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Biomedical subjects

A Peters

Publications and source records attributed to A Peters.

At least 73 records · Page 4Linked to original sources
PubMed2000

Testosterone treatment is immunosuppressive in superb fairy-wrens, yet free-living males with high testosterone are more immunocompetent.

The immunocompetence handicap hypothesis proposes that the immunosuppressive effect of testosterone enforces honesty of sexual signalling via a physiological trade-off between signal intensity and immunocompetence. However, evidence that testosterone is immunosuppressive is scant, particularly in birds. I studied the correlation between immunocompetence and testosterone in superb fairy-wrens (Malurus cyaneus), a species with intense intersexual selection. Males are seasonally dichromatic and testosterone increases during the moult from dull brown eclipse plumage into bright nuptial plumage. I determined the primary antibody response to immunization with sheep red blood cells (SRBCs) in (i) control and testosterone-implanted males in captivity, and (ii) a cross-section of free-living males with basal and elevated testosterone (in eclipse plumage, moulting and in nuptial plumage). Experimental treatment with testosterone decreased the likelihood of an antibody response to SRBCs in captive birds. In contrast, free-living males which had acquired the nuptial plumage and had naturally elevated testosterone were more likely to respond to SRBCs than males in eclipse plumage with basal testosterone levels. The association between higher immunocompetence and higher immunosuppressive testosterone could arise if both are positively correlated with male phenotypic quality In addition, the association could result if males compensate for potential immunosuppression by enhancing their humoral immune responses, particularly since high testosterone is linked to other demanding activities such as moulting and courtship displays.

Animals↗
PubMed2000

Effects of aging on myelinated nerve fibers in monkey primary visual cortex.

In monkeys, myelin sheaths of the axons in the vertical bundles of nerve fibers passing through the deeper layers of primary visual cortex show age-related alterations in their structure. These alterations have been examined by comparing the myelin sheaths in young monkeys, 5-10 years old, with those in old monkeys, between 25 and 33 years of age. The age-related alterations are of four basic types. In some sheaths, there is local splitting of the major dense line to accommodate dense cytoplasm derived from the oligodendrocytes. Other sheaths balloon out, and in these locations, the intraperiod line in that part of the sheath opens up to surround a fluid-filled space. Other alterations are the formation of redundant myelin so that a sheath is too large for the enclosed axon and the formation of double sheaths in which one layer of compact myelin is surrounded by another one. These alterations in myelin increase in frequency with the ages of the monkeys, and there is a significant correlation between the breakdown of the myelin and the impairments in cognition exhibited by individual monkeys. This correlation also holds even when the old monkeys, 25 to 33 years of age, are considered as a group. It is suggested that the correlation between the breakdown of myelin in the old monkeys and their impairments in cognition has not to do specifically with visual function but to the role of myelin in axonal conduction throughout the brain. The breakdown of myelin could impair cognition by leading to a change in the conduction rates along axons, resulting in a loss of synchrony in cortical neuronal circuits.

Aging↗
PubMed2000

[Daily mortality and air pollution in the northern Czech Republic].

BACKGROUND: Several studies have demonstrated that the increase of air pollutants is related to the increase of the diurnal mortality. The aim of the work was to find correlation among the diurnal mortality and changes in the concentration of SO2, total suspended particles (TSP), and dust particles with aerodynamic diameter smaller than 10 microns (PM10) and smaller than 2.5 microns (PM2.5) in the external air of the North Bohemian brown-coal basin. METHODS AND RESULTS: All that died in 1982-1994 in coal-basin districts of the North Bohemia region were included into the data set. Method of long time series and the model of logistic regression were applied with correction to long-term trends, seasons, respiratory diseases and meteorological condition. Investigating the described relation regardless to age and sex, the increase of TSP by 100 micrograms/m3 was connected with significant increase of the total diurnal mortality by 3.4%. Significant differences between males and females were found. Meanwhile the mortality of males younger than 65 years increased, that of equally old females decreased. Contrary to it, in population of females older than 65 mortality increased and that males significantly decreased. CONCLUSION: Monitoring of the diurnal mortality and air pollution in relation to the sex reveals important for the identification of sensitive and vulnerable population subgroups. Illogic and difficult to explain is the decrease of mortality in conditions of increased air pollutants. Authors recommend repeating the analysis also in different epidemiological studies in order to distinguish whether the presented results are accidental or have a more general significance.

