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Biomedical subjects

K Richter

Publications and source records attributed to K Richter.

At least 19 recordsLinked to original sources
PubMed1992

Isolation and sequence of a cDNA encoding the precursor of a bombesinlike peptide from brain and early embryos of Xenopus laevis.

A cDNA encoding the precursor of a bombesinlike peptide was isolated from brain of Xenopus laevis. The predicted end product resembles neuromedin B, which was originally isolated from mammalian spinal cord. The mRNA for this precursor was also present in gastrointestinal tract and in ovaries. Moreover, it could be detected in early embryos (stage 2 and stage 10) of X. laevis. These findings suggest novel roles for peptides of the bombesin family in oocyte maturation and early amphibian development.

Amino Acid Sequence↗
PubMed1992

A cDNA from brain of Xenopus laevis coding for a new precursor of thyrotropin-releasing hormone.

Thyrotropin-releasing hormone (TRH) is found in large amounts in the skin of Xenopus laevis. In this tissue, 3 TRH precursor mRNAs can be detected of which the 2 more expressed encode almost identical proteins. However, Northern blot analysis of TRH precursor mRNAs in the brain of X. laevis revealed the existence of a new mRNA of about 1200 nucleotides which was present along with the larger TRH precursor mRNA identified in the skin. A cloned cDNA of a TRH precursor, corresponding in size to this new mRNA, was isolated and sequenced from a Xenopus brain lambda gt11 library. It encodes a precursor polypeptide which also contains 7 copies of TRH. However, at the amino acid level it differs by about 16% from the corresponding prepro-TRHs from skin. We have also attempted to characterize the gene encoding this prepro-TRH from Xenopus brain. Only the first and part of the second exon could be detected which are separated by an intron containing more than 8000 base pairs. Interestingly, the 5'-flanking region of this gene does not contain the characteristic promoter elements of the mammalian TRH genes suggesting marked differences in the regulation of their expression.

Amino Acid Sequence↗
PubMed1992

Processing, intracellular transport, and functional expression of endogenous and exogenous alpha-beta 3 Na,K-ATPase complexes in Xenopus oocytes.

The minimal functional Na,K-ATPase unit is composed of a catalytic alpha-subunit and a glycosylated beta-subunit. So far three putative beta-isoforms have been described, but only beta 1-isoforms have been identified clearly as part of a purified active enzyme complex. In this study we provide evidence that a putative beta 3-isoform might be the functional component of Xenopus oocyte Na,K-ATPase. beta 3-isoforms are expressed in the oocyte plasma membrane together with alpha-subunits, but beta 3-isoforms are synthesized to a lesser extent than alpha-subunits. The unassembled oocyte alpha-subunits accumulate in an immature trypsin-sensitive form most likely in the endoplasmic reticulum (ER). Injection of both beta 1- and beta 3-cRNA into oocytes abolishes the transport constraint of the oocyte alpha-subunit, renders it trypsin-resistant, and finally leads to an increased number of functional pumps at the plasma membrane. In addition, beta 3-isoforms as beta 1-isoforms depend on the concomitant synthesis of alpha-subunits to be able to leave the ER and to become fully glycosylated. Finally, alpha-beta 1 and alpha-beta 3 complexes expressed at the plasma membrane appear to have similar transport properties as assessed by ouabain binding, rubidium uptake, and electrophysiological measurements in oocytes coexpressing exogenous alpha 1- and beta 1- or beta 3-isoforms. Thus our data indicate that beta 3-isoforms have functional qualities similar to beta 1-isoforms. They can assemble and impose a structural reorganization to newly synthesized alpha-subunits which permits the exit from the ER and the expression of functional Na,K-pumps at the plasma membrane.

Animals↗
PubMed1992

Interaction of talinolol and sulfasalazine in the human gastrointestinal tract.

