Comparison of continuation or cessation of growth hormone (GH) therapy on body composition and metabolic status in adolescents with severe GH deficiency at completion of linear growth

Although GH replacement improves the features of GH deficiency (GHD) in adults, it has yet to be established whether cessation of GH at completion of childhood growth results in adverse consequences for the adolescent with GHD. Effects of continuation or cessation of GH on body composition, insulin sensitivity, and lipid levels were studied in 24 adolescents (13 males, 11 females, aged 17.0 +/- 0.3, yr, mean +/- se, puberty stage 4 or 5) in whom height velocity was less than 2 cm/yr. Provocative testing confirmed severe GHD [peak GH < 9 mU/liter (3 microg/liter)] in all cases and was followed by a lead-in period of 3 months during which the pediatric dose of GH continued unchanged. Baseline investigations were then performed using dual-energy x-ray absorptiometry (body composition), lipid measurements, and assessment of insulin sensitivity by both homeostasis model assessment and a short insulin tolerance test. Twelve patients remained on GH (0.35 U/kg.wk), and 12 patients ceased GH treatment. The groups were followed up in parallel with repeat observations made after 6 and 12 months.No endocrine differences were evident between the groups at baseline. GH cessation resulted in a reduction of serum IGF-I Z score [-1.62 +/- 0.29, baseline vs. -2.52 +/- 0.12, 6 months (P < 0.05) vs. -2.52 +/- 0.10, 12 months (P < 0.01)] but values remained unchanged in those continuing GH replacement. Lean body mass increased by 2.5 +/- 0.5 kg ( approximately 6%) over 12 months in those receiving GH but was unchanged after GH discontinuation. Cessation of GH resulted in increased insulin sensitivity [short insulin tolerance test, 153 +/- 22 micromol/liter.min, baseline vs. 187 +/- 20, 6 months (P < 0.05) vs. 204 +/- 14, 12 months (P = 0.05)], but no significant change was seen during 12 months of GH continuation. Lipid levels remained unaltered in both groups.Continuation of GH at completion of linear growth resulted in ongoing accrual of lean body mass (LBM), whereas skeletal muscle mass remained static after GH cessation in these adolescents with GHD. This divergence of gain in LBM is of potential importance because increases in LBM occur as a feature of healthy late adolescent development. GH is a major mediator of insulin sensitivity, independent of body composition in adolescents. Further studies are required to determine whether discontinuation of GH in the adolescent with severe GHD once linear growth is complete results in long-term irreversible adverse physical and metabolic consequences and to determine conclusively the benefits of continuing GH therapy.     

Continuation of growth hormone (GH) substitution during fasting in GH-deficient patients decreases urea excretion and conserves protein synthesis.

The consequences of GH deficiency during conditions in which endogenous GH release is acutely stimulated are largely unknown. Short-term fasting constitutes a robust GH stimulus, but the metabolic significance of GH during fasting is uncertain. To address both of these issues, we therefore evaluated the effect of GH on substrate metabolism during fasting in adults with GH deficiency. Seven hypopituitary GH-deficient patients were each studied twice during a 40-h fast: once with GH replacement continued and once with GH discontinued during the fast. After 40 h of fasting, protein synthesis and turnover were higher with than without GH replacement [phenylalanine incorporation (micromol/kg fat free mass/h): 36.6 +/- 1.2 (GH) vs. 32.8 +/- 1.4, P < 0.05; phenylalanine flux (micromol/kg fat free mass/h): 41.3 +/- 1.0 (GH) vs. 38.0 +/- 1.8, P < 0.05]. During continued GH replacement, urea excretion decreased during nighttime [urea excretion (mmol/24 h): 269 +/- 51 (GH) vs. 390 +/- 69, P < 0.05], and a significant decline in urea-N synthesis rate was found [urea-N synthesis rate (mmol/h): 14.7 +/- 1.6 (GH) vs. 21.1 +/- 2.2, P < 0.01]. GH replacement was associated with increased lipid oxidation [lipid oxidation (mg/kg per min): 0.91 +/- 0.07 (GH) vs. 0.70 +/- 0.03, P < 0.05]. Finally, continuation of GH induced moderate elevations in plasma glucose levels without significant changes in total glucose turnover or oxidation. In summary, continued GH substitution during fasting conserves nitrogen, which involves stimulation or maintenance of protein synthesis. Our data support the importance of GH replacement in hypopituitary adults.     

The effects on insulin action in adult hypopituitarism of recombinant human GH therapy individually titrated for six months.