Adolescent↗
PubMed2000

[A rare cause of muscle pain and elevated creatine kinase level--the paroxysmal non-hereditary angioedema].

Systemic capillary leak syndrome is a rare idiopathic disorder characterized by recurrent episodes of hypotension and hemoconcentration due to sudden transient extravasation of up to 70% of plasma. Less than 40 cases have appeared in the literature. Mortality rates 5 years after diagnosis have been reported to be up to 75%. Clinical findings are generalized edema and intravasal fluid deficiency. Laboratory features include hypoalbuminemia and extreme hemoconcentration. A common finding is a monoclonal gammopathy. Rare manifestation of this syndrome is rhabdomyolysis due to increased compartment pressure and ischemic myonecrosis. Early diagnosis and exclusion of other clinical disorders like rheumatic myopathies and myositis are critical concerning prognosis and therapy. We describe a 46-year-old woman with rhabdomyolysis and systemic capillary leak syndrome whose condition is stable for a total of 30 months under a prophylactic regimen with oral terbutaline plus theophylline. A brief survey of the literature is given.

Adrenergic beta-Agonists↗
PubMed2000

Enhanced lymphocyte proliferation in patients with adrenoleukodystrophy treated with erucic acid (22:1)-rich triglycerides.

Lymphocytopenia and depression of natural killer cells have been observed in patients with adrenoleukodystrophy (ALD) treated with glycerol trioleate and glycerol trierucate ('Lorenzo's oil'). To investigate possible alterations of cellular immunoreactivity, we measured lymphocyte proliferation in response to mitogens (PHA, Con A, PWM, OKT3) in 27 patients on treatment and in 14 patients without treatment. In patients on treatment, lymphocyte proliferation in response to the mitogens PHA and Con A was significantly higher than in patients without treatment. Lymphocyte proliferation in patients without treatment was comparable to that of normal control lymphocytes. Additionally, we found increased concentrations of erucic acid, C22:1, in lymphocytes from patients with treatment. The enhanced proliferation of lymphocytes in response to mitogens is an indication of increased reactivity of cellular immunity to unspecific immunological stimuli. Long-term side-effects on cellular immunoreactivity have to be considered in ALD patients treated with Lorenzo's oil.

Adolescent↗
PubMed2000

Preserved hypothermic response to hypoglycemia after antecedent hypoglycemia.

Hypoglycemia is known to decrease the body temperature and to stimulate counterregulatory hormone secretion. Although it is well established that antecedent hypoglycemia reduces the hormonal response to subsequent hypoglycemia, the effects of antecedent hypoglycemia on the subsequent hypothermic response are obscure. In the present study, body temperature was measured orally during a total of 90 glucose clamp experiments in 45 healthy men. The clamps lasted 6 hours and were performed under 6 different experimental conditions: a euglycemic clamp with a low rate of insulin infusion, 1.5 mU/kg x min (low insulin-eu), a euglycemic clamp with a high rate of insulin infusion, 15.0 mU/kg x min (high insulin-eu), a hypoglycemic clamp with a low rate of insulin infusion, 1.5 mU/kg x min (low insulin-hypo), a hypoglycemic clamp with a high rate of insulin infusion, 15.0 mU/kg x min (high insulin-hypo), and 2 hypoglycemic clamps following an antecedent 2.5-hour hypoglycemia (56 mg/dL) induced by either a low (1.5 mU/kg x min, low insulin-ante-hypo) or a high (15.0 mU/kg x min, high insulin-ante-hypo) rate of insulin infusion. Plasma glucose was maintained normal during the euglycemic clamps and was decreased stepwise during the hypoglycemic clamps (76 --> 66 --> 56 --> 46 mg/dL). During the hypoglycemic clamps, body temperature decreased by 0.26 degrees +/- 0.09 degrees C in low insulin-hypo, 0.28 degrees +/- 0.09 degrees C in high insulin-hypo, 0.29 degrees +/- 0.09 degrees C in low insulin-ante-hypo, and 0.41 + 0.11 degrees C in high insulin-ante-hypo (all P < .01). There were no differences in the hypothermic response to hypoglycemia among the different hypoglycemic conditions (P > .1 for all comparisons). In contrast, body temperature remained unchanged during the euglycemic clamps, so the changes in body temperature differed significantly during the euglycemic clamps versus the hypoglycemic clamps (P < .05 for all comparisons). The data show that the body temperature decreases during hypoglycemia and this decrease is influenced neither by antecedent hypoglycemia nor by circulating insulin levels.

