Biomedical subjects

H J Merker

Publications and source records attributed to H J Merker.

At least 37 records · Page 2Linked to original sources

PubMed1997

Electron microscopic and immunomorphological investigations on the mucosa of the human paranasal sinuses.

The morphology of the mucosa from the human paranasal sinuses was investigated by electron microscopy. A total of 27 specimens was taken from 11 patients following midfacial fractures. All tissue samples were biopsied during surgery after informed consent had been given. In accordance with light microscopic investigations, the mucosa represented a highly prismatic epithelium consisting of kinocilia-carrying and mucus-producing (goblet) cells. Other cell types, such as those occurring in the respiratory epithelium of other areas, could not be demonstrated. Electron microscopic and immunomorphological investigations revealed collagen type VII beneath the lamina densa of the basal lamina. According to findings obtained to date, this collagen type accompanies only a multilayered epithelium. Another peculiarity was the small number of basophils and eosinophils. Pronounced acute reactions of the mucosa in this area cannot be expected, which is in contrast to that of the nasal mucosa.

Adult↗

PubMed1997

[Comparative stability evaluation of dynamic hip screw and gamma-nail osteosyntheses in unstable pertrochanteric femoral osteotomies].

In 24 human cadaver femora standardized instable pertrochanteric osteotomies were created. The right and left femur of each pair were alternately selected for osteosyntheses with the gamma nail and the dynamic hip screw. Afterwards an examination of stability was performed. Cyclical loads were increased in 500 N increments to the maximum loading capacity, while the deformation rate was continuously measured. Radiographs were taken to prove the results of loading. The mean deformation was much greater in the DHS group than for the gamma nail, the maximum load to failure was significantly lower. Femoral shaft fractures caused by the loading occurred five times as often in the gamma nail osteosyntheses than in the DHS.

Aged↗

PubMed1997

Quinolone-induced arthropathy: exposure of magnesium-deficient aged rats or immature rats, mineral concentrations in target tissues and pharmacokinetics.

Quinolone treatment or magnesium deficiency induce identical cartilage lesions in juvenile rats and show additive arthropathogenic effects. It has been shown previously that neither condition is arthropathogenic in 8-week-old rats. Joint cartilage from aged individuals is rather prone to pathological alterations but information on prolonged quinolone treatment and/or dietarily induced magnesium deficiency in aged animals is not available. We treated magnesium-deficient (n = 9) aged Wistar rats (age 15 months) and age-matched controls with daily doses of 600 mg ofloxacin/kg body wt. by gastric intubation for 28 days. Further groups of magnesium-deficient and control rats (n = 9 and n = 10, respectively) received the vehicle only. Peak plasma concentrations of ofloxacin in adult rats were 20.5 +/- 5.6 mg/l (mean +/- SD) following treatment with a single dose of 600 mg/kg body wt. At the end of the experiment the degree of magnesium deficiency was most pronounced in plasma (Mg2+-def., 0.33 +/- 0.12 mmol/l; control, 0.97 +/- 0.08 mmol/l) and less pronounced in sternal cartilage (Mg2+-def., 10.8 +/- 3.6 mmol/kg dry wt; control, 13.3 +/- 2.8 mmol/kg dry wt), whereas the magnesium concentration in femoral bone remained unchanged (Mg2+-def., 201 +/- 13 mmol/kg dry wt; control, 204 +/- 11 mmol/kg dry wt). Histological investigation of the knee joints revealed no cartilage lesions following ofloxacin treatment, magnesium deficiency or a combination of both conditions. By contrast, cartilage lesions such as scars and erosions of the joint surface, chondrocyte clusters within acellular areas of the cartilage matrix and persisting clefts were detectable in knee joints from 7 of 10 adult rats (age 9 months) which had been treated with 4 x 600 mg fleroxacin/kg body wt. at 5 weeks of age. Mean plasma concentration of fleroxacin in juvenile rats was approx. 50 mg/l between 1.5 and 6 h after dosing and the drug was still detectable in plasma 48 h after dosing (0.4 +/- 0.1 mg/l). Our data indicate that joint cartilage in aged rats is not altered by a 4-week quinolone treatment, even during magnesium deficiency. Cartilage lesions in adult rats were only detectable if the animals had been treated during the sensitive phase at 5 weeks postnatally.

