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Biomedical subjects

R Christensen

Publications and source records attributed to R Christensen.

At least 91 records · Page 5Linked to original sources
PubMed1981

Effect of Soybean Casein Digest Agar Lot on Number of Bacillus stearothermophilus Spores Recovered.

In recent years it has become increasingly apparent that Bacillus stearothermophilus spores are affected by various environmental factors that influence the performance of the spores as biological indicators. One environmental factor is the recovery medium. The effect of different lots of commercial soybean casein digest agar on the number of colony-forming units per plate was examined in two series of experiments: (i) several lots of medium from two manufacturers were compared in single experiments, and (ii) paired media experiments with four lots of medium were carried out and yielded three-point survivor curves. The results demonstrate that commercial soybean casein digest agar is variable on a lot-to-lot basis. The variation was lowest when recovering unheated or minimally heated spores and increased greatly with the severity of heating.

Journal Article↗
PubMed1979

Sex differences in feelings attributed to a woman in situations involving coercion and sexual advances.

This study investigated sex differences of feelings attributed to a woman in situations involving varying degrees of coercion and sexual advances. Sixteen vignettes (12 dealing with sex and coercion, 4 dealing with coercion only) were rated on 17 semantic differential scales by 59 undergraduates (44 females, 15 males) and 45 graduate students (18 females, 27 males). The 16 vignettes yielded factors of Sexual Flattery/Overtures, Sexual Aggressiveness, and Violence. Factor analyses of the 17 semantic differential scales yielded factors of Helplessness, Aversiveness, and Threat. High agreement was found between males and females in both the graduate and undergraduate samples on the relative intensity of feelings attributed to the woman across the sex/coercion vignettes for the three dimensions of Helplessness, Aversiveness, and Threat. Even more importantly, systematic differences between males and females on intensity of attributed feelings across the semantic differential factors were independently replicated using the graduate and undergraduate samples. Analyses of variance revealed that males showed significantly greater attributions on the factors Helplessness and Threat on scenes mainly dealing with sexual flattery/overtures, whereas they showed significantly less attributions on the factor Aversiveness on scenes dealing with sexual aggressiveness and rape. In short, while there was strong agreement between men and women, there were also replicated significant systematic differences with men overestimating the psychological impact of less intense incidents and underestimating the psychological impact on women of more intense incidents.

Attitude↗
PubMed1976

UV mutagenesis in radiation-sensitive strains of yeast.

The yeast Saccharomyces cerevisiae appears to possess a single mutagenic or "error prony" pathway for the repair of UV damage; rev1, rev2, rev3 (Lemontt 1971a), rad6, rad8, rad9 and rad18 (Lawrence et al. 1974; present results). Strains carrying rad6 are the most sensitive to the lethal effects of UV light in this group and double mutants carrying rad6 and either rev1, rev3, rad9 or rad18 are no more sensitive than this single mutant strain, rev3 rad6 doubl- mutant diploids failed to show any UV-induced reversion of the normally highly reversion of the normally highly revertible ochre allele cycl-9, even though a total of more than 2.5 X 10(9) viable cells was examined, suggesting that strains of this kind are entirely UV-immutable; spontaneous revertants could be recovered, however.-The rad6 and rev3 gene products would appear to be necessary for all kinds of mutagenic events at all sites within the genome, but the products of the other genes that act in the "error-prone" pathway have a more restricted role and are involved in the production of only some kinds of mutations. It is suggested that such selectivity arises from the interaction of some repair enzymes with specific nucleotide sequences.

DNA Repair↗
PubMed1975

Influence of repair on the specificity of ultraviolet-induced reversion of an ochre alleles of the structural gene for iso-1-cytochrome c.

The specific action of UV on the reversion of the ochre allele cycl-9, in which 21 out of 23 revertants have been shown to arise from A-T-to-G.C transitions at position one in the UAA codon, was found to depend on the function of the RAD6 gene, since cycl-9 reversion occurred by a variety of single-base-pair substitutions in a strain carrying the rad6-1 allele.

Alleles↗
PubMed1974

Repair of radiation-induced strand breaks as related to the inducible inhibitor of postirradiation DNA degradation.

