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Biomedical subjects

K Dick

Publications and source records attributed to K Dick.

11 recordsLinked to original sources
PubMed2000

Leptogenesis with dirac neutrinos

We describe a "neutrinogenesis" mechanism whereby, in the presence of right-handed neutrinos with sufficiently small pure Dirac masses, (B+L)-violating sphaleron processes create the baryon asymmetry of the Universe, even when B = L = 0 initially. It is shown that the resulting neutrino mass constraints are easily fulfilled by the neutrino masses suggested by current experiments. We present a simple toy model which uses this mechanism to produce the observed baryon asymmetry of the Universe.

Journal Article↗
PubMed1999

Can one really measure magnesium deficiency using the short-term magnesium loading test?

OBJECTIVE: To compare a 1-h-version of a magnesium-loading-test (MLT) designed for outpatients in healthy controls with the 8-h standard; to establish the test in patients after renal transplantation prone to develop magnesium (Mg) deficiency; to correlate femur Mg-concentration and percentage retention of the given load. DESIGN: Comparison of mean values from healthy controls with respective from the literature; a prospective, randomized, controlled 4-month study; an intra-individual correlation of Mg-serum values and loading-test data with femur-Mg concentrations. SETTING: One centre study in a medical university; outpatients from the transplant unit; inpatients from the orthopedic unit. SUBJECTS: Twenty-four healthy controls aged 36.7 +/- 7.4 years; 34 patients after renal transplantation (46.5 +/- 14.3 years); 41 patients with hip replacement therapy (63.9 +/- 18.6 years). INTERVENTION: Baseline Mg values were measured by atomic absorption spectroscopy (AAS) in serum and urine. An intravenous Mg load with 0.1 mmol Mg-aspartate hydrochloride per kilogram bodyweight was given during 1 h. In 24 h-urine, the amount of excreted Mg was measured by AAS and the percentage retention of the given load calculated according to the formula: 1 - [Mg 24 h-urine/Mg test dose] x 100. Femur Mg was measured by AAS in a peace of the femur neck. Patients after renal transplantation were randomized after the first Mg load to either obtain daily 5 mmol Mg-aspartate hydrochloride per kilogram bodyweight, or placebo. Four months later a second loading-procedure was performed. MAIN OUTCOME MEASURE: Serum Mg, percentage retention of the given Mg load (%Ret) and femur Mg concentration. RESULTS: Mean serum Mg values were within the normal range. In controls, %Ret was -18 +/- 21 and not different from the literature. In the first MLT after renal transplantation, %Ret was 47 +/- 43. In patients under Mg medication it decreased significantly to 16 +/- 26, but was 58 +/- 27 in the placebo group. Femur Mg concentration was 62.6 +/- 20.9 mmol kg-1 dry substance and the corresponding %Ret was 14 +/- 28 with r = - 0.7093. CONCLUSION: The short-term version of the MLT is as good as the standard and was easily applied in outpatients. The indication from the good correlation between bone-Mg and %Ret and a marked decrease in %Ret in patients after Mg medication was that one can really measure magnesium deficiency.

Adolescent↗
PubMed1996

Magnesium metabolism: basic aspects and implications of ciclosporine toxicity in rats.

In rapidly growing male Sprague-Dawley rats with an initial body weight of 100 +/- 10 g, we investigated how alimentary magnesium (Mg) supply, Mg metabolism and ciclosporine (Ci)-associated nephrotoxicity are interrelated. Food with 100 ppm Mg (1Mg) or 1,000 ppm Mg (stMg) or 10,000 ppm Mg (rMg), Ci 20 mg/kg body weight daily or olive oil were applied for 3 months (n = 10/group). Mg concentrations in various compartments were measured by atomic absorption spectrophotometry. Creatinine clearance (Jaffe), urinary N-acetyl-beta-D-glucosaminidase (NAG) activity (fluorometrically), urinary sodium excretion (flame photometry) and osmolality were measured. Histomorphological examination was done and renal renin expression was studied by monoclonal antibodies. Ci reduced the Mg concentration of the femur under 1Mg (72.6 +/- 9.7 vs. 112.6 +/- 14.3 mmol/kg dry substance, p < 0.05) and under stMg (150.6 +/- 16.6 vs. 194.1 +/- 10.2 mmol/kg dry substance, p < 0.05), thus indicating Ci-related Mg deficiency. This was due to a significant increase in Mg excretion in Ci treatment compared to dietary controls. Under rMg, there was no difference between Ci-treated and control animals. Ci treatment lowered creatinine clearance in 1Mg (1.42 +/- 0.05 vs. 3.02 +/- 0.58 ml/min) and in stMg (1.04 +/- 0.45 vs. 2.18 +/- 0.51 ml/min), NAG/creatinine and urinary sodium excretion were negatively affected by Ci under 1Mg and stMg. Histomorphology showed macrocalcifications due to Mg deficiency and Ci-specific findings, which were markedly enhanced in 1Mg and stMg. Animals with plentiful Mg supply had no functional alterations due to Ci and no or weakly expressed histomorphological lesions. Renin-positive stained cells were higher in Ci-treated animals. This seems to be functionally relevant under 1Mg and stMg, since it was associated with sodium retention and elevated relative heart weight, indicating hypertension. Alimentary or drug-induced Mg deficiency plays a relevant role in the pathophysiology of chronic Ci nephrotoxicity. Our data suggest that Mg supplementation is helpful to reduce Ci toxicity, even if there is 'normal' alimentary Mg intake.

