Biomedical subjects

Dirk Hagemann

Publications and source records attributed to Dirk Hagemann.

12 recordsLinked to original sources

PubMed2006

Glucagon-like peptide 2 inhibits ghrelin secretion in humans.

INTRODUCTION: The growth hormone secretagogue receptor ligand ghrelin is known to play a pivotal role in the central nervous control of energy homeostasis. Circulating ghrelin levels are high under fasting conditions and decline after meal ingestion, but the mechanisms underlying the postprandial drop in ghrelin levels are poorly understood. In the present study we addressed, whether (1) exogenous GLP-2 administration decreases ghrelin levels and (2) what other endogenous factors are related to ghrelin secretion under fasting conditions. PATIENTS AND METHODS: Fifteen healthy male volunteers were studied with the intravenous infusion of GLP-2 (2 pmol l(-1) min(-1)) or placebo over 120 min in the fasting state. Plasma concentrations of glucose, insulin, C-peptide, glucagon, intact GLP-2 and ghrelin were determined. RESULTS: During the infusion of GLP-2, plasma concentrations of intact GLP-2 increased from 10.0+/-1.5 pmol/l to steady-state levels of 207.7+/-8.3 pmol/l (p < 0.0001). Administration of GLP-2 led to an approximately 10% reduction in ghrelin concentrations, whereas placebo administration was without an effect (p < 0.001). After cessation of the GLP-2 infusion, ghrelin levels returned to baseline values, and were no longer different from those in the placebo experiments. There was a strong inverse linear relationship between the fasting concentrations of ghrelin and the respective levels of glucose, insulin and C-peptide (r = 0.49, p < 0.01; r = 0.55, p < 0.01 and r = 0.59, p < 0.001, respectively). In contrast, there was no detectable association between fasting ghrelin levels and the ambient concentrations of glucagon or intact GLP-2. CONCLUSIONS: GLP-2 inhibits ghrelin secretion in humans at plasma levels of approximately 200 pmol/l. However, the physiological importance of this effect appears to be minor compared to the actions of insulin and glucose.

Adult↗

PubMed2005

13C-methionine breath test detects distinct hepatic mitochondrial dysfunction in HIV-infected patients with normal serum lactate.

OBJECTIVE: To assess mitochondrial respiratory chain dysfunction in different treatment groups of HIV-infected patients with normal serum lactate by measuring hepatic mitochondrial decarboxylation capacity by the C-methionine breath test (MeBT) and to correlate MeBT results with mitochondrial DNA (mtDNA) content in peripheral blood mononuclear cells (PBMCs). METHODS: Four groups were studied: HIV-negative controls (n = 10), treatment-naive patients (n = 15), antiretroviral therapy (ART)-treated patients with asymptomatic disease (n = 15), and patients with long-term treatment and clinical evidence of lipoatrophy (n = 15). After oral administration of C-methionine, CO2 exhalation was determined by infrared spectroscopy. MtDNA content in PBMCs was assessed by real-time polymerase chain reaction quantification. RESULTS: CO2 exhalation in lipoatrophic patients and therapy-naive patients was distinctly decreased when compared with that in healthy controls and asymptomatic patients (P < 0.001). The functional mitochondrial impairment in lipoatrophic patients was associated with a 47% decline in mtDNA content. MeBT results and mtDNA were significantly correlated in ART-treated patients (r = 0.77, P < 0.0001). CONCLUSIONS: MeBT is a simple noninvasive method to detect mitochondrial dysfunction in HIV-infected patients that correlates with mtDNA depletion in PBMCs of ART-treated individuals. Decreased hepatic methionine metabolism in therapy-naive patients may reflect the functional relevance of viral-mediated mitochondrial toxicity.

Adult↗

PubMed2005

Motivated executive attention--incentives and the noise-compatibility effect.

The motivational context is an important variable in experimental research. The present study investigates the effects of reward and punishment on performance in a noise-compatibility-task [Eriksen, B.A., Eriksen, C.W., 1974. Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception and Psychophysics 16 (1), 143-149]. Flanking distractors indicated a response, which was identical, undefined, or opposite to the appropriate response indicated by the central target. At the beginning of each trial a cue specified positive, negative or no reinforcement in order to elicit three different motivational states: approach, avoidance and a non-reinforced neutral state. Fifty-three subjects (aged 20-27 years) participated. Incompatibility effects on reaction times and percentage errors were analysed as a function of motivational state, as were the effects on two ERPs, the lateralised readines potential (LRP) and the N2. Error and LRP data showed effects of reinforcement only when incompatible distractors were present, which indicates that controlled processing depends on the motivational context. In contrast to previous findings, the N2 was not found to depend on response conflict.