The absorption of talinolol (TA) 50 mg was investigated without and together with the co-administration of sulfasalazine (SASP) 4 g in 11 healthy young volunteers, in order to clarify gastrointestinal transit of TA. Without SASP, the tmax of TA was 2.8 h, Cmax was 112 ng.ml-1 and the half life was 12 h; the AUCo-t was 958 ng.ml-1.h. In the case of concomitant administration of SASP, TA was found only in serum from 3 individuals, with a Cmax of 23 ng.ml-1 and a mean AUCo-t of 84 ng.ml-1.h. TA was not detectable in 5 subjects and it was at the limit of detection (2 ng.ml-1) in 3 subjects. Pharmacokinetic analysis was not possible in any of those individuals. The reason for the interaction appears to be the adsorption of TA by SASP. An interval of 2-3 h should elapse between giving SASP and other drugs.

Adrenergic beta-Antagonists↗
PubMed1992

[Thoracic radiographs with the AMBER system. A comparison of the diagnostic image quality of film-screen and storage-phosphor radiographs on the grid-partition stand and the AMBER system].

Since April 1990, chest radiographs in the Mannheim clinic have been performed with a slit technique (Kodak AMBER System). In this study, image quality from conventional film/screen combination and from storage phosphor radiography was compared with that from the AMBER system. Phantoms were used to measure spatial resolution and to determine the detectability of nodules. Image quality affecting various structures within the thorax was evaluated on 200 p.a. and 48 lateral radiographs by three radiologists from Mannheim and four from Berlin. In the retrocardiac, retrodiaphragmatic, mediastinal and peripheral portions the best image quality was obtained by film/screen with the AMBER system. Compared with conventional film/screen images, there was no improvement from the AMBER system within the lung parenchyma. The use of storage phosphor plates with the AMBER system did not lead to any further improvement in image quality.

Evaluation Studies as Topic↗
PubMed1992

The biliary and renal elimination of the new muscarinic-1-antagonist AWD 26-06 in volunteers with T-tube after cholecystectomy.

The biliary and renal elimination of the new muscarinic-1-antagonist AWD 26-06 were investigated in 6 female volunteers (age: 26-69 years) 9-14 days after cholecystectomy and T-tube construction. After a single oral dose of 50 mg AWD 26-06 as an aqueous solution the amount of the unchanged substance was determined in serum, T-tube bile and urine with a special HPLC-method. The concentration maximum was reached earlier and higher in bile (60 +/- 22 min; 10.8 +/- 5.7 micrograms/ml) than in serum (73 +/- 28 min; 0.98 +/- 0.53 micrograms/ml). During the whole observation time of 24 h the AWD 26-06 concentration in bile was 2-21-fold higher than in serum. In mean 2.3 +/- 1.5% of the administered dose were eliminated unchanged by bile and 12.2 +/- 5.9% by urine. More than 70% of the dose were metabolized. The results gave a hint at active liver transport processes and an enterohepatic recirculation. A drug interaction was observed with valproic acid on the metabolic level. The great interindividual variability of pharmacokinetic data can be caused by the heterogeneity of the subject group and a genetic polymorphism in the metabolism of AWD 26-06. The bile sampling by means of a T-tube is a simple but effective method under consideration of special conditions.

Adult↗
PubMed1992

[The pharmacokinetic behavior of AWD 26-06 in humans following single and multiple administration].

