Anabolic effects of oral leucine-rich protein with and without β-hydroxybutyrate on muscle protein metabolism in a novel clinical model of systemic inflammation-a randomized crossover trial

BACKGROUND

β-lactoglobulin (BLG) stimulates muscle protein synthesis and β-hydroxybutyrate (BHB) inhibits muscle breakdown. Whether combining the 2 can additively attenuate disease-induced muscle loss is unknown.

OBJECTIVE

Based on previous observations of anticatabolic effects of protein and ketone bodies during inflammation, and using a novel model combining ongoing systemic inflammation, fasting, and immobilization, we tested whether the anticatabolic muscle response to oral amino acids is altered compared with control conditions, as well as whether coadministration of oral BHB and BLG further improves the muscle anabolic response. Muscle net balance (NBphe) was the primary outcome and intramyocellular signals were assessed.

METHODS

In a randomized crossover design, 8 young men underwent either preconditioning with LPS (prestudy day: 1 ng/kg, study day: 0.5 ng/kg) combined with a 36-h fast and bed rest to mimic catabolic inflammatory disease (CAT) or an overnight fast (control [CTR]) prior to isocaloric nutritional interventions on 3 occasions separated by ∼6 wk (range 42 to 83 d).

RESULTS

NBphe increased similarly upon all conditions (interaction P = 0.65). From comparable baseline rates, both Rdphe [muscle synthesis, median ratio (95% CI): 0.44 (0.23, 0.86) P = 0.017] and Raphe [muscle breakdown, median ratio (95% CI): 0.46 (0.27, 0.78) P = 0.005] decreased following BHB + BLG compared with BLG. BLG increased Rdphe more under CAT conditions compared with CTR (interaction P = 0.02). CAT increased inflammation, energy expenditure, and lipid oxidation and decreased Rdphe and anabolic signaling [mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4EPB1) phosphorylation].

CONCLUSION

In contrast to our initial hypothesis, NBphe increased similarly following BLG during CAT and CTR conditions; CAT however, specifically stimulated the BLG-mediated increase in protein synthesis, whereas BHB coadministration did not affect NBphe, but distinctly dampened the BLG-induced increase in muscle amino acid fluxes thereby liberating circulating amino acids for anabolic actions elsewhere.

Oral 3-hydroxybutyrate ingestion decreases endogenous glucose production, lipolysis, and hormone-sensitive lipase phosphorylation in adipose tissue in men: a human randomized, controlled, crossover trial

AIMS

To test whether oral administration of D/L-3-hydroxybutyrate as a sodium salt inhibits lipolysis and intracellular lipid signalling, in particular, hormone-sensitive lipase, and whether D/L-3-hydroxybutyrate alters endogenous glucose production.

METHODS

We studied six young men in a randomized, controlled, crossover study after ingestion of Na-D/L-3-hydroxybutyrate (hyperketotic condition) or saline (placebo control). We quantified lipolysis and endogenous glucose production using [9,10-³ H]-palmitate and [3-3H]glucose tracers, and adipose tissue biopsies were collected to investigate key lipolytic enzymes.

RESULTS

After ingestion, D/L-3-hydroxybutyrate increased by more than 2.5 mmol/l, free fatty acid concentrations decreased by >70%, and palmitate rate of appearance was halved. Protein kinase A phosphorylation of perilipin was reduced and hormone-sensitive lipase 660 phosphorylation in adipose tissue biopsies was 70-80% decreased in the hyperketotic condition and unchanged in the control. Compared to the control, endogenous glucose production was reduced by close to 20% (P<0.05) after 3-hydroxybutyrate ingestion.

CONCLUSION

We conclude that oral D/L-Na-3-hydroxybutyrate increases D/L-3-hydroxybutyrate concentrations within half an hour, decreases free fatty acid concentrations, lowers lipolysis and endogenous glucose production, and dephosphorylates hormone-sensitive lipase. Collectively these phenomena may be viewed as an orchestrated feedback loop, controlling endogenous glucose production, lipolysis and ketogenesis. Such effects would be beneficial in insulin-resistant states. (www.clinicaltrials.gov ID number: NCT02917252).

Effect of Dosage of 17ß-Estradiol on Uterine Growth in Turner Syndrome-A Randomized Controlled Clinical Pilot Trial

CONTEXT

Most Turner syndrome (TS) girls need exogenous estrogen treatment to induce puberty and normal uterine growth. After puberty, the optimal estrogen treatment protocol has not been determined.

OBJECTIVE

To compare 2 doses of oral 17ß-estradiol on uterine size.

DESIGN

A double-blind, 5-year randomized controlled clinical trial.

SETTING

Ambulatory care.

PARTICIPANTS

Twenty young TS women (19.2 ± 2.5 years, range 16.0-24.9) participated. Sixteen patients completed the study. No patients withdrew due to adverse effects.

INTERVENTION

The lower dose (LD) group took 2 mg 17ß-estradiol/d orally and placebo. The higher dose (HD) group took 4 mg 17ß-estradiol/d orally.

MAIN OUTCOME MEASURE(S)

Uterine volume evaluated by transabdominal ultrasound yearly.

RESULTS

Uterine size increased significantly more in the HD group compared with the LD group (P = 0.038), with a gain in uterine volume within the first 3 years of treatment of 19.6 mL (95% confidence interval [CI] = 4.0-19.0) in the HD group compared with 11.5 mL (95% CI = 11.2-27.9) in the LD group. The difference in 3-year gain was 8.1 mL (95% CI = 0.7-15.9). At the last visit, there were no significant differences in uterine volume between the groups.

CONCLUSION

HD oral 17ß-estradiol induces a steeper increase in uterine volume within the first years of treatment compared with the LD. However, the uterine growth potential seems to be the same in most young TS women making the duration of treatment equally significant as estrogen dose, although a few TS women did not experience sufficient uterine growth on 2 mg of estradiol.

CLINICALTRIALS.GOV

NCT00134745Abbreviations: BMI, body mass index; BSA, body surface area; DHEAS, dihydroepiandrosteronesulfate; HD, higher dose; HRT, hormone replacement therapy; LD, lower dose; TS, Turner syndrome; US, ultrasound.

Amino acid supplementation is anabolic during the acute phase of endotoxin-induced inflammation: A human randomized crossover trial

BACKGROUND & AIMS

Inflammation is catabolic and causes muscle loss. It is unknown if amino acid supplementation reverses these effects during the acute phase of inflammation. The aim was to test whether amino acid supplementation counteracts endotoxin-induced catabolism.

METHODS

Eight young, healthy, lean males were investigated three times in randomized order: (i) normal conditions (Placebo), (ii) endotoxemia (LPS), and (iii) endotoxemia with amino acid supplementation (LPS + A). Protein kinetics were determined using phenylalanine, tyrosine, and urea tracers. Each study day consisted of a four-hour non-insulin stimulated period and a two-hour hyperinsulinemic euglycemic clamp period. Muscle biopsies were collected once each period.

RESULTS

Endotoxin administration created a significant inflammatory response (cytokines, hormones, and vital parameters) without significant differences between LPS and LPS + A. Whole body protein breakdown was elevated during LPS compared with Placebo and LPS + A (p < 0.05). Whole body protein synthesis was higher during LPS + A than both Placebo and LPS (p < 0.003). Furthermore, protein synthesis was higher during LPS than during Placebo (p < 0.02). Net muscle phenylalanine release was markedly decreased during LPS + A (p < 0.004), even though muscle protein synthesis and breakdown rates did not differ significantly between interventions. LPS + A increased mammalian target of rapamycin (mTOR) phosphorylation (p < 0.05) and eukaryotic translation factor 4E-binding protein 1 (4EBP1) phosphorylation (p = 0.007) without activating AMPK or affecting insulin signaling through Akt. During insulin stimulation net muscle phenylalanine release and protein degradation were further reduced.

CONCLUSIONS

Amino acid supplementation in the acute phase of inflammation reduces whole body and muscle protein loss, and this effect is associated with activation of mTOR and downstream signaling to protein synthesis through mTORC1, suggesting a therapeutic role for intravenous amino acids in inflammatory states.

CLINICAL TRIAL REGISTRY

The Central Denmark Region Ethics Commitee (1-10-71-410-12) www.clinicaltrials.gov (identification number NCT01705782).

Sustained AS160 and TBC1D1 phosphorylations in human skeletal muscle 30 min after a single bout of exercise

BACKGROUND

phosphorylation of AS160 and TBC1D1 plays an important role for GLUT4 mobilization to the cell surface. The phosphorylation of AS160 and TBC1D1 in humans in response to acute exercise is not fully characterized.

OBJECTIVE

to study AS160 and TBC1D1 phosphorylation in human skeletal muscle after aerobic exercise followed by a hyperinsulinemic euglycemic clamp.

DESIGN

eight healthy men were studied on two occasions: 1) in the resting state and 2) in the hours after a 1-h bout of ergometer cycling. A hyperinsulinemic euglycemic clamp was initiated 240 min after exercise and in a time-matched nonexercised control condition. We obtained muscle biopsies 30 min after exercise and in a time-matched nonexercised control condition (t = 30) and after 30 min of insulin stimulation (t = 270) and investigated site-specific phosphorylation of AS160 and TBC1D1.

RESULTS

phosphorylation on AS160 and TBC1D1 was increased 30 min after the exercise bout, whereas phosphorylation of the putative upstream kinases, Akt and AMPK, was unchanged compared with resting control condition. Exercise augmented insulin-stimulated phosphorylation on AS160 at Ser(341) and Ser(704) 270 min after exercise. No additional exercise effects were observed on insulin-stimulated phosphorylation of Thr(642) and Ser(588) on AS160 or Ser(237) and Thr(596) on TBC1D1.