Adult↗
PubMed2000

Comparison of the inhibitory effect of insulin and hypoglycemia on insulin secretion in humans.

Although both insulin and hypoglycemia are known to inhibit endogenous insulin secretion, their potency to suppress insulin secretion has not been directly compared thus far. The serum C-peptide concentration was measured during 28 euglycemic and 28 stepwise hypoglycemic (4.1,3.6, 3.1, and 2.6 mmol/L) clamp experiments using either a low-rate (1.5 mU x min(-1) x kg(-1)) or high-rate (15.0 mU x mU(-1) x kg(-1)) insulin infusion. The experiments lasted 6 hours and were performed in 28 lean healthy men. During both the euglycemic and hypoglycemic clamps, serum insulin was approximately 40-fold higher during the high-rates versus low-rate insulin infusion (euglycemia, 24,029 +/- 1,595 v 543 +/- 34 pmol/L; hypoglycemia, 23,624 +/- 1,587 v 622 +/- 32 pmol/L). Under euglycemic conditions, serum C-peptide decreased from 0.54 +/- 0.04 to 0.41 +/- 0.05 nmol/L during the low-rate insulin infusion (P < .05) and from 0.55 +/- 0.07 to 0.27 +/- 0.09 nmol/L during the high-rate insulin infusion (P < .001). Under hypoglycemic conditions, serum C-peptide decreased from 0.50 +/- 0.03 to 0.02 +/- 0.01 nmol/L during the low-rate insulin infusion (P< .001) and from 0.46 +/- 0.07 to 0.02 +/- 0.01 nmol/L during the high-rate insulin infusion (P< .001). In the euglycemic clamp condition, the high-rate insulin infusion reduced the C-peptide concentration more than the low-rate insulin infusion (P < .05). Independent of the rate of insulin infusion, the decrease in C-peptide was distinctly more pronounced during hypoglycemia versus euglycemia (P < .001). These data indicate that insulin inhibits insulin/C-peptide secretion in a dose-dependent manner. Hypoglycemia is a much stronger inhibitor of insulin secretion than insulin itself.

Adult↗
PubMed2000

[Causes and correction of abnormal gait patterns due to prosthesis in above-knee amputees].

Abnormal gait patterns cause an increase in the energy cost of walking in above-knee amputees. Disturbances of the walking pattern are often caused both by the amputated patient himself and by incorrect prosthetic fitting. The early detection and correction of causative factors is of great importance for successful rehabilitation of these amputees. During the follow-up examinations the prosthesis must be inspected for a correct fitting and individually appropriate knee stabilizing components. Prior to any corrective measures it must be excluded that the artificial limb has been put on incorrectly by the amputee himself.

Amputees↗
PubMed2000

Air pollution and incidence of cardiac arrhythmia.

Air pollution episodes have been associated with increased cardiovascular hospital admissions and mortality in time-series studies. We tested the hypothesis that patients with implanted cardioverter defibrillators experience potentially life-threatening arrhythmias after such air pollution episodes. We compared defibrillator discharge interventions among 100 patients with such devices in eastern Massachusetts, according to variations in concentrations of particulate matter, black carbon, and gaseous air pollutants that were measured daily for the years 1995 through 1997. A 26-ppb increase in nitrogen dioxide was associated with increased defibrillator interventions 2 days later (odds ratio = 1.8; 95% confidence interval = 1.1-2.9). Patients with ten or more interventions experienced increased arrhythmias in association with nitrogen dioxide, carbon monoxide, black carbon, and fine particle mass. These results suggest that elevated levels air pollutants are associated with potentially life-threatening arrhythmia leading to therapeutic interventions by an implanted cardioverter defibrillator.

Adult↗
PubMed2000

Glucose metabolism rather than insulin is a main determinant of leptin secretion in humans.

