Increased glucagon secretion during hyperthermia in a sauna

Plasma glucagon, adrenaline, noradrenaline, insulin and glucose concentrations were measured in 7 healthy young males during hyperthermia in a sauna bath: plasma glucagon levels increased from baseline values of 127.0 +/- 12.9 (SEM) pg X ml-1 to a maximum of 173.6 +/- 16.1 (SEM) pg X ml-1 at the 20th min of exposure. No change in plasma insulin and a slight increase in plasma glucose concentration were seen. Since a concomitant moderate increase in plasma catecholamine levels was also present, the adrenergic stimulus is believed to trigger glucagon release during hyperthermia. Diminished visceral blood flow, known to occur in sauna baths, may cause a decrease in the degradation of plasma glucagon and thus contribute to the elevated plasma glucagon levels.     

Increased resting energy expenditure in cystic fibrosis

To explore the hypothesis that there is an increased metabolic rate in cystic fibrosis, resting energy expenditure was measured by indirect calorimetry in 23 subjects with cystic fibrosis in a stable clinical state and in 42 normal control subjects. Resting energy expenditure was found to be elevated by an average of 0.45 MJ/24 h [95% confidence interval (CI) = 0.26-0.64, t = 4.91, P less than 0.001] (108 kcal/24 h), or 9.2% above expected values derived from the regression relating resting energy expenditure to whole body weight and sex in control subjects. When related to lean body mass, values were still elevated by 0.36 MJ/24 h (95% CI = 0.18-0.53, t = 4.15, P less than 0.001) (86 kcal/24 h), or 7.2%. The increased values were found to be independent of age, sex, or body size. There were significant correlations between increased values and poor pulmonary function as measured by the ratio of the forced expiratory volume in 1 s to forced vital capacity (r = -0.44, P less than 0.05) and subclinical infection as indicated by the blood leukocyte count (r = 0.40, P less than 0.05). However, the correlations were low, suggesting that other factors may contribute to the increased resting energy expenditure, possibly including the putative metabolic defect in cystic fibrosis.     

Helodermin stimulates glucagon secretion in the mouse

Helodermin is structurally similar to VIP (vasoactive intestinal peptide) and PHI (peptide histidine isoleucine). Since VIP and PHI both stimulate insulin and glucagon secretion, we investigated the effects of helodermin on insulin and glucagon secretion in the mouse, both in the basal state and during administration of glucose and the cholinergic agonist carbachol. After intravenous injection at dose levels between 0.5 and 8.0 nmol/kg, helodermin markedly enhanced basal plasma glucagon levels, for example at 8 nmol/kg from 139 +/- 14 to 421 +/- 86 pg/ml (p less than 0.001) after 6 minutes, without affecting basal plasma insulin levels. Together with glucose (2.8 mmol/kg), helodermin (2 and 8 nmol/kg) augmented plasma glucagon levels but had no effect on plasma insulin levels. When injected together with the cholinergic agonist carbachol (0.16 mumol/kg), helodermin markedly potentiated the increase in plasma glucagon levels (more than three-fold; p less than 0.001), again without affecting the plasma insulin levels. Combined alpha- and beta-adrenoceptor blockade (yohimbine + L-propranolol) reduced the augmenting effect of helodermin on glucagon secretion by approximately 60%. It is concluded helodermin stimulates glucagon secretion in the mouse by an effect that is partially antagonized by combined alpha- and beta-adrenoceptor antagonism.     

Testosterone secretion is severely impaired after hepatectomy in rat, dog and man

In 90%-hepatectomized rats, the plasma testosterone level (0.34 +/- 0.07 ng.ml, mean +/- SEM) is significantly lower (P less than 0.001) than in sham operated male rats (1.7 +/- 0.26 ng.ml, mean +/- SEM). In dogs, after 90% hepatectomy, the mean plasma testosterone concentration fell to 1/10 of the plasma testosterone level measured in sham operated animals either 24 or 72 h after surgery. In hepatectomized men, plasma testosterone is markedly decreased in contrast to what is observed after duodeno-pancreatectomy performed under the same conditions of anesthesia. These results suggest that 90% hepatectomy severely alters the Leydig cell function.     