There is controversy about the effect of replacement GH on insulin action in adult hypopituitary patients. GH replacement calculated from weight leads to unacceptable side effects in some patients. Recent studies suggest it should be individually titrated in adults using serum IGF-I levels. We have assessed the effect of titrated GH replacement on peripheral and hepatic insulin action in 13 adult-onset hypopituitary patients (8 males and 5 females; ages 47 +/- 10 yr, mean duration of hypopituitarism 6 yr) with confirmed GH deficiency (GHD; maximum GH <5 mU/liter during insulin induced hypoglycemia), ACTH deficiency, and normal glucose tolerance. All patients were on stable hydrocortisone replacement (15 mg with breakfast, 5 mg with evening meal) for at least 2 months before the trial. Insulin action was assessed by the euglycemic hyperinsulinemic glucose clamp technique (1 mU/kg x min) before and after 6 months of GH therapy. GH was started at 0.8 IU sc daily and titrated monthly until the serum IGF-I increased to within 1-2 SD of the mean of normal age-matched controls. Body mass index did not change significantly during the 6 months of GH therapy. Fasting plasma glucose and HbA1c increased significantly after 6 months (5.2 +/- 0.0 vs. 5.5 +/- 0.0 mmol/liter, P < 0.0001, and 4.5 +/- 0.1 vs. 4.7 +/- 0.1%, P < 0.0005, respectively). There was no increase in fasting serum insulin (51.6 +/- 10.2 vs. 60.0 +/- 10.2 pmol/liter, P = 0.12). Exogenous glucose infusion rates required to maintain euglycemia were similar after GH (23.0 +/- 0.4 vs. 21.1 +/- 0.3 micromol/kg x min, P = 0.6). Endogenous glucose production in the fasting state was also unchanged following GH (11.8 +/- 0.7 vs.12.3 +/- 0.9 micromol/kg x min, P = 0.5) and suppressed to a similar extent following insulin (4.4 +/- 0.8 vs. 5.5 +/- 0.8 micromol/kg x min, P = 0.3). In summary, GH therapy for 6 months, with serum IGF-I maintained in the upper physiological range, increased fasting plasma glucose and HbA1c. There was no effect on peripheral or hepatic insulin sensitivity. Patients receiving GH therapy require long-term monitoring of glucose tolerance.     

Left ventricular mass and function in children with GH deficiency before and during 12 months GH replacement therapy

OBJECTIVE: This open, prospective study was designed to evaluate the effect of GH deficiency (GHD) on left ventricular (LV) mass (LVM) and performance, by echocardiography, and on lipid profile during childhood. SUBJECTS: Twelve prepubertal children with GHD (eight boys and four girls) aged 8.1 +/- 1.7 years were studied before and after 6 and 12 months of GH replacement therapy at a dose of GH of 30 micro g/kg/day. Twelve healthy children sex-, height-, weight- and body surface area-matched with the patients, served as controls. METHODS: Echocardiography was performed at study entry and after 12 months both in GHD children and in controls. Only in GHD children, echocardiography was repeated also after 6 months of GH replacement. In all subjects, we measured LV posterior wall thickness (LVPWT), LV end-diastolic diameter (LVEDD), LVM index (LVMi), LV systolic and diastolic function. RESULTS: At study entry, LVPWT (5.3 +/- 0.8 vs. 6.2 +/- 1.1 mm, P < 0.05), LVEDD (34.0 +/- 2.4 vs. 36.7 +/- 2.1 mm, P < 0.007) and LVMi (47.0 +/- 6.9 vs. 59.6 +/- 9.5 g/m2, P < 0.005) were significantly lower in GHD children than in controls. Lipid profile, heart rate, blood pressure, LV systolic function and indices of ventricular filling were similar in patients and controls. After 12 months of GH replacement therapy, LVPWT (6.1 +/- 0.7 mm, P < 0.0005), LVEDD (38.8 +/- 4.3 mm, P < 0.002) and LVMi (71.5 +/- 12.7 g/m2, P < 0.0005) significantly increased in GHD children compared to pretreatment values. In particular, after 12 months of therapy GHD children achieved a normal LVMi when compared to controls (60.7 +/- 8.6, P = ns). LVMi increase was significantly correlated with the increase in IGF-I level (r = 0.49; P < 0.004). LV systolic performance, diastolic filling and blood pressure did not change significantly during GH therapy. After 12 months of treatment, the atherogenic index, measured as total/high-density lipoprotein-cholesterol ratio (2.7 +/- 0.8) was significantly lower than both pretreatment (3.4 +/- 0.3, P < 0.03) and control values (3.8 +/- 1.1, P < 0.04). CONCLUSIONS: GH deficiency in children affects heart morphology, by inducing a significant decrease in cardiac size, but does not modify cardiac function and lipid profile. Twelve months of GH replacement treatment normalizes cardiac mass, and reduces the atherogenic index.     

Nutrient oxidation patterns and protein metabolism in lean and obese subjects

The immediate metabolic response to eating has been compared in a group of grossly obese subjects (W/H2 = 45) with that in lean controls (W/H2 = 22). Dietary intake of energy for obese subjects was based on their estimated basal energy expenditure for ideal body weight (given at an hourly rate of 3 X BMR over a 4-h period). Lean subjects were measured twice: control 1 with the same intake of energy as the obese in terms of ideal body weight and control 2 with the same energy intake in relation to each subject's measured resting energy expenditure (2.2 X REE). The changes in energy expenditure and nutrient disposal with the onset of eating have been assessed by a method of combined respiratory gas analysis and intravenous infusion of 13C-labelled leucine. Leucine kinetics were used to quantitate rapid changes in protein oxidation and to assess protein synthesis and degradation. 1) Total energy expenditure was 20-30 per cent greater in obese subjects than lean subjects in fasting and feeding. Energy expenditure expressed per kg fat-free mass, from D2O dilution, was similar in obese and lean subjects in both fasting (5.8 v. 5.5 kJ/kg FFM/h) and feeding [6.7 v. 6.3 (Control 2) kJ/kg FFM/h]. 2) The onset of eating was associated with increased carbohydrate and protein oxidation with decreased fat oxidation in both lean and obese individuals. In obese subjects, however, both the decrease in fat oxidation and the increase in protein oxidation were significantly smaller (P less than 0.05) than the corresponding increments in lean subjects (Control 2). 3) The rate of protein synthesis was significantly (P less than 0.05) higher in obese subjects both in the fasting state (99 v. 84 mumols leucine/kg FFM/h) and in the fed state [94 v. 67 (Control 2) mumols leucine/kg FFM/h]. The rate of protein degradation was also higher in obese individuals in fasting (117 +/- 6 v. 106 +/- 4 mumol leucine/kg FFM/h) and feeding [65 +/- 4 v. 54 +/- 6 (Control 2) mumol leucine/kg FFM/h] though these differences are not statistically significant (P greater than 0.05). 4) The observed differences between obese and lean individuals in protein and energy metabolism in the fasted state and in the immediate response to eating do not support a hypothesis of greater metabolic efficiency in obesity.     