The repair of radiation-produced single-strand breaks observed under alkaline conditions is very apparent in cells which possess an inducible inhibitor of postirradiation DNA degradation. Previous induction of the inhibitor with ultraviolet light increases the amount of repair. In those cells which are genetically not inducible there is no increase following ultraviolet irradiation.

Centrifugation, Density Gradient↗
PubMed1974

Fine structure mapping in yeast with sunlamp radiation.

The X-ray mapping procedure of Manney and Mortimer (1964) is the most widely applicable and convenient method for fine structure analysis in yeast, but suffers the disadvantage that suitable X-ray machines or gamma ray sources are very expensive. Although many other recombinogens are known, none gives a linear dose-response like X-rays and few are as convenient or give as reproducible results. Experiments with Saccharomyces cerevisiae reported in this paper show, however, that the near-ultraviolet radiation emitted by fluorescent sunlamps gives linear dose-response relations, as reproducible results as ionizing radiations, and map distances which correlate highly with those obtained by using (60)Co gamma rays. It is suggested that this convenient recombinogen may be a suitable low-cost substitute for ionizing radiations in fine structure mapping.

Chromosome Mapping↗
PubMed1966

Residues of DDT in brains and bodies of birds that died on dosage and in survivors.

Residues of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethane (DDD) in brains of cowbirds (Molothrus ater) killed by dietary dosage of DDT were similar in birds that died after various lengths of time on dosage and in birds that died of delayed effects after as much as 40 days on clean food. Residues of DDT and DDD, but not of 1,1-dichloro-2,2-bis-(p-chlorophenyl)-ethylene (DDE), were much lower in survivors 112 days after dosage. The relative importance of DDT and DDD in brains could not be determined, but DDE appeared not to be critical. Residues in brains of cowbirds were similar to those reported for robins, sparrows, eagles, and white rats. Residues in livers and carcass remainders (with the possible exception of DDD in the liver) appeared unsuitable for diagnosing the cause of death.

Animals↗
PubMedDate not supplied

Adverse ocular effects of acetate hemodialysis.

In order to better define ocular dynamics during hemodialysis, we studied intraocular pressure (IOP) and anterior chamber depth (ACD) serially during both acetate and bicarbonate hemodialysis in 10 stable hemodialysis patients. IOP did not change significantly in any patient during dialysis. In contrast, however, ACD decreased significantly during acetate but not bicarbonate dialysis. ACD could be maintained during acetate dialysis by concomitant administration of mannitol. We conclude that acetate dialysis might adversely affect ocular dynamics in susceptible patients with glaucoma or recent ocular surgery. In such individuals administration of mannitol or use of a bicarbonate dialysate should be considered.

Acetates↗
PubMedDate not supplied

Human papillomavirus in oral verrucal-papillary lesions. A comparative histological, clinical and immunohistochemical study.

The purpose of this study was to determine the presence of Human Papillomavirus (HPV) virions in the verrucal-papillary (OVP) lesions by clinical, histological and immunohistochemical [peroxidase-antiperoxidase (PAP) features]. Thirty seven positive cases were compared with 47 negative cases. Considerable overlapping of clinical and histological features can be seen among all these lesions. The study provides evidence that there are no clinical or histologic features with taken alone are strongly correlated with the presence of virions in oral lesions.

Adult↗
PubMedDate not supplied

Diabetes and heart transplantation.

Diabetes mellitus remains a relative contraindication to heart transplantation. From June 1985 to December 1987, 71 patients underwent heart transplantation. Fifty-seven patients were nondiabetic, and nine had preexisting diabetes mellitus. Four patients were insulin dependent and three were not. All operative survivors (66) from these two groups were compared for survival and numbers of rejection and infection. Actuarial survival in the group with diabetes mellitus was 100% and 97.7% in the group without diabetes. Immunosuppression was maintained with cyclosporine, azathioprine, and low-dosage prednisone. In the group with diabetes two patients were maintained without prednisone. Selected diabetic patients can have successful transplantations. There is no significant difference in survival between the diabetic and nondiabetic patient. There is a tendency toward more rejections and fewer infections among the diabetic patients. In our experience diabetes mellitus is not a contraindication to heart transplantation.

Diabetes Complications↗