Age Factors↗

PubMed1997

Morphology of capillary-like structures in a three-dimensional aorta/collagen gel culture.

The morphology of capillary-like tubes was investigated by electron microscopy (TEM and SEM) using an in vitro model of capillarogenesis (aorta/collagen type I gel). This model allowed morphological comparisons with in vivo capillaries and an evaluation of the functional maturity of the endothelium to be made. The lumina developing in vitro were demarcated by endothelial cells of varying thickness (0.1-2 microns). Pericytes were resting on the outside. The endothelial cells were characterized by contacts of varying length with tight and gap junctions and occasional indentations. The inner surface exhibited areas both with pronounced and without any endocytotic activity. In addition to a large Golgi apparatus, a varying number of cell organelles occurred depending on the thickness of the endothelium. Bundles consisting of microfilaments were often located underneath the outer cell membrane and in the vicinity of contact areas. A lamina densa was in the process of formation. The capillaries grown in vitro closely resembled those in vivo and showed a high degree of differentiation. Hence, this in vitro model allows the study of a number of functions of endothelial cells.

Animals↗

PubMed1997

Formation of new capillary-like tubes in a three-dimensional in vitro model (aorta/collagen gel).

Direct sprouting (angiogenesis) does not occur during the formation of capillary-like tubes in an aorta/ collagen gel in the in vitro model. However, emigration of cells which stretch, arrange themselves side by side, form contacts (unspecific, tight and gap junctions), develop a lumen and show differentiation of endothelial cells (including the formation of a lamina densa and the appearance of pericytes) have been observed, i.e. vasculogenesis occurs. The origin of long, stretched cells is not known with certainty. They possibly represent smooth muscle cells. In addition, other cell types have been found, such as fibrocyte-like and fibroblast-like cells, elastoblasts, fat cells, monocytes and macrophages. All these cells are able to produce factors that promote the formation of new capillaries. Hence, a knowledge of these cells appears to be important for the analysis of in vitro systems. Moreover, the occurrence of these cell types must be considered when assessing possible effects.

Animals↗

PubMed1997

Testis damage induced by zinc deficiency in rats.

Male Wistar rats were fed a Zn-deficient diet (1.2 mg/kg of Zn) for 28 days. Testes were then studied by light and electron microscopy. Zn deficiency induced necroses of precursors of germ cells leading to tubular atrophy and affected differentiation of spermatids. This was expressed by the occurrence of 2-4 axoneme-dense fibre-mitochondria complexes in one spermatid. Moreover, outer dense fibres, which normally contain 90% of sperm Zn, were "uncoiled" and flattened. The multiplication of the axoneme-dense fibre-mitochondria complexes induced by Zn deficiency might have been produced by an increase of Fe in spermatids and an increased formation of oxygen free radicals.

Animals↗

PubMed1997

Reproductive toxicity and toxicokinetics of lindane in the male offspring of rats exposed during lactation.

1. Reproductive toxicity and toxicokinetics of lindane during lactation were studied. For the reproductive toxicity study the dams were treated with a single dose of 6 mg/kg on day 9 or 14 of lactation, or with 1 mg/kg on days 9 to 14 of lactation. The male offspring were investigated at puberty and adulthood. For the toxicokinetic study, two groups of dams were treated with 6 mg/kg on day 9 or 14 of lactation. The concentration of lindane was measured in maternal plasma and milk, as well as in male offspring organs. 2. At adulthood, testicular weight and the number of sperm and spermatids were significantly reduced in all treated groups. 3. The testosterone level of the groups treated with 6 mg/ kg was significantly reduced to approximately 50% at puberty as well as in adulthood. In the group treated with 1 mg/kg, the testosterone level was in both age periods reduced, however, only at puberty was the reduction statistically significant. 4. The concentration of lindane in the testis was similar to that found in brain and was half the concentration found in the liver. 5. Histologically some areas of the testis exhibited distinct alterations ranging from small changes to a pronounced effect. 6. Exposure to lindane during lactation induces reproductive hazards to male offspring rats which are detectable at adulthood.