New specific equation to estimate resting energy expenditure in severely obese patients

Calculating the estimated resting energy expenditure (REE) in severely obese patients is useful, but there is controversy concerning the effectiveness of available prediction equations (PE) using body weight (BW). We evaluated the efficacy of REE equations against indirect calorimetry (IC) in severely obese subjects and aimed to develop a new equation based on body composition compartments. One hundred and twenty severely obese patients had their REE measured (MREE) by IC and compared to the most commonly used PE (Harris-Benedict (HB), Ireton-Jones, Owen, and Mifflin St. Jeor). In a random sample (n = 60), a new REE equation based on fat-free mass (FFM) was developed and validated. All PE studied failed to estimate REE in severe obesity (low concordance correlation coefficient (CCC) and limits of agreement of nearly 50% of the sample ±10% of MREE). The HB equation using actual BW exhibited good results for all samples when compared to IC (2,117 ± 518 kcal/day by HB vs. 2,139 ± 423 kcal/day by MREE, P > 0.01); these results were blunted when patients were separated by gender (2,771 vs. 2,586 kcal/day, P < 0.001 in males and 1,825 vs. 1,939 kcal/day, P < 0.001 in females). A new resting energy expenditure equation prediction was developed using FFM, Horie-Waitzberg, & Gonzalez, expressed as 560.43 + (5.39 × BW) + (14.14 × FFM). The new resting energy expenditure equation prediction, which uses FFM and BW, demonstrates higher accuracy, precision, CCC, and limits of agreement than the standard PE in patients when compared to MREE (2,129 ± 45 kcal/day vs. 2,139 ± 423 kcal/day, respectively, P = 0.1).The new equation developed to estimate REE, which takes into account both FFM and BW, provides better results than currently available equations.     

Longitudinal changes in energy expenditure and body composition in obese women with normal and impaired glucose tolerance

Our primary objective was to evaluate changes in energy expenditure and body composition in women with normal glucose tolerance (NGT) and gestational diabetes mellitus (GDM). A secondary objective was to examine the relationship between maternal leptin and nutrient metabolism. Fifteen obese women, eight with NGT and seven with GDM, were evaluated before conception (P), at 12-14 wk (E), and at 34-36 wk (L). Energy expenditure and glucose and fat metabolism were measured using indirect calorimetry. Basal hepatic glucose production was measured using [6,6-2H2]glucose and insulin sensitivity by euglycemic clamp. There was a significant increase (6.6 kg, P = 0.0001) in fat mass from P to L. There was a 30% (P = 0.0001) increase in basal O2 consumption (VO2, ml/min). There were no significant changes in carbohydrate oxidation during fasting or storage from P to L. There was, however, a significant (P = 0.0001) 150% increase in basal fat oxidation (mg/min) from P to L. Under hyperinsulinemic conditions, there were similar 25% increases in VO2 (P = 0.0001) from P to L in both groups. Because of the significant increases in insulin resistance from P to L, there was a significant (P = 0.0001) decrease in carbohydrate oxidation and storage. There was a net change from lipogenesis to lipolysis, i.e., fat oxidation (30-40 mg/min, P = 0.0001) from P to L. Serum leptin concentrations had a significant positive correlation with fat oxidation at E (r = 0.76, P = 0.005) and L (r = 0.72, P = 0.009). Pregnancy in obese women is associated with significant increases in fat mass and basal metabolic rate and an increased reliance on lipids both in the basal state and during the clamp. These modifications are similar in women with NGT and GDM. The increased reliance on fat metabolism is accompanied by a concomitant decrease in carbohydrate metabolism during hyperinsulinemia. The increase in fat oxidation may be related to increased maternal serum leptin.     

Increased energy expenditure and leptin sensitivity account for low fat mass in myostatin-deficient mice

Myostatin deficiency causes dramatically increased skeletal muscle mass and reduced fat mass. Previously, myostatin-deficient mice were reported to have unexpectedly low total energy expenditure (EE) after normalizing to body mass, and thus, a metabolic cause for low fat mass was discounted. To clarify how myostatin deficiency affects the control of body fat mass and energy balance, we compared rates of oxygen consumption, body composition, and food intake in young myostatin-deficient mice relative to wild-type (WT) and heterozygous (HET) controls. We report that after adjusting for total body mass using regression analysis, young myostatin-deficient mice display significantly increased EE relative to both WT (+0.81 ± 0.28 kcal/day, P = 0.004) and HET controls (+0.92 ± 0.31 kcal/day, P = 0.005). Since food intake was not different between groups, increased EE likely accounts for the reduced body fat mass (KO: 8.8 ± 1.1% vs. WT: 14.5 ± 1.3%, P = 0.003) and circulating leptin levels (KO: 0.7 ± 0.2 ng/ml vs. WT: 1.9 ± 0.3 ng/ml, P = 0.008). Interestingly, the observed increase in adjusted EE in myostatin-deficient mice occurred despite dramatically reduced ambulatory activity levels (-50% vs. WT, P < 0.05). The absence of hyperphagia together with increased EE in myostatin-deficient mice suggests that increased leptin sensitivity may contribute to their lean phenotype. Indeed, leptin-induced anorexia (KO: -17 ± 1.2% vs. WT: -5 ± 0.3%) and weight loss (KO: -2.2 ± 0.2 g vs. WT: -1.6 ± 0.1, P < 0.05) were increased in myostatin-deficient mice compared with WT controls. We conclude that increased EE, together with increased leptin sensitivity, contributes to low fat mass in mice lacking myostatin.     