CONCLUSIONS

AS160 and TBC1D1 phosphorylations were evident 30 min after exercise without simultaneously increased Akt and AMPK phosphorylation. Unlike TBC1D1, insulin-stimulated site-specific AS160 phosphorylation is modified by prior exercise, but these sites do not include Thr(642) and Ser(588). Together, these data provide new insights into phosphorylation of key regulators of glucose transport in human skeletal muscle.

Growth hormone-induced insulin resistance in human subjects involves reduced pyruvate dehydrogenase activity

AIM

Insulin resistance induced by growth hormone (GH) is linked to promotion of lipolysis by unknown mechanisms. We hypothesized that suppression of the activity of pyruvate dehydrogenase in the active form (PDHa) underlies GH-induced insulin resistance similar to what is observed during fasting.

METHODS

Eight healthy male subjects were studied four times in a randomized, single-blinded parallel design: Control, GH, Fasting (36 h) and GH + Fasting. GH (30 ng × kg(-1) × min(-1)) or saline was infused throughout the metabolic study day. Substrate metabolism and insulin sensitivity were assessed by indirect calorimetry and isotopically determined rates of glucose turnover before and after a hyperinsulinemic euglycemic clamp. PDHa activity, PDH-E1α phosphorylation, PDK4 expression and activation of insulin signalling proteins were assessed in skeletal muscle.

RESULTS

Both fasting and GH promoted lipolysis, which was associated with ≈50% reduction in insulin sensitivity compared with the control day. PDHa activity was significantly reduced by GH as well as fasting. This was associated with increased inhibitory PDH-E1α phosphorylation on site 1 (Ser(293)) and 2 (Ser(300)) and up-regulation of PDK4 mRNA, while canonical insulin signalling to glucose transport was unaffected.

CONCLUSION

Competition between intermediates of glucose and fatty acids seems to play a causal role in insulin resistance induced by GH in human subjects.

The impact of calcineurin inhibitors on insulin sensitivity and insulin secretion: a randomized crossover trial in uraemic patients

AIMS

The calcineurin inhibitors cyclosporine and tacrolimus are implicated in post-transplant complications such as new-onset diabetes after transplantation. The relative contribution of each calcineurin inhibitor to new-onset diabetes after transplantation remains unclear. We sought to compare the impact of cyclosporine and tacrolimus on glucose metabolism in humans.

METHODS

Eight haemodialysis patients received 8-10 days of oral treatment followed by 5-h infusions with cyclosporine, tacrolimus and saline in a randomized, investigator-blind, crossover study. Glucose metabolism and β-cell function was investigated through: a hyperinsulinaemic-euglycaemic clamp, an intravenous glucose tolerance test and insulin concentration time series.

RESULTS

Cyclosporine and tacrolimus decreased insulin sensitivity by 22% (P = 0.02) and 13% (P = 0.048), respectively. The acute insulin response and pulsatile insulin secretion were not significantly affected by the drugs.

CONCLUSION

In conclusion, 8-10 days of treatment with cyclosporine and tacrolimus impairs insulin sensitivity to a similar degree in haemodialysis patients, while acute insulin responses and pulsatile insulin secretion remain unaffected.

Exenatide alters myocardial glucose transport and uptake depending on insulin resistance and increases myocardial blood flow in patients with type 2 diabetes

CONTEXT

Glucagon-like peptide-1 (GLP-1) and GLP-1 receptor agonists provide beneficial cardiovascular effects by protecting against ischemia and reperfusion injury. Type 2 diabetes mellitus patients have reduced glycolysis in the heart.

OBJECTIVE

We hypothesized that cardioprotection by GLP-1 is achieved through increased glucose availability and utilization and aimed to assess the effect of exenatide, a synthetic GLP-1 receptor agonist, on myocardial glucose uptake (MGU), myocardial glucose transport, and myocardial blood flow (MBF).

DESIGN AND METHODS

We conducted a randomized, double-blinded, placebo-controlled crossover study in eight male, insulin-naive, type 2 diabetes mellitus patients without coronary artery disease. Positron emission tomography was used to determine the effect of exenatide on MGU and MBF during a pituitary-pancreatic hyperglycemic clamp with (18)F-fluorodeoxyglucose and (13)N-ammonia as tracers.

RESULTS

Overall, exenatide did not alter MGU. However, regression analysis revealed that exenatide altered initial clearance of glucose over the membrane of cardiomyocytes and MGU, depending on the level of insulin resistance (P = 0.017 and 0.010, respectively). Exenatide increased MBF from 0.73 ± 0.094 to 0.85 ± 0.091 ml/g · min (P = 0.0056). Except for an increase in C-peptide levels, no differences in circulating hormones or metabolites were found.

CONCLUSIONS

The action of exenatide as an activator or inhibitor of the glucose transport and glucose uptake in cardiomyocytes is dependent on baseline activity of glucose transport and insulin resistance. Exenatide increases MBF without changing MGU.

Metabolic Effects of Short-term GLP-1 Treatment in Insulin Resistant Heart Failure Patients

We studied the metabolic effects of 48-h GLP-1 treatment in insulin resistant heart failure patients.

In a randomized placebo-controlled double-blinded cross-over study, 11 non-diabetic HF patients with IHD received 48-h GLP-1 and placebo-infusion. We applied OGTT, hyperinsulinemic clamp, indirect calorimetry, forearm, and tracer methods.

7 insulin resistant HF (EF 28%±2) patients completed the protocol. GLP-1 decreased plasma glucose levels (p=0.048) and improved glucose tolerance. 4 patients had hypoglycemic events during GLP-1 vs. none during placebo. GLP-1 treatment tended to increase whole body protein turnover (p=0.08) but did not cause muscle wasting. No significant changes in circulating levels of insulin, glucagon, free fatty acids or insulin sensitivity were detected.

GLP-1 treatment decreased glucose levels and increased glucose tolerance in insulin resistant HF patients with IHD. Hypoglycemia was common and may limit the use of GLP-1 in these patients. Insulin sensitivity, lipid-, and protein metabolism remained unchanged.

Data were collected at the examinational laboratories of Department of Endocrinology and Department of Cardiology, Aarhus University Hospital, Aarhus, Denmark

Insulin resistance after a 72-h fast is associated with impaired AS160 phosphorylation and accumulation of lipid and glycogen in human skeletal muscle

During fasting, human skeletal muscle depends on lipid oxidation for its energy substrate metabolism. This is associated with the development of insulin resistance and a subsequent reduction of insulin-stimulated glucose uptake. The underlying mechanisms controlling insulin action on skeletal muscle under these conditions are unresolved. In a randomized design, we investigated eight healthy subjects after a 72-h fast compared with a 10-h overnight fast. Insulin action on skeletal muscle was assessed by a hyperinsulinemic euglycemic clamp and by determining insulin signaling to glucose transport. In addition, substrate oxidation, skeletal muscle lipid content, regulation of glycogen synthesis, and AMPK signaling were assessed. Skeletal muscle insulin sensitivity was reduced profoundly in response to a 72-h fast and substrate oxidation shifted to predominantly lipid oxidation. This was associated with accumulation of both lipid and glycogen in skeletal muscle. Intracellular insulin signaling to glucose transport was impaired by regulation of phosphorylation at specific sites on AS160 but not TBC1D1, both key regulators of glucose uptake. In contrast, fasting did not impact phosphorylation of AMPK or insulin regulation of Akt, both of which are established upstream kinases of AS160. These findings show that insulin resistance in muscles from healthy individuals is associated with suppression of site-specific phosphorylation of AS160, without Akt or AMPK being affected. This impairment of AS160 phosphorylation, in combination with glycogen accumulation and increased intramuscular lipid content, may provide the underlying mechanisms for resistance to insulin in skeletal muscle after a prolonged fast.

Effects of adrenaline on lactate, glucose, lipid and protein metabolism in the placebo controlled bilaterally perfused human leg

AIM

Adrenaline has widespread metabolic actions, including stimulation of lipolysis and induction of insulin resistance and hyperlactatemia. Systemic adrenaline administration, however, generates a very complex hormonal and metabolic scenario. No studies employing regional, placebo controlled and adrenaline infusion exist. Our study was designed to test the hypothesis that local placebo controlled leg perfusion with adrenaline directly increases local lactate release, stimulates lipolysis, induces insulin resistance and leaves protein metabolism unaffected.

METHODS

  We studied seven healthy volunteers with bilateral femoral vein and artery catheters during 3-h basal and 3-h hyperinsulinemic (0.6 mU kg(-1) min(-1) ) euglycemic clamp conditions. One femoral artery was perfused with saline and the other with adrenaline (0.4 μg min m(-2) ). Lipid metabolism was quantified with [9,10-(3) H] palmitate and amino acid metabolism with (15) N-phenylalanine and lactate and glucose by raw arterio-venous differences.

RESULTS

  Femoral vein plasma adrenaline increased ≈eightfold in the perfused leg with unaltered blood flows. Adrenaline perfusion significantly increased local leg lactate release from 0.01 to 0.25 mmol min(-1) per leg, palmitate release in the basal state 11.5-16.9 μmol min(-1) per leg and during the clamp 2.62-8.44 μmol min(-1) per leg. Glucose uptake decreased during the clamp from ≈180 to 30 μmol min(-1) per leg. Phenylalanine kinetics was not affected by adrenaline.