Animals↗
PubMed1995

Color changes in dry-pigmented maxillofacial elastomer resulting from ultraviolet light exposure.

Five dry pigments and one maxillofacial elastomer were evaluated for color changes (delta E) resulting from prolonged exposure to two types of ultraviolet light. The elastomer, pigments, and pigmented elastomers were subjected to each ultraviolet light source for 400, 600, and 1800 hours, and delta E color shifts were determined. The unpigmented elastomer underwent minimally perceptible color change after 600 hours of exposure to both types of ultraviolet light. Two pigments underwent substantial color change after 400 hours, whereas the remaining three pigments remained color stable after 1800 hours. It was concluded that for the materials tested, early color changes in a prosthesis may be the result of degradation of certain ultraviolet light-susceptible pigments, whereas longer term color shifts may be caused by color changes within the elastomer.

Analysis of Variance↗
PubMed1993

Chromatic aberration and accommodation: their role in emmetropization in the chick.

The roles of chromatic aberration and accommodation as cues to emmetropization in the chick were investigated. Myopia was induced monocularly by lid suture for a period of 1-2 weeks from hatching, after which eyes were reopened and the recovery process followed. Monochromatic light (ML) rearing conditions and ciliary nerve section surgery were used to eliminate chromatic aberration and accommodative activity respectively. Control animals were reared in white light (WL). When accommodation was left intact, chickens reared under monochromatic light were able to recover normally. However, ciliary nerve section produced hyperopia, deepening of the anterior chamber and a tendency towards axial lens thinning, irrespective of the light conditions used. Hyperopic refractive errors peaked at 4 weeks (mean refractive errors: +5.7 D, +4.21 D for ML, WL groups respectively, 4 weeks), with the ML group still exhibiting significant hyperopia at 7 weeks. Ciliary nerve section did not prevent the myopic response to lid suture (mean refractive errors: -22.65 D; -25 D for ML, WL groups respectively, 1 week) nor the elimination of myopia when eyes were reopened. These data indicate that neither accommodation nor chromatic aberration are fundamental to the gross operation of the emmetropization process although they may be essential for the fine tuning of refraction.

Accommodation, Ocular↗
PubMed1991

Amphiregulin-associated protein: complete amino acid sequence of a protein produced by the 12-0-tetradecanoylphorbol-13-acetate-treated human breast adenocarcinoma cell line MCF-7.

Amphiregulin-associated protein (ARAP) was purified from serum-free conditioned medium of MCF-7, human breast carcinoma cells, treated with 12-0-tetradecanoylphorbol-13-acetate (TPA). ARAP is a single-chain, extremely hydrophilic, heparin-binding protein. Its apparent molecular weight is approximately 21,500 as assessed by gel chromatography and approximately 15,500 as determined by polyacrylamide gel electrophoresis. The complete amino acid sequence of ARAP was determined. The larger form contains 123 amino acids, whereas a shorter form is missing two amino acids at the amino-terminal. ARAP contains 10 cysteines and 30 basic amino acids (23 lysines and 7 arginines). ARP sequence has been found to be identical to protein encoded by human MK gene.

Adenocarcinoma↗
PubMed1984

Sequence analysis of the insertion element ISH1.8 and of associated structural changes in the genome of phage PhiH of the archaebacterium Halobacterium halobium.

We have sequenced the insertion element ISH1.8 which can be present in one or two copies in the genome of phage PhiH of Halobacterium halobium. ISH1.8 is 1895 bp long, has no inverted repeat at its ends, and one only of the two copies is flanked by two 5-bp duplications. An 8-bp sequence composed of 4 bp from each end of ISH1.8 is present in both sites lacking the element. This 8-bp sequence could either be a specific insertion sequence or a part of the element that is left behind upon deletion. The plasmid pPhiHL, consisting of the invertible L segment of the phage genome which is, in PhiH2 and PhiH5, flanked by two copies of ISH1.8, contains 112 bp of ISH1.8 and is released from the phage genome by recombination within a direct repeat of 9 bp. This 9-bp sequence (TCCCGCCCT) exists as an inverted repeat in ISH1.8 and therefore as two distinct repeats in phage genomes containing two copies of ISH1.8 in inverted orientation.

Journal Article↗