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Biomedical subjects

H J Merker

Publications and source records attributed to H J Merker.

At least 91 records · Page 5Linked to original sources
PubMed1991

Morphologic changes of the basal lamina in the small intestine of Xenopus laevis during metamorphosis.

Further investigations of the epithelial and mesothelial basal lamina of the duodenum of Xenopus laevis during metamorphosis were performed by means of scanning electron microscopy (SEM) and histochemical techniques using polyethyleneimine (PEI) to demonstrate anionic sites as well as light- and transmission-electron-microscopic methods involving morphometric analysis. The basal lamina of the duodenal epithelial cells was smooth, and it was occasionally curved along the processes of the epithelial cells (stages 56-59). The basal lamina became thicker by folding, and the thickness of the folded basal lamina exceeded 1 micron (stages 60-62). Subsequently, the folded basal lamina disappeared gradually and became almost smooth again and consisted of only one layer (stages 63-66). After removing the epithelium by boric acid, SEM revealed that the small ridges of the basal lamina protruded like a mesh-work into the luminal side, and the luminal surface of the basal lamina became smooth at later stages of the metamorphic climax. The electron-dense granules of PEI-positive material were localized at both sides of the lamina densa at regular intervals (80-100 nm). The basal lamina of the mesothelial cells was almost smooth at stages 56-59 and started to show occasional slight folding. This folding became continuous and deeper (stages 60-62). The folded mesothelial basal lamina disappeared except for the cell-associated basal lamina and became smooth again at later stages of the metamorphic climax (stages 63-66). These morphologic changes of the basal lamina observed in the epithelium and mesothelium may be induced by common factors. We suggest that physical changes in the small intestine involving the shortening and narrowing should be a main factor to cause these changes in the basal lamina. Furthermore, morphometric analysis proposed that the basal lamina becomes more complex by adding newly synthesized basal lamina material, especially in the epithelium.

Animals↗
PubMed1991

Morphological and histochemical pattern of response in rat testes after administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

Testes of rats, which had been injected with a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.3 micrograms/kg-25 micrograms/kg body weight [BW]), were studied after 7 days using morphological and histochemical means. Light and electron microscopic examination revealed that TCDD affected testicular morphology in a dose-dependent manner. TCDD led to decreased intercellular contact, indicated by wide intercellular spaces between Sertoli cells between and Sertoli cells and neighbouring germ cells. Morphological alaterations in rat testes after TCDD administration included the sloughing off of premature spermatids into the tubular lumen and numerical increase of necrotic germ cells, in particular pachytene spermatocytes. Compared with control animals, Sertoli cells of treated rats exhibited an increased amount of lipid droplets and phagolysosomes. Vacuolization of the cytoplasm and fragmentation of the Sertoli cells occurred frequently. Examination of the different spermatogenic stages revealed that no stage was specifically susceptible to TCDD. In Leydig cells a decrease in enzyme activity of 3 beta- and 17 beta-hydroxysteroid dehydrogenases became evident by histochemical investigation. This effect on steroidogenesis was already found at a dose of 1 microgram/kg BW TCDD, whereas morphological effects were seen in the germinal epithelium for the first time at 3 micrograms/kg BW.

17-Hydroxysteroid Dehydrogenases↗
PubMed1991

Morphology, differentiation and matrix production of liver cells in organoid cultures (high density cultures) of fetal rat livers.

