Search PubMed⌕ Search

Biomedical subjects

J Bakker

Publications and source records attributed to J Bakker.

At least 91 records · Page 5Linked to original sources
PubMed1997

Acute folate deficiency in a critically ill patient.

A 19-year-old male patient developed thrombocytopenia and leukopenia due to acute folate deficiency while recovering from a multiple organ failure syndrome. Risk factors for acute folate deficiency are extensive tissue damage due to sepsis, trauma or surgery and acute renal failure requiring renal replacement therapy. The diagnosis is based on bone marrow examination showing marked megaloblastic changes whereas serum folate levels and red cell folate levels are normal. Recognition of this serious complication of critical illness is important because it should be readily prevented by folic acid therapy.

Acute Disease↗
PubMed1997

Quantitative estimation of estrogen and androgen receptor-immunoreactive cells in the forebrain of neonatally estrogen-deprived male rats.

Using quantitative immunocytochemical procedures, the total number of estrogen and androgen receptors was estimated in a large number of hypothalamic and limbic nuclei of male rats, in which brain estrogen formation was inhibited neonatally by treatment with the aromatase inhibitor 1,4,6-androstatriene-3,17-dione. The highest densities of estrogen receptor immunoreactivity were observed in the periventricular preoptic area and the medial preoptic area. Neonatally estrogen-deprived males showed a higher estrogen receptor immunoreactivity than control males in the periventricular preoptic area and the ventrolateral portion of the ventromedial nucleus of the hypothalamus, i.e. those brain areas in which sex differences have been reported, with female rats showing a greater estrogen binding capacity than male rats. The highest densities of androgen receptor immunoreactivity were found in the septohypothalamic nucleus, the medial preoptic area, the posterior division of the bed nucleus of the stria terminalis and the posterodorsal division of the medial amygdaloid nucleus. No significant differences in distribution or total numbers of androgen receptors were found between neonatally estrogen-deprived males and control males. These findings suggest that neonatal estrogens, derived from the neural aromatization of testosterone, are involved in the sexual differentiation of the estrogen receptor system in the periventricular preoptic area and the ventromedial hypothalamus. The role of neonatal estrogens in the development of the forebrain androgen receptor system is less clear.

Androstatrienes↗
PubMed1996

Expression and functional characterization of a single chain Fv antibody directed against secretions involved in plant nematode infection process.

Expression in plants of antibodies directed against proteins essential for pathogenesis could provide an alternative approach to engineer new resistance traits into crops. Salivary secretions of the root-knot nematode Meloidogyne incognita are known to play a key role during this nematode infection process. From a hybridoma cell line producing an IgM monoclonal antibody specific to these secretions, we have constructed a synthetic gene that encodes an antigen-binding single-chain Fv protein (scFv). The scFv gene was created by polymerase chain reaction amplification of variable domain encoding regions from the IgM antibody. The cloned scFv was initially expressed in Escherichia coli as a 33-kDa protein which could be purified to near homogeneity by immobilized metal affinity chromatography. The produced scFv is fully functional since it shows the same specificity towards a crude extract of M. incognita infective larvae as the corresponding parental IgM. Transient expression assays with tobacco leaf protoplasts using different targeting signals resulted in a high intracellular accumulation of scFv, especially when fused to the tetrapeptide KDEL retention signal. Activity analysis and stability characterization of this scFv in tobacco protoplast represent the first step before plant transformation in order to test a new form of resistance to root-knot nematode in plants.

Amino Acid Sequence↗
PubMed1996

The C-terminal KDEL sequence increases the expression level of a single-chain antibody designed to be targeted to both the cytosol and the secretory pathway in transgenic tobacco.