Circulating plasma insulin and glucose levels are thought to be major regulators of leptin secretion. There is evidence from in vitro and animal experiments that glucose metabolism rather than insulin alone is a main determinant of leptin expression. Here, we tested the hypothesis that in humans also leptin secretion is primarily regulated by glucose uptake and only secondarily by plasma insulin and glucose. In 30 lean and healthy men we induced 4 experimental conditions by using the blood glucose clamp technique. A total of 60 hypoglycemic and euglycemic clamps, lasting 6 h each, were performed. During these clamps insulin was infused at either high (15.0 mU/min x kg) or low (1.5 mU/min x kg) rates, resulting in low-insulin-hypo, high-insulin-hypo, low-insulin-eu, and high-insulin-eu conditions. Serum leptin increased from 0-360 min by 20.5 +/- 4.1% in the low-insulin-hypo, 33.6 +/- 7.6% in the high-insulin-hypo, 39.6 +/- 6.0% in the low-insulin-eu, and 60.4 +/- 7.6% in the high-insulin-eu condition. Multiple regression analysis revealed a significant effect of circulating insulin (low vs. high insulin; P = 0.001) and blood glucose (hypoglycemia vs. euglycemia; P = 0.001) on the rise of serum leptin. However, when the total amount of dextrose infused during the clamp (grams of dextrose per kg BW) was included into the regression model, this variable was significantly related to the changes in serum leptin (P = 0.001), whereas circulating insulin and glucose had no additional effect. These findings in humans support previous in vitro data that leptin secretion is mainly related to glucose metabolism.

Adult↗
PubMed2000

Analysis of thyrotropin-releasing hormone-signaling components in pituitary adenomas of patients with acromegaly.

In many acromegalic patients the paradoxical release of GH in response to TRH has been well documented, but the mechanisms underlying this phenomenon are not understood. It has been suggested that aberrant GH secretion may result from TRH endogenously synthesized by the adenoma. In 32 adenomas from acromegalic patients, TRH-like immunoreactivity (TRH-LI) was measured using 2 well characterized antisera. TRH-LI was not detectable in 10 samples, and in 19 samples, TRH-LI was measured only by the less specific antibody. With the TRH-specific antibody, TRH-LI was identified only in 3 samples, 2 of which contained exceedingly high concentrations (40 and 96 pg/mg tissue). In the latter 2 samples, prepro-TRH messenger ribonucleic acid was identified by Northern blot analysis, but not in the control tissue sample of a patient without pituitary disease and also not in the other adenomas analyzed by this technique. Transcripts of the TRH receptor were almost undetectable in all adenomas analyzed. For the TRH-degrading ectoenzyme, a potential regulator of TRH signals at adenohypophyseal target sites, transcripts were significantly expressed only in the TRH-producing adenomas. We conclude that the TRH-signaling elements examined are, in general, not directly involved in the mechanisms causing paradoxical GH secretion in acromegalic patients.

Acromegaly↗
PubMed2000

Associations between mortality and air pollution in central Europe.

Increased mortality has been observed in association with elevated concentrations of air pollutants in European cities and in the United States. We reassessed the effects of particulate matter in Central Europe. Mortality and air pollution data were obtained for a highly polluted region of the Czech Republic and a rural region in Germany. Poisson regression analyses were conducted considering trend, season, meteorology, and influenza epidemics as confounders in both a parametric and a nonparametric approach. The Czech Republic had a 3.8% increase in mortality [95% confidence interval (CI), 0.8-6.9%] in association with 100 microg/m(3) total suspended particles (TSP) (lagged 2 days) for the time period 1982-1994. During the last 2 years of study, 68% of the TSP consisted of particulate matter [less than/equal to] 10 microm in aerodynamic diameter (PM(10)). An increase of 100 microg/m(3) TSP (lagged 1 day) was associated with a 9.5% increase in mortality (CI, 1.2-18.5%) and 100 microg/m(3) PM(10 )(lagged 1 day) showed a 9.8% increase in mortality (CI, 0.7-19.7%). We found no evidence for an association between mortality and particulate matter in the rural area in Germany at the Czech border. Data from the coal basin in the Czech Republic suggested an increase in mortality associated with the concentration of particulate matter in a highly polluted setting in Central Europe that is consistent with the associations observed in other western European cities and in the United States.

Adolescent↗
PubMed2000

Adaptation of cognitive function to hypoglycemia in healthy men.