The aim of this study was to demonstrate the morphology and matrix synthesis of embryonic rat liver cells (day 18 of gestation) in organoid cultures (high density cultures) with electron microscopic and immunomorphological techniques. For this purpose the cells of embryonic rat livers were isolated enzymatically and grown in an organoid culture (high density culture) for 3 weeks in a Trowell system. During the first 48 h a sorting-out process took place, i.e. liver and blood-forming cells met to form aggregates. In between mesenchymal cells were seen. Vessel-like cavities developed. Electron microscopic inspection of the hepatocytes did not reveal any lesions of the cell organelles after 14 days in culture. As late as after a 3-week culture period mitochondrial swellings and an increased number of autophagic vacuoles were observed. A rim of collagenous fibrils or fibrillar bundles and granular matrix structures was perceptible as early as after 7 days in culture. Immunofluorescence microscopic techniques revealed collagen types III, IV and VI as well as laminin, nidogen, heparansulfate-proteoglycan and fibronectin in these areas. Thus, the composition of the matrix in this culture system corresponds (apart from the absence of collagen type I) to the embryonic situation. Therefore, the organoid culture appears to be an appropriate technique to study the behaviour of hepatocytes in vitro. It is especially suited to demonstrate the formation of matrix components in liver cells and their extracellular occurrence.

Animals↗
PubMed1990

Effects of valproic acid, some of its metabolites and analogues on prenatal development of rats in vitro and comparison with effects in vivo.

Using a whole-embryo culture system valproic acid (VPA) and some of its metabolites (2-en-VPA, 4-en-VPA, 4,4'-dien-VPA) and analogues (ethyl-propyl-acetic acid, propyl-butyl-acetic acid, di-butyl-acetic acid, 2-methyl-2-ethyl-hexanoic acid, 1-methyl-1-cyclohexanoic acid) were tested for their potential to induce abnormal development. With regard to embryonic growth, development and abnormality rate, the tested compounds showed a wide range of "teratogenic potency" in vitro. In order to verify some of the in vitro results, in vivo experiments were performed. Pregnant rats were treated subcutaneously on day 10 of gestation with 2 x 330 mg VPA/kg, or 2 x 400 mg 2-en-VPA/kg, respectively. Evaluation of the embryos was performed on day 11.5 of gestation, corresponding to the in vitro experiments. VPA showed a high potential to induce abnormal development in vivo as well as in vitro, whereas 2-en-VPA was inactive under our experimental conditions. Problems connected with the evaluation of the predictive value of an in vitro test system for the detection of embryotoxic effects, such as "validation" and significance of pharmacokinetic data, are discussed.

Animals↗
PubMed1990

Effects of calcium channel blockers on the development of early rat postimplantation embryos in culture.

Rat embryos (9.5-day-old) were cultured for 48 h in the presence of nifedipine (NIF), nimodipine (NIM), nitrendipine (NIT), gallopamil HCl (GAL), verapamil HCl (VER) and diltiazem HCl (DIL). The effects on growth and morphogenetic differentiation in vitro were monitored. Dose-response relationships were evaluated, including an assessment of the "no-observed-effect-level" (NOEL) or the "lowest-observed-effect-level" (LOEL), and the lowest concentration tested inducing abnormalities in 100% of the embryos ("100% EL"). The morphological alterations observed at the highest concentrations were very similar for all six drugs. The abnormalities concerned yolk sac circulation and morphology, as well as heartbeat, the morphology of the heart, head, neural tube, or forelimbs, and the shape of the embryo. The abnormal embryos were also growth retarded (decrease in protein content and crown-rump length). Interference with calcium channel functions seems to represent an interesting model for studying a special kind of abnormal prenatal development, especially the differentiation of certain mesenchymal structures. The concentration ranges between NOELs and 100% ELs were found to be: NIM = 0.1-1 microgram/ml; NIT and VER = 1-10 micrograms/ml; DIL = 1-30 micrograms/ml, and LOELs-100% ELs were: GAL = 1-10 micrograms/ml; NIF = 10-30 micrograms/ml.

Abnormalities, Drug-Induced↗
PubMed1990

Ofloxacin in juvenile non-human primates and rats. Arthropathia and drug plasma concentrations.