CONCLUSION

  Adrenaline directly increases lactate release and lipolysis and inhibits insulin-stimulated glucose uptake in the perfused human leg. Adrenaline has no direct effects on peripheral amino acid metabolism. Adrenaline-induced lactate release from striated muscle may be an important mechanism underlying hyperlactatemia in the critically ill.

Growth hormone (GH)-induced insulin resistance is rapidly reversible: an experimental study in GH-deficient adults

CONTEXT

It is clinically relevant and of physiological interest to investigate whether GH-induced insulin resistance depends on the timing of GH exposure relative to when insulin sensitivity is assessed.

HYPOTHESIS

GH-induced insulin resistance is rapidly reversible.

DESIGN AND PARTICIPANTS

Eight male GH-deficient patients underwent a 6-h euglycemic-hyperinsulinemic glucose clamp thrice in a randomized crossover design receiving either no GH (study 0), a 7-h GH infusion (0.2-0.3 mg in total) that terminated 5 h before the clamp (study 1), or a similar GH infusion timed to continue during the first hour of the clamp (study 2). A muscle biopsy was obtained 30 min into the clamp. The patients were compared with eight healthy untreated control subjects (study c).

MAIN OUTCOME MEASURES

The glucose infusion rate, indirect calorimetry, and free fatty acid metabolism were assessed. In muscle biopsies, protein phosphorylation of signal transducer and activator of transcription 5, Akt, and Akt substrate 160 (phospho-Akt substrate signal) and gene expression of IGF-I and SOCS1-3 were assessed.

RESULTS

Insulin sensitivity differed significantly between the GH-deficiency studies (P = 0.005) with distinct insulin resistance in study 2 and increased insulin sensitivity in study 0 [area under the glucose infusion rate curve (mg/kg · min): 1663 ± 151 (study 0) vs. 1482 ± 166 (study 1) vs. 1123 ± 136 (study 2) vs. 1492 ± 229 (control group)]. Free fatty acid levels and lipid oxidation were elevated in response to GH exposure but became suppressed during the clamp. IGF-I and SOCS3 gene expression was increased in study 2.

CONCLUSIONS

Very-low-dose GH exposure evokes acute insulin resistance that subsides after 5 h. This time-dependent reversibility should be considered when assessing the impact of GH on glucose homeostasis.

Insulin dose-response studies in severely insulin-resistant type 2 diabetes--evidence for effectiveness of very high insulin doses

AIM

To combat diabetic complications strict glycaemic control is desirable in type 2 diabetes, but some patients are severely insulin resistant and it is not known whether high doses of insulin are effective. This study was designed to determine the acute dose-response effects of insulin in patients with type 2 diabetes and severe insulin resistance.

METHODS

We included eight insulin-resistant (mean insulin dose: 186 IU/day; body mass index: 35) subjects with type 2 diabetes in a single-blinded, randomized crossover study. Each subject was studied on two occasions. On each occasion, subjects underwent two 3-h hyperinsulinaemic euglycaemic clamps. The subjects were randomized to two low-dose insulin infusions (0.5 and 1.5 mU/kg/min in random order) on one occasion and to two high-dose insulin infusions (3.0 and 5.0 mU/kg/min in random order) on another occasion.

RESULTS

On all occasions, steady-state glucose infusion rates (SSGIRs) were accomplished and we observed a clear dose-response relationship with GIR values of 0.4 ± 0.2 (s.e.), 2.6 ± 0.6, 3.7 ± 0.8 and 4.9 ± 0.9 mg/kg/min during the 0.5, 1.5, 3.0 and 5.0 mU/kg/min insulin infusions, respectively (p < 0.001). Likewise, there was a dose-dependent suppression of endogenous glucose production (EGP) (p < 0.009), plasma free fatty acids (FFAs) (p < 0.001) and plasma glucagon (p = 0.001).

CONCLUSIONS

Our results show that the insulin dose response in terms of GIR and EGP is preserved for insulin doses corresponding to >800 IU/day, suggesting effectiveness of very high insulin doses in severely insulin-resistant subjects.

Uterus and ovaries in girls and young women with Turner syndrome evaluated by ultrasound and magnetic resonance imaging

OBJECTIVE

To determine uterine and ovarian size in Turner syndrome (TS) and to compare uterine and ovarian size evaluated by transabdominal ultrasound (US) and magnetic resonance imaging (MRI) in girls with TS and two groups of controls.

DESIGN

A cross-sectional study.

PATIENTS

Forty-one girls with TS (17·0 ± 3·3 years, range 11·2-24·9 years), 50 healthy age-matched controls (16·9 ± 3·2 years, range 12·5-25·0 years) and 107 Tanner-stage-matched controls (15·0 ± 3·2 years, range 10·1-24·2).

MEASUREMENTS

Uterine and ovarian volume by US and MRI.

RESULTS

Ovaries were detected in 37% in TS by US and in 55% in TS by MRI (P = 0·1). Total ovarian volume was lower in TS compared to both groups of controls (TS vs C-US: median 1·1 ml (range 0·1-29·3) vs 11·52 ml (1·9-77·9), P = 0·001, TS vs C-MRI: 1·0 ml (0·1-34·2) vs 13·2 ml (2·4-30·1), P < 0·0005). Mean difference in total ovarian volume measured by MRI and US in patients with TS was 2·3 ± 3·8 ml (P = 0·01). Mean uterine volume by MRI was lower in TS compared to controls (29·5 ± 25·1 vs 54·3 ± 23·3 ml, P < 0·0005). Uterine volume by US was lower in TS at Tanner stage B5 compared to controls (TS vs C: 33·6 ± 18·2 vs 50·2 ± 18·0 ml, P = 0·007).

CONCLUSIONS

A larger ovarian volume was detected by MRI in TS compared to US. This finding is important with the advancements of performing ovarian biopsies for cryopreservation and later reimplantation. Mean uterine volumes by MRI and US in fully matured TS were lower compared to controls despite appropriate hormonal replacement therapy in TS.

Time-course effects of physiological free fatty acid surges on insulin sensitivity in humans

AIM

Physiological elevations of free fatty acids (FFAs) occur in bell-shaped surges lasting some hours, observed nocturnally, during exercise and inflammation. The time-course effects of such FFA surges on insulin sensitivity are unknown. We therefore aimed to define the effects of a graded 4-h FFA elevation intended to mimick physiological excursions.

METHODS

Eight lean, healthy men were studied on two occasions: (1) control (saline) and (2) 4 h graded infusion of intralipid (20%)/heparin. Insulin sensitivity was continuously assessed by isotope dilution (3H-glucose) during an 8 h hyperinsulinemic-euglycaemic clamp (0.5 mU kg(-1) min(-1) ). Phosphorylation of Akt and ERK1/2 was measured in muscle biopsies taken at 0 and 120 min. Inflammatory cytokines were assessed with a Luminex Suspension Array System.

RESULTS

Infusion of intralipid caused a bell-shaped increase in FFA levels reaching peak levels ~1.9 mmol L(-1) and markedly impairing insulin sensitivity. Impairment of insulin sensitivity was apparent (P>0.05) 120 min after initiation of FFA infusion, significant after 270 min (P < 0.001) and peaked after 360 min. FFA induced insulin resistance prevailed 210 min after cessation of FFA infusion. No effect was observed on Akt and ERK1/2 phosphorylation.

CONCLUSIONS

(1) Physiological FFA elevations require at least 120 min to induce insulin resistance, (2) that insulin resistance peaks 360 min after initiation of FFA exposure and (3) ceases 210 min after termination of the FFA infusion. These observations add to our understanding of FFA induced insulin resistance in relation to circadian variations, exercise, generalized inflammation and exposure to stress hormones such as growth hormone.

Metabolic effects of free fatty acids during endotoxaemia in a porcine model--free fatty acid inhibition of growth hormone secretion as a potential catabolic feedback mechanism

Critical illness and severe inflammation are catabolic states characterised by breakdown of tissue and protein stores, by increased levels of free fatty acids, and by insulin resistance. These metabolic features contribute to morbidity and mortality. Growth hormone and insulin are the two major anabolic hormones. The present study was designed to test whether increased levels of free fatty acids (i) inhibit growth hormone secretion and (ii) induce insulin resistance during acute endotoxin exposure in a porcine model of critical illness. We studied 20 pigs for 6 h during combined anaesthesia and endotoxin infusion and a hyperinsulinaemic glucose clamp to control glucose, insulin, and free fatty acid concentrations. Pigs were randomised to two different continuous infusion rates of Intralipid resulting in different, sustained, and elevated free fatty acid concentrations (1.63 mmol l(-1) vs. 0.58 mmol l(-1), p=0.0002). Concomitantly, we observed reduced growth hormone concentrations in the group with high free fatty acid concentrations (3.5 ng ml(-1) vs. 6.6 ng ml(-1), p<0.003). No difference in insulin sensitivity, measured as the glucose infusion rate necessary to maintain euglycaemia, was observed. We conclude that high levels of free fatty acids reduce circulating growth hormone concentrations in porcine endotoxaemia; this probably constitutes a negative feedback mechanism whereby growth hormone induced-stimulation of free fatty acids release inhibit growth hormone secretion. This mechanism may further contribute to protein loss in critical illness. We found no evidence that the increment of plasma free fatty acids between groups contribute to insulin resistance in critical illness.

Forearm and leg amino acid metabolism in the basal state and during combined insulin and amino acid stimulation after a 3-day fast

AIM

Fasting is characterized by a progressive loss of protein, but data on protein kinetics are unclear and few have studied the effects of re-feeding. The present study was designed to test the hypothesis that a combined infusion of insulin and amino acids after fasting would induce compensatory increases in protein synthesis and reductions in protein breakdown at the whole body level and in muscle.