Inhibition of lipolysis during acute GH exposure increases insulin sensitivity in previously untreated GH-deficient adults

OBJECTIVE: Previous studies evaluating the lipolytic effect of GH have in general been performed in subjects on chronic GH therapy. In this study we assessed the lipolytic effect of GH in previously untreated patients and examined whether the negative effect of enhanced lipolysis on glucose metabolism could be counteracted by acute antilipolysis achieved with acipimox. METHODS: Ten GH-deficient (GHD) adults participated in four experiments each, during which they received in a double-blind manner: placebo (A); GH (0.88+/-0.13 mg) (B); GH+acipimox 250 mg b.i.d. (C); and acipimox b.i.d. (no GH) (D), where GH was given the night before a 2 h euglycemic, hyperinsulinemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry. RESULTS: GH increased basal free fatty acid (FFA) levels by 74% (P=0.0051) and insulin levels by 93% (P=0.0051). This resulted in a non-significant decrease in insulin-stimulated glucose uptakes (16.61+/-8.03 vs 12.74+/-5.50 micromol/kg per min (s.d.), P=0.07 for A vs B). The rates of insulin-stimulated glucose uptake correlated negatively with the FFA concentrations (r=-0.638, P<0.0001). However, acipimox caused a significant improvement in insulin-stimulated glucose uptake in the GH-treated patients (17.35+/-5.65 vs 12.74+/-5.50 micromol/kg per min, P=0.012 for C vs B). The acipimox-induced enhancement of insulin-stimulated glucose uptake was mainly due to an enhanced rate of glucose oxidation (8.32+/-3.00 vs 5.88+/-2.39 micromol/kg per min, P=0.07 for C vs B). The enhanced rates of glucose oxidation induced by acipimox correlated negatively with the rate of lipid oxidation in GH-treated subjects both in basal (r=-0.867, P=0.0093) and during insulin-stimulated (r=-0.927, P=0.0054) conditions. GH did not significantly impair non-oxidative glucose metabolism (6.86+/-5.22 vs 8.67+/-6.65 micromol/kg per min, P=NS for B vs A). The fasting rate of endogenous glucose production was unaffected by GH and acipimox administration (10.99+/-1.98 vs 11.73+/-2.38 micromol/kg per min, P=NS for B vs A and 11.55+/-2.7 vs 10.99+/-1.98 micromol/kg per min, P=NS for C vs B). On the other hand, acipimox alone improved glucose uptake in the untreated GHD patients (24.14+/-8.74 vs 16.61+/-8.03 micromol/kg per min, P=0.0077 for D vs A) and this was again due to enhanced fasting (7.90+/-2.68 vs 5.16+/-2.28 micromol/kg per min, P=0.01 for D vs A) and insulin-stimulated (9.78+/-3.68 vs 7.95+/-2.64 micromol/kg per min, P=0.07 for D vs A) glucose oxidation. CONCLUSION: The study of acute administration of GH to previously untreated GHD patients provides compelling evidence that (i) GH-induced insulin resistance is mainly due to induction of lipolysis by GH; and (ii) inhibition of lipolysis can prevent the deterioration of insulin sensitivity. The question remains whether GH replacement therapy should, at least at the beginning of therapy, be combined with means to prevent an excessive stimulation of lipolysis by GH.     

Serum homocysteine concentrations in children with growth hormone (GH) deficiency before and after 12 months GH replacement

OBJECTIVE: This open, prospective study was designed to evaluate the effect of growth hormone deficiency (GHD) and GH replacement therapy on serum homocysteine (Hcy) concentration in children with GHD. SUBJECTS: Seventeen prepubertal children with GHD (11 boys and six girls) aged 8.6 +/- 1.9 years were studied before and after 12 months of GH replacement therapy at a dose of GH of 30 microg/kg/day. Seventeen healthy children acted as controls and were matched for age, sex and body mass index (BMI). METHODS: At study entry, height, weight, blood pressure, serum Hcy, serum IGF-I, total-low density lipoprotein (LDL)- and high density lipoprotein (HDL) cholesterol, triglycerides, free T4, free T3, vitamin B12, folate, glucose and creatinine were measured in all subjects. The atherogenic index (AI) was also calculated as the ratio of total cholesterol/HDL cholesterol (T/HDL). In GHD children these parameters were also revaluated after 12 months of GH therapy. RESULTS: At study entry height and serum IGF-I were significantly lower, as expected, in GHD patients than in controls (P < 0.0001 and P < 0.007, respectively). Serum Hcy levels were significantly higher in GHD patients than in healthy children (8.4 +/- 2.9 vs. 6.0 +/- 2.9 micromol/l; P < 0.03), although the absolute values were within the normal values for age and sex. There were no significant differences at baseline with respect to blood pressure, serum vitamin B12, folate, fT3, fT4, lipid profile, creatinine and glucose levels. After 12 months of GH replacement therapy height and serum IGF-I increased significantly compared to pretreatment values (P < 0.0001); serum Hcy levels decreased significantly (6.0 +/- 3.3 micromol/l; P < 0.002) compared to baseline values, becoming similar to control values. Total cholesterol (3.5 +/- 0.6 mmol/l) and the AI (2.5 +/- 0.8) decreased significantly with respect to both pretreatment (4.2 +/- 1.0 mmol/l; P < 0.0002 and 3.4 +/- 0.8; < 0.002, respectively) and control values (4.2 +/- 0.4 mmol/l; P < 0.0005 and 3.3 +/- 1.1; P = 0.02, respectively). CONCLUSIONS: GHD in children is associated with higher serum levels of Hcy compared to controls, without significantly affecting the lipid profile. GH replacement for 12 months significantly decreased the Hcy levels and improved the lipid profile with a decrease of total cholesterol and the total/HDL cholesterol ratio, compared to pretreatment values. Given the small number of patients, further larger studies are needed to clarify whether these results may have significant effects in the prevention of cardiovascular disease in adulthood.     

