+10%) and insulin (+48%). Ghrelin levels decreased in 30 of 36 subjects by a mean of -29%, and leptin decreased by a mean of -24%. Adiponectin increased in the women only. The decreases in ghrelin and leptin correlated with changes in fat mass, fat-free mass, and IGF-I. The reductions in ghrelin were predicted independently of the changes in IGF-I and fat mass. It is likely that the reductions in ghrelin and leptin reflect the metabolic effects of GH on lipid mobilization and glucose production. Possibly, a suppression of ghrelin promotes loss of body fat in GH-deficient patients receiving treatment. The observed correlation between the changes in ghrelin and IGF-I may suggest that the GH/IGF-I axis has a negative feedback on ghrelin secretion.

Effects of growth hormone on lipid metabolism in humans

The most immediate effect of growth hormone (GH) administration in humans is a significant increase in free fatty acids after 1-2 h, reflecting stimulation of lipolysis and ketogenesis. This stimulation represents an important physiological adaptation to stress and fasting. When the capacity of GH to increase lipolysis is blocked, the protein-retaining and insulin-antagonistic effects of GH on glucose metabolism are either abolished or weakened dramatically, compatible with a key role for lipolysis in orchestrating the metabolic actions of GH.

Pharmacokinetics and acute lipolytic actions of growth hormone. Impact of age, body composition, binding proteins, and other hormones

The biologic actions of endogeneous growth hormone (GH) depend on its secretion and clearance rates as well as sensitivity at the receptor level. Aberrations in GH pharmacokinetics and pharmacodynamics may occur with increasing age, and have been implicated in diseases such as obesity, diabetes mellitus, and critical illness. In this review, recent insights into the association between GH metabolism and age, body composition, binding proteins and other hormones are discussed.

Effects of GH on protein metabolism during dietary restriction in man

The metabolic response to dietary restriction involves a series of hormonal and metabolic adaptations leading to protein conservation. An increase in the serum level of growth hormone (GH) during fasting has been well substantiated. GH has potent protein anabolic actions, as evidenced by a significant decrease in lean body mass and muscle mass in chronic GH deficiency, and vice versa in patients with acromegaly. The present review outlines current knowledge about the role of GH in the metabolic response to fasting, with particular reference to the effects on protein metabolism. Physiological bursts of GH secretion seem to be of seminal importance for the regulation of protein conservation during fasting. Apart from the possible direct effects of GH on protein dynamics, a number of additional anabolic agents, such as insulin, insulin-like growth factor-I, and free fatty acids (FFAs), are activated. Taken together the effects of GH on protein metabolism seem to include both stimulation of protein synthesis and inhibition of breakdown, depending on the nature of GH administration, which tissues are being studied, and on the physiological conditions of the subjects.

Use of amino acids as growth hormone-releasing agents by athletes

Specific amino acids, such as arginine, lysine and ornithine, can stimulate growth hormone (GH) release when infused intravenously or administered orally. Many individuals consume amino acids before strength training workouts, believing this practice accentuates the exercise-induced GH release, thereby promoting greater gains in muscle mass and strength. The GH response to amino acid administration has a high degree of interindividual variability and may be altered by training status, sex, age, and diet. Although parenteral administration consistently leads to increased circulating GH concentration, oral doses that are great enough to induce significant GH release are likely to cause stomach discomfort and diarrhea. During exercise, intensity is a major determinant of GH release. Although one study showed that arginine infusion can heighten the GH response to exercise, no studies found that pre-exercise oral amino acid supplementation augments GH release. Further, no appropriately conducted scientific studies found that oral supplementation with amino acids, which are capable of inducing GH release, before strength training increases muscle mass and strength to a greater extent than strength training alone. The use of specific amino acids to stimulate GH release by athletes is not recommended.

