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Biomedical subjects

F Peters

Publications and source records attributed to F Peters.

At least 37 records · Page 2Linked to original sources
PubMed2000

Low frequency voltage clamp: recording of voltage transients at constant average command voltage.

We implemented a simple feedback system that modifies the conventional current clamp mode of a patch clamp amplifier so that transient potentials, such as action potentials and synaptic potentials, can be measured as in the usual current clamp, while the average membrane potential is kept constant at a value chosen by the user. The circuit thus works like the current clamp for high frequency signals and like a voltage clamp for low frequency signals. We delineate its transfer properties and give application examples.

Animals↗
PubMed1999

Significance of size and nucleic acid content heterogeneity as measured by flow cytometry in natural planktonic bacteria.

Total bacterial abundances estimated with different epifluorescence microscopy methods (4',6-diamidino-2-phenylindole [DAPI], SYBR Green, and Live/Dead) and with flow cytometry (Syto13) showed good correspondence throughout two microcosm experiments with coastal Mediterranean water. In the Syto13-stained samples we could differentiate bacteria with apparent high DNA (HDNA) content and bacteria with apparent low DNA (LDNA) content. HDNA bacteria, "live" bacteria (determined as such with the Molecular Probes Live/Dead BacLight bacterial viability kit), and nucleoid-containing bacteria (NuCC) comprised similar fractions of the total bacterial community. Similarly, LDNA bacteria and "dead" bacteria (determined with the kit) comprised a similar fraction of the total bacterial community in one of the experiments. The rates of change of each type of bacteria during the microcosm experiments were also positively correlated between methods. In various experiments where predator pressure on bacteria had been reduced, we detected growth of the HDNA bacteria without concomitant growth of the LDNA bacteria, such that the percentage contribution of HDNA bacteria to total bacterial numbers (%HDNA) increased. This indicates that the HDNA bacteria are the dynamic members of the bacterial assemblage. Given how quickly and easily the numbers of HDNA and LDNA bacteria can be obtained, and given the similarity to the numbers of "live" cells and NuCC, the %HDNA is suggested as a reference value for the percentage of actively growing bacteria in marine planktonic environments.

Animals↗
PubMed1998

Expression and localization of members of the fibroblast growth factor family in the bovine mammary gland.

The goal of the study was to examine the expression and localization of members of the fibroblast growth factor family in the bovine mammary gland during different developmental and functional stages. Mammary tissue was obtained from German Brown Swiss cows (n = 23) during defined stages of mammogenesis (before and during pregnancy), lactogenesis, peak and late lactation, and involution. Extracted mRNA was analyzed by reverse transcription polymerase chain reaction and RNase protection assay. The tissue content of fibroblast growth factor-1 and fibroblast growth factor-2 was determined by radioimmunoassay, and the localization of fibroblast growth factor-2 was determined by immunohistochemistry. The highest mRNA concentration for fibroblast growth factor-1, -2, and -7 and their receptors was detected in the glands of virgin heifers or primigravid heifers during involution; less abundant fibroblast growth factor mRNA was detected during lactogenesis and galactopoiesis. Tissue protein concentrations of fibroblast growth factor-1 and fibroblast growth factor-2 showed similar tendencies. Immunoreactive fibroblast growth factor-2 was observed during mammogenesis and involution in endothelial cells, ductal epithelial cells, myoepithelial cells, and some alveolar cells. After positive staining, fibroblast growth factor-2 could only be observed in endothelial and myoepithelial cells during lactogenesis and could only be observed in myoepithelial cells during galactopoiesis. Expression, tissue concentration, and distinct localization suggest that fibroblast growth factors may be important in the local regulation of the bovine mammary gland.

Animals↗
PubMed1997

Expression of transforming growth factors alpha and beta-1 messenger RNA in the bovine mammary gland during different stages of development and lactation.