The cardiovascular risk of GH-deficient adolescents

To investigate the onset of the cardiovascular impairment in patients with GH deficiency (GHD), we prospectively studied cardiovascular risk parameters, cardiac mass and performance (by echocardiography) in 10 adolescent patients (5 with isolated GHD and 5 with multiple GHD) who reached their final height before GH replacement withdrawal, 6 months after GH replacement withdrawal, and 6 months after GH treatment was restarted, and in 10 sex- and age-matched controls. At study entry, when compared with controls, GHD adolescents had lower IGF-I levels (although still in the normal age range) and high-density lipoprotein (HDL)-cholesterol levels, higher total/HDL-cholesterol ratio, lower triglyceride levels, higher fibrinogen levels, and lower heart rate, systolic blood pressure, and early-to-late mitral flow velocity ratio (E/A). Left ventricular (LV) mass index and ejection fraction were normal. Six months after GH withdrawal, IGF-I levels decreased remarkably in all cases (from 176.6 +/- 8.3 to 77.5 +/- 8.9 microg/liter; P < 0.001), whereas low-density lipoprotein-cholesterol and triglyceride levels significantly increased. The total/HDL-cholesterol ratio (from 3.89 +/- 0.1 to 4.74 +/- 0.2; P < 0.05) and fibrinogen levels (from 261 +/- 7.1 to 287.5 +/- 6.4 mg/dl; P < 0.05) also significantly increased compared with study entry, without any change in the other parameters. In contrast, both LV mass index (from 94.2 +/- 1.6 to 87.8 +/- 1.7 g/m(2); P = 0.05) and E/A (from 1.32 +/- 0.05 to 1.12 +/- 0.03; P < 0.01) decreased, although remaining in the normal range. Six months after restarting GH replacement (at a median dose of 10 micro g/kg x d), lipid and cardiac parameters were brought back to the levels measured at study entry, but in no patient did IGF-I levels reach the 50th centile for age. HDL-cholesterol levels (P < 0.0001), heart rate (P < 0.05), systolic blood pressure (P < 0.01), LV ejection fraction (P < 0.005), and E/A (P < 0.0001) remained lower, whereas total/HDL-cholesterol ratio (P < 0.01), triglycerides, and fibrinogen levels (P < 0.05) remained higher than controls. In conclusion, GH discontinuation is inappropriate in adolescents with severe GHD, inducing impairment of lipid profile and cardiac morphology and performance. Because the results on the cardiovascular system and on the lipid profile were suboptimal, it is likely that the GH dose in severe GHD adolescents should be higher.     

Growth hormone and lean tissue catabolism during long-term glucocorticoid treatment

OBJECTIVES: The aim of the study was to determine whether growth hormone (GH) treatment decreased net protein catabolism of lean tissues in patients receiving chronic glucocorticoid treatment. DESIGN: Whole body leucine kinetics were measured in post-absorptive conditions using a 1-14C-leucine infusion before and during GH administration (0.0125 mg/kg/day; 0.033 U/kg/day) for 7 days. PATIENTS: We studied four patients (age range 31-71 years) who had taken prednisone (mean +/- SEM 0.21 +/- 0.03 mg/kg/day, total dose 10-27.5 mg/day) for longer than 5 months for various lung diseases. RESULTS: During GH treatment leucine oxidation decreased (baseline 0.44 +/- 0.07 vs GH 0.37 +/- 0.05 mumol/kg lean body mass/min, P = 0.01) and non-oxidative leucine disposal increased (1.95 +/- 0.10 vs 2.05 +/- 0.09 mumol/kg lean body mass/min, P = 0.02) but leucine appearance was unaltered. CONCLUSIONS: We conclude that GH decreased amino acid catabolism and improved protein synthesis without altering protein breakdown in patients receiving chronic glucocorticoid treatment. There may be a role for GH in mitigating the protein catabolic side-effects of prolonged glucocorticoid treatment.     

