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H Leonhardt

Publications and source records attributed to H Leonhardt.

At least 55 records · Page 3Linked to original sources
PubMed1988

Construction of a shuttle vector for inducible gene expression in Escherichia coli and Bacillus subtilis.

The construction of a shuttle vector for inducible gene expression allowing fast and easy cloning in Escherichia coli and subsequent transformation of Bacillus subtilis is presented. The expression is based on the regulation of the tac promoter by the Lac repressor which was assayed with the xylE gene from Pseudomonas putida as a marker gene. The lacIq gene, transcribed by the strong spo promoter, allowed full repression of the weak tac promoter.

Bacillus subtilis↗
PubMed1987

Compartments in the organum vasculosum laminae terminalis of the rat and their delineation against the outer cerebrospinal fluid-containing space.

Using intravenously injected horseradish peroxidase (HRP) as tracer, we demonstrate, that--in contrast to other neurohemal regions--the organum vasculosum laminae terminalis (OVLT) is composed of two functionally different divisions. Both parts of the OVLT are endowed with fenestrated capillaries which, however, obviously differ in their permeability for HRP. In one of these portions the neurohemal region remains unlabeled under the experimental conditions used, while the other portion, in analogy to the majority of neurohemal regions, is labeled by the tracer. The functionally different divisions of the OVLT are separated from one another by tanycytic processes and meningeal cells establishing a barrier between the two hemal compartments. The meningeal elements penetrate the organ in the form of an uninterrupted layer; they are continuous with the pia mater and produce large amounts of basal lamina-like material. Furthermore, they provide the delineation of the OVLT against the outer cerebrospinal fluid-containing compartment, a structural feature that is characteristic of both divisions of the OVLT and corresponds to the arrangement of meninges in all other portions of the brain where a blood vessel penetrates its surface.

Animals↗
PubMed1986

The absorption of piretanide from the gastro-intestinal tract is site-dependent.

The absorption of piretanide was investigated after placing the drug in the stomach, duodenum and ascending colon under visual control. The relative amounts absorbed and the rates of absorption were estimated from the area under the curve and the total mean time, respectively. Similar amounts of piretanide were absorbed and at almost the same rate after placement in the stomach and duodenum; the area under the curve for the stomach was 250 ng h/ml and for the duodenum 243 ng h/ml, the mean absorption times being 1.97 h and 1.51 h respectively. A marked difference was observed in the rate of from the ascending colon; the area amounted to 66 ng h/ml and the mean time to 3.99 h. Although area values for the colon were significantly different from those observed with the stomach and duodenum, it must be emphasised that the amount absorbed depends on the time the drug is in contact with the absorbing surface. There is discussion of whether the differences in absorption between the duodenum and colon can be explained by the physico-chemical properties of the drug alone, or whether the results reflect a saturable transport mechanism.

Adult↗
PubMed1985

Absorption of glibenclamide from different sites of the gastro-intestinal tract.

In a study of eight volunteers and six patients, glibenclamide was placed at different sites of the gastro-intestinal tract under visual control. The dose was instilled once into the stomach and once into the duodenum of the eight volunteers in a randomized crossover design. The six patients underwent diagnostic colonoscopy, and the dose was placed into the ascending colon if pathological findings were not present. The area under the concentration-time curve, completed by extrapolation, and the mean residence time of the drug in the body were calculated. These pharmacokinetic characteristics were examined using a Jonckheere test for ordered alternatives and a Wilcoxon signed rank pair test. The means of the areas under the curve were 477 +/- 131 ng . h ml-1 for the stomach, 475 +/- 142 ng . h ml-1 for the duodenum and 486 +/- 301 ng . h ml-1 for the colon. The mean residence time changed from 2.67 +/- 0.35 h for the stomach to 2.42 +/- 0.48 h for the duodenum and 3.55 +/- 0.68 h for the colon. These results indicate that although glibenclamide is absorbed from all three sites of the gastro-intestinal tract to the same extent, the rates of absorption are different. It is discussed whether these findings really confirm the pH-partition hypothesis in drug absorption. Since glibenclamide--a weak acid--has a pK-value of about 6.5, these data seem to confirm the pH-partition hypothesis of drug absorption.

Adolescent↗
PubMed1984

Compartments and perivascular arrangement of the meninges covering the cerebral cortex of the rat.

The intercellular clefts of the brain and the leptomeninges, and the perivascular spaces were studied with reference to the results obtained in a previous study (Krisch et al. 1983). The spatial relationships of these compartments were analyzed at the electron-microscopic level. Horseradish peroxidase (HRP) was injected into the brain or into the contralateral ventricle. The pattern of distribution of HRP depends on the boundary situation in the individual compartments. The inner and outer pial layers accompany the vessels intruding into the brain. In the Virchow-Robin space the pial funnel obliterates within a short distance. The inner arachnoid layer is continuous with the outer arachnoid layer when it covers the vessels traversing the meningeal space. The perivascular compartment is not in communication with the arachnoid space; moreover, the pial funnel within the Virchow-Robin space is sealed off against the arachnoid space. Thus, blood vessels traversing the meningeal spaces and subsequently penetrating the brain surface are exposed to the common intercellular compartment represented by the intercellular clefts of the brain and the leptomeninges; this compartment does not communicate with the other compartments. The cerebrospinal fluid located in this intercellular compartment is preferentially drained into the upper cervical lymph nodes.

Animals↗
PubMed1983

The meningeal compartments of the median eminence and the cortex. A comparative analysis in the rat.