Age dimorphism in the association between growth-hormone status and the respiratory quotient

OBJECTIVE

To investigate the impact of age on the association between the respiratory quotient (RQ) and growth-hormone (GH) secretion and to investigate the acute lipolytic response to an exogenous GH bolus.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study of 36 non-obese healthy subjects (18 women and 18 men) from two age groups was used: "younger" (mean age, 29.5 years; range, 27 to 34 years) and "older" (mean age, 50.8 years; range, 47 to 59 years). Endogenous GH secretion by means of deconvolution analysis of 24-hour serum GH concentrations was measured every 20 minutes. Resting RQ was measured after a 12-hour overnight fast. The lipolytic response to an intravenous exogenous GH bolus (200 microg) was assessed by measuring serum levels of free fatty acids as well as changes in RQ. Additional measurements included body composition (regional computed tomography scan and DXA) and physical fitness (VO(2)max).

RESULTS

Resting RQ did not differ between the two age groups: 0.81 +/- 0.01 (young) vs. 0.82 +/- 0.01 (older; not significant). Several estimates of GH release correlated positively with RQ in the younger group, whereas a negative correlation was detected in the older subjects [GH production rate (microg/liter x kg) vs. RQ: r = 0.62, p < 0.01 (younger); r = -0.53; p = 0.02 (older)]. By regression analysis, 52% to 58% of the variation in RQ could be explained by GH status. After an exogenous GH bolus, the incremental response in nonesterified fatty acid was slightly higher in younger individuals (p = 0.09).

DISCUSSION

Resting RQ is significantly correlated with GH status. This association is positive in younger individuals and negative in older individuals. The lipolytic response to exogenous GH is moderately higher in younger compared with older individuals. GH status should be taken into account when investigating the residual variation in RQ.

GH administration and discontinuation in healthy elderly men: effects on body composition, GH-related serum markers, resting heart rate and resting oxygen uptake

BACKGROUND AND OBJECTIVES

GH administration results in increased lean body mass (LBM), decreased fat mass (FM) and increased energy expenditure (EE). GH therapy may therefore have potential benefits, especially in the elderly, who are known to have decreased function of the GH/IGF-I axis. Several studies have focused on effects of GH administration in the elderly in the last decade. However, very limited information is available regarding changes in body composition and EE upon GH discontinuation in the elderly. The present study therefore investigated the effects of 12 weeks of GH administration and subsequent discontinuation on body composition, resting oxygen uptake (VO2), resting heart rate (HR) and GH related serum markers in healthy elderly men.

SUBJECTS AND METHODS

Sixteen healthy men [age 74 +/- 1 years (mean +/- SEM), height 174.2 +/- 1.6 cm, body weight 80.7 +/- 2.6 kg, body fat 27.5 +/- 1.1%] completed the study protocol. Recombinant human GH (1.80 +/- 0.24 IU/day) was administered for 12 weeks in a single-blinded, placebo-controlled design. Body composition (dual energy X-ray absorptiometry), resting VO2 (indirect calorimetry), resting HR (telemetry) and serum IGF-I, IGF-II, IGFBP-3 and acid labile subunit (ALS) were measured at baseline, after 12 weeks of GH administration and, additionally in the GH group, 1, 2, 3, 4, 5 and 9 days after GH discontinuation.

RESULTS

Body weight was unchanged from baseline to 12 weeks in both groups. However, GH administration caused a decrease in FM (3.4 +/- 1.0 kg, P < 0.012), paralleled by a similar increase in LBM (3.2 +/- 0.4 kg, P < 0.0002). Resting VO2 and resting HR increased by 31 +/- 3.6% and 7.3 +/- 1.9 per minute, respectively, in the GH-group, where significant increases in serum IGF-I, IGFBP-3 and ALS also were noted. None of the above parameters changed in the placebo group. Within 2-3 days after GH discontinuation, the GH related serum markers and resting HR returned to baseline levels, whereas resting VO2 remained elevated even 9 days after GH discontinuation. In addition, GH discontinuation caused a significant decrease in body weight (1.86 +/- 0.35 kg), derived exclusively from a decrease in LBM (1.63 +/- 0.43 kg), while the decreased FM was maintained (12 weeks: 17.93 +/- 1.65 kg, +9 days: 17.74 +/- 1.62 kg).