Animals↗

PubMed1997

Ganciclovir induces reproductive hazards in male rats after short-term exposure.

1. The effect of short-term treatment of ganciclovir on male reproduction in adult rats was studied. The animals were treated subcutaneously with either a single dose of 60 mg/kg daily for 5 days (Gan5day) or with 100 mg/kg administered three times at 4 h-intervals (Gan1day). The effects were investigated every 2 weeks up to 8 weeks, followed by investigations 16 and 24 weeks after treatment to detect the potential of recovery. 2. Time to mating was significantly increased in Gan1day group. The pregnancy index and outcome were only decreased 8 weeks (Gan5day and Gan1day) or 16 weeks (Gan1day) after treatment. 3. The lowest values of sperm variables studied were registered 8 weeks after treatment: The number of spermatid was reduced up to 4% (Gan5day) or 2% (Gan1day) of control; the sperm number was 5% and 8% of control in Gan5day and Gan1day, respectively. Over 80% of sperm were abnormal in Gan5day group, and only few normal sperm was detected in Gan1day group. 4. Morphological investigation of testes revealed a clearcut time-dependency effect. Four weeks after treatment distinct alterations were located exclusively in the peripheral part of the tubuli which included fat inclusions, cell and pyknotic nuclear debris and swellings of Sertoli cells. The effect was reversible 24 weeks after treatment. 5. Ganciclovir induces testicular damage and affects sperm variables after short-term exposure. The intensity and degree of the hazards varied in between the time of investigation after treatment.

Animals↗

PubMed1996

Integrins on joint cartilage chondrocytes and alterations by ofloxacin or magnesium deficiency in immature rats.

Recently, we showed that magnesium deficiency induces lesions in knee joint cartilage from 5-week-old rats that are very similar to ofloxacin-induced cartilage defects. We concluded that quinolone-induced arthropathy is probably due to chelation of magnesium and thus a deficit in functionally available magnesium in joint cartilage (Stahlmann et al. 1995). As magnesium deficiency in joint cartilage could impair chondrocyte-matrix interaction which is mediated by cation-dependent integrin receptors of the beta 1-subfamily, we investigated integrin expression in joint cartilage from untreated, ofloxacin-treated and magnesium-deficient Wistar rats. With immunohistochemical methods using monoclonal and polyclonal antibodies, we showed that the integrin pattern in joint cartilage from rats corresponded largely to integrin expression described for human cartilage tissue: beta 1, alpha 1, alpha 3 and alpha v subunits and the alpha 5 beta 1 and alpha v beta 3 heterodimers were consistently expressed. Joint cartilage lesions were detected in ofloxacin-treated and magnesium-deficient rats. Lesions were more pronounced in the quinolone-treated group. Expression of several integrins was reduced in the vicinity of lesions after oral treatment with 2 x 600 mg ofloxacin/kg for 1 day. Gross-structural lesions (e.g., cleft formation, unmasked collagen fibres) in magnesium-deficient rats were very similar but changes in integrin expression were less pronounced. On the other hand, changes in cartilage matrix composition showed similar alterations in ofloxacin-treated and magnesium-deficient rats: fibronectin deposition in the cartilage matrix increased in both groups while glycosaminoglycan content decreased. In summary, similar defects occur in ofloxacin-treated and magnesium-deficient rats and with immunohistochemical methods subtle differences are demonstrable.

Animals↗

PubMed1996

Quinolone-induced cartilage lesions are not reversible in rats.