The intervascular segments of the leptomeninges of the rat were studied by the use of horseradish peroxidase (HRP) in short-term experiments. HRP was injected (i) intravenously, (ii) into the lateral ventricle, (iii) into the cortex, and (iv) into the meninges. The composition of the meninges covering the median eminence (ME) was analyzed in comparison to the results obtained with the parietal cortex. The meninges covering the cortex show the following pattern of layers and compartments: The intercellular compartment comprises the intercellular clefts of the neuropil, the subpial space, and the intercellular clefts of the leptomeninges. The pial space establishes a second compartment. The third compartment is the arachnoid space. The intercellular clefts of the dura form the fourth compartment. At the border of the ME, the neurothelium and the outer arachnoid layer are rolled up to form a tissue frame around a hollow pit that is covered by a diaphragm consisting of meningeal cells; the latter separate the hemal milieu of the ME from that of the dura. The hemal and the cerebrospinal fluid (CSF) milieus may communicate to a limited extent only within the subpial space adjacent to the ME. The CSF-containing compartments of the pial and arachnoid spaces terminate at the brain-facing insertion of the tissue frame. According to the present results, an anatomical basis for a short-loop feedback from and to the neurohemal region of the ME via the CSF does not exist.

Animals↗
PubMed1981

Red blood cell aging as a model to influence pharmacologically the red cell filterability.

A method to filter whole blood through 5-micron filters at a pressure of 20 cm column of water and the use of aging red cells as a reproducible procedure to generate rigidified cells is described. The system is sensitive enough to evaluate in pharmacologic screening possible influences of chemical agents on red cell deformability. Investigations with the methylxanthine derivates pentoxifylline and theophylline, the beta-blocker penbutolol and prednisolone, revealed that only the first compound has a dose-dependent effect on red deformability.

Blood Flow Velocity↗
PubMed1981

[Retrospective evaluations on the importance of laparoscopy in the differentiation of acute oedematous and acute hemorrhagic necrotising pancreatitis in the early stage of the disease (author's transl)].

Of 32 patients with acute pancreatitis on whom laparoscopy was performed within 3 days after the pain symptoms started, the type of inflammation could be assessed in 31 cases. Technically, the intervention did not cause any problems. In one case the examination had to be stopped prematurely due to hypotension, in another case the pain reaction led to premature discontinuance of the examination; other complications did not occur. The present experiences with this morphological diagnostic method have proven to be particularly useful for the indication regarding surgical interventions; it is, therefore, justifiable to compare the value of this method with that of noninvasive morphological methods (ultrasonography, and computer tomography).

Acute Disease↗
PubMed1980

[Improvement of blood viscosity in sickle-cell anaemia by pentoxifylline (author's transl)].

An 18-yer-old girl with homozygotic sickle-cell anaemia (HbSS: HbS 65% and HbF 4.9%) suffered from painful haemolytic crises since six years of age, these crises occurring almost weekly of late. Pentoxifylline (2.4 g daily in three divided doses) decreased blood viscosity in vitro from 6.7 to 4.9 (normal 4.3-5.3 at 46 s-1 shear rate) and erythrocyte filtration accelerated from 127 to 77 s (normally 30-49 s). Although pentoxifylline could not prevent haemolysis, previously necessary analgesics were no longer required, even during haemolytic crises. Thus the drug lowers viscosity also in vivo and thus improves microcirculation. It has a prophylactic effect against vaso-occlusive complications of sickle-cell anaemia.

Adolescent↗
PubMed1980

Luliberin and somatostatin fiber-terminals in the subfornical organ of the rat.

With the aid of light- and electron- microscopic immunocytochemistry, somatostatin- and luliberin (LRF)-positive fibers can be demonstrated in the rat subfornical organ (SFO). Each of the neurohormones has a specific location: LRF in the lateral parts of the organ, and somatostatin in the center of the posterior zone. Common to both neurohormone-containing fibers is the pattern in which they reach the organ as well as the fact that their terminals are located in the perivascular spaces of fenestrated vessels, i.e., within the limited neurohemal regions of the organ. Since injection of India ink of different colors demonstrates that the capillary bed of the SFO is connected with the central capillaries of the choroid plexus, the question arises as to whether the neurohormones released in the area of the SFO influence the choroid plexus.

Animals↗
PubMed1980

An intermittent somatostatin-immunoreactivity in the cortex and basal ganglia of the rat.

Using light microscopic immunohistochemistry, somatostatin-positive structures were observed in the cortex of the rat. These structures, including cells and fibers, are widely distributed in all cortical laminae and are also found in the basal ganglia. The positive results were obtained exclusively in two groups of animals sacrificed during two different months of two subsequent years. The reason for this variability in the immunocytochemical stainability of cortical structures remains enigmatic.

Animals↗
PubMed1980

Neurohormones in the intercellular clefts and in glia-like cells of the rat brain.

With the aid of electron microscopic immunocytochemistry following the application of antisera against somatostatin and luliberin (LRF), a labeling of the intercellular clefts in different areas of the brain was observed. This labeling is especially conspicuous near the basal pose of the cuboidal ependymal cells, but is also generally present in all regions containing neurohormone-producing perikarya or their processes (for example, the preoptic area, the basal ganglia and the cortex). Furthermore, in all these regions displaying labeled intercellular clefts, glia-like cells and sparsely ciliated ependymal cells are found, the secondary lysosomes of which exhibit an immunoreactivity resembling that observed in the intercellular clefts. As sources of the immunoreactive material the following possibilities are discussed: (i) perikarya producing somatostatin or LRF, situated in the wall of the third ventricle and sending fibers between the cuboidal ependymal cells, (ii) hypothalamic and extrahypothalamic projections of both peptidergic systems, and (iii) in the case of somatostatin, immunoreactive perikarya in the cortex.

Animals↗