Adult↗

PubMed2005

The relation of cortical activity and BIS/BAS on the trait level.

The behavioral activation system (BAS) and the behavioral inhibition system (BIS) have been proposed to be related to anterior asymmetry in the BIS/BAS model of anterior asymmetry. As an alternative, it may be suggested that behavioral activation comprises approach and withdrawal motivation and that the BAS is related to bilateral frontal trait activity. The aim of the present study was an empirical investigation on the relation between cortical trait activity, BIS and BAS. Data of 59 subjects on four occasions were analyzed. On each occasion, cortical activity was evaluated with resting EEG, and the BIS and BAS strength was assessed with questionnaires. Subjects with greater bilateral frontal cortical activity showed higher BAS scores. The latter result may suggest that behavioral activation comprises approach and withdrawal motivation.

Adult↗

PubMed2005

The latent state-trait structure of resting EEG asymmetry: replication and extension.

Recent research on brain asymmetry suggested that resting electroencephalographic (EEG) asymmetry represents a superimposition of a trait-like asymmetry with state-dependent fluctuations. The present study tested this hypothesis and additionally examined individual differences in state changes. A 61-channel EEG was collected from 59 participants in a resting state on three occasions of measurement. An analysis of latent state-trait models suggested that between 40% and 50% of the variance of anterior asymmetry measures was due to individual differences on a latent trait and approximately the same portion of the variance was due to occasion-specific fluctuations. A further analysis of true intraindividual change models indicated that there were large individual differences in intraindividual change over time. These data replicate previous findings and substantiate that resting asymmetry has trait and state properties.

Adult↗

PubMed2004

Individual differences in anterior EEG asymmetry: methodological problems and solutions.

In the last two decades, a substantive body of empirical work investigated the association between individual differences of electroencephalogram (EEG) alpha asymmetry and affective/motivational dispositions. Recent work indicated that several methodological problems persist in this field. The present paper reviews these problems with a focus on the reliability and validity of measures of anterior resting EEG asymmetry, which serve as a proxy for trait-like asymmetries of cortical activity. These issues include the treatment of ocular and muscle artifacts, the choice of the EEG reference, the use of current source density (CSD) measures, the state-trait nature of resting asymmetry, and the treatment of state-like fluctuations of the measures. In addition, the statistical problem of inflated type-I error due to multiple testing is also considered and different approaches to counteract this problem are suggested.

Electroencephalography↗

PubMed2004

On the selective relation of frontal cortical asymmetry and anger-out versus anger-control.

The model of anterior asymmetry and emotion proposes an asymmetric representation of approach and withdrawal systems in the left and right anterior brain regions. Within this framework, 3 different concepts have been related to anterior asymmetry: affective valence, motivational direction, and behavioral activation. The aim of the present study was an empirical investigation into the relation between anterior cortical activity and questionnaire measures related to the 3 dimensions positive versus negative affect, approach versus withdrawal motivation, and behavioral activation versus inhibition. Subjects with relative greater left than right frontal cortical activity showed higher anger-out scores and lower anger-control scores. These results support the hypothesis that motivational direction is related to frontal asymmetry (approach-left and withdrawal-right). Furthermore, subjects with greater bilateral (left and right) frontal cortical activity showed higher behavioral activation scores. This finding might suggest that behavioral activation is related to approach and withdrawal motivation.

Adult↗

PubMed2003

Gastric inhibitory polypeptide does not inhibit gastric emptying in humans.