The effects of subcellular localization on single-chain antibody (scFv) expression levels in transgenic tobacco was evaluated using an scFv construct of a model antibody possessing different targeting signals. For translocation into the secretory pathway a secretory signal sequence preceded the scFv gene (scFv-S). For cytosolic expression the scFv antibody gene lacked such a signal sequence (scFv-C). Also, both constructs were provided with the endoplasmic reticulum (ER) retention signal KDEL (scFv-SK and scFv-CK, respectively). The expression of the different scFv constructs in transgenic tobacco plants was controlled by a CaMV 35S promoter with double enhancer. The scFv-S and scFv-SK antibody genes reached expression levels of 0.01% and 1% of the total soluble protein, respectively. Surprisingly, scFv-CK transformants showed considerable expression of up to 0.2% whereas scFv-C transformants did not show any accumulation of the scFv antibody. The differences in protein expression levels could not be explained by the steady-state levels of the mRNAs. Transient expression assays with leaf protoplasts confirmed these expression levels observed in transgenic plants, although the expression level of the scFv-S construct was higher. Furthermore, these assays showed that both the secretory signal and the ER retention signal were recognized in the plant cells. The scFv-CK protein was located intracellularly, presumably in the cytosol. The increase in scFv protein stability in the presence of the KDEL retention signal is discussed.

Amino Acid Sequence↗
PubMed1996

Neonatal inhibition of brain estrogen synthesis alters adult neural Fos responses to mating and pheromonal stimulation in the male rat.

Neonatal inhibition of brain estrogen formation in male rats by administration of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), permanently changes aspects of their mating behavior and partner preference in adulthood. The medial preoptic area receives chemosensory inputs via a sexually dimorphic vomeronasal projection circuit, which responds to reproductively relevant pheromonal cues. The medial preoptic area also receives genital somatosensory inputs via the midbrain central tegmental field and the medial amygdala. We used Fos immunoreactivity as a marker of neuronal activation to determine whether there is a correspondence between the behavioral profiles of neonatally ATD-treated male rats and their neuronal responses in the medial preoptic area and other brain regions to somatosensory and chemosensory stimuli. Achieving eight intromissions with an estrous female led to a greater neuronal Fos immunoreactivity in the medial preoptic area of neonatally ATD-treated male rats compared with neonatally cholesterol-treated male rats. Exposure for 1.5 h to chemosensory cues derived from soiled bedding of estrous females induced Fos immunoreactivity throughout the vomeronasal pathway (i.e. medial amygdala, bed nucleus of the stria terminalis and medial preoptic area) in both ATD and cholesterol males (Experiment 2a). By contrast, exposure for 1.5 h to chemosensory cues derived from soiled bedding of sexually active males revealed clear differences between ATD and cholesterol males in neuronal Fos immunoreactive (Experiment 2b). At peripheral portions of the vomeronasal pathway (i.e. the accessory olfactory bulb and the medial amygdala), there were no differences in the number of Fos immunoreactivity neurons between ATD and cholesterol males. However, neurons in the more central portions of the vomeronasal pathway (i.e. the bed nucleus of the stria terminalis and the medial preoptic area) showed increased Fos immunoreactivity after exposure to odors from sexually active males in ATD males as opposed to cholesterol males. Females, like ATD males, showed neuronal Fos immunoreactivity at each level of the vomeronasal pathway after being exposed to odors from sexually active males. These results suggest that the responsiveness of neurons in the central portion of the vomeronasal projection circuit to odors from sexually active males, but not estrous females, is sexually differentiated in male rats due to the neonatal action of estrogens.

Androstatrienes↗
PubMed1996

Serial blood lactate levels can predict the development of multiple organ failure following septic shock.