Arthropathia in juvenile animals is the most important toxic effect induced by quinolones. We conducted pharmacokinetic and morphological studies with ofloxacin on non-human primates (Callithrix jacchus, Marmosets) and rats. In the marmoset, electron microscopy and the application of immuno-morphological methods proved to be suitable for the detection of specific alterations in cartilage (e.g. loss of proteoglycans and altered chondrocytes). Subsequently performed electron microscopic examinations in rats showed similar specific alterations of the femur cartilage surface after multiple oral applications of 600 mg ofloxacin/kg body wt. These results were correlated with pharmacokinetic data obtained for the same species. After single oral application of 100, 300 or 600 mg ofloxacin/kg body wt to 5 week-old rats peak plasma levels were achieved 15-45 min after administration indicating a rapid absorption of the drug. The following peak concentrations were measured for the three doses applied (mean +/- SD): 8.9 +/- 2.1, 22.6 +/- 7.5 mg/l and 33.5 +/- 9.8 mg/l, respectively. After 360 min the concentrations were 1.1 +/- 0.4, 5.9 +/- 2.5 and 15.9 +/- 5.1 mg/l, respectively. After subcutaneous injection of 100 mg ofloxacin/kg body wt the mean peak concentration was 27.7 +/- 2.6 mg/l after 45 min (0.5 +/- 0.2 mg/l after 360 min). In the marmoset higher plasma concentrations were measured with comparable doses. One, 3, and 6 h after the last of nine administrations of 200 mg ofloxacin/kg body wt, the mean (+/- SD) plasma concentrations were: 42.7 +/- 16.7, 40.6 +/- 9.5, and 26.5 +/- 3.6 mg ofloxacin/l plasma. Typical alterations of the joint cartilage of juvenile rats (e.g. opened chondrocyte cavities, swelling of rough endoplasmic reticulum and mitochondrial swelling in the chondrocytes) were induced by oral administration of ofloxacin at doses that were approximately 100 times higher than therapeutic ones, but led to peak plasma concentrations which were only approximately 10 times above the therapeutic level.

Administration, Oral↗
PubMed1990

Immunofluorescence-microscopic localization of collagen type IV and VI, laminin and nidogen in the livers of Callithrix jacchus during pre- and postnatal development.

The distribution of collagen type IV and VI, laminin and nidogen was investigated by immunofluorescence microscopy in the livers of marmosets (Callithrix jacchus) at various stages of development, i.e. on days 93, 111, 116 and 134 of gestation, 1 day postpartum and at the mature stage. Large amounts of collagen type IV could in all cases be demonstrated in the sinus wall and in all basal laminae outside the lobule. After the application of antibodies against collagen type VI the sinus wall showed a weak fluorescence reaction at the early stages and a strong binding towards the end of gestation which persisted up to the adult stage. In the periportal field it was mainly localized at the border between lobule and connective tissue. Laminin also increased gradually but could be demonstrated only until birth. In contrast, nidogen was present during the total prenatal and postnatal period. Therefore, collagen type IV and VI were not very suitable for the demonstration of an increase in matrix components under pathological conditions, because they occur already in large amounts in normal livers. However, the occurrence of laminin that was missing in the adult liver must be interpreted as pathological indication. The different occurrence of laminin and nidogen showed that these two substances were expressed and regulated independently of each other.

Aging↗
PubMed1990

Nude mice are not hairless. A morphological study.

In the present study, the morphological aspect of the skin and the hairs of athymic, macroscopically nude mice (NMRI, nu/nu) was investigated by descriptive light- and electron-microscopical methods and compared with the appearance of the skin and the hairs in normally haired mice (NMRI). These morphological studies revealed that athymic, macroscopically nude mice are not at all hairless, but have about the same number of hair bulbs, embedded in the hypodermis, as normally haired animals. However, within the hair follicles of athymic mice, the keratinization processes are obviously deeply impaired, resulting in the formation of short, crippled and bent hair shafts which only seldom emerge from the hair follicles. The cuticles of the inner root sheath and the hair are not built up, the cortex of the hair being composed by abnormal globular aggregates. The epidermis shows similar disturbances of keratinization, which are reflected by the presence of only few and thin bundles of tonofilaments in the basal, spinous and granular layers of the epidermis and, in the stratum corneum, by bizarrely formed and irregularly arranged lamellae of corneocytes, separated from one another. These results demonstrate that athymic, nude mice are not hairless but that the development and differentiation of hairs are severely injured in this mouse mutant. Analogously, the keratinization of the epidermis is also impaired. In view of the previously shown ectodermal defect as primary cause for the dysgenesis of the thymus, it seems to be probable that defects of the ectoderm are actually the common reason for both the thymus dysgenesis and the severe disturbances of hair development in 'athymic, nude' mice.

