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Biomedical subjects

J Arends

Publications and source records attributed to J Arends.

At least 19 recordsLinked to original sources
PubMed1992

Effects of fluoride and methanehydroxydiphosphate on enamel and on dentine demineralization.

The aim of this article was to investigate the effects of methanehydroxydiphosphonate (MHDP) and fluoride (F) separately and combined, on the demineralization process in enamel and in dentine under constant composition conditions. The demineralization was carried out in solutions containing 3 mM calcium, 3 mM phosphate, pH = 5.0, and either 6 microM MHDP, 12 microM F or 6 microM MHDP and 12 microM F. After demineralization periods (t) between 24 and 140 h, the lesion depth l and the mineral loss delta Z were measured by transverse microradiography of the enamel and dentine specimens. The amount of mineral lost during demineralization averaged over the lesion depth, R = delta Z/l, was calculated. R approximately 17 vol% for both enamel and dentine, both delta Z and l being greater for dentine than for enamel by approximately the same factor. The results show that under the same conditions dentine is attacked much more strongly than enamel. The lesion progress with time is quite different for the two tissues: in enamel the lesion depth progresses als l3 = alpha t + beta, in dentine as l2 = alpha't + beta'. The slopes alpha and alpha' decrease in the order MHDP > F > MHDP+F. In enamel the combined inhibitor effect is only slightly larger than the effect of F alone; in dentine the inhibiting effects of F and MHDP are approximately additive. The inhibitor interactions can be described by the Langmuir adsorption theory.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1979

Purification of peroxidase-conjugated antibody for enzyme immunoassay by affinity chromatography on concanavalin A.

Preparation of peroxidase-conjugated antibody contaminated with very small amounts of unconjugated antibody for highly sensitive enzyme immunoassays is described. The purification process is dependent upon the differential affinity of antibody and peroxidase-conjugated antibody for concanavalin A (Con A). Application of peroxidase and radioactive labelled IgG alone or as a mixture to Con A-Sepharose columns showed that 62-83% of IgG and 0% of peroxidase could be eluted under starting conditions, while 70-83% of peroxidase and about 6% of IgG could be eluted with appropriate buffer. The contamination of the conjugate with unconjugated antibody is dependent on the ratio of conjugated to unconjugated antibody in the mixture to be purified. Using this procedure on IgG conjugated with peroxidase with a ratio of unconjugated to conjugated IgG of about 2 : 1 a preparation was obtained where the ratio was changed to 0.1 : 1.

Antibodies↗
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↗