BACKGROUND: Despite successful initial resuscitation, septic shock frequently evolves into multiple system organ failure (MSOF) and death. Since blood lactate levels can reflect the degree of cellular derangements, we examined the relation between serial blood lactate levels and the development of MSOF, or mortality, in patients with septic shock. PATIENTS AND METHODS: In 87 patients with a first episode of septic shock, we measured initial lactate (at onset of septic shock), final lactate (before recovery or death), "lactime" (time during which blood lactate was > 2.0 mmol/L, and the area under the curve (AUC) for abnormal values (above 2.0 mmol/L). These measurements were correlated with survival and organ failure and scored for four systems (ie, respiratory, renal, hepatic, and coagulation), adding to a maximal score of 8. RESULTS: Thirty-three (38%) patients survived. Of the 54 (62%) nonsurvivors, the 13 patients who died during the first 24 hours of septic shock had higher initial blood lactate levels than those who died later (mean +/- standard deviation 9.6 +/- 5.3 mmol/L versus 5.6 +/- 3.7 mmol/L, P< 0.05). The 74 patients who survived the first 24 hours of shock, were studied in more detail. On presentation, survivors had a significantly higher mean arterial pressure (76 +/- 12 mm Hg versus 63 +/- 20 mm Hg, P < 0.001) and arterial pH (7.40 +/- 0.07 versus 7.37 +/- 0.09, P< 0.05) than nonsurvivors. Although the differences in initial blood lactate levels between survivors and nonsurvivors did not reach statistical significance (4.7 +/- 2.5 mmol/L versus 5.6 +/- 3.7 mmol/L), only the survivors had a significant decrease during the first 24 hours of septic shock. The survivors had a significantly lower lactime and AUC than the nonsurvivors. The duration of lactic acidosis was the best predictor of survival (multiple regression analysis, R2 = 0.266, P <0.001), followed by age, heart rate, and mean arterial pressure. Patients with lower organ failure scores had lower initial blood lactate, lactime, and AUC. The duration of lactic acidosis was the only significant predictor of organ failure. CONCLUSIONS: In patients with septic shock, serial determinations of blood lactate levels are good predictors of the development of MSOF an death. In this respect, the duration of lactic acidosis is more important than the initial lactate value. Although a number of factors may contribute to hyperlactatemia, these observations are compatible with a direct role of prolonged tissue hypoxia in the development of complications following septic shock.

Adult↗
PubMed1996

Sexual differentiation of odor and partner preference in the rat.

Previous studies have shown that adult male rats, in which brain estrogen formation was inhibited neonatally by SC administration of the aromatase inhibitor 1,4, 6-androstatriene-3,17-dione (ATD), show an altered sexual partner preference. When tested in a three-compartment box, such gonadally intact ATD males approach and mate both with the estrous female and the sexually active male, whereas normal males prefer to approach and mate with the estrous female, avoiding the stimulus male. After castration in adulthood and estradiol treatment, ATD males prefer sexually active males. Similarly treated normal males prefer estrous females, and estrous females prefer to mate with males. In the present study, we asked what stimulus characteristics of active males vs. estrous females determined the different sexual preferences of males, ATD males, and of females. Were they chemosensory cues or more distal cues such as actually seeing and hearing the stimulus animals or the reward of sexual activity with the stimulus animals? Sex differences in preference were evident when animals were given a choice between soiled bedding from estrous females and from sexually active males. ATD and control males spent significantly more time on soiled bedding from estrous females than on soiled bedding from sexually active males. Control females spent significantly more time on soiled bedding from sexually active males than on soiled bedding from estrous females. More distal cues, such as seeing and hearing the stimulus animals, revealed differences in preference between control males and females, but not between ATD and control males. Physical interaction with the stimulus animals was a prerequisite for revealing differences in preference between ATD and control males. Then, the behavior of ATD males was clearly intermediate between that of normal male and female rats. In conclusion, neonatal estradiol is important for the psychosexual development of the male rat. However, the present data suggest that the psychosexual development of the male rat also requires either prenatal estradiol or perinatal testosterone.

Androstatrienes↗
PubMed1996

Secretory granule proteins from the subventral esophageal glands of the potato cyst nematode identified by monoclonal antibodies to a protein fraction from second-stage juveniles.

Sodium dodecyl sulfate-extracted proteins from second-stage juveniles (J2) of the potato cyst nematode Globodera rostochiensis were fractionated by preparative continuous flow electrophoresis, and monoclonal antibodies (MAbs) were raised against the 38- to 40.5-kDa protein fraction. Screening of the hybridoma culture fluids by immunofluorescence microscopy of J2 resulted in the identification of 12 MAbs that bound specifically to the subventral esophageal glands. On Western blots of J2 these MAbs identified four protein bands with apparent molecular masses of 30, 31, 39, and 49 kDa. Immunoelectron microscopy with one of these MAbs showed an intense labeling of the electron dense core of the secretory granules in the subventral gland cells of J2. It is concluded that one or more of these proteins are localized within these secretory granules. Immunofluorescence microscopy of J2 from other plant parasitic nematode species showed that most of these MAbs also bind to the subventral glands of G. pallida and G. tabacum but not of Heterodera schachtii, H. glycines, Meloidogyne incognita, or M. hapla.