METHODS

We included 10 healthy male volunteers and studied them twice: (1) in the post-absorptive state and (2) after 72 h of fasting. Amino acid kinetics was measured using labelled phenylalanine and tyrosine, whole body energy expenditure was assessed and urea nitrogen synthesis rates were calculated.

RESULTS

After fasting we observed an increase in arterial blood concentration of branched chain amino acids and a decrease in gluconeogenic amino acids (P < 0.05). Isotopically determined whole body, forearm and leg phenylalanine fluxes were unaltered apart from a 30% decrease in phenylalanine-to-tyrosine conversion (2.0 vs. 1.4 mumol kg(-1) h(-1), P < 0.01). During infusion of insulin and amino acids, amino acid concentrations increased.

CONCLUSION

Our data indicate that after a 72-h fast basal and insulin/amino acid-stimulated regional phenylalanine fluxes in leg and forearm muscle are unaltered. During fasting concentrations of gluconeogenic amino acids decrease and hepatic and/or renal phenylalanine-to-tyrosine conversion decreases. Thus, as opposed to glucose and lipid metabolism, fasting does not induce insulin resistance as regards amino acid metabolism.

Dose-response effects of free fatty acids on amino acid metabolism and ureagenesis

AIM

Free fatty acids (FFAs) are important fuels and have vital protein-sparing effects, particularly during conditions of metabolic stress and fasting. However, it is uncertain whether these beneficial effects are evident throughout the physiological range or only occur at very high FFA concentrations. It is also unclear whether secondary alterations in hormone levels and ketogenesis play a role. We therefore aimed at describing dose-response relationships between amino acid metabolism and circulating FFA concentrations at clamped hormone levels.

METHODS

Eight healthy men were studied on four occasions (6 h basal, 2 h glucose clamp). Endogenous lipolysis was blocked with acipimox and Intralipid was infused at varying rates (0, 3, 6 or 12 microL kg(-1) min(-1)) to obtain four different levels of circulating FFAs. Endogenous growth hormone, insulin and glucagon secretion was blocked by somatostatin (300 microg h(-1)) and replaced exogenously. 15N-phenylalanine, 2H4-tyrosine and 13C-urea were infused continuously to assess protein turnover and ureagenesis.

RESULTS

We obtained four distinct levels of FFA concentrations ranging from 0.03 to 2.1 mmol L(-1) and 3-hydroxybutyrate concentrations from 10 to 360 micromol L(-1). Whole-body phenylalanine turnover and phenylalanine-to-tyrosine degradation decreased with increasing FFA levels as did insulin-stimulated forearm fluxes of phenylalanine. Phenylalanine, tyrosine and urea concentrations also decreased progressively, whereas urea turnover was unperturbed.

CONCLUSION

Circulating FFAs decrease amino acid concentrations and inhibit whole-body phenylalanine fluxes and phenylalanine-to-tyrosine conversion. Our data cover FFA concentrations from 0 to 2 mmol L(-1) and indicate that FFAs exert their protein conserving effects in the upper physiological range (>1.5 mmol L(-1)).

Effects of glucose, glycerol, 3-hydroxybutyrate, insulin, and leptin on placental growth hormone secretion in placental explants

Placental growth hormone (PGH) is secreted from the syncytiotrophoblast in increasing amounts during pregnancy. The physiology and regulation of PGH is not well known; however, low glucose levels appear to stimulate PGH liberation IN VITRO and IN VIVO. PGH appears to have lipolytic effects, and inverse correlations between maternal body mass index and serum PGH levels have been reported. Therefore, substances related to maternal adipose tissue metabolism could influence PGH secretion. The effect of insulin, glycerol, 3-hydroxybutyrate (3-OHB), and leptin on PGH and human placental lactogen (hPL) secretion from cultured placental explants was studied. In glucose-free media, PGH content increased upto 237.5+/-28.4% of control media (p<0.001, ANOVA). Insulin levels were without effect on PGH secretion, as were 3-OHB, leptin, and glycerol at 0.02 mmol/l. Glycerol at 0.2 mmol/l increased PGH in all of the placental explants studied (n=8; mean increase 27.3+/-7.1%), and this difference was significantly different from the control explants (p=0.004). The liberation of hPL to culture media was different from PGH and was influenced by glucose and insulin. In conclusion, the absence of glucose profoundly increased PGH secretion in cultured placental explants. Addition of glycerol in physiologically relatively high concentrations showed a less pronounced stimulatory effect.

Effects of a 3-day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue

AIM

Fasting is characterized by increased whole body lipolysis and lipid oxidation, decreased glucose oxidation and insulin resistance. To identify the regional sources and underlying mechanisms, we studied 10 healthy male volunteers post-absorptively and after 72 h of fasting.

METHODS

Each study comprised a 3-h basal period and a 3-h hyperinsulinaemic euglycaemic clamp and we used a combination of leg and forearm arteriovenous techniques, upper and lower body microdialysis and glucose and palmitate tracers.

RESULTS

In the basal state, plasma levels, fluxes and oxidation rates of free fatty acids all roughly doubled after fasting. Palmitate fluxes across the forearm and leg also increased by two to threefold and interstitial leg muscle glycerol concentrations doubled. Subcutaneous femoral glycerol concentrations and blood flows were unaltered, but abdominal subcutaneous blood flow increased by 50% in the presence of unchanged glycerol concentrations, indicating stimulated abdominal lipolysis. During the clamp, we observed whole body insulin resistance and glucose uptake across the leg and forearm decreased by 60%.

CONCLUSION

Our data show that fasting induces insulin resistance in upper and lower body muscles and suggest that increased lipolysis, is primarily due to the activation of lipolysis in muscle-associated fat (in the leg) and in upper body subcutaneous fat, whereas peripheral subcutaneous fat is spared.

Dose-response effects of free fatty acids on glucose and lipid metabolism during somatostatin blockade of growth hormone and insulin in humans

CONTEXT

GH and other stress hormones stimulate lipolysis, which may result in free fatty acid (FFA)-mediated insulin resistance. However, there are also indications that FFAs in the very low physiological range have the same effect.

OBJECTIVE

The objective of the study was to address systematically the dose-response relations between FFAs and insulin sensitivity.

DESIGN

We therefore examined eight healthy men for 8 h (6 h basal and 2 h glucose clamp) on four occasions.

INTERVENTION

Intralipid was infused at varying rates (0, 3, 6, 12 microl.kg(-1).min(-1)); lipolysis was blocked by acipimox; and endogenous GH, insulin, and glucagon secretion was blocked by somatostatin and subsequently replaced at fixed rates.

RESULTS

This resulted in four different FFA levels between 50 and 2000 micromol/liter, with comparable levels of insulin and counterregulatory hormones. Both in the basal state and during insulin stimulation, we saw progressively decreased glucose disposal, nonoxidative glucose disposal, and forearm muscle glucose uptake at FFA levels above 500 micromol/liter. Apart from forearm glucose uptake, the very same parameters were decreased at low FFA levels (approximately 50 micromol/liter). FFA rate of disposal was linearly related to the level of FFAs, whereas lipid oxidation reached a maximum at FFA levels approximately 1000 micromol/liter.

CONCLUSION

In the presence of comparable levels of all major metabolic hormones, insulin sensitivity peaks at physiological levels of FFAs with a gradual decrease at elevated as well as suppressed FFA concentrations. These data constitute comprehensive dose-response curves for FFAs in the full physiological range from close to zero to above 2000 micromol/liter.

Abnormalities of whole body protein turnover, muscle metabolism and levels of metabolic hormones in patients with chronic heart failure

OBJECTIVE

It is well known that chronic heart failure (CHF) is associated with insulin resistance and cachexia, but little is known about the underlying substrate metabolism. The present study was undertaken to identify disturbances of basal glucose, lipid and protein metabolism.

DESIGN

We studied eight nondiabetic patients with CHF (ejection fraction 30 +/- 4%) and eight healthy controls. Protein metabolism (whole body and regional muscle fluxes) and total glucose turnover were isotopically assayed. Substrate oxidation were obtained by indirect calorimetry. The metabolic response to exercise was studied by bicycle ergometry exercise.

RESULTS

Our data confirm that CHF patients have a decreased lean body mass. CHF patients are characterised by (i) decreased glucose oxidation [glucose oxidation (mg kg(-1) min(-1)): 1.25 +/- 0.09 (patients) vs. 1.55 +/- 0.09 (controls), P < 0.01] and muscle glucose uptake [a - v diff(glucose) (micromol L(-1)): -10 +/- 25 (patients) vs. 70 +/- 22 (controls), P < 0.01], (ii) elevated levels of free fatty acids (FFA) [FFA (mmol L(-1)): 0.72 +/- 0.05 (patients) vs. 0.48 +/- 0.03 (controls), P < 0.01] and 3-hydroxybutyrate and signs of elevated fat oxidation and muscle fat utilization [a - v diff(FFA) (mmol L(-1)): 0.12 +/- 0.02 (patients) vs. 0.05 +/- 0.01 (controls), P < 0.05] and (iii) elevated protein turnover and protein breakdown [phenylalanine flux (micromol kg(-1) h(-1)): 36.4 +/- 1.5 (patients) vs. 29.6 +/- 1.3 (controls), P < 0.01]. Patients had high circulating levels of noradrenaline, glucagon, and adiponectin, and low levels of ghrelin. We failed to observe any differences in metabolic responses between controls and patients during short-term exercise.

CONCLUSIONS

In the basal fasting state patients with CHF are characterized by several metabolic abnormalities which may contribute to CHF pathophysiology and may provide a basis for targeted intervention.

