Effect of physical training on mitochondrial respiration and reactive oxygen species release in skeletal muscle in patients with obesity and type 2 diabetes.

AIM/HYPOTHESIS: Studies have suggested a link between insulin resistance and mitochondrial dysfunction in skeletal muscles. Our primary aim was to investigate the effect of aerobic training on mitochondrial respiration and mitochondrial reactive oxygen species (ROS) release in skeletal muscle of obese participants with and without type 2 diabetes. METHODS: Type 2 diabetic men (n = 13) and control (n = 14) participants matched for age, BMI and physical activity completed 10 weeks of aerobic training. Pre- and post-training muscle biopsies were obtained before a euglycaemic-hyperinsulinaemic clamp and used for measurement of respiratory function and ROS release in isolated mitochondria. RESULTS: Training significantly increased insulin sensitivity, maximal oxygen consumption and muscle mitochondrial respiration with no difference between groups. When expressed in relation to a marker of mitochondrial density (intrinsic mitochondrial respiration), training resulted in increased mitochondrial ADP-stimulated respiration (with NADH-generating substrates) and decreased respiration without ADP. Intrinsic mitochondrial respiration was not different between groups despite lower insulin sensitivity in type 2 diabetic participants. Mitochondrial ROS release tended to be higher in participants with type 2 diabetes. CONCLUSIONS/INTERPRETATION: Aerobic training improves muscle respiration and intrinsic mitochondrial respiration in untrained obese participants with and without type 2 diabetes. These adaptations demonstrate an increased metabolic fitness, but do not seem to be directly related to training-induced changes in insulin sensitivity.

Oxytocin receptors: triggers for parturition and lactation?

Specific binding of tritiated oxytocin to uterine receptors of pregnant rats increases dramatically at term and is maximal during labor. In mammary glands the increase in binding is gradual, reaching a maximum during the lactation period. Concomitant changes in the sensitivity of the uterus and mammary gland to oxytocin indicate that the receptor concentration is of functional significance. Oxytocin receptors, therefore, may regulate the response of the target organs to circulating oxytocin and thereby control the onset of labor and lactation. Ovarian steroids participate in the regulation of oxytocin receptors in a manner as yet unclarified.

Oxytocin receptors and human parturition: a dual role for oxytocin in the initiation of labor.

The concentration of oxytocin receptors increased in the myometrium of pregnant women and reached maximum levels in early labor. Concentrations of oxytocin receptors were also high in the decidua and reached a maximum at parturition. In vitro, prostaglandin production by the decidua, but not by the myometrium, was increased by the addition of oxytocin. Oxytocin may therefore stimulate uterine contractions by acting both directly on the myometrium and indirectly on decidual prostaglandin production. Oxytocin receptors are probably crucial for the onset of human labor, and the stimulus for the increase in uterine prostaglandins may be oxytocin originating from the fetus.

The differential effects of pp120 (Ceacam 1) on the mitogenic action of insulin and insulin-like growth factor 1 are regulated by the nonconserved tyrosine 1316 in the insulin receptor.

pp120 (Ceacam 1) undergoes ligand-stimulated phosphorylation by the insulin receptor, but not by the insulin-like growth factor 1 receptor (IGF-1R). This differential phosphorylation is regulated by the C terminus of the beta-subunit of the insulin receptor, the least conserved domain of the two receptors. In the present studies, deletion and site-directed mutagenesis in stably transfected hepatocytes derived from insulin receptor knockout mice (IR(-/-)) revealed that Tyr(1316), which is replaced by the nonphosphorylatable phenylalanine in IGF-1R, regulated the differential phosphorylation of pp120 by the insulin receptor. Similarly, the nonconserved Tyr(1316) residue also regulated the differential effect of pp120 on IGF-1 and insulin mitogenesis, with pp120 downregulating the growth-promoting action of insulin, but not that of IGF-1. Thus, it appears that pp120 phosphorylation by the insulin receptor is required and sufficient to mediate its downregulatory effect on the mitogenic action of insulin. Furthermore, the current studies revealed that the C terminus of the beta-subunit of the insulin receptor contains elements that suppress the mitogenic action of insulin. Because IR(-/-) hepatocytes are derived from liver, an insulin-targeted tissue, our observations have finally resolved the controversy about the role of the least-conserved domain of insulin and IGF-1Rs in mediating the difference in the mitogenic action of their ligands, with IGF-1 being more mitogenic than insulin.

Medical strategies for weight loss in the overweight and obese patient.