Animals↗
PubMed1996

Gene pool similarities of potato cyst nematode populations assessed by AFLP analysis.

AFLP was used to characterize 24 potato cyst nematode populations. This novel DNA fingerprinting technique enabled the identification of 987 marker loci by screening only 12 primer combinations. Data on presence or absence polymorphisms and data on the intensities of corresponding DNA fragments were collected. Separate analysis of both data sets revealed similar dendrograms for the nine G. rostochiensis populations included in this study. Both dendrograms consisted of two groups containing three and five related populations, respectively. One population differed from either of these groups. Each group represented a different pathotype as defined by Kort et al. (J. Kort, H. Ross, H. J. Rumpenhorst, and A. R. Stone, Nematologica 23:333-339, 1977). Previously, a similar arrangement was found after analysis of the genetic variation using random amplified polymorphic DNA (RAPD) (R. T. Folkertsma, J. N. A. M. Rouppe van der Voort, M. P. E. van Gent-Pelzer, K. E. de Groot, W. J. van den Bos, A. Schots, J. Bakker, and F. J. Gommers, Phytopathology 84:807-811, 1994). For the 15 G. pallida populations analyzed, complex AFLP patterns were obtained and therefore only qualitative AFLP data were used. Incongruities were observed between clustering on the basis of AFLP data and classical pathotyping. This strongly confirms earlier findings obtained with RAPDs, because the AFLP markers used in this study outnumbered the population characteristics revealed by RAPDs by a factor of five. To arrive at a reliable pathotype designation of potato cyst nematode populations molecular data and virulence characteristics should be integrated. Possible causes for the difference in distribution of polymorphisms among g. rostochiensis and G. pallida populations are discussed.

Animals↗
PubMed1996

Validation of large data sets, an essential prerequisite for data analysis: an analytical survey of the Bone Marrow Donors Worldwide.

Large data sets like the Bone Marrow Donors Worldwide (BMDW) data set can be used for population genetic analyses. The qualities of such data sets are unique. To be able to use the BMDW data for analyses, several problems, like limited size and selective DR typing, of the data have to be solved and the quality of the registry data subsets has to be examined. We describe these problems and methods to overcome them. Also, we give an overview of the qualities of the different registry subsets. Sixteen of the twenty-nine examined subsets contain data that can be used for population genetic analysis. We will deal with these analyses in the future. Additionally, we present a method to calculate the minimum number of individuals required for reliable haplotype frequency estimation.

Bone Marrow Transplantation↗
PubMed1995

Killing of Entamoeba invadens using liposome-encapsulated drugs.

Liposomes are used as carriers of drugs intended to manipulate macrophage functions. The normal in vivo fate of liposomes is phagocytosis, followed by phospholipase-mediated disruption of their phospholipid bilayers and intracellular release of their contents. Using this method for intracellular delivery of drugs, we have developed an approach for in vivo depletion of macrophages. Phagocytosis also forms a major feature of parasitic amoebae. In the present experiments, we investigated whether amoebae could be killed using the same approach (liposome-mediated "suicide" of amoebae). The results confirm that liposomes are ingested by Ent-amoeba invadens cultured under routine laboratory conditions. From various chelator molecules and their metalion complexes that were active in the liposome-mediated elimination of macrophages, Cu-ethylenediaminetetraacetic acid (EDTA) complexes appeared to be the most efficacious compounds in the elimination of E. invadens.

Animals↗
PubMed1995

Postweaning housing conditions and partner preference and sexual behavior of neonatally ATD-treated male rats.