Alpha-adrenoceptor blockade by phentolamine inhibits beta-adrenergically and cholinergically induced glucagon secretion in the mouse

Glucagon secretion is known to be stimulated by activation of the alpha-adrenoceptors. In this study, we investigated whether alpha-adrenoceptor blockade by phentolamine affects basal and stimulated glucagon secretion in the mouse. Phentolamine was injected intraperitoneally to mice at dose levels varying from 2.6 to 260 mumol/kg. It was found that, while decreasing plasma glucose levels, phentolamine did not over this wide dose range affect basal glucagon concentrations indicating an inhibition of the hypoglycaemia-induced glucagon secretion. Further, phentolamine clearly inhibited the glucagon secretory response to beta-adrenergic or cholinergic stimulation. Thus, phentolamine (2.6 mumol/kg), impaired the glucagon secretory response to the beta 2-adrenoceptor agonist terbutaline by 51% (P less than 0.01), and to the cholinergic agonist carbachol by 44% (P less than 0.02). We conclude that alpha-adrenoceptor blockade by phentolamine inhibits the glucagon secretion following hypoglycaemia or stimulation by beta-adrenergic and cholinergic agonists. Thus, the alpha-adrenoceptors seem to be of great importance for glucagon secretion in the mouse.     

Impaired insulin secretion in a mouse model of ataxia telangiectasia

Ataxia telangiectasia (A-T) is an autosomal recessive disease caused by mutations in the A-T mutated (ATM) gene. The gene encodes a serine/threonine kinase with important roles in the cellular response to DNA damage, including the activation of cell cycle checkpoints and induction of apoptosis. Although these functions might explain the cancer predisposition of A-T patients, the molecular mechanisms leading to glucose intolerance and diabetes mellitus (DM) are unknown. We have investigated the pathogenesis of DM in a mouse model of A-T. Here we show that young Atm-deficient mice show normal fasting glucose levels and normal insulin sensitivity. However, oral glucose tolerance testing revealed delayed insulin secretion and resulting transient hyperglycemia. Aged Atm-/- mice show a pronounced increase in blood glucose levels and a decrease in insulin and C-peptide levels. Our findings support a role for ATM in metabolic function and point toward impaired insulin secretion as the primary cause of DM in A-T.     

Increased serum 2-oxoglutarate associated with high myocardial energy expenditure and poor prognosis in chronic heart failure patients

Myocardial energy expenditure (MEE) and 2-oxoglutarate are elevated in chronic heart failure (CHF) patients compared with healthy controls. To explore whether 2-oxoglutarate could reflect the levels of MEE and predict the prognosis of CHF, 219 CHF patients and 66 healthy controls were enrolled. 2-Oxoglutarate was assayed with Liquid Chromatography–Mass Spectrometry/Mass Spectrometry (LC/MS/MS). CHF patients were divided into 4 groups according to interquartile range of MEE and followed for death or recurrent hospital admission due to CHF for the mean follow-up time 6.64 ± 0.16 months. 2-Oxoglutarate was increased in CHF patients compared with controls (P < 0.01) and correlated with estimated glomerular filtration rate (r = 0.142, P = 0.036), age (r = − 0.269, P < 0.01) and MEE levels (r = 0.307, P < 0.01) in a multiple linear correlation analysis in CHF patients. Furthermore, 2-oxoglutarate (OR = 3.470, 95% CI = 1.557 to 7.730, P = 0.002), N-terminal pro-B-type natriuretic peptide (OR = 4.013, 95% CI = 1.553 to 10.365, P = 0.004), age (OR = 1.611, 95% CI = 1.136 to 2.283, P = 0.007) and left ventricular ejection fraction (OR = 7.272, 95% CI = 3.110 to 17.000, P < 0.001) were independently associated with MEE on multiple logistic regression analysis. Kaplan–Meier event curves showed that high 2-oxoglutarate levels were associated with adverse outcomes (Log Rank, Chi² = 4.026, P = 0.045). This study showed that serum 2-oxoglutarate is associated with MEE levels, which can be used as potential biomarkers for MEE, and it can reflect the clinical severity and short-term outcome of CHF.     