The effect of GH replacement therapy on endothelial function and oxidative stress in adult growth hormone deficiency

OBJECTIVES: Controversy persists with regard to the atherogenic risk associated with adult growth hormone deficiency (GHD). Endothelial dysfunction and enhanced oxidative stress are early features of atherogenesis. Therefore, we have studied the effect of three months of low dose GH replacement therapy (0.03IU/kg/day) on these parameters in GHD adults. SUBJECTS AND METHODS: Eight hypopituitary GHD adults (4 male, 4 female), who were receiving conventional hormone replacement therapy, were studied before and after 3 months of GH replacement (0.03IU/kg/day). All observations obtained were compared with similar measurements made in 8 matched control subjects. All study subjects were non-smokers, normotensive and gave no personal or family history of premature vascular disease. Endothelial function was assessed using a specialised vessel wall tracking system to measure endothelium-dependent, flow-mediated, brachial artery dilatation (FMD). Measurements were repeated following glyceryl-trinitrate (GTN) (endothelium-independent dilatation). Oxidative stress was assessed by directly measuring lipid-derived free radicals in venous blood by electron paramagnetic resonance spectroscopy. Fasting lipids, insulin, plasma glucose and IGF-I were also measured at baseline and following GH replacement. RESULTS: FMD, expressed as a percentage change from resting base-line diameter, was significantly impaired in the pre-treatment GHD patients compared with controls (3.1+/-2.1% vs 6.1+/-0.9%, P<0. 001; means+/-s.d.) indicating endothelial dysfunction. Significant increase in FMD was noted following GH therapy (3.1+/-2.1% vs 6. 5+/-1.9%, P<0.001). Free radicals (arbitrary units) were elevated in the pre-treatment GHD patients compared with controls (0.36+/-0.09 vs 0.11+/-0.12, P<0.05) and fell significantly following GH therapy (0.23+/-0.03 vs 0.36+/-0.09, P<0.05), although they remained elevated compared with controls. Fasting insulin was significantly higher (25.9+/-18.8 vs 13.9+/-6.7mu/l, P<0.05) and IGF-I concentrations lower (10.8+/-4.7 vs 20.2+/-6.3nmol/l, P<0.05) in the pre-treatment GHD subjects. After treatment there were no changes in insulin concentration, although IGF-I levels were normalised (10. 8+/-2.3 vs 23.6+/-11.4nmol/l, P<0.05). CONCLUSIONS: Endothelial dysfunction and enhanced oxidative stress are features of adult GHD. This study suggests plausible mechanisms underlying any proatherogenic tendency in adult GHD and demonstrates improvement of these factors following GH replacement.     

The effect of long-term pharmacological antilipolysis on substrate metabolism in growth hormone (GH)-substituted GH-deficient adults

The lipolytic properties of GH are essential for the acute effects on glucose metabolism and insulin sensitivity, whereas its more long-term impact on substrate metabolism is uncertain. The aim of the study was to evaluate the influence of pharmacological antilipolysis on substrate metabolism during constant and continued GH exposure. Seven adult GH-deficient (GHD) patients were studied twice in a double-blind randomized order: 1) after 4 wk of acipimox treatment (250 mg, orally, three times daily) and 2) after 4 wk of placebo treatment. Daily GH replacement was continued throughout both study periods. At the end of each period glucose and lipid oxidation rates were assessed by indirect calorimetry, and the protein oxidation rate was estimated by urinary excretion of urea. Endogenous glucose production and whole body protein metabolism were assessed by isotope dilution techniques using tritiated glucose and stable phenylalanine and tyrosine isotopes, respectively. GH and IGF-I levels were not different between periods, whereas FFA and glycerol levels were distinctly suppressed after 4 wk of pharmacological antilipolysis [FFA, 256 +/- 63 (acipimox) vs. 596 +/- 69 (placebo) micromol/liter; P = 0.001]. Likewise, plasma levels of total and low density lipoprotein cholesterol as well as triglycerides were significantly reduced after acipimox. Despite this, lipid oxidation rates were identical at the end of the two treatment periods [589 +/- 106 (acipimox) vs. 626 +/- 111 (placebo) kcal/24 h; P = 0.698]. The total and oxidative rates of glucose as well as protein oxidation and urea excretion were identical at the end of the two treatment periods (P > 0.05). Phenylalanine flux, a measure of protein turnover, was increased [34.62 +/- 1.83 (acipimox) vs. 33.15 +/- 1.61 (placebo) micromol/kg.h; P = 0.049] as was phenylalanine incorporation into protein, a measure of protein synthesis [30.79 +/- 1.67 (acipimox) vs. 28.97 +/- 1.51 (placebo) micromol/kg.h; P = 0.035]. The following conclusions were reached: 1) prolonged antilipolysis by means of acipimox stimulates protein turnover without affecting net protein balance; and 2) acipimox in combination with constant GH exposure results in sustained suppression of circulating levels of FFA, glycerol, and triglycerides without a reduction in the rate of lipid oxidation. The site and origin of lipid fuels for oxidation during suppression of lipolysis remain to be determined.     

The hyperinsulinemic amino acid clamp increases whole-body protein synthesis in young subjects