OBJECTIVE: Antecedent hypoglycemia reduces hypoglycemic counterregulation and symptoms, thereby provoking the hypoglycemia unawareness syndrome. The effects of antecedent hypoglycemia on hypoglycemia-induced cognitive dysfunction are less well established. RESEARCH DESIGN AND METHODS: To determine whether antecedent hypoglycemia also reduces hypoglycemic cognitive dysfunction, we performed stepwise hypoglycemic clamp experiments (4.1, 3.6, 3.1, and 2.6 mmol/l) during a 6-h period in 30 young healthy men. A total of 15 subjects additionally received a 2.5-h antecedent hypoglycemic clamp (3.1 mmol/l) on the preceding day (prior-hypo group), whereas the other 15 subjects did not (control group). Cognitive function was assessed by auditory-evoked brain potentials (AEBPs) and reaction time during a vigilance task and short-term memory recall. Tests were performed during the stepwise hypoglycemic clamp at baseline and at each hypoglycemic plateau. RESULTS: In both groups, performance on all measures of cognitive function deteriorated during stepwise hypoglycemia (all P < 0.01). However, after antecedent hypoglycemia, the hypoglycemia-induced decrease in the amplitude of the P3 of the AEBP was distinctly reduced compared with the control condition (P < 0.05). Also, short-term memory performance was less impaired in the prior-hypo group than in the control group (P < 0.005), and a minor hypoglycemic impairment of reaction time (P < 0.05) was evident in the prior-hypo group. CONCLUSIONS: Data provide evidence that a single episode of mild antecedent hypoglycemia (3.1 mmol/l) attenuates several aspects of cognitive dysfunction during subsequent hypoglycemia 18-24 h later.

Adaptation, Physiological↗
PubMed2000

Bactericidal properties of ozone and its potential application as a terminal disinfectant.

The efficacy of ozone as a terminal disinfectant was evaluated under laboratory conditions. Different microorganisms of importance to the food industry were inoculated onto stainless steel squares and incubated at various temperatures and relative humidities for up to 4 h. Survival of microorganisms from these controls was compared with identically incubated squares exposed to ozone. Exposure of the contaminated surfaces to ozone (2 ppm for 4 h) resulted in a reduction in microbial viability that ranged, depending on organism type, from 7.56 to 2.41 log values. For all the microorganisms tested, this loss in viability was significantly greater (P < 0.05) than that observed in the absence of ozone. Gram-negative bacteria were more sensitive to ozone than gram-positive organisms; bacteria were more sensitive than the yeast strain tested. Exposure to ozone (2 ppm for 4 h) in the presence of ultra-high temperature (UHT) milk resulted in a reduction in bacterial viability that ranged from 5.64 to 1.65 log values. In most cases, this reduction was significantly less (P < 0.05) than that achieved in the absence of organic material, although still significantly greater (P < 0.05) than that observed in the absence of ozone. The presence of a meat-based broth reduced the effectiveness of ozone to a greater extent, although the number of surviving gram-negative organisms was still significantly less (P < 0.05) than in the absence of ozone. Less than 1 log unit of yeast cells was destroyed when exposed to ozone in the presence of UHT milk or meat-based broth. Results of this investigation suggest that if applied after adequate cleaning ozone could be used as an effective disinfectant.

Animals↗
PubMed2000

Daily mortality and air pollution in northern Bohemia: different effects for men and women.

UNLABELLED: The association between short term changes in ambient air concentrations of TSP and SO2 and day to day fluctuations in mortality was analyzed in the highly polluted Northern Bohemia region inhabited by approximately 630,000 people. A logistic regression model was adjusted for long term trends, seasonal cycles, influenza epidemics and weather parameters. The pollution and mortality data were available from 1982 to 1994. When the association was evaluated regardless of gender and age, 100 micrograms/m3 increase of TSP, but not SO2, was associated with a 3.4% increase of daily mortality lagged by 2 days. Evident differences in this association have been found between men and women. A significant increase in daily total and CVD mortality was observed in men below 65 while in women of the same age we found no association or even significant decrease in daily mortality. For the population over 65 the differences between genders were again apparent. The mortality in women increased significantly while in men significant decrease was demonstrated. CONCLUSIONS: The evaluation with respect to gender might contribute to identifying susceptible subgroups.

Adolescent↗