Dopamine release is impaired in a mouse model of DYT1 dystonia

Early onset torsion dystonia, the most common form of hereditary primary dystonia, is caused by a mutation in the TOR1A gene, which codes for the protein torsinA. This form of dystonia is referred to as DYT1. We have used a transgenic mouse model of DYT1 dystonia [human mutant-type (hMT)1 mice] to examine the effect of the mutant human torsinA protein on striatal dopaminergic function. Analysis of striatal tissue dopamine (DA) and metabolites using HPLC revealed no difference between hMT1 mice and their non-transgenic littermates. Pre-synaptic DA transporters were studied using in vitro autoradiography with [(3)H]mazindol, a ligand for the membrane DA transporter, and [(3)H]dihydrotetrabenazine, a ligand for the vesicular monoamine transporter. No difference in the density of striatal DA transporter or vesicular monoamine transporter binding sites was observed. Post-synaptic receptors were studied using [(3)H]SCH-23390, a ligand for D(1) class receptors, [(3)H]YM-09151-2 and a ligand for D(2) class receptors. There were again no differences in the density of striatal binding sites for these ligands. Using in vivo microdialysis in awake animals, we studied basal as well as amphetamine-stimulated striatal extracellular DA levels. Basal extracellular DA levels were similar, but the response to amphetamine was markedly attenuated in the hMT1 mice compared with their non-transgenic littermates (253 +/- 71% vs. 561 +/- 132%, p < 0.05, two-way anova). These observations suggest that the mutation in the torsinA protein responsible for DYT1 dystonia may interfere with transport or release of DA, but does not alter pre-synaptic transporters or post-synaptic DA receptors. The defect in DA release as observed may contribute to the abnormalities in motor learning as previously documented in this transgenic mouse model, and may contribute to the clinical symptoms of the human disorder.     

Hypersecretion of glucagon and gastrin in severely burnt patients.

Hyperglucagonaemia and hypergastrinaemia were observed in some severely burnt patients during their illness. Hyperglucagonaemia seemed to be related to the severity of illness rather than to the burn itself, and the close correlation of glucagon concentrations with glucose and urea and its inverse correlation with bicarbonate concentrations suggest that glucagon might contribute to the hypercatabolic state. One patient developed high levels of gastrin and massive bleeding from a stress ulcer of the duodenum. Possibly gastrin hypersecretion may have a role in the pathogenesis of Curling''s ulcer.     

Adrenalectomy-induced alterations in glucagon binding and lipolysis in isolated rat adipocytes.

Adipocytes from adrenalectomized rats nearly lost their lipolytic response to glucagon concomitant with a 90% decrease in the number of glucagon receptors per cell. Quantitative analysis of the relation between amount of cell-bound glucagon and hormone-stimulated lipolysis revealed that the ability of the remaining 10% of glucagon receptors to induce lipolysis was not impaired. Binding of the beta-adrenergic antagonist [3H]dihydroalprenolol and maximal lipolysis induced by (-)-isoproterenol, (Bu)2cAMP, 3-isobutyl-1-methylxanthine, and adenosine deaminase were reduced only 10 to 20% after adrenalectomy. Furthermore, glucagon-stimulated cAMP production was greatly decreased in adrenalectomized animals, but isoproterenol-stimulated cAMP production was not. Hydrocortisone replacement in adrenalectomized rats only partially prevented the loss of glucagon receptors and glucagon effects on both cAMP production and lipolysis. These findings suggest that lipolytic cascade distal to hormone receptors was not greatly impaired in adipocytes after adrenalectomy and that the unresponsiveness of these cells to glucagon was mostly due to a marked reduction in the number of glucagon receptors.     