The insulinotropic gut hormone gastric inhibitory polypeptide (GIP) has been demonstrated to inhibit gastric acid secretion and was proposed to possess "enterogastrone" activity. GIP effects on gastric emptying have not yet been studied. Fifteen healthy male volunteers (23.9 +/- 3.3 yr, body mass index 23.7 +/- 2.3 kg/m(2)) were studied with the intravenous infusion of GIP (2 pmol.kg(-1).min(-1)) or placebo, each administered to the volunteers on separate occasions from -30 to 360 min in the fasting state. At 0 min, a solid test meal (250 kcal containing [(13)C]sodium octanoate) was served. Gastric emptying was calculated from the (13)CO(2) exhalation rates in breath samples collected over 360 min. Venous blood was drawn in 30-min intervals for the determination of glucose, insulin, C-peptide, and GIP (total and intact). Statistical calculations were made by use of repeated-measures ANOVA and one-way ANOVA. During the infusion, GIP rose to steady-state concentrations of 159 +/- 15 pmol/l for total and 34 +/- 4 pmol/l for intact GIP (P < 0.0001). Meal ingestion further increased GIP concentrations in both groups, reaching peak levels of 265 +/- 20 and 82 +/- 9 pmol/l for total and 67 +/- 7 and 31 +/- 9 pmol/l for intact GIP during the administration of GIP and placebo, respectively (P < 0.0001). There were no differences in glucose, insulin, and C-peptide between the experiments with the infusion of GIP or placebo. Gastric half-emptying times were 120 +/- 9 and 120 +/- 18 min (P = 1.0, with GIP and placebo, respectively). The time pattern of gastric emptying was similar in the two groups (P = 0.98). Endogenous GIP secretion, as derived from the incremental area under the curve of plasma GIP concentrations in the placebo experiments, did not correlate to gastric half-emptying times (r(2) = 0.15, P = 0.15 for intact GIP; r(2) = 0.21, P = 0.086 for total GIP). We conclude that gastric emptying does not appear to be influenced by GIP. The secretion of GIP after meal ingestion is not suppressed by its exogenous administration. The lack of effect of GIP on gastric emptying underlines the differences between GIP and the second incretin glucagon-like peptide 1.

Adult↗

PubMed2003

Central and autonomic nervous system integration in emotion.

Emotions involve physiological responses that are regulated by the brain. The present paper reviews the empirical literature on central nervous system (CNS) and autonomic nervous system (ANS) concomitants of emotional states, with a focus on studies that simultaneously assessed CNS and ANS activity. The reviewed data support two primary conclusions: (1) numerous cortical and subcortical regions show co-occurring activity with ANS responses in emotion, and (2) there may be reversed asymmetries on cortical and subcortical levels with respect to CNS/ANS interrelations. These observations are interpreted in terms of a model of neurovisceral integration in emotion, and directions for future research are presented.

Affect↗

PubMed2003

Individual difference variables, affective differentiation, and the structures of affect.

Methodological arguments are usually invoked to explain variations in the structure of affect. Using self-rated affect from Italian samples (N=600), we show that individual difference variables related to affective differentiation can moderate the observed structure. Indices of circumplexity and congruence coefficients to the hypothesized target were used to quantify the observed structures. Results did not support the circumplex model as a universal structure. A circular structure with axes of activation and valence was approximated only among more affectively differentiated groups: students and respondents with high scores on Openness to Feelings and measures of negative emotionality. A different structure, with unipolar Positive Affect and Negative Affect factors, was observed among adults and respondents with low Openness to Feelings and negative emotionality. The observed structure of affect will depend in part on the nature of the sample studied.

Adolescent↗

PubMed2002

Dual site phospholamban phosphorylation and its physiological relevance in the heart.

Phospholamban (PLB) plays a primary role in regulating cardiac sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity. Dephosphorylated PLB suppresses the SR Ca(2+) pump activity, whereas phosphorylation of PLB leads to deinhibition. A widely accepted sequential model of dual site PLB phosphorylation states that PKA-dependent phosphorylation of Ser(16) is obligatory to phosphorylation of Thr(17) by Ca(2+)/calmodulin-dependent kinase II, and mainly accounts for beta-adrenergic receptor mediated cardiac relaxation. However, emerging evidence supports independent phosphorylation of Ser(16) and Thr(17) and their independent contributions to cardiac relaxation. Furthermore, concurrent activation of PKA and CaMKII signaling pathways exhibits a robust synergistic effect on phosphorylation of Thr(17), but not of Ser(16). Thus, the synergistic interaction may masquerade as a sequential phosphorylation of Ser(16) and Thr(17) under certain circumstances. Further studies are required to determine the exact process of dual site PLB phosphorylation and its functional roles in healthy and diseased hearts.

Animals↗

PubMed2002

Does resting electroencephalograph asymmetry reflect a trait? an application of latent state-trait theory.

Recent research on brain asymmetry and emotion treated measures of resting electroencephalograph (EEG) asymmetry as genuine trait variables, but inconsistency in reported findings and modest retest correlations of baseline asymmetry are not consistent with this practice. The present study examined the alternative hypothesis that resting EEG asymmetry represents a superimposition of a traitlike activation asymmetry with substantial state-dependent fluctuations. Resting EEG was collected from 59 participants on 4 occasions of measurement, and data were analyzed in terms of latent state-trait theory. For most scalp regions, about 60% of the variance of the asymmetry measure was due to individual differences on a temporally stable latent trait, and 40% of the variance was due to occasion-specific fluctuations, but measurement errors were negligible. Further analyses indicated that these fluctuations might be efficiently reduced by aggregation across several occasions.

Adolescent↗