Search PubMed⌕ Search

Biomedical subjects

A Visser

Publications and source records attributed to A Visser.

87 records · Page 5Linked to original sources
PubMed1983

Binding and repair of 2-acetylaminofluorene adducts in distinct liver cell populations.

The study of the binding of the liver carcinogen, N-acetyl-2-aminofluorene, to the DNA of the target organ-as the probable initial step in the process of carcinogenesis-has shown that three modes of interaction occur. N-Acetyl-2-aminofluorene is covalently bound with the nitrogen to the carbon 8 of guanine (I) and with the 3-position to the free NH(2)-group of guanine (II). The third mode of interaction is formed by a covalent bond between the nitrogen of 2-aminofluorene and the carbon 8 of guanine (III). In this study the different modes of interaction were measured separately in stromal and parenchymal cells of the rat liver, after a single intraperitoneal dose. The DNA was isolated from nuclei that had been separated by 1g sedimentation. In parenchymal DNA the types of interaction I and III occur in the same amounts one day after application. In stromal cells the amount of interaction I is relatively small and interaction III predominates (ratio III:I = 5). The amount of interaction III in tetraploid hepatocytes (the largest cell population in the studied rats) per mg DNA is about two times higher than in the stromal cells. While the removal of the total amount of DNA-bound carcinogen takes place at the same rate in the two cell types, a difference in rate and efficiency of repair is observed for the different types of interaction. In tetraploid hepatocytes, interaction I is almost completely removed from the DNA 2 weeks after application, while interaction III diminishes to about 1/3 during the first week but the remaining part disappears very slowly. As shown in earlier studies, interaction II remains in the DNA at a constant level.

2-Acetylaminofluorene↗
PubMed1982

Electrical activity of the pregnant uterus in the cynomolgus monkey.

Electromyographic activity in six pregnant cynomolgus monkeys was recorded in vivo by means of bipolar electrodes individually attached to the surface of the uterine corpus. These data were compared with recordings of intra-amniotic pressure obtained simultaneously by means of an open-ended, fluid-filled catheter placed in the amniotic cavity. During the last third of pregnancy, the electromyograms showed recurrent electrical complexes (trains of potentials, TOP) which lasted for about 2 minutes and whose rate of occurrence varied during the nyctohemeral period. The initiation of electrical activity in various uterine areas was always synchronous with and was related to mechanical contraction. The complex, polyphasic contractions that were observed can be explained, largely, by the variations of potentials within a train of potentials. However, a simple quantitative relationship between the mean frequency of the potentials within the TOP and the mean amplitude of the change in pressure could not be demonstrated. In contrast to data available on the woman, the increase in contractile strength at the onset of labor in the macaque appears to be due to a higher frequency of excitation of individual cells rather than the result of an improved functional coordination between the active muscular elements.

Action Potentials↗
PubMed1982

Multiplication of fluorescent pseudomonads at low substrate concentrations in tap water.

Two fluorescent pseudomonads, strains P17 and P500, belonging to different biotypes were tested for growth in tap water supplied with different concentration of acetate and glutamate, low concentrations (10 and 20 micrograms of C per liter) of various other substrates and mixtures of related substrates, the latter being present in amounts of 1 microgram of C per liter each. Amino acids appeared to be excellent substrates for both isolates, but many other substrates were utilized at very low concentrations as well. Saturation constants (Ks) of P17 with acetate, arginine, aspartate, glutamate, lactate, succinate, malonate, p-hydroxybenzoate and glucose were all below 1 microM. The Ks values of strain P500 were about 5 times larger than those of P17. Since especially P17 is able to use a large number of different substrates at low concentrations, assessment of maximal colony counts of this organism by growth experiments in various types of tap water may give information about the concentrations of easily assimilable organic carbon.

Acetates↗
PubMed1981

Partial persistency of 2-aminofluorene and N-acetyl-2-aminofluorene in rat liver DNA.

Male rats were treated with [ring-3H]N-acetyl-2-aminofluorene and sacrificed at different periods of time after a single i.p. dose. Chromatin was isolated from liver homogenates and treated with RNAse and proteinase K. The resulting crude DNA was purified as the N-hexadecyl-N-trimethylammonium salt. The amounts of 2-aminofluorene and N-acetyl-2-aminofluorene bound to carbon-8 of guanine were determined in the DNA via acid hydrolysis and high pressure liquid chromatography of the hydrolysate. These two major interaction products of the carcinogen decreased rapidly during the first 2 weeks but in the second 2 weeks the decrease of both interactions was much smaller and approximately 15% of the amount that was bound after 24 h remained persistently bound to the DNA. Differences in liver DNA binding after 24 h were observed between male rats of the strain R-Amsterdam (Wistar-related) and Sprague Dawley males. At equal dose levels of N-acetyl-2-aminofluorene, liver DNa of Sprague Dawley rats contained 1/3 of the amount of N-(guanin-8-yl)-2-aminofluorene and 1/2 of the amount of N-(guanin-8-yl)-N-acetyl-2-aminofluorene present in liver DNA of the R-Amsterdam strain.

2-Acetylaminofluorene↗
PubMed1980

Variations in the distribution of glycosaminoglycans in the uterine cervix of the pregnant woman.