Immortalized mouse mammary fibroblasts lacking dioxin receptor have impaired tumorigenicity in a subcutaneous mouse xenograft model

Although the dioxin receptor, the aryl hydrocarbon receptor (AhR), is considered a major regulator of xenobiotic-induced carcinogenesis, its role in tumor formation in the absence of xenobiotics is still largely unknown. Trying to address this question, we have produced immortalized cell lines from wild-type (T-FGM-AhR+/+) and mutant (T-FGM-AhR-/-) mouse mammary fibroblasts by stable co-transfection with the simian virus 40 (SV-40) large T antigen and proto-oncogenic c-H-Ras. Both cell lines had a myofibroblast phenotype and similar proliferation, doubling time, SV-40 and c-H-Ras expression and activity, and cell cycle distribution. AhR+/+ and AhR-/- cells were also equally able to support growth factor- and anchorage-independent proliferation. However, the ability of T-FGM-AhR-/- to induce subcutaneous tumors (leimyosarcomas) in NOD/SCID-immunodeficient mice was close to 4-fold lower than T-FGM-AhR+/+. In culture, T-FGM-AhR-/- had diminished migration in collagen-I and decreased lamellipodia formation. VEGFR-1/Flt-1, a VEGF receptor that regulates cell migration and blood vessel formation, was also down-regulated in AhR-/- cells. Signaling through the ERK-FAK-PKB/AKT-Rac-1 pathway, which contributes to cell motility and invasion, was also significantly inhibited in T-FGM-AhR-/-. Thus, the lower tumorigenic potential of T-FGM-AhR-/- could result from a compromised adaptability of these cells to the in vivo microenvironment, possibly because of an impaired ability to migrate and to respond to angiogenesis.     

Hypertension and impaired vascular function in a female mouse model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease that predominantly affects women during their reproductive years. Although women with SLE have hypertension, the underlying mechanisms for this have not been examined. Despite the fact that inflammation is associated with altered endothelial and vascular function, the role of altered vascular function in the development of hypertension during SLE is unclear. In the present study, we tested whether a mouse model of SLE (NZBWF1) develops hypertension and examined whether increased blood pressure was associated with impaired endothelial-dependent relaxation. Female NZBWF1 mice were studied at 8, 20, and 36 wk of age. By 36 wk, urinary albumin and antinuclear antibodies were increased in SLE compared with control mice. Mean arterial pressure, measured by radiotelemetry, was significantly increased in SLE mice (124 +/- 4 mmHg, n = 10) compared with control NZW/LacJ mice (111 +/- 3 mmHg, n = 7) at 36 wk. Isolated carotid arteries from NZBWF1 mice, precontracted with U-46619 for assessment of endothelial-dependent relaxation, demonstrated a progressively impaired relaxation to ACh with age, although endothelial nitric oxide synthase mRNA expression was not different. Maximal tension generated by 5-hydroxytryptamine was increased in carotid arteries from NZBWF1 mice compared with controls at 8, 20, and 36 wk of age, suggesting a role for altered vascular function early on in the progression of SLE. Taken together, our data support a role for altered endothelial function as a contributing factor to the development of hypertension during SLE.     

Gelucire44/14 improves fat absorption in rats with impaired lipolysis

Clinically relevant fat malabsorption is usually due to impaired intestinal fat digestion (lipolysis) and/or to impaired solubilization of the lipolytic metabolites. We hypothesized that Gelucire^®44/14 – a semi-solid self-micro-emulsifying excipient – could increase fat absorption. In relevant rat models for impaired lipolysis or for impaired solubilization we tested whether administration of Gelucire^®44/14 enhanced fat absorption. Rats with impaired lipolysis (lipase inhibitor Orlistat diet) and rats with reduced solubilization (permanent bile diversion) underwent a 72 h fat balance test to assess fat absorption. The absorption kinetics of a stable isotope-labeled fatty acid was assessed in rats with reduced solubilization, in the presence or absence of Gelucire^®44/14. Gelucire^®44/14 improved fat absorption in rats with impaired lipolysis (from 70% to 82%, p < 0.001). In rats with reduced solubilization, Gelucire^®44/14 did not increase fat absorption nor did it reconstitute the absorption kinetics of ¹³C-labeled palmitate, compared with control rats administered buffer without Gelucire^®44/14. The present data show that Gelucire^®44/14 might enhance fat absorption under conditions of impaired lipolysis, but not during impaired solubilization. We speculate that, due to its self-micro-emulsification properties, Gelucire^®44/14 stabilizes and improves residual lipolytic enzyme activity in vivo, which could be of therapeutic value in clinical conditions of fat malabsorption due to impaired lipolysis.