The pharmacokinetics of the muscarinolytic drug AWD 26-06 was investigated in two subjects after a single dose of 50 and 100 mg, respectively, and with six subjects after repeated dosage. The half time (t1/2) is 2.4 and 2.6 h, respectively, the height of the concentration maximum (Cmax) 500 and 1400 ng.ml-1, respectively, and the area under the curve (AUC) 2155 and 4334 ng.ml-1.h, respectively. The repeated dosage (25 mg every 8 h for 7 d) showed a small increase of the serum level. The t1/2 and the mean residence time (MRT) at the 1st and the 8th d are 2.6 h (range: 1.8-2.9 h) and 4 h (range: 2.7-5.8 h), respectively. The point (tmax) and the Cmax were not different at the 1st and 8th d: mean tmax (1st d) 1.1 h (range: 1.0-1.5 h), mean tmax (8th d) 0.9 h (range: 0.75-1.0 h); Cmax (1st d) 227 ng.ml-1 (range: 160-320 ng.ml-1), Cmax (8th d) 282 ng.ml-1 (range: 168-320 ng.ml-1). There were also no differences for the AUC0-t at the 1st and 8th d (1st d) 815 ng.ml-1.h (range: 610-1134 ng.ml-1.h). The simulation of the serum level by means of the data from the single dose were established by this investigation. Typical subjective muscarinolytic symptoms (e.g. dryness of the mouth, diminution of accommodation) were observed after the 2nd/3rd dosage. These signs diminished 24-36 h after discontinuation of the dosage. The parameter ALAT, proteins of plasma, and blood cell count were not changed at the end of therapy in comparison to the beginning.

Adult↗
PubMed1991

A family of bombinin-related peptides from the skin of Bombina variegata.

A peptide fraction was isolated from the skin of Bombina variegata that showed antimicrobial activity. This fraction contained several molecular species, all of them consisting of 27 amino acid residues, with a constant C-terminal region (from residues 14-27), including an amidated carboxyl end and a variable N-terminal segment. These peptides are related but not identical to bombinin [Csordas, A. & Michl, H. (1970) Monatsh. Chem. 101, 182-189]. By using synthetic oligonucleotides corresponding to the C-terminal region of the peptides, a cDNA library from the skin of B. variegata was screened and several positive clones coding for the corresponding peptide precursors were isolated and sequenced. Each clone contained the genetic information for a different bombinin-like peptide. The antimicrobial activity towards different bacterial species of a synthetic peptide corresponding to one of the variants deduced from cDNA sequences was tested. This peptide was found to be mainly active against different isolates of Staphylococci and Escherichia coli.

Amino Acid Sequence↗
PubMed1991

Prevalence of antibodies to recombinant hepatitis C virus protein C100-3 and of elevated transaminase levels in blood donors from Northern Germany.

Antibody to recombinant hepatitis C virus protein C100-3 (anti-C100-3) was assayed by a first generation enzyme-linked immunosorbent assay (ELISA; Ortho Diagnostics) in 116,700 blood donors who had not been tested before. Total prevalence of repeatably positive donors was 0.72% (n = 842). Prevalence increased significantly from 0.42% at 18-27 years of age to 1.26% at greater than or equal to 58 years. Donors with elevated serum transaminase levels were significantly more often anti-C100-3 positive, but in 98.7% of donors with current or 99.1% with previous transaminase elevations, anti-C100-3 was not found. Elevated transaminases were more often associated with positive anti-C100-3 in females than in males. However, in the total donor population no significant differences of anti-C100-3 prevalence were found between the sexes. During follow up at three subsequent blood donations, 1.08% of donors were positive at least once, but only 0.48% were consistently positive. The cutoff of the Ortho ELISA was not in the minimum of the frequency distribution between positive and negative samples, but far within the range of the negative signals, i.e. the test is likely to produce a significant number of false-positive results. In retesting positive samples with two ELISAs from other producers only a 22% to 65% agreement was found. In a low prevalence group such as German blood donors, the first generation ELISAs for anti-C100-3 produced more false than specific positive results. Most donors with elevated alanine aminotransferase (ALT) are anti-C100-3 negative.

Adolescent↗
PubMed1991

A model for cryosectioning based on the morphology of vitrified ultrathin sections.