The effect of submaximal exercise on immuno- and bioassayable IGF-I activity in patients with GH-deficiency and healthy subjects

OBJECTIVE

Growth hormone (GH) increases during exercise, but the response of the insulin-like growth factor (IGF) system has not been as definitive. Therefore, we investigated the effect of the exercise-induced GH response on the circulating IGF-system in GH-deficient (GHD) and intact adults.

DESIGN

Eight GHD adults were studied on 2 occasions, with (+GH) and without (-GH) GH administered (0.4 IU) during exercise (45 min of cycle ergometer exercise at the lactate threshold). Eight age-matched controls were only studied on one occasion. Blood samples were drawn at baseline, during and post-exercise. IGFBP-3 proteolysis was measured by an in vitro proteolytic activity assay, IGF-I bioactivity by novel IGF-I kinase receptor activation assay (KIRA) and other hormones by immunoassay.

RESULTS

GH administration to GHD adults resulted in a serum GH peak similar to the exercise-stimulated GH response in GH intact controls, but exercise had only a small impact on the IGF system. IGF-I concentration was lower in controls but was only significantly lower than the +GH day. Neither IGF-I nor -II levels changed over time. IGFBP-1 demonstrated a time effect (P<0.01) in all groups, and a time x group interaction (P<0.01) with a rise at 75 min post-exercise, which was greater in the GHD subjects than controls. IGFBP-2 and -3 increased significantly (P<0.01) over time in the GHD subjects, but not in the controls. No change in IGFBP-3 proteolysis or IGF-I bioactivity was found during exercise or recovery in either group.

CONCLUSION

Submaximal exercise induced minor changes in IGFBP-1, -2 and -3, without affecting IGFBP-3 proteolysis and IGF-I bioavailability. Thus the metabolic status during submaximal exercise does not require a change in plasma IGF-I bioavailability. Administration of GH to GHD adults does not result in changes in proteolysis or bioavailability.

Lower urinary tract symptoms after total and subtotal hysterectomy: results of a randomized controlled trial

The aim of this Danish multicenter trial was to compare the proportion of women with lower urinary tract symptoms after total abdominal hysterectomy (TAH) and subtotal abdominal hysterectomy (SAH) for benign uterine disorders. A total of 319 women were randomized to TAH (n = 158) or SAH (n = 161). Women were followed up for 1 year by strict data collection procedures, including postal questionnaires. Results were analyzed by intention-to-treat analyses. Urinary incontinence was found less often among TAH women than among SAH women. This was due to a larger reduction of the number of women with stress and urinary incontinence in the TAH group. No other differences were found between the two operation methods. The number of women with urinary incontinence and frequency was reduced from study entry for follow-up, while double/triple voiding was increased. Incontinent women had significantly lower quality of life scores than continent women

Metabolic consequences of GH deficiency

Patients with active acromegaly are insulin resistant and glucose intolerant, whereas children with GH deficiency are insulin sensitive and may develop fasting hypoglycemia. Surprisingly, however, hypopituitary adults with unsubstituted GH deficiency tend to be insulin resistant which may worsen during GH substitution. A unifying mechanism explaining insulin resistance in both conditions could be increased flux of free fatty acids (FFA) caused by visceral obesity (untrated GHDA) and enhanced lipid oxidation (GH substitution), respectively. During fasting, which may be considered the natural domain for the metabolic effects of GH, the induction of insulin resistance by GH is associated with enhanced lipid oxidation and protein conservation. In this particular context, insulin resistance appears to constitute a favorable metabolic adaptation. The problem is that GH substitution results in elevated circadian GH levels in non-fasting patients. The best way to address this challenge is to employ evening administration of GH and to tailor the dose. Insulin therapy may cause hypoglycemia, and GH substitution may cause hyperglycemia. Such untoward effects should be minimised by carefully monitoring the individual patient. It is also plausible that the long-term beneficial effects of GH on body composition will balance the insulin antagonistic effects on glucose metabolism.

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.

Sexuality after total vs. subtotal hysterectomy

BACKGROUND

The effect of hysterectomy on sexuality is not fully elucidated and until recently total and subtotal hysterectomies have only been compared in observational studies.

AIMS

To compare total abdominal hysterectomy (TAH) to subtotal abdominal hysterectomy (SAH) regarding effects on sexuality.

METHODS

In a Danish multicenter trial 319 women were randomized to TAH (n = 158) or SAH (n = 161); 185 women had self-selected TAH (n = 80) or SAH (n = 105) in a simultaneously conducted observational study. Women were followed for 1 year by strict data collection procedures, including postal questionnaires. Results were analyzed by intention to treat (ITT) analyses.

RESULTS

No significant differences were observed between TAH and SAH at 1-year follow-up in both the randomized trial and the observational study regarding women's desire for sex, frequency of intercourse, frequency of orgasm, quality of orgasm, localization of orgasm, satisfaction with sexual life, and dyspareunia. None of these sexual variables changed significantly from entry to the 1-year follow-up, apart from dyspareunia, which was significantly (p = 0.009) reduced in both intervention groups. Significant (p < 0.05) predictors for satisfaction with sexual life after hysterectomy were the preoperative satisfaction with sexual life [odds ratio (OR) 32, 95% confidence interval (CI) 10-125], good relationship with partner (OR 50, 95% CI 9-354), physical well-being (OR 0.30, 95% CI 0.09-0.88) and hormone replacement therapy (OR 0.23, 95% CI 0.06-0.78).

CONCLUSIONS

Both TAH and SAH significantly reduce dyspareunia without having a negative effect on sexual function. The shift toward SAH seems unwarranted.

Exercise, hormones, and body temperature. regulation and action of GH during exercise

That physical exercise stimulates pituitary GH secretion has been known for forty years, but the underlying mechanisms as well as the physiological significance remain elusive. We have previously shown that the concomitant increase in core temperature is essential for the exercise-induced GH release, inasmuch as exercise performed at 4 C results in a suppression of GH secretion, whereas passive heating constitutes a potent stimulus for GH release. Moreover, studies in normal subjects show that GH stimulates sweat production and evaporative heat loss during heat exposure with and without exercise, whereas GH-deficiency is associated with reduced sweat secretion and increased heat storage during similar conditions. The neurotransmitters involved in GH secretion during exercise remain uncertain; we therefore investigated the putative role of ghrelin, which is a gut-derived endogenous ligand for the GHS receptor. We measured circulating ghrelin levels before during and after submaximal aerobic exercise in healthy subjects and GH-deficient patients. The circulating ghrelin levels were unchanged during and after exercise in all subjects. Growth hormone stimulates lipolysis and lipid oxidation during basal and fasting conditions and we recently investigated whether GH also regulates substrate metabolism during exercise. The design involved GH-deficient patients studied during exercise with and without GH administration as compared to untreated healthy subjects. Growth hormone predominantly stimulated the turnover of free fatty acids in the recovery phase after exercise.

CONCLUSIONS

1) the increase in GH release during exercise is associated with the concomitant increase in body temperature, 2) GH stimulates sweat secretion and heat evaporation during exercise, which seems to be of distinct physiological significance, 3) ghrelin is not involved in exercise-induced GH release, 4) the impact of GH on substrate metabolism during exercise includes increased FFA turnover.

Effects of cortisol on lipolysis and regional interstitial glycerol levels in humans

Cortisol's effects on lipid metabolism are controversial and may involve stimulation of both lipolysis and lipogenesis. This study was undertaken to define the role of physiological hypercortisolemia on systemic and regional lipolysis in humans. We investigated seven healthy young male volunteers after an overnight fast on two occasions by means of microdialysis and palmitate turnover in a placebo-controlled manner with a pancreatic pituitary clamp involving inhibition with somatostatin and substitution of growth hormone, glucagon, and insulin at basal levels. Hydrocortisone infusion increased circulating concentrations of cortisol (888 +/- 12 vs. 245 +/- 7 nmol/l). Interstitial glycerol concentrations rose in parallel in abdominal (327 +/- 35 vs. 156 +/- 30 micromol/l; P = 0.05) and femoral (178 +/- 28 vs. 91 +/- 22 micromol/l; P = 0.02) adipose tissue. Systemic [(3)H]palmitate turnover increased (165 +/- 17 vs. 92 +/- 24 micromol/min; P = 0.01). Levels of insulin, glucagon, and growth hormone were comparable. In conclusion, the present study unmistakably shows that cortisol in physiological concentrations is a potent stimulus of lipolysis and that this effect prevails equally in both femoral and abdominal adipose tissue.