In recent years, obesity has become a major public health problem in Western countries. The World Health Organization has defined obesity as a global epidemic of the third millennium. Treatment options for weight management include dietary intervention, physical activity, behavior modification, pharmacotherapy and surgery. However, the complexity of this chronic condition necessitates a coordinated multidisciplinary team-approach to the care of obese patients who fail weight control. The long-term duration of the treatment and the necessity of monitoring compliance and effectiveness should be considered. The objective of this article was to review the major controlled randomized clinical trials dealing with the different medical strategies for weight loss and its maintenance in overweight and obese patients.

Liver cell-specific transcriptional regulation of connexin32.

Gap junctional intercellular communication facilitates liver homeostasis and growth control in the liver. The major gap junction protein expressed by hepatocytes is connexin32 (Cx32) and non-parenchymal hepatic cells do not express this gene. We investigated the regulation of Cx32 transcription by trans-activating factors in liver cells. Transient transfection assays using deletions of the rat Cx32 promoter (nt -753 to -33) linked to the luciferase gene were performed in MH1C1 rat hepatoma cells that express endogenous Cx32 compared with WB-F344 rat liver epithelial cells that do not. The basal promoter element was located within nt -134 to -33 and was 1.4-fold more active in MH1C1 cells than WB-F344 cells whereas the entire promoter fragment (nt -754 to -33) was four-fold more active in MH1C1 cells. Specific nuclear protein-DNA complexes that bound to Sp1 consensus sites within the basal promoter were formed using nuclear extracts from both types of cells. Additional promoter sequences increased promoter activity more strongly in MH1C1 cells than WB-F344 cells and this was correlated with the binding of hepatocyte nuclear factor-1 (HNF-1) to two HNF-1 consensus sites centered at -187 and -736. Expression of HNF-1 and binding to these elements was only observed with MH1C1 cells. Other specific protein-DNA complexes were formed, however, that included YY-1- and NF-1-containing complexes, but these were not related to promoter activity. Dexamethasone increased Cx32 promoter activity and expression in MH1C1 cells, but had little effect in WB-F344 cells and did not alter protein-DNA complex formation. These data suggest that Sp1 is responsible for Cx32 promoter basal activity, that HNF-1 determines the cell-specific expression of Cx32, and that dexamethasone increases Cx32 expression through other mechanisms.

Direction of weight change in recurrent depression. Consistency across episodes.

The direction and extent of weight change during two separate episodes of severe, unipolar depression were assessed in 53 (unmedicated) outpatients in the Pittsburgh (Pa) study of maintenance therapy of depression. There was a high concordance (45 of 53 patients) of direction of self-reported weight change during the two episodes. Twenty-three patients lost weight during both episodes, 17 gained weight, and 5 showed no change. The extent of weight change between the two episodes was highly correlated. Self-reported weight change corresponded closely to measured weight changes in a large sample of the study population. Changes in appetite paralleled those in body weight. Duration of the episode and body mass index were related to the weight change, but two features of depression with which weight loss in depression has been associated (the endogenous character of the depression and it severity) were not. Direction and extent of weight change in unipolar depression appear to be stable patient characteristics across episodes and are thus potential markers for subtypes of depression. This stability of weight change is in sharp contrast to the lack of stability of the endogenous subtype in consecutive episodes of major depression.

Alterations in serotonin activity and psychiatric symptoms after recovery from bulimia nervosa.

BACKGROUND: Women with bulimia nervosa (BN) have disturbances of mood and behavior and alterations of monoamine activity when they are bingeing and purging. It is not known whether these alterations are secondary to pathological eating behavior or traits that could contribute to the pathogenesis of BN. METHODS: To avoid the confounding effects of pathological eating behavior, we studied 30 women after long-term recovery (>1 year with no bingeing or purging, normal weight, and regular menstrual cycles) from BN. Subjects were compared with 31 healthy volunteer women. We assessed psychiatric diagnoses and symptoms to determine whether there was any persistent disturbance of behavior after recovery. We measured cerebrospinal fluid (CSF) levels of the major metabolites of serotonin (5-hydroxyindoleacetic acid [5-HIAA]), dopamine (homovanillic acid [HVA]), and norepinephrine (3-methoxy-4-hydroxyphenylglycol [MHPG]) as well as hormonal and behavioral response to m-chlorophenylpiperazine (m-CPP), a serotonin-specific agent. RESULTS: Women who were recovered from BN had mild to moderate negative moods and obsessions with perfectionism and exactness and exaggerated core eating disorder symptoms compared with healthy volunteer women. Recovered BN women had increased levels of CSF 5-HIAA compared with control women (117 +/- 33 vs 73 +/- 15 pmol/mL; P< or =.001) but normal CSF HVA and MHPG concentrations. Recovered BN women had an anxious and disorganized behavioral response to m-CPP but a normal hormonal response. CONCLUSIONS: Persistent serotonergic and behavioral abnormalities after recovery raise the possibility that these psychobiological alterations might be trait-related and contribute to the pathogenesis of BN.