Electron microscopy of vitrified ultrathin sections allows cell ultrastructure to be studied in the hydrated state. Sectioning of the frozen material is, however, a limiting step, since the cutting forces cause severe mechanical deformation. In order to address this problem, we have investigated the surface of cryosections. It is shown that cryosections have two fundamentally different surfaces. One surface is rough, deformed by cutting-induced deformation lines which are orientated perpendicular to the cutting direction. The other surface, in comparison, is not affected by those deformation lines. Except for knife marks it is smooth. In order to explain the observations, the following model is proposed. The rough relief corresponds to the former block face. Its roughness originates from material that is squeezed out of the section plane when the section is compressed in the cutting direction and bent away from the specimen block. The smooth section surface is the surface in contact with the knife during the sectioning. This contact keeps the surface smooth while imprinting the knife marks.

Animals↗
PubMed1991

The influence of food on the absorption of diclofenac as a pure substance.

The interaction of diclofenac as a pure substance was investigated without and with concomitant administration of food in 8 healthy, male volunteers (age: 23-29 years, body weight: 60-87 kg). Diclofenac was given as a pure substance by means of a rapid dissolving capsule in a dose of 50 mg. Paracetamol (1.5 g), a marker of gastric emptying rate, was administered simultaneously with diclofenac in order to elucidate the influence of gastric emptying rate on diclofenac absorption. The bioavailability was determined according to the time (tmax) of the concentration maximum in plasma (Cmax) and the area under the curve (AUC). Food significantly delays tmax of diclofenac (without food: [mean +/- SD] 0.8 +/- 0.5 h, range: 0.5 +/- 2 h; with food: 2.4 +/- 0.9 h, range: 1.5-4 h) and diminishes Cmax (without food: 1,125 +/- 765 ng/ml, range: 95-2,100 ng/ml; with food: 434 +/- 151 ng/ml, range: 250-555 ng/ml). The AUC is not influenced (without food: 1,217 +/- 368 ng/ml x h; with food: 1,037 +/- 267 ng/ml x h). The bioavailability of paracetamol is unchanged. It is concluded that the diminishing of Cmax and the delay of tmax of diclofenac are possibly the consequence of an interaction with food and not of the delayed gastric emptying per se.

Acetaminophen↗
PubMed1991

Localization of a nervous system-specific class II beta-tubulin gene in Xenopus laevis embryos by whole-mount in situ hybridization.

A neural-specific beta-tubulin mRNA is expressed in the developing central nervous system shown by whole-mount in situ hybridization experiments. Of special interest is the fact that from the late blastula (stage 9; Nieuwkoop and Faber, 1967; Hausen and Ribesell, 1991) until the early neurula (stage 13) the signal can be found not only in the presumptive neural plate but also in the presumptive epidermis. Later in development (from stage 13) the specific mRNA becomes restricted to the presumptive brain and spinal cord area. The results are discussed in the context of predisposition and (pre)determination.

Animals↗
PubMed1991

Freezing: facts and hypothesis.

Hexagonal ice crystals formed in frozen biological specimens are large and branched. They can produce severe structural damage by solute segregation but there are also cases where they seem to cause only minor damage. When cooling is more rapid, cubic ice crystals can be formed. These are small and in general, they cause little damage. These observations can be readily explained with the hypothesis that large hexagonal ice crystals can originate from the rewarming induced transformation of a large number of cubic ice crystals. This transformation would take place without significant solute displacement.

Animals↗
PubMed1991

[Merkel cell tumor (neuroendocrine carcinoma of the skin) in an unusual location. Immunohistochemical and lectin histochemical findings].

Neuroendocrine carcinoma of the skin usually occurs in elderly individuals. Head and neck are the most common primary sites followed by the extremities and trunk. As this tumor represents a remarkable rarity in younger people, we report the case of a 33-year-old woman with a neuroendocrine carcinoma in an unusual localization. Diagnosis was based on the results of the examination of a metastasis in the inguinal lymph nodes. The lesion at the Labium minus pudendi which is to be considered the primary tumor was detected several months later. Diagnosis of Merkel cell tumor until recently had depended on ultrastructural demonstration of dense-core membrane-bound granules. Today, diagnosis can be secured also by optical light microscopy, on the basis of a certain constellation of immunohistochemical and lectin histochemical findings.

Adult↗