Skeletal muscle glucose uptake, glycogen synthase activity and GLUT 4 content during hypoglycaemia in type 1 diabetic subjects

In healthy subjects, hypoglycaemia induces a profound 80% reduction in skeletal muscle glucose uptake and a similar suppression of glycogen synthase activity. The aim of this study was to examine the efficacy of this counterregulatory mechanism in type 1 diabetic subjects, who are especially prone to hypoglycaemic incidents. Nine type 1 diabetic male subjects were examined twice; during 120 min of hyperinsulinaemic (1.5 mU x kg(-1) x min(-1)) euglycaemia followed by (i) 240 min of graded hypoglycaemia (glucose nadir 2.8 mM) or (ii) 240 min of euglycaemia. At 345-360 min a muscle biopsy was taken and indirect calorimetry was performed at 210-240 and 320-340 min. The sensitivity of glycogen synthase to glucose-6-P was reduced by hypoglycaemia, as shown by an increase in A0.5 for glucose-6-P (at 0.07 mmol/L) from 0.21+/-0.02 to 0.28+/-0.03 mM (p=0.06). Likewise, the fractional velocity for glycogen synthase was reduced by 25%; i.e. from 20.8+/-2.0 to 15.5+/-1.4% (p<0.05). Total glucose disposal was decreased during hypoglycaemia (5.3+/-0.6 vs. 8.3+/-0.7 mg x kg(-1) x min(-1) (euglycaemia), n = 9; p<0.05), primarily due to a reduction of non-oxidative glucose disposal (2.7+/-0.3 vs. 5.1+/-0.6 mg x kg(-1) x min(-1) (euglycaemia), n=7; p<0.05). Forearm arteriovenous glucose differences were decreased by 50% in the hypoglycaemic situation (0.7+/-0.1 vs. 1.4+/-0.3 mmol/L (320-340 min)), and counterregulatory hormonal responses seemed less conspicuous than described in healthy subjects. We conclude that hypoglycaemia induces decrements of forearm glucose uptake and glycogen synthase activity in type 1 diabetic subjects. The study indicates a decreased magnitude of these responses, but this remains to be confirmed.

Pharmacological antilipolysis restores insulin sensitivity during growth hormone exposure

Stimulation of lipolysis and the induction of resistance to insulin's actions on glucose metabolism are well-recognized effects of growth hormone (GH). To evaluate whether these two features are causally linked, we studied the impact of pharmacologically induced antilipolysis in seven GH-deficient patients (mean [+/- SE] age 37 +/- 4 years). Each subject was studied under four different conditions: during continuation of GH replacement alone (A), after discontinuation of GH replacement for 2 days (B), after GH replacement and short-term coadministration of acipimox (250 mg, p.o., b.i.d., for 2 days) (C), and after administration of acipimox alone (D). At the end of each study, total and regional substrate metabolisms were assessed in the basal state and after a 3-h hyperinsulinemic/euglycemic clamp. Serum levels of free fatty acids (FFAs) were elevated with GH alone (A) and suppressed with acipimox (C and D). Basal rates of lipid oxidation were highest with GH alone (A), and suppressed by 50% with acipimox (B versus D, P < 0.01; A versus C, P < 0.05). Basal glucose oxidation rates were lowest with GH alone (A) and highest with acipimox (C and D) (P = 0.01). Insulin-stimulated rates of total glucose turnover were significantly lower with GH alone as compared with all other conditions (P = 0.004). Insulin sensitivity as assessed by the M value (rate of glucose infusion) was reduced with GH alone as compared with all other conditions (M value in mg. kg(-1). min(-1): GH alone [A], 2.55 +/- 0.64; discontinuation of GH [B], 4.01 +/- 0.70; GH plus acipimox [C], 3.96 +/- 1.34; acipimox alone [D], 4.96 +/- 0.91; P < 0.01). During pharmacological antilipolysis, GH did not significantly influence insulin sensitivity (C versus D; P = 0.19). From our results, we reached the following conclusions: 1) Our data strongly suggest that the insulin antagonistic actions of GH on glucose metabolism are causally linked to the concomitant activation of lipolysis. 2) In addition, GH may induce residual insulin resistance through non-FFA-dependent mechanisms. 3) The cellular and molecular mechanisms subserving the insulin antagonistic effects of GH remain to be elucidated.

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.

Physiological levels of glucagon do not influence lipolysis in abdominal adipose tissue as assessed by microdialysis

To determine whether glucagon stimulates lipolysis in adipose tissue, seven healthy young male volunteers were studied, with indwelling microdialysis catheters placed sc in abdominal adipose tissue. Subjects were studied three times: 1) during euglucagonemia (EG; glucagon infusion rate, 0.5 ng/kg.min); 2) during hyperglucagonemia (HG; (glucagon infusion rate, 1.5 ng/kg.min); and 3) during EG and a concomitant glucose infusion mimicking the glucose profile from the day of HG (EG+G). Somatostatin (450 microg/h) was infused to suppress hormonal secretion, and replacement doses of insulin and GH were administered. Sampling was done every 30 min for 420 min. Baseline circulating values of insulin, C-peptide, glucagon, GH, glycerol, and free fatty acids were comparable in all three conditions. During EG and EG+G, plasma glucagon was maintained at fasting level (20-40 ng/L); whereas, during HG, it increased (110-130 ng/L). Interstitial concentrations of glycerol were similar in the three conditions [30,870 +/- 5,946 (EG) vs. 31,074 +/- 7,092 (HG) vs. 29,451 +/- 6,217 (EG+G) micromol/L.120 min, P = 0.98]. Plasma glycerol (ANOVA, P = 0.5) and free fatty acids (ANOVA, P = 0.3) were comparable during the different glucagon challenges. We conclude that HG per se does not increase interstitial glycerol (and thus lipolysis) in abdominal sc adipose tissue; nor does modest hyperglycemia, during basal insulinemia and glucagonemia, influence indices of abdominal sc lipolysis.

The protein-retaining effects of growth hormone during fasting involve inhibition of muscle-protein breakdown

The metabolic response to fasting 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. The present study was designed to test the hypothesis that GH may be a principal mediator of protein conservation during fasting and to assess the underlying mechanisms. Eight normal subjects were examined on four occasions: 1) in the basal postabsorptive state (basal), 2) after 40 h of fasting (fast), 3) after 40 h of fasting with somatostatin suppression of GH (fast-GH), and 4) after 40 h of fasting with suppression of GH and exogenous GH replacement (fast+GH). The two somatostatin experiments were identical in terms of hormone replacement (except for GH), meaning that somatostatin, insulin, glucagon and GH were administered for 28 h; during the last 4 h, substrate metabolism was investigated. Compared with the GH administration protocol, IGF-I and free IGF-I decreased 35 and 70%, respectively, during fasting without GH. Urinary urea excretion and serum urea increased when participants fasted without GH (urea excretion: basal 392 +/- 44, fast 440 +/- 32, fast-GH 609 +/- 76, and fast+GH 408 +/- 36 mmol/24 h, P < 0.05; serum urea: basal 4.6 +/- 0.1, fast 6.2 +/- 0.1, fast-GH 7.0 +/- 0.2, and fast+GH 4.3 +/- 0.2 mmol/1, P < 0.01). There was a net release of phenylalanine across the forearm, and the negative phenylalanine balance was higher during fasting with GH suppression (balance: basal 9 +/- 3, fast 15 +/- 6, fast-GH 17 +/- 4, and fast+GH 11 +/- 5 nmol/min, P < 0.05). Muscle-protein breakdown was increased among participants who fasted without GH (phenylalanine rate of appearance: basal 17 +/- 4, fast 26 +/- 9, fast-GH 33 +/- 7, fast+GH 25 +/- 6 nmol/min, P < 0.05). Levels of free fatty acids and oxidation of lipid decreased during fasting without GH (P < 0.01). In summary, we find that suppression of GH during fasting leads to a 50% increase in urea-nitrogen excretion, together with an increased net release and appearance rate of phenylalanine across the forearm. These results demonstrate that GH-possibly by maintenance of circulating concentrations of free IGF-I--is a decisive component of protein conservation during fasting and provide evidence that the underlying mechanism involves a decrease in muscle protein breakdown.

Effects of oral glucose on systemic glucose metabolism during hyperinsulinemic hypoglycemia in normal man

The widespread use of oral glucose in the treatment of hypoglycemia is mainly empirically based, and little is known about the time lag and subsequent magnitude of effects following its administration. To define the systemic impact and time course of effects following oral glucose during hypoglycemia, we investigated 7 healthy young men twice. On both occasions, a 6-hour hyperinsulinemic (1.5 mU/kg/min)-hypoglycemic clamp was performed to ensure similar plasma glucose profiles during a stepwise decrease toward a nadir less than 50 mg/100 mL after 3 hours. On the first occasion, subjects ingested 40 g glucose and 4 g 3-ortho-methylglucose ([3-OMG] to trace glucose absorption) dissolved in 400 mL tap water after 3.5 hours. The second examination was identical except for the omission of 40 g oral glucose, and glucose levels were clamped at hypoglycemic concentrations similar to those recorded on the first examination. Plasma glucose curves were superimposable, and all participants reached a nadir less than 50 mg/100 mL. Similar increases in growth hormone (GH) and glucagon were observed in both situations. The glucose infusion rates (GIRs) were lower after oral glucose, with the difference starting after 5 to 10 minutes, being statistically significant after 20 minutes, and reaching a maximum of 8.5 +/- 1.6 mg/kg/min after 40 minutes. Circulating 3-OMG increased after 20 minutes. In both situations, infusion of insulin resulted in insulin levels of approximately 150 microU/mL and a suppression of C-peptide levels from 2.0 to 1.1 nmol/L (P < .01). After glucose ingestion, both serum C-peptide and glucagon-like peptide-1 (GLP-1) increased (C-peptide from 1.1 +/- 0.05 to 1.4 +/- 0.05 nmol/L and GLP-1 from 3.2 +/- 0.8 to 18.1 +/- 3.3 pmol/L), in contrast to the situation without oral glucose (P < .05). Isotopically determined glucose turnover was similar. In conclusion, our data suggest that oral glucose affects systemic glucose metabolism rapidly after 5 to 10 minutes. Quantitatively, the immediate impact is relatively small, with the gross impact observed after approximately 40 minutes. Future studies aiming to identify therapeutic oral agents with prompt effect seem warranted.