Male rats were neonatally treated with cholesterol or a substance that blocks the aromatization of testosterone to estradiol (1,4,6-androstatriene-3,17-dione: ATD). At weaning (21 days) they were either housed alone or in small groups (2-3 animals) and tested for partner preference behavior (PPB) in adulthood. Choice was between an estrous female and an active male (Part I) and between an estrous female and an ATD-male (Part II). Tests were carried out in a 3-compartment box. Social isolation did not have major effects on PPB except when sexual interaction with the stimulus animals was prevented (Part I). In this case, isolates (ATD and control) showed higher preference scores (PS) for the estrous female and spent less time in the empty middle compartment. When the choice was between an estrous female and an ATD-male, partner PS decreased in all males, most clearly in ATD-males. The latter animals spent more time with the stimulus ATD-male than they had done in previous PPB tests with the normal stimulus male. In contrast to partner preference behaviors, sexual behavior was clearly affected by social isolation. Isolates (ATD and control) displayed lower frequencies of mounts and intromissions. These effects persisted over consecutive tests. Ejaculation was not affected. In conclusion, the present results confirm earlier findings about the significance of neonatal endocrine conditions for the organization of adult PPB in male rats. The presence or absence of social conspecifics after weaning appears to have little influence on adult PPB.

Androstatrienes↗
PubMed1995

Detection of tissue hypoxia by arteriovenous gradient for PCO2 and pH in anesthetized dogs during progressive hemorrhage.

The present study tested the hypothesis that, during acute bleeding, the development of tissue hypoxia might be reflected by an abrupt widening in arteriovenous gradient for PCO2 (AV PCO2) and for pH (AV pH) as accurately as by an increase in blood lactate levels. Twenty-four anesthetized (isoflurane 1.4% end-tidal), paralyzed, and mechanically ventilated dogs submitted to progressive hemorrhage were studied. Oxygen uptake (VO2) was derived from expired gas analysis and oxygen delivery (DO2) was calculated by the product of the thermodilution cardiac index and the arterial O2 content. During the first part of the protocol, VO2 remained stable as the progressive reduction in DO2 was associated with a corresponding increase in O2 extraction (O2ER). Blood lactate increased slightly but not significantly. AV PCO2 and AV pH increased significantly, essentially related to venous respiratory acidosis. The critical value of DO2 below which VO2 decreased was 8.95 +/- 1.60 mL.min-1.kg-1. Below this value, there was a marked increase in blood lactate and an abrupt widening in AV PCO2 and AV pH gradients. The critical value of DO2 obtained from blood lactate, AV PCO2 and AV pH were similar to those obtained from VO2 (8.60 +/- 1.12; 8.73 +/- 1.40; 8.78 +/- 1.37, respectively; P = not significant). A significant correlation was found, during the hemorrhage protocol, between blood lactate and AV PCO2 (r = 0.84; P < 0.001) or AV pH (r = 0.78; P < 0.001). Therefore, AV PCO2 and AV pH represent simple but reliable indicators of tissue hypoxia during hemorrhagic shock.

Animals↗
PubMed1995

Endogenous reproductive hormones and nocturnal rhythms in partner preference and sexual behavior of ATD-treated male rats.

Male rats received subcutaneously silastic capsules, containing the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD), shortly after birth. Control males were given silastic capsules containing cholesterol. The capsules were removed at the age of 21 days. In adulthood, blood serum was collected early and late in the dark phase of the light/dark cycle (experiment I). Testosterone and luteinizing hormone and follicle stimulating hormone (FSH) fluctuated nocturnally, both in ATD and control males, with highest levels late in the dark phase. FSH levels were significantly higher in ATD males. Nocturnal levels of inhibin, a selective suppressor of pituitary FSH secretion, also fluctuated in both ATD and control males, with lowest levels late in the dark phase. In experiment II, ATD and control males were tested for partner preference behavior in a three-compartment box (choice: sexually active male vs. estrous female) early and late in the dark phase. When gonadally intact, ATD males, but not controls, showed a clear nocturnal rhythmicity in partner preference behavior and sexual behavior. Early in the dark phase, such ATD males preferred the vicinity of and interaction with a sexually active male. Late in the dark phase, this preference for the active male shifted to a preference for the estrous female. Control males preferred the estrous female. After castration and subsequent treatment with testosterone via silastic capsules, which ensured constant blood serum levels, ATD males continued to show their nocturnal rhythms in partner preference behavior and in sexual behavior. Thus, the underlying mechanism of the nocturnal rhythmicity phenomenon is an organizational effect of neonatal ATD treatment rather than an activational effect of fluctuating serum hormone levels.