The reversibility of quinolone-induced cartilage lesions has not been studied in detail. We treated five groups of five to seven juvenile Wistar rats (male and female; age: 5 weeks) with 2 x 600 mg ofloxacin/kg by gastric intubation on 1 day only (9:00 a.m. and 5:00 p.m.) and studied the knee joints histologically 3 days, 1, 3, 8 and 17 weeks later. In addition, joint cartilage specimens from vehicle-treated control rats (n = 21) at corresponding age were examined. Cartilage lesions such as matrix swelling, loss of proteoglycans and horizontal clefts were found in nearly all knee joints (26 of 27 joints; incidence: 96%) of the ofloxacin-treated rats. Within the observation period of 4 months the size of these lesions in knee joint cartilage did not decrease significantly. The diameter of the lesions at the time points of evaluation was 1146 +/- 535, 1713 +/- 309, 1250 +/- 585, 1406 +/- 356, and 1542 +/- 467 microns, respectively (mean values +/- sd). Chondrocyte clusters producing glycosaminoglycans were observed 3 weeks after dosing and at later time points. They are considered to reflect the onset of repair but chondrocyte organization did not normalize during the study period, thus indicating the irreversibility of the effect under the experimental conditions. In principle, long-term joint cartilage damage has to be taken into account when the use of quinolones in children is considered. More detailed pharmacokinetic data are necessary for a reasonable risk assessment approach.

Animals↗

PubMed1996

Intracellular collagen-like material in mouse embryonic mesenchymal cells incubated with TNF-alpha and IL-1 beta in organoid culture.

Blastemal cells of embryonic mouse limb buds (day 12) were cultivated in organoid cultures in the presence of the human recombinant cytokines interleukin-1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF-alpha). The effects of both cytokines (applied alone or together) on mesenchymal cells were demonstrated by electron microscopy. Cultures treated with TNF-alpha (alone or in combination with IL-1 beta) showed several mesenchymal cells with numerous irregularly shaped membrane-bordered cavities containing thick bundled tannic-acid-positive fibrillar structures that resembled loosened collagen fibrils, whereas cells exposed to IL-1 beta alone did not exhibit such changes. These findings are discussed in the light of two hypotheses: the phagocytosis of extracellular collagen fibrils, and fibrillogenesis resulting from incongruity of synthesis and secretion rates of procollagen; our results favour the former.

Animals↗

PubMed1996

C-cells of marmosets (Callithrix jacchus).

The localization and fine structure of C-cells of the thyroid glands from 31 marmosets (Callithrix jacchus) of different age groups (newborn to 11 years old) were investigated by electron microscopy and immunomorphology (APAAP, calcitonin). Calcitonin-positive cells were found concentrated in the middle third of the gland. Their localization in the follicular wall or in the interstitial space could not clearly be demonstrated by light microscopy. In adult animals, they were always located within the basal lamina, as revealed by electron microscopy. In newborn animals, their localization was difficult because of the dense cell packing. The fine structure of the C-cells with their 200 nm electron-dense granules corresponded to that of other species. Two cell types could be distinguished: (1) granule-rich cells in the storing phase and (2) cells with fewer granules and well-developed rough endoplasmic reticulum in the synthesis phase. The concentration of C-cells in the middle third of the marmoset thyroid gland renders this species especially suitable for morphological investigations and in vitro experiments.

Aging↗

PubMed1996

Reproductive toxicity and tissue concentrations of lindane in adult male rats.

1. The effects of lindane on the reproductive system and its concentration in different tissues were investigated. Groups were dosed orally with 6 mg lindane/kg for 5 days or with a single dose of 30 mg/kg body weight. 2. The results indicate that the number (mio) of spermatids counted in the testes of both treated groups 2 weeks after treatment were significantly reduced compared to the control rats. Effects on the number of sperms were observed in both treated groups, but significant differences were only revealed on those with 30 mg/kg. 3. The concentration (microgram/g tissue) of lindane in adipose tissue, liver, brain and testis was determined 24 h and 2 weeks after the last treatment. Lindane was detected in the testis of both groups 24 h and 2 weeks after the last treatment. 4. Histological investigation by electron microscopy revealed a pronounced ballooning of Sertoli cells accompanied by fragmentation or complete loss of organelles. 5. According to the result obtained, it is evident that lindane passes through the testis and exerts its toxic effect.