It is now widely accepted that the mammary gland is under interconnected hormonal and local control. Growth factors are involved in the intercellular signalling of the gland. Our aim was the detection of transforming growth factors alpha (TGF-alpha) and beta 1 (TGF-beta 1) messenger RNA during mammogenesis, lactogenesis, galactopoiesis and involution in the bovine mammary gland (total n = 27). During these stages the RNA was assessed by means of ribonuclease protection assay and reverse transcription-polymerase chain reaction (RT-PCR). To study possible influences of oestrogen, progesterone and prolactin on growth factor expression, mammary RNA was obtained from heifers after induced mammogenesis and lactogenesis, with and without additional prolactin inhibition (total n = 20). Very low levels of TGF-alpha and TGF-beta 1 expression were detected during lactogenesis and galactopoiesis, increasing levels during mammogenesis of primigravid heifers, and highest levels during mammogenesis of virgin heifers and during involution. TGF-alpha expression after induced mammogenesis was greater than after induced lactogenesis or physiological mammogenesis during pregnancy. Furthermore, TGF-alpha mRNA contents increased after prolactin inhibition. TGF-beta 1 expression was almost equal after induced mammogenesis and lactogenesis, but greater than during the physiological mammogenesis and lactogenesis. In conclusion, it can be assumed that growth promoting TGF-alpha and growth inhibiting TGF-beta 1 are co-expressed in the bovine mammary gland. Higher mRNA contents of both factors during mammogenesis and involution may indicate autocrine or paracrine functions for these growth factors during proliferation and reorganisation of the mammary tissue.

Animals↗
PubMed1996

Detection and quantitation of specific mRNAs by ribonuclease protection assay using denaturing horizontal polyacrylamide gel electrophoresis: a radioactive and nonradioactive approach.

A radioactive (32P) and nonradioactive (digoxigenin) ribonuclease protection assay (RPA) has been developed to detect mRNAs of housekeeping proteins and growth factors. A modification of polyacrylamide gel electrophoresis (PAGE) to simplify RPA is described. Both Cleangels (Pharmacia) and laboratory-cast polyacrylamide gels, in a denaturing, horizontal electrophoresis system, were used. The amount of toxic chemicals and waste was reduced, in comparison with sequencing gels normally used for RPA. The protected RNA fragments were shown to be well-separated, with sufficient sensitivity in this modified, quick gel system.

Animals↗
PubMed1993

[Clarithromycin, a new macrolide antibiotic. Effectiveness in puerperal infections and pharmacokinetics in breast milk].

The aims of this study were, to determine the pharmacokinetic parameters of clarithromycin and to study the passage of the drug into breast milk. Twelve patients (age 24 to 38; weight 44 to 83 kg), suffering from puerperal infections, were treated orally with 250 mg clarithromycin b.i.d. for 6 days. Samples of blood and breast milk were taken at timed intervals. The specimens were assayed for clarithromycin and its active metabolite 14-hydroxy-clarithromycin by HPLC and electrochemical detection. Serum concentrations of clarithromycin in the investigated patients were higher than those reported in healthy volunteers. The mean peak concentrations of clarithromycin and 14-hydroxy-clarithromycin in breast milk were about 25%, and 75% respectively of the corresponding serum concentrations. All patients recovered within 2 to 4 days and no drug-associated side effects (eg. gastrointestinal) were noted. Clarithromycin appears to be an appropriate antibiotic for the treatment of puerperal infections and (because of its considerable concentrations in breast milk) for puerperal mastitis as well.

Administration, Oral↗
PubMed1992

A site-directed mutagenesis study to identify amino acid residues involved in the catalytic function of the restriction endonuclease EcoRV.

We have used site-directed mutagenesis of the EcoRV restriction endonuclease to change amino acid side chains that have been shown crystallographically to be in close proximity to the scissile phosphodiester bond of the DNA substrate. DNA cleavage assays of the resulting mutant proteins indicate that the largest effects on nucleolytic activity result from substitution of Asp74, Asp90, and Lys92. We suggest on the basis of structural information, mutagenesis data, and analogies with other nucleases that Asp74 and Asp90 might be involved in Mg2+ binding and/or catalysis and that Lys92 probably stabilizes the pentacovalent phosphorus in the transition state. These amino acids are part of a sequence motif, Pro-Asp...Asp/Glu-X-Lys, which is also present in EcoRI. In both enzymes, it is located in a structurally similar context near the scissile phosphodiester bond. A preliminary mutational analysis with EcoRI indicates that this sequence motif is of similar functional importance for EcoRI and EcoRV. On the basis of these results, a proposal is made for the mechanism of DNA cleavage by EcoRV and EcoRI.

Amino Acid Sequence↗
PubMed1992

Multicentre study of gestrinone in cyclical breast pain.