We propose that hyperinsulinemia stimulates protein synthesis when postabsorptive plasma amino acid (AA) concentrations are maintained. During a euglycemic hyperinsulinemic clamp, many AA, notably the branched-chain amino acids (BCAA), decline markedly. Therefore, we tested whether individual plasma AA could be maintained within the range of postabsorptive concentrations to assess the effects of insulin, infused at 40 mU/m(2) x min on whole-body protein and glucose metabolism, using [1-(13)C]-leucine and [3-(3)H]-glucose methodology. Validation studies of background [(13)C] enrichment and breath (13)CO(2) recovery factors were performed in a subset of 6 subjects. In 10 healthy, young men, infusion rates of an AA solution were based on fluorometric determinations of total BCAA every 5 minutes. All 21 plasma AA remained in the target range; 15, including the BCAA, alanine, and glycine were within 13% of baseline, and only 6 (Thr, His, Arg, Asn, Cit, Tyr) varied more (18% to 42%). Notably, both leucine flux and nonoxidative leucine R(d) (protein synthesis) increased with insulin (2.36 +/- 0.06 to 2.81 +/- 0.10 and 1.79 +/- 0.05 to 2.18 +/- 0.10 micromol/kg fat-free mass (FFM) x min, respectively; P <.0005) while leucine oxidation only tended to increase (P =.05) and endogenous leucine R(a) (protein breakdown) decreased by 18% (2.36 +/- 0.06 to 1.94 +/- 0.09 micromol/kg FFM x min; P <.0005), resulting in a marked elevation of net protein synthesis (-0.57 +/- 0.02 to 0.24 +/- 0.02 micromol/kg FFM x min; P <.0000001). Thus, in vivo protein anabolism was induced when maintaining postabsorptive plasma amino acid concentrations during hyperinsulinemia through a suppression of whole-body protein breakdown, no significant change in oxidation and an elevation of synthesis compared with postabsorptive conditions.     

Growth hormone blunts protein oxidation and promotes protein turnover to a similar extent in abdominally obese and normal-weight women

Abdominally obese individuals have reduced 24-h plasma GH concentrations. Their normal plasma IGF-I levels may reflect GH hypersensitivity. Alternatively, obesity-associated hyposomatotropism may cause less biological effect in target tissues. We therefore determined whole-body responsiveness to the anabolic effects of GH in abdominally obese (OB) and normal weight (NW) premenopausal women. A 1-h iv infusion of GH or placebo was randomly administered to six NW (body mass index, 21.1 +/- 1.9 kg/m(2)) and six OB (body mass index, 35.5 +/- 1.5 kg/m(2)) women in a cross-over design. Endogenous insulin, glucagon and GH secretion was suppressed by infusion of somatostatin. Whole-body protein turnover was measured using a 10-h infusion of [(13)C]-leucine. GH administration induced a similar plasma GH peak in NW and OB women (49.8 +/- 10.4 vs. 45.1 +/- 5.6 mU/liter). GH, compared with placebo infusion, increased nonoxidative leucine disposal, P < 0.0001) and endogenous leucine appearance (R(a), P = 0.0004) but decreased leucine oxidation (P = 0.0051). All changes were similar in both groups. Accordingly, whole-body GH responsiveness, defined as the maximum response of nonoxidative leucine disposal, leucine R(a), and oxidation per unit of GH, was not different in OB and NW women (0.25 +/- 0.18 vs. 0.19 +/- 0.17 micro mol/kg.h, 0.21 +/- 0.23 vs. 0.13 +/- 0.17 micro mol/kg.h, and -0.10 +/- 0.08 vs. -0.08 +/- 0.05 micro mol/kg.h, respectively). These results indicated that whole-body tissue responsiveness to the net anabolic effect of GH is similar in OB and NW women. Hence, we inferred that hyposomatotropism may promote amino acid oxidation and blunt protein turnover in abdominal obesity. However, hyposomatotropism cannot account for all anomalous features of protein metabolism in abdominally obese humans.     

Regulation of protein metabolism in middle-aged, premenopausal women: roles of adiposity and estradiol

The age-related loss of fat-free mass (FFM) is accelerated in women during the middle-age years and continues at an increased rate throughout the postmenopausal period. Because protein is the primary structural component of fat-free tissue, changes in FFM are largely due to alterations in protein metabolism. Knowledge of the hormonal and physiological correlates of protein metabolism in middle-aged women, therefore, has important implications for understanding the mechanisms underlying changes in FFM. We measured leucine kinetics (expressed relative to FFM: micromol/kg FFM/h) in 46 middle-aged, premenopausal women (mean +/- SD, 47 +/- 3 yr) after an overnight fast (i.e. basal) and during euglycemic hyperinsulinemia (40 mU/m2/min) using a 5.5-h infusion of [1-13C]leucine. Additionally, we measured insulin-stimulated glucose disposal by euglycemic hyperinsulinemic clamp, body composition by dual energy x-ray absorptiometry, abdominal fat distribution by computed tomography, and hormone levels by RIA as possible correlates of protein metabolism. Under basal conditions, stepwise regression analysis showed that leucine appearance (i.e. protein breakdown) was related to percent body fat and serum estradiol (r2 = 40%; P < 0.01), and leucine oxidation was related to serum estradiol and percent body fat (r2 = 26%; P < 0.05). Under euglycemic hyperinsulinemic conditions, no variables correlated with the percent change in leucine appearance. The percent change in leucine oxidation was related to intraabdominal adipose tissue area and glucose disposal rate (r2 = 48%; P < 0.01). Correlates and r2 values for nonoxidative leucine disposal (i.e. protein synthesis) under basal and euglycemic hyperinsulinemic conditions were similar to those observed for leucine appearance. From these results, we conclude that adiposity and/or serum estradiol may contribute to the regulation of protein metabolism and FFM in middle-aged, premenopausal women.     

Synergistic effect of insulin-like growth factor-I administration on the protein-sparing effects of total parenteral nutrition in fasted lambs.

