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Biomedical subjects

J Arends

Publications and source records attributed to J Arends.

At least 289 records · Page 16Linked to original sources
PubMed1979

Ultrastructural studies of synthetic apatite crystals.

In this paper a survey is given of some ultrastructural properties of synthetic hydroxyapatite. The preparation method by which single crystals with a length in the range of 0.1-3.0mm and a defined purity and stoïchiometry can be produced is given. Two groups of materials are considered in detail: carbonate-rich (greater than 0.1% CO3) and low-carbonate hydroxyapatites. The experiments on carbonate-rich material, being the most interesting from a biological point of view, show that acids attack at an active site in the hexagonal basal-plane of the crystals. Later on the crystals dissolve in the center of the crystal parallel to the c-axis forming tube-like structures. The active site can be protected from dissolution if the crystals are pretreated by EHDP or MFP. A comparison with lattice defect theory shows that most likely dislocations of the "hollow-core" type are responsible for the preferential dissolution.

Acids↗
PubMed1979

Effect of fasting on the release of insulin and somatostatin from perifused islets of Langerhans.

Release of somatostatin and insulin from perifused islets of fasted and control rats was compared. After a fasting period of 48 h glucose-induced insulin release but not somatostatin release was diminished. Islets from fasted rats released significantly more somatostatin in the presence of 3.3 mM glucose than islets from controls. Simultaneously, the somatostatin content of isolated islets from fasting rats was significantly decreased. The results indicate that the low secretory activity of islet B cells in the fasting state is associated with a high secretory activity of islet D cells.

Animals↗
PubMed1979

SnF2 treatment of enamel, hydroxyapatite or brushite at 37 degrees C and 50 degrees C: an infra-red investigation.

The effect of 4% SnF2 on brushite, hydroxyapatite and powdered bovine enamel applied for short, 15 or 30 minute, periods was investigated using infra-red spectroscopy. It was found that brushite was converted into a fluoridated hydroxyapatite, a reaction which was both time and temperature dependent. The reactions of hydroxyapatite and powdered enamel with SnF2 were similar. There was a drop in the OH- peak intesities. X-ray diffraction analysis of these samples showed that F- ions occupied mainly OH positions in the hydroxyapatite lattice structure. In all reactions an increase in temperature from 37 degrees C to 50 degrees C increased the reaction speed by at least a factor 2. The most probable result of in vivi SnF2 application on sound enamel is the formation of a fluoridated hydroxyapatite together wity stannous complexes and amorphous CaF2. In demineralized areas some of the brushite is converted into a fluoridated hydroxyapatite as is some of the remaining hydroxyapatite. In the more protected area of an enamel lesion these reactions may well continue for some time after the topical fluoride application; Sn2F3PO4 may also therefore be formed.

Animals↗
PubMed1978

Alpha-fetoprotein and human chorionic gonadotropin in a patient with a primary intracranial germ cell tumor.

A 17 year old man with a primary intracranial germ cell tumor in the pituitary region is reported. Both serum alpha-fetoprotein (AFP) and serum human chorionic gonadotropin (hCG) were found elevated preoperatively. Normal levels of serum AFP and hCG were found after operation and radiotherapy. By indirect immunofluorescence staining of the tumor tissue a slight staining for AFP was localized to the endodermal vesicles, whereas a more intensive staining for hCG could be identified in the giant cells.

Adolescent↗
PubMed1978

Serum alpha-fetoprotein and human chorionic gonadotropin as markers for the effect of postoperative radiation therapy and/or chemotherapy in testicular cancer.

Human alpha1-fetoprotein (AFP) and chroiongonadotropin (hCG) have been studied in 67 patients with malignant germ cell neoplasia of the testis admitted to the Radium Centre, Aarhus Municipal Hospital within an 18 month period. In 34 patients with nonseminoma, AFP was elevated in 35% of cases and hCG in 38% of cases. Nonseminoma patients who presented with or developed distant metastases showed a significantly higher incidence of elevated tumor markers than patients with local or regional disease. In patients with distant metastases monitoring of AFP and/or hCG was a most sensitive and reliable indicator of disease activity. In the management of such patients these tests are as important as clinical and x-ray examinations.

Antineoplastic Agents↗
PubMed1978

Crystallites dimensions of enamel.

In this paper the average diameter of enamel crystallites in mature, deciduous and fluorosed human enamel as well as in bovine enamel (in vivo and in vitro remineralized) is discussed. The investigation was carried out on broken surfaces of the various kinds of enamel with a scanning electron microscope. Corrections have been applied for the thickness of the gold-layer deposited. The average crystallite diameters for sound, deciduous and fluorosed human enamel were : 36 nm; 46 nm and 81 nm, respectively. The values for sound, remineralized in vitro and remineralized in vivo bovine enamel were 57 nm; 97 nm and 63 nm, respectively. The results indicate furthermore that if a correction for the sputtered goldlayer is applied, the results for SEM and TEM microscopy are in good agreement with each other. The difference between in vivo and in vitro remineralized bovine enamel is most likely due to differences in speed of remineralization and/or the presence of saliva.

Animals↗
PubMed1978

Diffusion of fluoride ions in dental enamel at pH 7.

The penetration and uptake of both radioactive (18F) and stable fluoride (19F) in bovine enamel were investigated. Buffered pH 7 NaF solutions were employed. Penetration profiles of both 18F and 19F in enamel were determined by using a sectioning technique. 18F and 19F concentrations decreased exponentially with increasing penetration distance. The uptake of 18F in enamel can be described by a power function of the immersion time, with an average power of 0.76. The results agree reasonably with our previously published theoretical model for the diffusion in enamel, based on simultaneous diffusion in enamel pores and in the hydroxyapatite crystallites. The diffusion coefficients of fluoride ions in enamel obtained from the application of the model to the results presented here, were: D = 0.9 x 10(-17) cm2/s in the crystallites and D' = 3.3 x 10(-10) cm2/s in the enamel pores. An average penetration depth of fluoride ions at pH 7.0 of 8 micron in 4 hours has been calculated.

Animals↗