Although the aetiology of cyclical mastalgia is poorly understood, the consistent finding of an increased prolactin stimulation response probably due to oestrogen dominance has led to the use of treatment with prolactin-lowering drugs and antioestrogens. The efficacy and safety in cyclical mastalgia of gestrinone, which has androgenic, anti-oestrogenic, and antiprogestagenic properties, were investigated in a multicentre study. In a double-blind randomisation procedure, 72 patients were allocated placebo and 73 treatment with gestrinone (2.5 mg twice a week) for 3 months. The patients recorded the severity of breast pain on a visual analogue scale before and during treatment and scored other breast symptoms as not present (0), mild (1), moderate (2), or severe (3). The gestrinone group had significantly greater reductions than the placebo group in breast pain score at months 1, 2, and 3 of treatment (mean reduction 59.5 [SD 22.6] to 11.7 [17.0] vs 58.2 [17.6] to 36.7 [23.0] at month 3; p less than 0.0001). All six breast symptoms had lower scores in the gestrinone than in the placebo group by the end of treatment. In a subset of 30 participants (15 from each group), serum concentrations of oestradiol, progesterone, and tri-iodothyronine were significantly lower than baseline after 3 months of gestrinone, but concentrations of luteinising hormone, follicle-stimulating hormone, prolactin, thyroid-stimulating hormone, and thyroxine did not change. 41% of gestrinone-treated and 14% of placebo-treated patients reported at least one side-effect; most of these were androgen-mediated. 11 placebo-treated patients and 4 on gestrinone discontinued treatment. Thus, gestrinone was very effective in the treatment of cyclical mastalgia and was well tolerated.

Adolescent↗
PubMed1992

[Hand disinfection as the central factor in prevention of puerperal mastitis. Clinical study and results of a survey].

The incidence of puerperal mastitis was evaluated in the course of two 12-month periods with and without additional hand disinfection at the bedside. Disinfection was available throughout both periods for all patients, mounted at the door of each room. Without additional disinfection at the bedside, 32 patients developed mastitis. With reference to the birth rate of 1095 during this period, the incidence of mastitis was 2.9%. When additional bedside disinfection was available, mastitis dropped to 8 cases per 12 months (1212 births = 0.66%) (p less than 0.001). A telephone survey, at 55 obstetrical units revealed that 41.8% of maternity clinics do not provide hand disinfectants at the bedside. These results indicate to the breast-feeding mother, that in the pathogenesis of puerperal mastitis, the essential recommendation emphasises, that puerperal women practise strict hygiene in maternity.

Breast Feeding↗
PubMed1992

Effects of Temperature on Two Psychrophilic Ecotypes of a Heterotrophic Nanoflagellate, Paraphysomonas imperforata.

Two different psychrophilic types of the heterotrophic nanoflagellate Paraphysomonas imperforata were isolated from Newfoundland coastal waters and the Arctic Ocean. When fed bacteria without food limitation, both isolates were able to grow at temperatures from -1.8 to 20 degrees C, with maximum growth rates of 3.28 day at 15 degrees C and 2.28 day at 12.3 degrees C for the Newfoundland and the Arctic isolates, respectively. Ingestion rates increased with temperature from 14 to 62 bacteria flagellate h for the Newfoundland isolate and from 30 to 99 bacteria flagellate h for the Arctic isolate. While temperature did not affect cell yields (number of protozoa produced divided by number of bacteria consumed), it affected flagellate sizes. This differential effect of temperature on cell yield and cell size resulted in a changing gross growth efficiency (GGE) in terms of biovolume; colder temperatures favored higher GGEs. The comparison of Q(10) values for growth rates and ingestion rates between the isolates shows that the Arctic isolate is better adapted to extremely cold temperature than the Newfoundland isolate. At seawater-freezing temperature (-1.8 degrees C), the estimated maximum growth rates and maximum ingestion rates are 0.81 day and 30 bacteria flagellate h for the Arctic isolate and 0.54 day and 12 bacteria flagellate h for the Newfoundland isolate. Our findings about psychrophilic nanoflagellates fit the general characteristics of cold-water-dwelling organisms: reduced physiological rates and higher GGEs at lower temperatures. Because of the large and persistent differences between the isolates, we conclude that they are ecotypes adapted to specific environmental conditions.

Journal Article↗
PubMed1991

[Drainage of large breast abscesses with reference to esthetic and functional aspects].

In 11 puerperal women, a breast abscess was treated by drainage from the inframammary fold. Eight patients wished to continue breast feeding. During the healing period, the babies were not breast fed on the operated side. In 3 patients, the skin over the abscess necrotised, resulting in a defect of 1 to 2 cm. In 2 patients, a small seroma had to be punctured after removing the drainage tube. Aesthetic results were judged by the patients as good. Resumation of suckling on the operated side revealed only 15 to 20% milk yield compared to that of the other breast. This treatment meets aesthetic and function-preserving criteria.