A study was made of the modifications of glycosaminoglycans in the uterine cervix and the relationship to gestation. These substances are essential constituents of connective tissue, and a modification of their concentration could affect the physical and chemical characteristics of the cervix. Glycosaminoglycans were extracted from cervical biopsies obtained from pregnant and non-pregnant women. This study showed dermatan sulfte to be quantitatively the most important glycosaminoglycan in the cervix of both the groups studied, and that a significant decrease in the concentration of both dermatan sulfate and chondroitin sulfates occurred in the biopsies obtained just after delivery. This was related to a decrease of collagen in the cervix at the end of gestation, as the proteoglycans containing dermatan sulfate are principally associated with collagen.

Adult↗
PubMed1980

Growth of Aeromonas hydrophila at Low Concentrations of Substrates Added to Tap Water.

The ability of an Aeromonas hydrophila isolate obtained from filtered river water to grow at low substrate concentrations was studied in batch experiments with tap water supplied with low concentrations of substrates. Growth was assessed by colony count determinations. The isolate only multiplied in the used tap water (2 to 3 mg of dissolved organic carbon per liter) after the addition of a small amount of an assimilable carbon compound. d-Glucose especially caused growth of the organism even at initial concentrations below 10 mug of C per liter. At initial glucose concentrations below the K(s) value (12 mug of C per liter), generation times and yield (colony-forming units per milligram of substrate-C) were nonlinear with 1/initial glucose concentrations and initial glucose concentrations, respectively. From these observations, the maintenance coefficient m was calculated (m = 0.015 mg of glucose per mg [dry wt] per h at 12 degrees C). At initial concentrations below the K(s) value of starch (73 mug of C per liter), no growth was observed, but complete use of starch occurred in these situations after the addition of 10 mug of glucose-C per liter. The results of this study show that information of ecological significance may be obtained by very simple batch experiments. Moreover, the isolate studied may be used in growth experiments to assess the maximum concentration of glucose which might be present in water, particularly tap water.

Journal Article↗
PubMed1979

Quantitative analysis of N-(guanin-8-yl)-N-acetyl-2-aminofluorene and N-(guanin-8-yl)-2-aminofluorene in modified DNA by hydrolysis in trifluoroacetic acid and high pressure liquid chromatography.

N-acetyl-2-aminofluorene (AAF)- and 2-aminofluorene (AF)-modified DNA was hydrolyzed in dry trifluoroacetic acid (TFA). The hydrolysate was analyzed by high-pressure liquid chromatography. Using this procedure N-(guanin-8-yl)-[G-3H]2-aminofluorene was released quantitatively from DNA, modified by the reaction with [G-3H]N-hydroxy-2-aminofluorene. From DNA that had been reacted with [G-3H]N-acetoxy-N-acetyl-2-aminofluorene, 70% of the total bound radioactivity was isolated as N-guanin-8-yl)-[G-3H]-N-acetyl-2-aminofluorene. Thirty eight percent of the DNA bound radioactivity after i.p. injection of [G-3H]N-acetyl-2-aminofluorene followed by isolation of the rat liver DNA and subsequent hydrolysis in trifluoroacetic acid was identified as N-(guanin-8-yl)-[G-3H]-N-acetyl-2-aminofluorene. In this DNA the corresponding deacetylated compound N-(guanin-8-yl)-[G-3H]2-aminofluorene could not be detected.

Animals↗
PubMedDate not supplied

Genetic education and counseling.

This special issue of Patient Education and Counseling on genetic education and counseling provides an overview of studies and findings in this field. It features a mixture of papers dealing with five different topics related to several psychosocial aspects of genetic education and counseling. Attention is paid to new issues in counseling for hereditary cancer and Huntington Disease. Articles are presented on information recall of counseled individuals, the use and impact of genetic services on counselees (acceptance of testing; knowledge of inherited cancer susceptibility; risks of genetically testing children). Also topics are addressed with respect to the counselor (neutral attitude; understandable language; information recall; satisfaction with the services provided by the genetic counselor). Furthermore, recommendations are discussed for screening practices for women with a family history of breast cancer, and in addition, the effectiveness of genetic counseling is addressed. In conclusion several suggestions for future research are given.

Female↗
PubMedDate not supplied

Quality assurance in brachytherapy: the role of the ICRU in achieving uniformity in dose and volume specification for reporting.

A quality assurance programme in brachytherapy implies a general consensus on the method of dose and volume specification for reporting. This in turn implies a consensus on certain definitions of terms and concepts. For several decades, the ICRU (International Commission on Radiation Units and Measurements) has been actively involved in an effort to reach a consensus between different brachytherapy centres worldwide, and to improve uniformity in reporting. The ICRU has prepared two reports containing recommendations for reporting brachytherapy treatments. The first, report #38 published in 1985, deals with intracavitary therapy in gynecology. The second deals with interstitial therapy, and is now in press. A summary of these two ICRU reports is presented here. Some definitions of terms and concepts are first recalled and discussed: Total Reference Air Kerma (TRAK), gross tumor volume (GTV), clinical target volume (CTV), treated volume, mean central dose, dose uniformity parameters, etc. Specific recommendations for reporting interstitial and intracavitary brachytherapy are then presented.

Brachytherapy↗