CONCLUSIONS

The increases in serum IGF-I, IGFBP-3, ALS and resting heart rate induced by 12 weeks of GH administration in elderly men returned to baseline levels within 2-3 days after GH discontinuation. However, resting VO2 remained elevated for a longer period. GH administration reduced fat mass but maintained body weight by increasing lean body mass. In contrast, 9 days of GH discontinuation reduced body weight exclusively by reducing lean body mass.

Endurance training and GH administration in elderly women: effects on abdominal adipose tissue lipolysis

In the present study, the effect of endurance training alone and endurance training combined with recombinant human growth hormone (rhGH) administration on subcutaneous abdominal adipose tissue lipolysis was investigated. Sixteen healthy women [age 75 +/- 2 yr (mean +/- SE)] underwent a 12-wk endurance training program on a cycle ergometer. rhGH was administered in a randomized, double-blinded, placebo-controlled design in addition to the training program. Subcutaneous abdominal adipose tissue lipolysis was estimated by means of microdialysis combined with measurements of subcutaneous abdominal adipose tissue blood flow (ATBF; (133)Xe washout). Whole body fat oxidation was estimated simultaneously by indirect calorimetry. Before and after completion of the training program, measurements were performed both at rest and during 60 min of continuous cycling at a workload corresponding to 60% of pretraining peak oxygen uptake. Endurance training alone did not affect subcutaneous abdominal adipose tissue lipolysis either at rest or during exercise, as reflected by identical levels of interstitial adipose tissue glycerol, subcutaneous abdominal ATBF, and plasma nonesterified fatty acids before and after completion of the training program. Similarly, no effect on subcutaneous abdominal adipose tissue lipolysis was observed when combining endurance training with rhGH administration. However, in both the placebo and the GH groups, fat oxidation was significantly increased during exercise performed at the same absolute workload after completion of the training program. We conclude that the changed lipid metabolism during exercise observed after endurance training alone or after endurance training combined with rhGH administration is not due to alterations in subcutaneous abdominal adipose tissue metabolism in elderly women.

Effects of short-term administration of growth hormone in healthy young men, women, and women taking oral contraceptives

OBJECTIVE

Effects of short-term administration of growth hormone (GH) with respect to gender and oral contraceptives (OCs) were investigated in healthy young adults.

DESIGN

Open, prospective 2-week study.

SETTING

Clinical research centre, university hospital.

SUBJECTS

Three groups of healthy young adults were included: six men, six women with normal menstrual cycles, and six women taking OCs.

INTERVENTIONS

The subjects were given recombinant human GH subcutaneously for 2 weeks: 1 U m-2 body surface daily during the first week, and 3 U m-2 daily during the second week.

MAIN OUTCOME MEASURES

Serum samples were drawn in the morning after overnight fasting on days 0, 3, 7, 10 and 14, and were analysed for GH, insulin-like growth factor 1 (IGF-1), insulin, testosterone, sex hormone-binding globulin (SHBG), lipids and markers of bone metabolism. Second-void morning urine was analysed for deoxypyridinoline (Dpyr).

RESULTS

During administration of GH, serum IGF-1 increased in the men and in the women without OCs (86 and 52%, respectively). In the OC women, IGF-1 did not change significantly. Serum insulin increased in all three groups, with the largest change (122%) in the men and the smallest (47%) in the OC women. Blood glucose was unchanged. Total cholesterol, low-density lipoprotein (LDL) cholesterol and the LDL/high-density lipoprotein cholesterol ratio were reduced in the men only. Biochemical markers of bone resorption (serum procollagen type I, urinary Dpyr) increased in the men, and markers of bone formation (serum osteocalcin and telopeptide of collagen type I) increased in the men as well as in the women not taking OCs. The testosterone/SHBG ratio increased in the men on account of a reduction in SHBG.

CONCLUSION

The response to short-term administration of GH differed in the three groups, with the largest effect in the men and the smallest in the OC women. The inhibitory influence of contraceptives underlines the role of sex steroids in modulating the susceptibility to GH.