Animals↗
PubMed1990

Enzyme histochemical and histological changes in the adult rat kidney after prenatal gentamicin exposure.

Treatment of rats between day 15 and 20 of gestation with gentamicin caused histological as well as enzyme histochemical lesions in the kidney of the one year old offspring (F1 generation). Other organs were not significantly affected. Primarily in the female kidney dilated convoluted proximal tubulus with reduced or absent staining for brush border and lysosomal proteases, phosphatases and glycosidases and mitochondrial dehydrogenases were observed. In comparison, glomeruli were less frequently damaged and contained fewer capillary loops or irregularly arranged tissue elements with lowered or no activities for plasma membrane-associated proteases as well as specific and non-specific phosphatases. In addition, the activities of proteases and phosphatases in cortical and medullary endothelial cells of capillaries were reduced or even abolished in the kidney of the female and male F1 generation after treatment of their mothers with gentamicin.

Animals↗
PubMed1989

Influence of 13-cis and all-trans retinoic acid on rat embryonic development in vitro: correlation with isomerisation and drug transfer to the embryo.

In vitro experiments using whole rat embryo cultures show that all-trans retinoic acid (all-trans RA) administered at low concentrations (30 ng/ml culture medium) is 10 times more active than 13-cis retinoic acid (13-cis RA) and 3 times more active when administered at high concentrations (1000 ng/ml culture medium). Morphological investigation of the embryos shows that both substances directly influence embryonic development in an identical manner. Isomerisation products of the administered compounds (all-trans RA from 13-cis RA and vice versa) were detected by HPLC both in the culture medium and the embryo. Correlation of embryonic retinoid concentration with the observed effects led us to suggest that the isomerisation to all-trans RA is crucial in regard to 13-cis RA-induced abnormal embryonic development. A 100% effect can be induced in vitro with very low amounts of all-trans RA (7.2 ng/g) in the embryo.

Animals↗
PubMed1989

Reproductive toxicity and pharmacokinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 1. Effects of high doses on the fertility of male rats.

A study on the reproductive toxicity of 14C-TCDD in male rats was performed. Two dose regimes were applied subcutaneously: TCDD-25 (initial dose: 25 micrograms/kg body wt; maintenance dose: 5 micrograms/kg body wt) and TCDD-75 (initial dose: 75 micrograms/kg body wt; maintenance dose: 15 micrograms/kg body wt); the maintenance dose was administered once weekly. The rats were treated for 10 weeks before they were mated and throughout the entire mating period. The dose regime TCDD-75 led to a mortality rate of 93% within a period of 16 weeks. The first animals died during 4 weeks, and an LD50 was reached after 8 weeks. The dose regime TCDD-25 did not cause any mortality over a period of 12 weeks; but an LD10 was reached within 13-20 weeks. The body weight was significantly decreased in both groups treated with TCDD after 1 week of treatment. It stabilized in the TCDD-25-group 4 weeks after treatment and stayed at this level until the end of the treatment period. The most significant finding is the delayed fertilization by the treated males; 15% of the males were found to be sterile. The mating index (84%) and fertility index (14 +/- 11 days) of the TCDD-25-group were lower when compared with controls (95%, 8 +/- 5), but the pregnancy index was not reduced. Application of the chosen TCDD doses led to clear-cut morphological changes of the testes. The Sertoli cells were changed (increased occurrence of vacuoles, swelling of endoplasmatic cavities), and the contact between the Sertoli cells and spermatogonia was disturbed, which might indicate an inhibited maturation of spermatozoa precursors.