Animals↗
PubMed1995

Effects of N-acetyl-L-cysteine on regional blood flow during endotoxic shock.

We previously reported that N-acetyl-L-cysteine (NAC), an oxygen free-radical scavenger, can increase the oxygen extraction capabilities during endotoxic shock when blood flow is progressively reduced. In the present study, we investigated whether the protective effects of NAC are related to an improvement in regional blood flow following endotoxemia. Fourteen anesthetized, saline-infused and ventilated dogs were divided into two groups: 7 dogs received NAC (150 mg/kg, followed by a 20 mg/kg.h infusion), and the other 7 dogs served as a control time-matching group. Thirty minutes later all the dogs received Escherichia coli endotoxin (2 mg/kg) i.v. A saline infusion was started 30 min after endotoxin challenge to restore pulmonary artery occlusion pressure to baseline and maintain it constant. Regional blood flow was measured by ultrasonic volume flowmeter. In the control group, arterial pressure, left ventricular stroke work index and systemic vascular resistance remained lower than baseline. Mesenteric, renal and femoral arterial blood flow increased but only femoral blood flow returned to baseline levels. In the NAC group, cardiac index and left ventricular stroke work index remained higher and systemic and pulmonary vascular resistance were lower than in the control group. Blood flow in mesenteric, renal and especially femoral arteries was higher than in the control group. Fractional blood flow increased only in the femoral artery. PaO2 and PvO2 had similar courses in the two groups. A higher venous admixture was associated with a higher cardiac index and a lower pulmonary vascular resistance in the NAC group. Oxygen delivery and oxygen-uptake were higher in the NAC-treated than in the control animals throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗
PubMed1995

Cardiac arrest following an iatrogenic 3,4-diaminopyridine intoxication in a patient with Lambert-Eaton myasthenic syndrome.

Syndromes with impaired neuromuscular transmission are frequently treated with pyridine derivates. 3,4-diaminopyridine is thought to have fewer side effects than the commonly used, but less potent, 4-aminopyridine. We describe a patient with an initially unrecognized iatrogenic intoxication with 3,4-diaminopyridine. Except for a life threatening arrhythmia, symptoms were similar to a 4-aminopyridine intoxication. The patient made a full recovery with symptomatic treatment and withdrawal of the drug.

4-Aminopyridine↗
PubMed1994

Coordinate expression of antibody subunit genes yields high levels of functional antibodies in roots of transgenic tobacco.

To explore the feasibility of employing antibodies to obtain disease resistance against plant root pathogens, we have studied the expression of genes encoding antibodies in roots of transgenic plants. A model monoclonal antibody was used that binds to a fungal cutinase. Heavy and light chain cDNAs were amplified by PCR, fused to a signal sequence for secretion and cloned behind CaMV 35S and TR2' promoters in a single T-DNA. The chimeric genes were cloned both in tandem and in a divergent orientation. The roots of tobacco plants transformed with these constructs produced antibodies that were able to bind antigen in an ELISA. Immunoblotting showed assembly to a full-size antibody. In addition, a F(ab')2-like fragment was observed, which is probably formed by proteolytic processing. Both antibody species were properly targeted to the apoplast, but the full-size antibody was partially retained by the wall of suspension cells. The construct with divergent promoters showed a better performance than the construct with promoters in tandem. It directed the accumulation of functional antibodies to a maximum of 1.1% of total soluble protein, with half of the plants having levels higher than 0.35%. The high efficiency of this construct probably results from coordinated and balanced expression of light and heavy chain genes, as evidenced by RNA blot hybridization.

Amino Acid Sequence↗