Adipose Tissue↗

PubMed1995

Development of a suspension organ culture of the fetal rat palate.

On the basis of an already established suspension organ culture system of mouse palate anlagen, we developed a corresponding culture system for rat palate anlagen. In order to optimize the culture results we systematically studied the influence of main "culture conditions" such as dissection technique, rotation speed, gassing schedule, and developmental stage at the onset of culture for mice and rat palate anlagen. This system allows culturing rat palate anlagen from day 15 of gestation to day 18 + 8 h (80 h) under serum- and antibiotic-free conditions using a chemically defined medium, resulting in 90% fused palates. The explants, containing the maxillary vault and the palatal shelves, were cultured in siliconized culture flasks at a rotation speed of 12 rpm and a temperature of 37 degrees C (Table 1).

Animals↗

PubMed1995

The interstitial space of the thyroid gland of marmosets (Callithrix jacchus).

The interstitial space of the thyroid gland of adult marmosets contains, like the stroma of other organs, cells and intercellular substance (matrix), blood vessels (predominantly capillaries), lymph vessels and unmyelinated nerves. It is demarcated from the follicular epithelium, the capillaries and Schwann cells by a basal lamina (BL). The perifollicular BL shows thickenings of up to 3 microns over long distances or a multilayered arrangement. These thickened segments exhibit numerous epithelial processes and ridges; in other words, the contour of the basal cell membrane is very irregular in these areas. Indentations of capillaries into the epithelium are rarely observed. The endothelium is only slightly porous. Lymph capillaries occur in large numbers. They originate freely in the interstitial space, show gaps or unspecific contacts between the thin endothelial cells; a basal lamina is missing. Bundles of 10-nm thick filaments (anchor filaments) extend to the endothelial cells of the lymph capillaries. Thin and very long (up to 8 microns) plate-like processes surround the capillaries or run parallel to the outer contour of the follicles. They originate at the poles of oval, fibroblast-like cells. Since these cells are FXIII- and C3bi-positive, they can be considered as dendritic cells. They obviously play a role in the frequently-observed autoimmune diseases of this species. In addition, monocytes and all transitional forms including macrophages, fibrocytes and lymphocytes as well as numerous mast cells occur. In the region of the BL, integrins of the beta 1-group (alpha 6) can be demonstrated immunohistologically in addition to the usual components (collagen type IV, laminin and heparan sulfate-proteoglycan). Of the fibrillar collagens type I does not occur, type III occurs only in small amounts, whereas types V and VI are observed in large amounts. The presented findings may serve as basis for more extensive experiments on these primates.

Animals↗

PubMed1995

Magnesium deficiency induces joint cartilage lesions in juvenile rats which are identical to quinolone-induced arthropathy.

Quinolones accumulate in cartilage, and because they form chelate complexes with divalent cations, they possess the potential to induce a deficiency of functionally available magnesium. To test the hypothesis that quinolone-induced arthropathy is caused (or aggravated) by magnesium deficiency in cartilage, we induced magnesium deficiency by feeding juvenile rats a magnesium-deficient diet for 9 days and treated the rats with single oral doses of ofloxacin (0, 100, 300, 600, or 1,200 mg/kg of body weight) during this period. Additional groups of juvenile rats on a normal diet were treated with ofloxacin correspondingly. Typical cartilage lesions (e.g., swollen matrix, cleft formation) were found in knee joints of all magnesium-deficient rats, including those without ofloxacin treatment. Lesions in these groups were not distinguishable from lesions induced by a single dose of 600 mg of ofloxacin per kg of body weight or higher in rats on a normal diet. Ofloxacin levels in plasma after 600 mg/kg of body weight were approximately 10-fold higher than those in humans during therapy with this quinolone. Lesions in rats treated with ofloxacin plus magnesium deficiency were more pronounced than those in rats with normal magnesium concentrations. After intake of a magnesium-deficient diet for 9 days, the magnesium concentration in serum (mean +/- standard deviation) was 0.18 +/- 0.05 mmol/liter (control on normal diet, 0.82 +/- 0.10 mmol/liter). Magnesium concentrations in bone (femur) and cartilage (processus xiphoideus) samples were 64.7 +/- 10.5 and 14.3 +/- 3.9 mmol/kg of dry weight, respectively, which corresponded to approximately 50% of the concentrations measured in controls on a normal diet. It was concluded that quinolone-induced arthropathy is probably caused by a deficit of available magnesium in joint cartilage due to the formation of quinolone-magnesium chelate complexes. If juvenile patients must be treated with quinolones for serious infections, it seems prudent to ensure that these patients do not have a disturbed magnesium balance.