Using primed constant isotopic infusions, we investigated the effects of recombinant human insulin-like growth factor-I (IGF-I) infusion on protein kinetics in both fasted and parenterally fed (TPN) lambs. Infusion of IGF-I at a dose of 50 micrograms/kg.h in fasted animals increased (P less than 0.005) the mean plasma IGF-I concentration from 77.5 +/- 9.7 to 454.4 +/- 51.4 ng/ml. During IGF-I infusion the rate of net protein catabolism (NPC) was decreased (P less than 0.005) by 17% from 3.5 +/- 0.2 to 2.9 +/- 0.2 g/kg.day, and the rate of appearance (Ra) of leucine in plasma decreased (P less than 0.01) from 5.0 +/- 0.4 to 3.4 +/- 0.4 mumol/kg.min. In addition, the fractional synthetic rate of protein in cardiac and diaphragmatic muscle increased by 100% (P less than 0.05) during the same period. After 3 h of TPN, the rate of NPC was decreased (P less than 0.01) in the TPN animals compared to that in their fasted counterparts (1.89 +/- 2.27 vs. 4.1 +/- 0.2 g/kg.day, respectively). The rate of NPC was further decreased after another 300 min of TPN to 0.76 +/- 0.27 g/kg.day. However, the Ra of leucine was not changed compared to the initial value. Infusion of IGF-I concurrently with TPN reversed (P less than 0.001) the rate of NPC from 1.02 +/- 0.21 g/kg.day after 180 min of TPN alone to a state of net protein gain of 0.14 +/- 0.19 g/kg.day after a further 300 min of combined IGF-I and TPN infusion. The Ra of leucine decreased (P less than 0.01) from 3.9 +/- 0.8 to 2.5 +/- 0.47 mumol/kg.min during IGF-I and TPN infusion. Similarly, the fractional synthetic rates of protein in cardiac muscle, diaphragm, adductor muscle, psoas muscle, and hepatic tissue were increased (P less than 0.05) compared to those in animals that received only TPN. The protein-sparing effects of IGF-I and TPN were synergistic, and the infusion of both agents resulted in the induction of a protein anabolic state within 60 min of commencing IGF-I infusion. In contrast, neither IGF-I nor TPN alone resulted in a state of net protein anabolism, and neither had an effect on protein kinetics until 120 min into the infusion. Consequently, IGF-I shows considerable potential as an anticatabolic agent when used synergistically with nutritional support.     

Common carotid intima-media thickness in growth hormone (GH)-deficient adolescents: a prospective study after GH withdrawal and restarting GH replacement

We prospectively investigated the risk of early atherosclerosis, by classical cardiovascular risk factors and intima-media thickness (IMT) at the common carotid arteries, in 23 adolescents diagnosed as GH deficient (GHD) during childhood and in 23 healthy sex-, age-, and BMI-matched controls. Measurements were performed in all subjects before stopping GH replacement. Because the diagnosis of GHD had been confirmed in 15 of the 23 adolescents, the protocol changed according to the diagnosis as follows: measurements were repeated after 6 months of GH withdrawal and 6 months of GH reinstitution in the 15 with GHD, and after 6 and 12 months of GH withdrawal, measurements were also taken in the eight non-GHD subjects. Serum IGF-I levels were in the normal range for age in all patients before GH withdrawal. When compared with controls, before GH withdrawal, GHD adolescents had reduced high-density lipoprotein cholesterol levels and increased total/high-density lipoprotein cholesterol ratio, fibrinogen, low-density lipoprotein cholesterol, and glucose levels; non-GHD adolescents had increased glucose, insulin, and homeostasis model assessment score. IMT at the common carotid arteries was similar in GHD and controls (0.52 +/- 0.03 vs. 0.55 +/- 0.06 mm; P = 0.23) and was higher in non-GHD than in controls (0.62 +/- 0.03 vs. 0.54 +/- 0.06 mm; P = 0.01). In GHD adolescents, 6 months of GH treatment withdrawal and 6 months of GH treatment reinstitution modified IGF-I levels, lipid profile, and insulin resistance but not IMT or systolic and diastolic peak velocities at the common carotid arteries. In non-GHD subjects, 12 months of GH treatment withdrawal significantly decreased IGF-I levels, IMT (to 0.54 +/- 0.06 mm; P < 0.001 vs. baseline), systolic and diastolic peak velocities, and improved insulin resistance. In conclusion, the discontinuation of GH in confirmed GHD adolescents is not followed by significant alterations of the common carotid arteries, despite the profound negative alterations of the lipid profile. In adolescents who were not confirmed to have GHD, IMT was increased while on GH therapy and normalized when they were taken off of GH.     

Endocrine responses to ghrelin in adult patients with isolated childhood-onset growth hormone deficiency