Solubilization and properties of oxytocin receptors from rat mammary gland.

Oxytocin (OT)-binding activity was extracted with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]2-hydroxy-1-propanesulfonate (CHAPSO) from rat involuted mammary glands with about 20% yield. The binding in detergent extracts was characterized and shown to be similar or identical to that of OT receptors on intact plasma membranes. Solubilized receptors had a high affinity site (Kd approximately 2 nM) and a lower affinity component, whereas the membrane receptor has only the high affinity site. Several synthetic OT analogs inhibited [3H]OT binding in the same rank order in both solubilized and intact membrane preparations. Both solubilized and membrane-associated receptor required Mn2+ for [3H]OT binding. The concentration of OT-binding sites in solubilized extracts of uterine myometrium from rats in late pregnancy was substantially greater in uteri from rats in labor than in that from rats 2 days before labor, as we have seen previously with receptors on intact membranes. The affinity of the solubilized myometrial receptor (Kd approximately 5 nM) was comparable to that of the membrane-associated receptor. Binding of [3H]OT to solubilized extracts of intestinal smooth muscle, which is not a target for OT, was negligible. Gel filtration analysis on columns of Sepharose 6B indicated that the solubilized [3H]OT-binding component from mammary gland was present in multiple mol wt forms, but the smallest major form eluted with an average apparent mol wt of about 40,000. These studies indicate that CHAPSO-solubilized binding sites for [3H]OT are the same as those in intact membranes and, therefore, are components of the OT receptor.

Purification and characterization of mammary myoepithelial and secretory cells from the lactating rat.

Myoepithelial and secretory cells from the mammary gland of the lactating rat have been isolated, purified, and characterized. Mammary tissue was dissociated with collagenase into basket-like networks of myoepithelial cells and single secretory cells. Because of their larger size, the myoepithelial cell networks could be separated from other mammary and blood cells by differential centrifugation. Isolated secretory cells were purified by isopycnic centrifugation in 25% bovine serum albumin. The purified myoepithelial and secretory cells were viable, as shown by the incorporation of 32P into distinct macromolecules that were separable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both myoepithelial and secretory cells retained their characteristic morphology after isolation and purification, as shown by light, transmission, and scanning electron microscopies. The isolated myoepithelial cells were unique and, thus, distinguishable from other mammary cells in a number of respects; they 1) contracted in response to the addition of oxytocin, 2) bound [3H]oxytocin specifically, 3) accounted for the content of alkaline phosphatase and [Na+ + K+]ATPase in mammary tissue, and 4) reacted specifically with antiserum prepared against purified myoepithelial cells. The purified secretory cells were unique in possessing glucose-6-phosphate dehydrogenase activity. The different cell markers not only gave independent estimates of the purity of the cell fractions, but they also may be helpful in identifying mammary cells in stages of differentiation and neoplastic transformation.

Short-term neuroendocrine effects of a large oral dose of monosodium glutamate in fasting male subjects.

Fasting male subjects received each of four treatments on different days: a large oral dose of monosodium L-glutamate (MSG; 12.7 g), the MSG vehicle, an iv injection of TRH, or a high protein meal. Blood samples were drawn via an indwelling venous line before and at 20-min intervals after each treatment for 4 h. Plasma glutamate levels rose 11-fold within 1 h of MSG ingestion, but did not change appreciably with any of the other treatments. Plasma PRL levels rose 10-fold after TRH infusion and 2-fold after the protein meal, but did not rise significantly after MSG ingestion. No effects resulted from any of the treatments on plasma LH, FSH, testosterone, GH, or cortisol concentrations. Plasma levels of TSH, T4, and T3 showed minimal changes after any of the treatments except TRH; TRH elevated plasma TSH and T3 levels. Self-rating instruments of mood and side-effects revealed no treatment-related effects on mood or physical state for up to 48 h after each treatment. Together, these results suggest that acute pharmacological elevations of plasma glutamate levels in adult men produce minimal, if any, effects on hypothalamic or pituitary function.

Appetite and food preference in depression: effects of imipramine treatment.