Effects of a physiological GH pulse on interstitial glycerol in abdominal and femoral adipose tissue

Physiologically, growth hormone (GH) is secreted in pulses with episodic bursts shortly after the onset of sleep and postprandially. Such pulses increase circulating levels of free fatty acid and glycerol. We tested whether small GH pulses have detectable effects on intercellular glycerol concentrations in adipose tissue, and whether there would be regional differences between femoral and abdominal subcutaneous fat, by employing microdialysis for 6 h after administration of GH (200 microgram) or saline intravenously. Subcutaneous adipose tissue blood flow (ATBF) was measured by the local Xenon washout method. Baseline of interstitial glycerol was higher in adipose tissue than in blood [220 +/- 12 (abdominal) vs. 38 +/- 2 (blood) micromol/l, P < 0.0005; 149 +/- 9 (femoral) vs. 38 +/- 2 (blood) micromol/l, P < 0.0005] and higher in abdominal adipose tissue compared with femoral adipose tissue (P < 0.0005). Administration of GH induced an increase in interstitial glycerol in both abdominal and femoral adipose tissue (ANOVA: abdominal, P = 0. 04; femoral, P = 0.03). There was no overall difference in the response to GH in the two regions during the study period as a whole (ANOVA: P = 0.5), but during peak stimulation of lipolysis abdominal adipose tissue was, in absolute but not in relative terms, stimulated more markedly than femoral adipose tissue (ANOVA: P = 0. 03 from 45 to 225 min). Peak interstitial glycerol values of 253 +/- 37 and 336 +/- 74 micromol/l were seen after 135 and 165 min in femoral and abdominal adipose tissue, respectively. ATBF was not statistically different in the two situations (ANOVA: P = 0.7). In conclusion, we have shown that a physiological pulse of GH increases interstitial glycerol concentrations in both femoral and abdominal adipose tissue, indicating activated lipolysis. The peak glycerol increments after GH were higher in abdominal adipose tissue, perhaps due to a higher basal rate of lipolysis in this region.

The stressful condition as a nutritionally dependent adaptive dichotomy

The injured body manifests a cascade of cytokine-induced metabolic events aimed at developing defense mechanisms and tissue repair. Rising concentrations of counterregulatory hormones work in concert with cytokines to generate overall insulin and insulin-like growth factor 1 (IGF-1), postreceptor resistance and energy requirements grounded on lipid dependency. Salient features are self-sustained hypercortisolemia persisting as long as cytokines are oversecreted and down-regulation of the hypothalamo-pituitary-thyroid axis stabilized at low basal levels. Inhibition of thyroxine 5'-deiodinating activity (5'-DA) accounts for the depressed T3 values associated with the sparing of both N and energy-consuming processes. Both the liver and damaged territories adapt to stressful signals along up-regulated pathways disconnected from the central and peripheral control systems. Cytokines stimulate liver 5'-DA and suppress the synthesis of transthyretin (TTR), causing the drop of retinol-binding protein (RBP) and the leakage of increased amounts of T4 and retinol in free form. TTR and RBP thus work as prohormonal reservoirs of precursor molecules which need to be converted into bioactive derivatives (T3 and retinoic acids) to reach transcriptional efficiency. The converting steps (5'-DA and cellular retinol-binding protein-I) are activated by T4 and retinol, themselves operating as limiting factors of positive feedback loops. Healthy adults with normal macrophage functioning and liver parenchymal integrity, who submitted to a stress of medium severity, are characterized by TTR-RBP plasma levels reduced by half and an estimated ten-fold increase in free ligand disposal to target cells during the days ensuing injury. This transient hyperthyroid and hyperretinoid climate creates a second defense line strengthening and fine-tuning the effects primarily initiated by cytokines. The suicidal behavior of thyroxine-binding globulin (TBG), corticosteroid-binding globulin (CBG), and IGFBP-3 allows the occurrence of peak endocrine and mitogenic influences at the site of inflammation. The production rate of TTR by the liver is the main determinant of both the hepatic release and blood transport of holoRBP, which explains why poor nutritional status concomitantly impairs thyroid- and retinoid-dependent acute-phase responses, hindering the stressed body to appropriately face the survival crisis. The prognostic significance of low TT4 blood levels may be assigned to the exhaustion of extrathyroidal hormonal pools normally stored in liver and plasma but markedly shrunken in protein-depleted states. These data offer new insights into the mechanisms whereby preexisting malnutrition and stressful complications are interrelated, emphasizing the pivotal role played by TTR in that context.