OBJECTIVE: Ghrelin, a 28 amino acid acylated peptide, is a natural ligand of the GH secretagogues (GHS) receptor (GHS-R), which is specific for synthetic GHS. Similar to synthetic GHS, ghrelin strongly stimulates GH secretion but also displays significant stimulatory effects on lactotroph and corticotroph secretion. It has been hypothesized that isolated GH deficiency (GHD) could reflect hypothalamic impairment that would theoretically involve defect in ghrelin activity. PATIENTS: In the present study, we verified the effects of ghrelin (1 microg/kg i.v.) on GH, PRL, ACTH and cortisol levels in adult patients with isolated severe GHD [five males and one female, age (mean +/- SEM) 24.7 +/- 2.6 years, BMI 25.7 +/- 2.7 kg/m2]. In all patients, the GH response to insulin-induced hypoglycaemia (ITT, 0.1 IU regular insulin i.v.) and GH releasing hormone (GHRH) (1 microg/kg i.v.) + arginine (ARG, 0.5 g/kg i.v.) was also studied. The hormonal responses in GHD were compared with those in age-matched normal subjects (NS, seven males, age 28.6 +/- 2.9 years, BMI 22.1 +/- 0.8 kg/m2). RESULTS: IGF-I levels in GHD were markedly lower than in NS (69.8 +/- 11.3 vs. 167.9 +/- 19.2 microg/l, P < 0.003). Ghrelin administration induced significant increase in GH, PRL, ACTH and cortisol levels in all GHD. In GHD, the GH response to ghrelin was higher (P < 0.05) than that to GHRH + ARG, which, in turn, was higher (P < 0.05) than that to ITT (9.2 +/- 4.1 vs. 5.3 +/- 1.7 vs. 1.4 +/- 0.4 microg/l). These GH (1 microg/l = 2 mU/l) responses in GHD were markedly lower (P < 0.0001) than those in NS (ghrelin vs. GHRH + ARG vs. ITT 92.1 +/- 16.7 vs. 65.3 +/- 8.9 vs. 17.7 +/- 3.5 microg/l). In GHD, the highest individual peak GH response to ghrelin was markedly lower than the lowest peak GH response in NS (28.5 vs. 42.9 microg/l). GHD and NS showed overlapping PRL (1 microg/l = 32 mU/l) (10.0 +/- 1.4 vs. 14.9 +/- 2.2 microg/l), ACTH (22.3 +/- 5.3 vs. 18.7 +/- 4.6 pmol/l) and cortisol responses (598.1 +/- 52.4 vs. 486.9 +/- 38.9 nmol/l). CONCLUSIONS: This study shows that ghrelin is one of the most powerful provocative stimuli of GH secretion, even in those patients with isolated severe GHD. In this condition, however, the somatotroph response is markedly reduced while the lactotroph and corticotroph responsiveness to ghrelin is fully preserved, indicating that this endocrine activity is fully independent of mechanisms underlying the GH-releasing effect. These results do not support the hypothesis that ghrelin deficiency is a major cause of isolated GH deficiency but suggest that ghrelin might represent a reliable provocative test to evaluate the maximal GH secretory capacity provided that appropriate cut-off limits are assumed.     

Administration of recombinant human growth hormone on alternate days is sufficient to increase whole body protein synthesis and lipolysis in growth hormone deficient adults

OBJECTIVE: At present, the duration of the effect of recombinant human growth hormone (rhGH) on the rates of protein synthesis and lipolysis in GH deficient (GHD) adults is unknown. This study was designed to establish the frequency of rhGH administration necessary to provide the beneficial metabolic effects of the hormone in GHD adults. DESIGN AND PATIENTS: Two different studies (A and B) were performed in two groups of five GHD men. In study A, whole body protein and lipid kinetics was determined in the basal state (Bas), 12 (GH12h) and 36 (GH36h) h after the last of seven injections of rhGH (3.3 microg/kg), given at bedtime on alternate days. In study B, the same parameters were determined in the basal state (Bas), 60 (GH60h) and 84 (GH84h) h after the last of seven injections of rhGH (3.3 microg/kg), given at bedtime at 3 day intervals. MEASUREMENTS: The rates of protein metabolism were estimated by infusing [1-13C]leucine, and those of lipolysis by infusing [1,1,2,3, 3-D5]glycerol. RESULTS: Leucine oxidation decreased (P < 0.01) by approximately 30% after GH12h and GH36h but did not change after GH60h and GH84h. Non-oxidative leucine disposal increased after GH12h and GH36h by approximately 13% (P < 0.05) whereas it did not change after GH60h and GH84h. Glycerol appearance increased (P < 0. 01) by approximately 45% after GH12h and GH36h but did not change after GH60h and GH84h. CONCLUSIONS: The effects on protein and lipid metabolism following the injection of rhGH last longer than 36 and less than 60 h. In fact, rhGH administration on alternate days induced a sustained increase in the rates of protein synthesis and lipolysis of GHD adults, whereas a longer interval of administration (3 days) had no effect by 60 h.     

Response of leucine metabolism to hyperinsulinemia in hypothyroid patients before and after thyroxine replacement

We have investigated the effect of hypothyroidism and insulin on protein metabolism in humans. Six hypothyroid patients were studied in a postabsorptive state before and after 5 months of regular treatment for hypothyroidism (153 +/- 17 microg/day of L-T4). The effect of insulin was assessed under hyperinsulinemic euglycemic and eukalemic conditions. Insulin was infused for 140 min at 0.0063 +/- 0.0002 nmol/kg x min. An amino acid infusion was used to blunt insulin-induced hypoaminoacidemia. Whole body protein turnover was measured using L-[1-13C] leucine. When compared to L-T4-induced subclinical thyrotoxic state, hypothyroidism induced a significant decrease (P < 0.05) in leucine endogenous appearance rate (a reflection of proteolysis; 0.89 +/- 0.09 vs. 1.33 +/- 0.05 micromol/kg x min), oxidation (0.19 +/- 0.02 vs. 0.25 +/- 0.03 micromol/kg x min), and nonoxidative disposal (a reflection of protein synthesis; 0.87 +/- 0.11 vs. 1.30 +/- 0.05 micromol/ kg x min). Insulin lowered proteolysis during both the subclinical thyrotoxic and hypothyroid states. Hypothyroidism impaired the antiproteolytic effects of insulin. Thyroid hormones are, therefore, essential for the normal antiproteolytic action of insulin.