Animals↗
PubMed1989

Differentiation of rat intestinal epithelial cells is induced by organotypic mesenchymal cells in vitro.

Stromal-epithelial interaction is a potent driving force in the developing intestinal mucosa which ensures tissue specific cellular differentiation. The mechanisms involved are relevant to tissue renewal in adult organs yet they have not been elucidated because of the lack of appropriate in vitro models. In this study, we have investigated the interaction between intestinal mesenchymal and epithelial cells at the cellular level in vitro. Fetal rat intestinal epithelial cell colonies explanted in vitro on the 15th day of gestation, which failed to mature in plain monocultures, were reassociated in coculture with three different types of mesenchyme:fetal skin, gastric and intestinal mesenchyme. Only fetal epithelial cells cocultured with intestinal (homologous) mesenchyme acquired definite signs of differentiation within three to six days. These primitive epithelial cells were shown by electronmicroscopy to become highly polarized, connected by tight junctions and covered with a regular brush border. Three brush border enzymes were strongly expressed in homologous cocultures and their activity was sensitive to dexamethasone. In contrast, fetal epithelial cells cocultured with skin or stomach derived mesenchyme under identical conditions failed to differentiate in vitro: they remained flat, unpolarised and expressed only low enzyme activity. The unique potential of the small intestinal mesenchyme to promote intestinal epithelial differentiation is discussed.

Animals↗
PubMed1989

Connective tissue of the livers of newborn and adult marmosets (Callithrix jacchus).

Immunofluorescence microscopic and electron microscopic investigations revealed components of the matrix and of the basal lamina (collagen type I, III, IV and V, BL-heparan sulfate and fibronectin) in the sinus wall (Disse's space) of the livers of newborn and adult marmosets (Callithrix jacchus). Collagen type I was missing in both the two age groups. Small amounts of laminin were present in the livers of newborn and absent in those of adult animals, whereas collagen type III occurred in the form of delicate fibres. Light microscopic inspection showed a continuous distribution of all other components in the sinus wall. The amount of collagen type III and V increased depending on the age. Electron microscopic investigations revealed single or bundled fibrils (20-30 nm) and filaments (10-12 nm). After addition of tannic acid, plaques of a fine-filamentous network and incorporated granules were observed. After addition of resting Ruthenium Red, electron-dense granules (20-60 nm) were irregularly distributed in the structureless space, resting on collagenous fibrils and cell membranes. The fibrils were allocated to collagen type III, the filaments to collagen type V. The plaques were supposed to contain heparan sulfate, collagen type IV and fibronectin. The absence of a Lamina densa of the basal lamina was attributed to the absence of laminin which probably plays an important role in the formation of this layer. Differences in the distribution pattern of the matrix components and thus a functional mosaic of the permeability of Disse's space were assumed. The complete absence of collagen type I and laminin in the lobules makes the adult marmoset liver especially suited for studies on the importance of this collagen type under pathological conditions, since both components are expressed in this way.

Animals↗
PubMed1988

Prenatal toxicity of acyclovir in rats.