Abscess↗
PubMed1991

Thyrotrophin-releasing hormone--a lactation-promoting agent?

OBJECTIVE: To study the lactational and hormonal responses to nasal administration of thyrotrophin-releasing hormone (TRH) in puerperal women with inadequate lactation. DESIGN: Prospective randomized double-blind placebo-controlled study. SUBJECTS: 19 puerperal women with inadequate lactation (less than 50% of normal milk yield) on the 5th day postpartum. INTERVENTIONS: 10 women were allocated to receive TRH administered by a nasal spray of 1 mg, four times daily, between suckling episodes, for 10 consecutive days starting on day 6 postpartum. Nine women were allocated to receive placebo sprays. MAIN OUTCOME MEASURES: Daily milk yield, serum levels of prolactin and thyroid hormones. RESULTS: Before treatment all the women had significant prolactin responses to TRH and suckling stimuli. At the end of 10 days of treatment, milk yield increased significantly in the TRH group from a mean of 142.0 (SD 33.9) to 253.0 (SD 105.3) g/day (P = 0.014). There was no significant change in the placebo group. Basal prolactin levels increased from a mean of 117.4 micrograms/l (SD 45.2) to 173.3 micrograms/l (SD 55.5) (P less than 0.001) in the TRH group whereas in the placebo group prolactin levels decreased from 137.2 (SD 69.5) to 82.0 (SD 37.7) micrograms/l. A further rise in prolactin levels and milk yield was seen in seven women in the TRH group who received a second 10-day course of TRH treatment at their own request. There was no significant change in levels of thyroid stimulating hormone, thyroxine and triiodothyronine during treatment in either of the two treatment groups and no signs of hyperthyroidism. CONCLUSION: Repeated nasal TRH administration between suckling episodes may improve defective lactation.

Administration, Intranasal↗
PubMed1990

The influence of the concentrations of elongation factors and tRNAs on the dynamics and accuracy of protein biosynthesis.

Computer simulations of the elongation cycle of bacterial protein biosynthesis demonstrate that the accuracy of protein biosynthesis cannot be explained by a mechanism which involves only an initial selection and a proofreading reaction. It is suggested that only a combination of initial selection, proofreading and a retardation of non-cognate flows at the level of the EF-Tu-catalyzed GTPase reaction and the peptidyl transfer can guarantee sufficient accuracy at reasonable costs. According to this view the ribosome functions as an allosteric enzyme which, in both its affinity and enzymatic activity, responds optimally only to the cognate substrate. Detailed calculations show, furthermore, that increasing the concentration of EF-G and EF-Ts above the level prevailing in vivo only slightly increases the rate of elongation. In contrast, increasing the concentration of EF-Tu over aminoacyl-tRNA (aa-tRNA) leads to a sharp decline in the rate of elongation. While varying the concentration of EF-G has no effect on the accuracy of protein synthesis, excess of EF-Tu over aminoacyl-tRNA leads to a large increase in accuracy. These results suggest a mechanism by which the accuracy of protein biosynthesis is preserved during amino acid starvation.

Computer Simulation↗
PubMed1989

Hyperprolactinemia and nonpuerperal mastitis (duct ectasia).

In 108 patients with nonpuerperal mastitis (inflammatory symptoms of duct ectasia), serum prolactin levels were determined before, during, and after treatment. Twenty-nine patients (26.8%) exhibited transiently elevated prolactin levels during the period of inflammation (mean +/- SD level, 42 +/- 22 micrograms/L) that returned to normal within 4 weeks. Twenty-two patients (20.4%) presented with more severe hyperprolactinemia (78 +/- 56 micrograms/L), and 15 were found to have pituitary microadenomas. In 11 cases, mastitis was the first symptom of hyperprolactinemia. A second group of 83 patients with known hyperprolactinemia and 83 normoprolactinemic controls were interviewed with regard to recent symptoms or past treatment of nonpuerperal mastitis. Sixteen hyperprolactinemic women (19.3%) and none of the controls reported that they had experienced mastitis. We conclude that duct ectasia is due in part to increased prolactin secretion. Thus, nonpuerperal mastitis may be a symptom of hyperprolactinemia. On the other hand, nonpuerperal mastitis may induce transient hyperprolactinemia (neurogenic hyperprolactinemia) of about 3 weeks' duration that is less pronounced than central hyperprolactinemia.

Adenoma↗