A nutritional survey, the Pittsburgh Appetite Test (PAT), was developed to study potential changes in appetite and food preference reported by patients during a depressive episode and during antidepressant treatment. We examined a group of 50 depressed outpatients who were drug-free for 2 weeks prior to treatment with imipramine and psychotherapy for 4 months. A significant increase in the desire for "sweets" (carbohydrate--fat-rich foods) was observed during a depressive episode, compared to periods when patients recalled feeling well (retrospective data). During imipramine treatment, no further changes were observed in preference for either "sweets" or carbohydrates when compared to the medication-free period. Alterations in patient self-reports of appetite and body weight change were noted during imipramine treatment.

Twenty-four-hour food intake in patients with anorexia nervosa and in healthy control subjects.

Ad libitum feeding over 24 hours was assessed in underweight restrictor anorectic (RAN) women (n = 8) and matched healthy control subjects (n = 9) in a relatively naturalistic laboratory setting. RAN consumed 828 +/- 210 kcal/day (20 +/- 6 kcal/kg/day); controls ingested 2274 +/- 564 kcal/day (41 +/- 13 kcal/kg/day). Expressed as macronutrient consumption, RAN, compared to healthy controls, ate less fat (13% vs 31%), more carbohydrate (73% vs 57%), and similar amounts of protein (14% vs 12%). RAN initiated fewer eating episodes than controls (4 vs 7). This study quantitatively confirms the growing body of evidence suggesting that RAN avoid fat-containing foods. Such persistent fat avoidance may significantly contribute to the difficulty RAN experience in gaining and maintaining body weight.

Effects of acute tryptophan depletion on mood in bulimia nervosa.

BACKGROUND: The present study investigated the role of serotonin in the pathophysiology of bulimia nervosa (BN) by studying the affective and appetitive responses of women ill with BN to an acute tryptophan depletion (ATD) paradigm. METHODS: Twenty-two women with BN and 16 healthy control women (CW) were studied on 2 separate days during the follicular stage of the menstrual cycle. Participants drank a control mix of essential amino acids (100 g + 4.6 g tryptophan) on one day and a tryptophan deficient (100 g - 4.6 g tryptophan) mixture (ATD) on the other in a double-blind fashion. Mood/appetite ratings and blood samples were taken at baseline and at intervals up to 420 minutes. Participants were then presented with an array of foods and were allowed to binge and vomit if they desired. RESULTS: CW and BN women had a similar and significant reduction in plasma tryptophan levels and the tryptophan: LNAA ratio after ATD. After ATD, the BN women had a significantly greater increase in peak (minus baseline) depression, mood lability, sadness and desire to binge compared to the CW. BN subjects and CW had similar peak changes in mood after the control amino acid mixture. BN subjects and CW consumed similar amounts of food after the two amino acid treatments. CONCLUSIONS: Women with BN seem more vulnerable to the mood lowering effects of ATD, suggesting they have altered modulation of central 5-HT neuronal systems.

Abnormal caloric requirements for weight maintenance in patients with anorexia and bulimia nervosa.

OBJECTIVE: This study tested previous findings that patients with eating disorders who attain normal weight have abnormal caloric requirements for maintaining weight. METHOD: Fifty-three female patients meeting the DSM-III-R criteria for anorexia nervosa and/or bulimia nervosa were divided into four subgroups, and their daily caloric intake was measured over a weight-stable period. Patients with anorexia nervosa (restricting and bulimic subtypes) were studied 4 weeks after refeeding and weight gain, when they had attained 95% of average body weight. Patients with normal-weight bulimia (previously anorexic or never previously anorexic) were studied 1-4 weeks after admission to an inpatient unit. RESULTS: After weight restoration, restricting anorexic patients required significantly more calories per day to maintain weight than did bulimic anorexic patients, as measured with corrections for weight, body surface area, and fat-free mass. Previously anorexic normal-weight bulimic patients required significantly more calories per day to maintain weight than never-anorexic normal-weight bulimic patients, as measured with correction for weight but not with the other factors used to correct caloric intake. CONCLUSIONS: To maintain stable weight after weight restoration, restricting anorexic patients require a significantly higher caloric intake than do bulimic anorexic patients. Differences in caloric needs between normal-weight bulimic patients with and without histories of anorexia may depend on the methods used to correct caloric requirements. Body surface area may be the most precise correction factor across different subgroups of eating disorder patients. Elevated caloric requirements, when coupled with reduced food intake, may particularly contribute to relapse in anorexic patients.

Acute tryptophan depletion and increased food intake and irritability in bulimia nervosa.