Pregnant rats were treated during organogenesis with s.c. injections of acyclovir and the embryos were evaluated on day 11.5 of gestation (crown-rump length, somites, protein content, score, abnormalities, histological examination). After eight injections of 50 mg/kg body wt on days 9, 10, and 11 of pregnancy a reduction of the crown-rump length was noticed. After 100 mg/kg this effect was more pronounced. With two or three applications of this dose on day 10 specific embryonic abnormalities were visible: the shape of the head was abnormal, the width of the skull had decreased resembling a beak-like visceral cranium. With a single administration of 200 mg/kg on day 10 we found a similar but slightly more pronounced outcome. A drastic change of all variables was obtained after eight injections of 100 mg/kg on days 9, 10, and 11. Comparatively we measured maternal plasma concentrations of acyclovir 1 h after the administration of 50, 100 or 200 mg/kg body wt. After an injection of 50 mg/kg on days 9, 10, and 11 of gestation (three injections/day) the plasma levels ranged from 19.1 to 40.0 mg/l (1 mg/l = 4.44 microM). No cumulation was observed. In contrast, a cumulative effect was detected following a dose of 100 mg/kg. After the first injection of this dose a mean value (+/- SD) of 60.3 +/- 14.7 mg/l (n = 16) was obtained. In this case a third injection increased the mean plasma level to 124.6 +/- 16.6 mg/l (n = 5). Further injections, however, led to decreasing levels. One hour after administration of 200 mg/kg body wt acyclovir levels ranged from 120.0 to 163.9 mg/l. We conclude that acyclovir, at doses leading to plasma concentrations well above the therapeutic level in the dam, interferes with the embryonic development in the rat. Acyclovir induces typical gross structural abnormalities which have been first observed using a whole embryo culture system.

Acyclovir↗
PubMed1988

Embryotoxic effects of thalidomide-derivatives in the non-human primate Callithrix jacchus. I. Effects of 3-(1,3-dihydro-1-oxo-2H-isoindol-2-yl)-2,6-dioxopiperidine (EM12) on skeletal development.

The response of pregnant marmosets (Callithrix jacchus) to the thalidomide derivative EM 12 was evaluated. EM 12 was selected for these studies because it is more active than thalidomide and is much more stable for hydrolysis. Skeletal gross structural abnormalities were observed when EM 12 was given to marmosets for 3-7 days during the period between days 49 and 60 post ovulation. Using the treatment schedule finally adapted in our laboratory, i.e. treatment during days 51-57 post ovulation, doses of 5 (or 10) mg EM 12/kg body wt induced the typical limb abnormalities known from man with an 80-100% certainty. In some animals we could observe the typical pattern of abnormalities even with doses as low as 1 mg EM 12/kg body wt. Abnormalities of the skeleton induced during this sensitive period are described. None of these (except some bifurcations of ribs) were seen in any of the ten litters (23 fetuses) serving as controls during the period of the study.

Abnormalities, Drug-Induced↗
PubMed1988

Hypertension and nephrotoxic lesions in rats 1 year after prenatal exposure to gentamicin.

Using the aminoglycoside antibiotic gentamicin persistent functional and morphological changes were induced prenatally in the rat kidney. After 6 days of s.c. treatment (110 mg gentamicin/kg body wt) from day 10 to 15 of pregnancy complete resorption was noticed in 8 of the 14 treated animals. Fifty-three newborn were obtained from six dams. One year later only 26 rats (16 male, 10 female) were still alive. The systolic arterial pressure of the female offspring was significantly increased (139 +/- 15 mm Hg versus 112 +/- 9 mmHg) compared with controls. No statistically significant effect could be noticed in the male offspring (128 +/- 15 mm Hg versus 118 +/- 21 mm Hg). Corresponding results were obtained from analysis of urea plasma concentrations. Another cohort of pregnant rats received daily injections of gentamicin from day 15 to 20 of pregnancy (110 mg/kg body wt s.c.). In this group 59 newborn from a total of 109 died within the first 5 days after birth. Six litters were observed postnatally. One year after birth the following blood pressure values were determined: 122 +/- 14 mm Hg (male) and 132 +/- 17 mm Hg (female). Urea plasma concentrations were significantly higher in female, but not in male, offspring. Light and electron microscopic inspection revealed pathological changes in the kidneys of the female offspring only. The degree of maternal kidney damage - which shows considerable variations - was monitored during the treatment period. For this purpose the plasma gentamicin and urea concentrations were measured on 3 days of treatment in all of the pregnant animals. The postnatal data (mortality, blood pressure, and urea plasma concentrations) show a correlation to the degree of maternal kidney impairment.

Animals↗