Effects of leptin on basal and FSH stimulated steroidogenesis in human granulosa luteal cells

BACKGROUND

Body weight influences fertility and studies in mice have indicated that leptin is one of the mediators of this effect. Leptin is believed to centrally stimulate the hypothalamic-pituitary axis resulting in increased gonadotropin release. Moreover, leptin is present in follicular fluid and the receptor is expressed in the human ovary. The aim of this study was to evaluate the direct effect of leptin on cultured human granulosa cell steroidogenesis.

METHODS

Granulosa cells were obtained in connection with IVF procedures, and then cultured in a serum-free medium containing androstenedione (1 microM) for a total of 4 days. After 2 days of culture the medium was changed and the hormones under study were added. We tested the effect of leptin (1, 20, 100 ng/ml) on basal, FSH (10-100 ng/ml), and FSH (10-100 ng/ml)+IGF-I (30 ng/ml) stimulated steroidogenesis.

RESULTS

Leptin (20 ng/ml and 100 ng/ml) significantly reduced basal and FSH-stimulated estradiol secretion (p<0.05). Basal and FSH (10 and 30 ng/ml) stimulated progesterone production was significantly inhibited by leptin 20 ng/ml, whereas leptin 100 ng/ml significantly reduced basal but not FSH stimulated progesterone production. Finally, steroidogenesis stimulated by IGF-I alone and in combination with FSH was not influenced by leptin.

CONCLUSION

These results suggest that leptin acts directly to inhibit basal and FSH stimulated estradiol and progesterone production in cultured human granulosa cells. This raises the possibility that high circulating leptin levels as seen in obese women may compromise fertility through peripheral mechanisms.

Continuation of growth hormone (GH) therapy in GH-deficient patients during transition from childhood to adulthood: impact on insulin sensitivity and substrate metabolism

The appropriate management of GH-deficient patients during transition from childhood to adulthood has not been reported in controlled trials, even though there is evidence to suggest that this phase is associated with specific problems in relation to GH sensitivity. An issue of particular interest is the impact of GH substitution on insulin sensitivity, which normally declines during puberty. We, therefore, evaluated insulin sensitivity (euglycemic glucose clamp) and substrate metabolism in 18 GH-deficient patients (6 females and 12 males; age, 20 +/- 1 yr; body mass index, 25 +/- 1 kg/m2) in a placebo-controlled, parallel study. Measurements were made at baseline, where all patients were on their regular GH replacement, after 12 months of either continued GH (0.018 +/- 0.001 mg/kg day) or placebo, and finally after 12 months of open phase GH therapy (0.016 mg/kg x day). Before study entry GH deficiency was reconfirmed by a stimulation test. During the double-blind phase, insulin sensitivity and fat mass tended to increase in the placebo group [deltaM-value (mg/kg x min), -0.7 +/- 1.1 (GH) vs. 1.3 +/- 0.8 (placebo), P = 0.18; deltaTBF (kg), 0.9 +/- 1.2 (GH) vs. 4.4 +/- 1.6 (placebo), P = 0.1]. Rates of lipid oxidation decreased [delta lipid oxidation (mg/kg x min), 0.02 +/- 0.14 (GH) vs. -0.32 +/- 0.13 (placebo), P < 0.05], whereas glucose oxidation increased in the placebo-treated group (P < 0.05). In the open phase, a decrease in insulin sensitivity was found in the former placebo group, although they lost body fat and increased fat-free mass [M-value (mg/kg x min), 5.1 +/- 0.7 (placebo) vs. 3.4 +/- 1.0 (open), P = 0.09]. In the group randomized to continued GH treatment almost all hormonal and metabolic parameters remained unchanged during the study. In conclusion, 1) discontinuation of GH therapy for 1 yr in adolescent patients induces fat accumulation without compromising insulin sensitivity; and 2) the beneficial effects of continued GH treatment on body composition in terms of decrease in fat mass and increase in fat-free mass does not fully balance the direct insulin antagonistic effects.

Effects of growth hormone administration on protein dynamics and substrate metabolism during 4 weeks of dietary restriction in obese women

OBJECTIVE

Treatment of obesity with very low calorie diet (VLCD) is complicated by protein loss. We evaluated the effects of coadministration of GH on protein turnover, substrate metabolism, and body composition in VLCD treated obesity.

DESIGN AND PATIENTS

Fifteen obese women underwent 4 weeks of very low calorie diet (VLCD) in parallel with GH treatment (n = 7) or placebo (n = 8).

MEASUREMENTS

Protein metabolism and total glucose turnover were isotopically assayed. Plasma concentrations of amino acids were determined by an HPLC system. Estimated rates of lipid and glucose oxidation were obtained by indirect calorimetry. Fat free mass was determined by DEXA-scan.

RESULTS

Protein breakdown decreased in both groups (tyrosine flux micromol/h): -12% +/- 3 (GH) vs. - 9% +/- 3 (placebo)). Phenylalanine degradation in relation to phenylalanine concentration decreased by 9% in the GH group, whereas an increase of 8% was observed in the placebo group (P = 0.1). Plasma concentrations of several amino acids were significantly decreased in the placebo group, while urea excretion decreased in the GH group. A decrease in FFM was found in placebo treated patients (2.14% +/- 1.9 (GH) vs. - 3.54% +/- 1.6 (placebo), P < 0.05). Rates of lipid oxidation tended to be increased by GH treatment (lipid oxidation (mg/minutes): 79.7 +/- 5.9 (GH) vs. 64.6 +/- 5.9 (placebo), P = 0.1).

CONCLUSION

During dietary restriction GH primarily seems to conserve protein by a reduced hepatic degradation of amino acids.

The kidney is an important site for in vivo phenylalanine-to-tyrosine conversion in adult humans: A metabolic role of the kidney

Synthesis of Tyr in the human body occurs by hydroxylation of the indispensable amino acid Phe. Until now, it was believed that in humans, this process was restricted to the liver, but we provide compelling evidence of production of Tyr from Phe in the kidney. To determine whether the human kidney produces Tyr, we measured Tyr balance, the Tyr appearance rate, and the Phe-to-Tyr conversion in 12 healthy human subjects by using [(15)N]Phe and [(2)H(4)]Tyr as tracers. Renal plasma flow was measured by using paraaminohippurate, and sampling from the femoral artery and renal veins was performed. The results were compared with those obtained in 12 control subjects undergoing hepatic vein catheterization and infusion of identical tracers. In all 12 subjects, there was a net uptake of Phe by the kidney (2.2 +/- 1.2 micromol/min), whereas Tyr was released (5.3 +/- 1.5 micromol/min). In contrast, there was a net uptake of both Phe (9.5 +/- 1.2 micromol/min) and Tyr (14.3 +/- 1.3 micromol/min) by the splanchnic bed. Phe conversion to Tyr occurred at a rate of 5.2 +/- 1.2 micromol/min in kidney and 3.0 +/- 0.7 micromol/min in the splanchnic bed. The kidney contributed a substantial amount of Tyr to the systemic circulation where the splanchnic bed was a net remover of Tyr. Our results demonstrate that the kidney is the major donor of Tyr to the systemic circulation by its conversion of Phe to Tyr. This observation may have important clinical implications for patients with both renal and hepatic disease, who may be at risk of Phe overloading and Tyr deficiency, and it should be considered when parenteral or enteral nutrients are administered rich in Phe and low in Tyr.

Muscle mass and function in thyrotoxic patients before and during medical treatment

OBJECTIVE

Development of muscle weakness and atrophy are well known complications of thyrotoxicosis, although little is known about its clinical course. The present longitudinal study was therefore undertaken to monitor muscle mass and strength before and during treatment of hyperthyroidism.

DESIGN AND PATIENTS

Five patients (2 male, 3 female; Age 41 +/- 6 years; BMI 22.2 +/- 1.1 kg/m2) with newly diagnosed hyperthyroidism were studied with respect to muscle area, muscle strength, body composition and substrate metabolism at baseline and after 1, 3, 6, 9 and 12 months of treatment.

MEASUREMENTS

Midthigh muscle areas were assessed by computed tomography (CT), while bioelectrical impedance analysis (BIA) was used for assessment of body composition. The isometric strength of the biceps brachialis and quadriceps muscles was assessed by means of a dynamometer and the maximal static ins- and ex-piratory mouth pressures were measured with a respiratory pressure module.

RESULTS

Prior to treatment thyrotoxic patients all displayed elevated levels of total and free T3 and T4 together with suppressed TSH. BMI, fat mass and lean body mass increased significantly during the treatment period, while energy expenditure (EE) decreased. Thigh muscle areas increased by 24% (101.5 +/- 11.5 vs. 125.3 +/- 13.1 cm2, P < 0.05) from entry to peak. Peak time was 9 +/- 0.9 months. During treatment a significant (P < 0.01) increase in muscle strength was observed; arm capacity increased by 48%, while leg capacity increased by 51%. Peak time (months) was: Right arm: 8 +/- 3, left arm: 7 +/- 2, right leg: 5 +/- 3, left leg: 9 +/- 2. Respiratory muscle strength, expressed as maximal ins- or ex-piratory mouth pressure, was significantly impaired among patients at entry. A significant increase in inspiratory and expiratory strength was found from entry to peak (P < 0.05), as inspiratory strength increased by 35% and expiratory by 19%. Inspiratory strength peaked after 7 +/- 1 months, expiratory muscle strength after 6 +/- 1 months.

CONCLUSIONS

In conclusion we find that in patients with thyrotoxicosis muscle mass is reduced by approximately 20% and muscle strength by approximately 40% and that between 5 and 9 months elapse before normal muscle mass and function are reestablished.

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.