Free fatty acid kinetics and oxidation in congestive heart failure

To characterize fuel utilization of patients with congestive heart failure (CHF), we measured serum free fatty acid (FFA), counterregulatory hormone concentrations, whole body substrate oxidation rates (indirect calorimetry), and the turnover and oxidation rates of FFA ([1-(14)C]-palmitate infusion) in 7 patients with CHF and in 7 cardiac patients without CHF after an overnight fast. Plasma glucose and serum insulin concentrations were comparable, whereas serum FFA, blood ketone body, and fasting blood lactate (p <0.05 for all) concentrations were significantly increased in patients with CHF compared to those without CHF. Fasting plasma norepinephrine (p <0.05), serum cortisol (p <0.01), and growth hormone (p <0.01) concentrations were also higher in patients with CHF than in those without CHF. Rates of energy expenditure at rest (62 +/- 2 vs 56 +/- 1 J x kg(-1) x min(-1), p <0.05), FFA turnover (6.5 +/- 0.5 vs 5.0 +/- 0.4 micromol x kg(-1) x min(-1), p <0.05), and oxidation (2.0 +/- 0.2 vs 1.5 +/- 0.1 micromol x kg(-1) x min(-1)], p <0.05) were significantly higher in patients with CHF than in control subjects. In univariate analysis, the left ventricular ejection fraction was inversely correlated and the plasma norepinephrine concentration positively correlated with both energy expenditure at rest, FFA turnover, and the FFA oxidation rate. In multivariate analysis, the plasma norepinephrine concentration was the most significant predictor of increased FFA oxidation rate. We conclude that release of FFAs to the circulation and their subsequent oxidation are increased in patients with severe CHF after an overnight fast. These changes might reflect stress hormone-induced lipolysis and accompanying stimulation of serum FFA oxidation via mass action.

Diurnal variations in twenty-four-hour energy expenditure during growth hormone treatment of adults with pituitary deficiency

The effects of growth hormone (GH) treatment on 24-h energy expenditure (EE) were studied in a open trial over a period of 4 weeks. Five subjects, four men and one woman, with a history of complete GH deficiency were included. All the subjects were examined on 2 consecutive days on baseline and, thereafter, at six occasions during a period of 1 month (days 1, 2, 5, 8, 15, and 30). The dose of GH was 0.25 U/kg.week, administered sc once a day in the evening. EE was determined in a chamber for indirect calorimetry. Body composition was determined with dual-energy x-ray absorptiometry and computed tomography using a four-scan technique. Blood samples were examined using well-established RIAs. During the first 2 weeks, 24-h EE increased by 6 +/- 3% (range 1-8%) from 40.9 +/- 4.8 to 42.9 +/- 4.8 kcal/24 h.kg (P < 0.05), sleeping metabolic rate by 14 +/- 3% (range 10-18%) from 28.4 +/- 1.9 to 32.9 +/- 2.2 kcal/24h.kg (P < 0.001), and basal metabolic rate by 11 +/- 7% (range 0-18%) from 29.6 +/- 2.4 to 33.3 +/- 2.6 kcal/24h.kg (P < 0.05). No change was found in daytime EE. The increase in EE covaried with changes in insulin-like growth factor 1, the free T3/free T4 ratio, insulin-like growth factor-binding protein-3, and the aminoterminal procollagen III peptide but not with changes in body composition. It is suggested that the stimulating effect of GH on EE occurs gradually during a 2-week period and is only detectable during night and morning hours, when significant levels of GH occur.