Animals↗

PubMed1995

Basement membrane formation of fetal mouse intestinal epithelial cells in organoid cultures.

Basement membrane formation of fetal mouse intestinal epithelial cells was investigated in organoid cultures. Intestinal cells were dissociated with a commercial collagenase/dispase preparation, and the cells were grown at high density on a membrane filter at the interface between the medium and air. This type of culture allows the histotypical reorganization of cells. After 2 days in culture, epithelial cells began to accumulate on the surface, in particular the periphery of the culture. These cells were usually cuboid, and small vesicles were formed in the center of the culture. Laminin-positive material was observed at peripheral sites. However, no basement membrane could be identified beneath the epithelial cells at the electron-microscopic level. After 3 days, epithelial cells that had gathered at the periphery became columnar in shape. Laminin-positive material extended across the surface of the culture. However, the vesicles formed in the center of the culture were not associated with laminin-positive material. Basement membrane was observed by electron microscopy at some sites beneath groups of epithelial cells, but did not extend continuously beneath these cells. Some epithelial cells made contact with the underlying mesenchymal cells through the discontinuous basement membrane via intercellular contacts. After 5-6 days, the surface of the culture was almost completely covered with epithelial cells and, at some sites, villus-like structures were visible. Laminin-positive material was clearly detectable under epithelial cells, as well as around epithelial vesicles located in the center of the culture. By electron microscopy, basement membrane was clearly visible between the epithelial and mesenchymal cells. After 9 days, villus-like structures were rarely observed. After 3 weeks, the cell mass had become smaller and villi had disappeared. Basement membrane was extensively folded and no basement membrane was visible at some sites. Formation of basement membrane by epithelial cells in monolayer culture occurs in an incomplete and irregular manner. It occurs rapidly in organoid cultures that include mesenchyme and epithelium. The organoid culture used here should be a useful tool for studies of the formation and degeneration of the basement membrane as well as interactions between the epithelium and mesenchyme.

Animals↗

PubMed1995

Changes in integrin expression during chondrogenesis in vitro: an immunomorphological study.

Integrins are receptors composed of ligand-specific alpha-chains and cell type-specific beta-chains which are involved in cell-cell and cell-matrix interactions. The distribution of alpha 1- and alpha 3-integrins as well as collagen Types I and II, was investigated by immunofluorescence and immunoelectron microscopy during chondrogenesis in organ culture after various culture periods. Mesenchymal cells from limb buds of Day 12 mouse embryos were grown at high density. Within the first 2 days of the culture period, only alpha 1-integrin could be detected. Formation of cartilage-specific matrix on Day 3 was accompanied by the occurrence of alpha 3-integrin. On Day 7, alpha 3 was present only in cartilage nodules, whereas alpha 1 was strongly expressed in the perichondrium and was more or less homogeneously distributed in the surrounding mesenchyme. On Day 14, alpha 1-integrin was again detectable in cartilage. We suggest that the change in collagen formation from Type I to Type II during chondrogenesis is accompanied by a change in integrin expression from alpha 1 to alpha 3. Conversely, dedifferentiation of chondrocytes in aging cartilage is accompanied by the occurrence of collagen Type I and alpha 1-integrin. Therefore, a strict correlation between the collagen type synthesized by the cells and the appropriate receptor presented by the cells is suggested.

Animals↗