OBJECTIVE: Data suggest that serotonin activity is reduced in women at normal weight who have bulimia nervosa. The authors tested whether acute perturbations in serotonin activity could alter short-term eating behavior and mood. METHOD: They examined the effect of acute tryptophan depletion in 10 women with and 10 women without bulimia nervosa. RESULTS: Women with bulimia nervosa exhibited an increase in caloric intake and mood irritability after acute tryptophan depletion. CONCLUSIONS: These results indicate that women with bulimia nervosa have an exaggerated or pathological response to transient alterations in serotonin activity.

Brain tryptophan concentrations and serotonin synthesis remain responsive to food consumption after the ingestion of sequential meals.

The response of brain tryptophan concentration and serotonin synthesis to the ingestion of two sequential meals was examined in rats. Fasted rats ingested a carbohydrate meal followed 2 h later by a protein-containing meal and were examined 2 or 4 h after the first meal. Other rats ingested a protein meal first, followed by a carbohydrate meal. When the carbohydrate meal was fed first, brain tryptophan concentrations and serotonin synthesis increased at 2 h; these changes were reversed at 4 h if the second meal contained protein. When the protein meal was fed first, there were no changes in brain tryptophan or serotonin at 2 h, and a second carbohydrate meal at 2 h did not raise brain tryptophan or serotonin 2 h later. Carbohydrate ingestion 3 h after a protein meal, however, did raise brain tryptophan and serotonin 2 h later. Brain tryptophan concentrations and serotonin synthesis are thus responsive to the sequential ingestion of protein and carbohydrate meals if there is a sufficient interval between meals.

Effects of aspartame ingestion on the carbohydrate-induced rise in tryptophan hydroxylation rate in rat brain.

Effects of aspartame (aspartyl-phenylalanine-methylester) on increases in brain-tryptophan level and hydroxylation rate following a high-carbohydrate, protein-free meal were tested. After an overnight fast, rats consumed a protein-free meal containing one of several levels of aspartame. Blood and brain amino acid levels and the in vivo rate of tryptophan hydroxylation in brain were estimated at intervals thereafter. Ingestion of the meal alone increased brain-tryptophan level and hydroxylation rate. Aspartame did not modify these effects, except at doses of 530 mg/kg body weight or more. Results suggest a threshold dose of aspartame can be identified for the rat in single-meal studies above which suppression of carbohydrate-induced increases in brain-tryptophan level and serotonin synthesis occurs. This dose, however, is large and, when corrected for species differences in metabolic rate, is unlikely to be ingested by a human subject as a single load.

In vivo tyrosine hydroxylation in rat retina: effect of aspartame ingestion in rats pretreated with p-chlorophenylalanine.

Rats were pretreated with p-chlorophenylalanine (PCPA) to inhibit hepatic phenylalanine hydroxylase. Two days later, oral aspartame (APM; aspartylphenylalanine methylester) administration substantially increased serum phenylalanine (Phe) concentrations and the ratio, in serum, of Phe to the sum of its competitors for transport into brain and retina (the other large neutral amino acids). Smaller changes occurred in serum tyrosine (Tyr) concentrations and in the ratio, in serum, of Tyr to the sum of its competitors. P-chlorophenylalanine-pretreated rats showed normal increases in retinal Tyr hydroxylation rate after Tyr injection, indicating that the enzyme was functionally normal. APM (0, 500, 1000, 1500 mg/kg body wt) intubation of PCPA-pretreated rats produced a dose-related increment in retinal Phe concentrations (up to six times normal values), no changes in retinal Tyr concentration, and no changes in retinal Tyr hydroxylation rate. The results thus indicate that very large increments in retinal Phe concentrations produced by enormous doses of APM do not modify Tyr hydroxylation in vivo.

Metabolic effects of nicotine after consumption of a meal in smokers and nonsmokers.

The thermogenic effect of nicotine intake after calorie consumption was investigated to determine if nicotine influences metabolic response to a calorie challenge. Smokers and nonsmokers (10 males in each group), matched for body weight, age, and physical fitness, each participated in four sessions that involved consuming a liquid calorie load (4.77 kcal/kg body wt) or water, followed by nicotine (15 micrograms/kg body wt) or placebo via nasal spray every 20 min for 2 h. Energy expenditure was significantly increased above baseline resting metabolic rate (RMR) over the 2 h by nicotine alone (6.5% of RMR, p less than 0.01). However, the combined effect of nicotine after calorie load (20.1% of RMR, p less than 0.001) was not significantly greater than the effect of calorie load alone (18.4% of RMR, p less than 0.001). Smokers and nonsmokers did not differ in baseline RMR or in response to nicotine or calorie load. These results confirm the thermogenic effect of nicotine but suggest that the effect of nicotine after calorie consumption is less than additive.