Effects of the amylin analogue pramlintide on hepatic glucagon responses and intermediary metabolism in Type 1 diabetic subjects

AIMS

Hepatic glycogen stores have been shown to be depleted, and glucagon stimulated hepatic glucose production reduced, in Type 1 diabetic subjects. Co-administration of amylin and insulin has been shown to replete hepatic glycogen stores in diabetic animal models. The aim of the present study was to investigate the effect of amylin replacement on hepatic glucagon responsiveness in humans.

METHODS

Thirteen Type 1 diabetic men were studied in a double-blind, placebo-controlled, cross-over study after 4 weeks of subcutaneous pramlintide (30 microg q.i.d.) or placebo administration. Following an overnight fast, plasma glucose was kept above 5 mmol/l (baseline 210-240 min) with an insulin infusion rate of 0.25 mU x kg(-1) x min(-1). To control portal glucagon levels, somatostatin was infused at a rate of 200 microg/h. Basal growth hormone (2 ng x kg(-1) x min(-1)) and glucagon (0.7 ng x kg(-1) x min(-1)) were replaced. Glucagon infusion was increased to 2.1 ng x kg(-1) x min(-1) at 240-360 min (step 1) and to 4.2 ng x kg(-1) x min(-1) at 360-420 min (step 2).

RESULTS

Baseline plasma glucose (5.59+/-0.16 vs. 5.67+/-0.25 mmol/l) and endogenous glucose production (EGP) (1.32+/-0.22 vs. 1.20+/-0.13 mg x kg(-1). min(-1)) were similar and the response to glucagon was unaffected by pramlintide (glucose: step 1; 6.01+/-0.31 vs. 5.94+/-0.38 mmol/l, step 2; 6.00+/-0.37 vs. 5.96+/-0.50 mmol/l, EGP: step 1; 1.91+/-0.18 vs. 1.83+/-0.15 mg x kg(-1) x min(-1), step 2; 2.08+/-0.17 vs. 1.96+/-0.16 ng x kg(-1) x min(-1), pramlintide vs. placebo). Glucose disposal rates were similar at baseline (2.44+/-0.13 vs. 2.28+/-0.09 mg x kg(-1) x min(-1), pramlintide vs. placebo) as well as during the glucagon challenge (P-values all > 0.2).

CONCLUSIONS

Co-administration of pramlintide and insulin to Type 1 diabetic subjects for 4 weeks does not change the plasma glucose or endogenous glucose production response to a glucagon challenge, following an overnight fast. In addition, pramlintide administration does not appear to alter insulin-mediated glucose disposal.

The amylin analog pramlintide improves glycemic control and reduces postprandial glucagon concentrations in patients with type 1 diabetes mellitus

To explore further the effects of the human amylin analog pramlintide on overall glycemic control and postprandial responses of circulating glucose, glucagon, and metabolic intermediates in type 1 diabetes mellitus, 14 male type 1 diabetic patients were examined in a double-blind, placebo-controlled, crossover study. Pramlintide (30 microg four times daily) or placebo were administered for 4 weeks, after which a daytime blood profile (8:30 AM to 4:30 PM) was performed. Serum fructosamine was decreased after pramlintide (314+/-14 micromol/L) compared with placebo (350+/-14 micromol/L, P = .008). On the profile day, the mean plasma glucose (8.3+/-0.7 v 10.2+/-0.8 mmol/L, P = .04) and postprandial concentrations (incremental areas under the curve [AUCs] from 0 to 120 minutes) were significantly decreased during pramlintide administration (P < .01 for both) despite comparable circulating insulin levels (359+/-41 v 340+/-35 pmol/L). Mean blood glycerol values were reduced (0.029+/-0.004 v 0.040+/-0.004 mmol/L, P = .01) and blood alanine levels were elevated (0.274+/-0.012 v 0.246+/-0.008 mmol/L, P = .03) after pramlintide versus placebo. Blood lactate concentrations did not differ during the two regimens. During pramlintide administration, the AUC (0 to 120 minutes) for plasma glucagon after breakfast was diminished (P = .02), and a similar trend was observed following lunch. In addition, peak plasma glucagon concentrations 60 minutes after breakfast (45.8+/-7.3 v 72.4+/-8.0 ng/L, P = .005) and lunch (47.6+/-9.0 v 60.9+/-8.2 ng/L, P = .02) were both decreased following pramlintide. These data indicate that pramlintide (30 microg four times daily) is capable of improving metabolic control in type 1 diabetics. This may relate, in part, to suppression of glucagon concentrations. Longer-term studies are required to ascertain whether these findings are sustained over time.

Hepatic amino- to urea-N clearance and forearm amino-N exchange during hypoglycemic and euglycemic hyperinsulinemia in normal man

BACKGROUND/AIMS

Hypoglycemia has well-described effects on glucose metabolism, whereas the possible effects on hepatic amino nitrogen conversion in relation to muscle amino nitrogen flux are more uncertain.

METHODS

We studied six healthy young male subjects three times, i.e. for 6 h in the basal state, during a 6-h euglycemic hyperinsulinemic (1.5 mU/kg/min) clamp and during a 6-h hypoglycemic (plasma glucose below 2.8 mmol/l) clamp. Alanine (2 mmol/kg body weight/h) was infused for 3 h to describe the relationship between blood amino nitrogen concentrations and hepatic ureagenesis estimated from urea urine excretion and accumulation in body water. The slope of this relationship is denoted functional hepatic nitrogen clearance (FHNC) and quantifies substrate-independent alterations in hepatic amino nitrogen degradation. In parallel, amino nitrogen balances across muscles were estimated by the forearm flux method.

RESULTS

Euglycemia decreased circulating glucagon values (100+/-25 ng/l vs. 160+/-30 ng/l), whereas hypoglycemia doubled glucagon (350+/-45 ng/l, p<0.05). Hepatic nitrogen clearance (FHNC) decreased during hyperinsulinemic euglycemia (19.5+/-3.4 l/h vs. 30.6+/-5.7 l/h, p<0.01), whereas forearm net uptake of amino nitrogen increased (130+/-40 nmol/100 ml x min vs. control: -10+/-4 nmol/100 ml x min). During hypoglycemia there was a 3-fold increase in hepatic nitrogen clearance up to 83.0+/-16.8 l/h (p<0.01) and increased release of amino nitrogen from the forearm (-100+/-30 nmol/100 ml x min, p<0.01).

CONCLUSION

Hypoglycemia in man induces a marked increase in hepatic amino- to urea-N clearance. This catabolic response to hypoglycemia in the liver may be of primary importance for muscle amino acid release. Our data are compatible with the notion that liver and muscle together are responsible for catabolism during hypoglycemia, and that glucagon may be the primary mediator via its effect on liver metabolism.

Serum leptin concentrations during short-term administration of growth hormone and triiodothyronine in healthy adults: a randomised, double-blind placebo-controlled study

The regulation of adipose tissue mass and energy expenditure is currently subject to intensive research, which primarily relates to the discovery of leptin. Leptin is a peptide, which is the product of the obese (ob) gene expressed in adipose tissue of several species icluding humans. Leptin is supposed to serve both as an index of fat mass and as a sensor of energy balance. Administration of recombinant murine leptin in ob/ob-mice, which do not produce leptin, decreases food intake and increases thermogenesis both of which result in a reduction in body weight and adipose tissue mass. The calorigenic effect of leptin presumably acts through an increase in sympathetic outflow which in turn activates the beta3 adrenergic receptor in brown adipose tissue. The regulation and action of endogenous leptin in humans are less well understood, and clinical grade recombinant human leptin is so far not available. Serum leptin correlates logarithmically with total body fat in both normal weight and obese subjects, which suggest insensitivity to leptin in obese patients. Furthermore, more rapid excursions in serum leptin have been reported following short-term changes in caloric intake and administration of insulin. Growth hormone (GH) exerts pronounced effects on lipid metabolism and resting energy expenditure. The lipolytic actions of GH appear to involve both increased sensitivity to the beta-adrenergic pathway, and a suppression of adipose tissue lipoprotein lipase activity. The calorigenic effects of GH have been shown not only to be secondary to changes in lean body mass. Growth hormone administration furthermore increases the peripheral conversion of thyroxine to triiodothyronine, which may contribute to the overall actions of GH on fuel and energy metabolism. So far, little is known about the effects of GH and iodothyronines on serum leptin levels in humans. We therefore measured serum leptin levels and energy expenditure before and after the administration of GH and triiodothyronine, alone and in combinaion, in a randomized double-blind placebo-controlled study in healthy young male adults. The dose of triiodothyronine was selected to obtain serum levels comparable to those seen after GH administration.

Regional leptin kinetics in humans

BACKGROUND

Leptin is known to be cleared by the kidney, a tissue with substantial leptin receptor mRNA expression; however, lung, liver, and muscle tissues also express leptin receptor messenger RNA and it is not known whether these tissues also clear leptin from the circulation.

OBJECTIVE

This study was conducted to determine whether net leptin clearance takes place in the pulmonary, splanchnic, and leg tissue beds to a similar extent as in the kidney.

DESIGN

Plasma leptin concentrations were measured in blood entering and exiting the renal bed, pulmonary bed, splanchnic bed, and leg in 4 groups of subjects. Regional plasma flow was measured in 3 of the 4 groups.

RESULTS

Renal leptin uptake was substantial, whereas no net uptake of leptin by the splanchnic or pulmonary vascular beds was detected; leg tissue was a net leptin producer. Net leptin release by leg tissue, relative to leg adipose tissue mass, was comparable with that reported previously for abdominal subcutaneous adipose tissue.

CONCLUSION

These results confirm that the kidney is a significant site of leptin clearance in humans, whereas pulmonary and splanchnic beds are not.