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Biomedical subjects

R Evans

Publications and source records attributed to R Evans.

At least 469 records · Page 26Linked to original sources
PubMed1975

Quantitative and qualitative differences in DNA complementary to avian myeloblastosis virus between normal and leukemic chicken cells.

Hybridization of avian myeloblastosis virus (AMV) RNA with DNA immobilized on filters or in liquid with a vast DNA excess was used to measure the viral specific DNA sequences in chicken cells. Newly synthesized viral DNA (v-DNA) appears within an hour after infection of chicken embryo fibroblasts (CEF) with avian oncornaviruses. A fraction of newly synthesized v-DNA becomes integrated into the cellular genome and the remainder gradually disappears. A covalent linkage between v-DNA and cellular DNA was demonstrated to exist in CEF and in leukemic myeloblasts by alkaline sucrose velocity sedimentation. Hybridization of AMV RNA in DNA excess has revealed that there are 2 clases of viral specific sequences within normal as well as in leukemic cells. The 2 types of sequences differ in their rate of hybridization. The amount of both types of DNA sequences is about 2 times higher in leukemic cells than in normal cells. Both the fast- and slowly reacting sequences in leukemic cells exhibit a higher Tm (2 degrees C) than the respective DNA sequences in normal cells. Furthermore, when nucleotide sequences in AMV RNA complementary to normal DNA are removed first by exhaustive hybridization with normal DNA, the residual RNA only hybridizes with leukemic DNA but not with normal DNA. These results suggest that leukemic cells contain viral specific DNA sequences which are absent in normal cells. Endogenous v-DNA has been shown to be integrated in cellular DNA region(s) with a reiteration frequency of approximately 1,200 copies per cell and each integration unit appears to have a size approximately equivalent to the 35S RNA subunit of the viral genome. Viral sequences acquired after infection appear to be integrated in the unique region of cell DNA, or in tandem with the endogenous viral sequences.

Animals↗
PubMed1975

The antiarrhythmic and hemodynamic actions of alpha, alpha-dimethyl-4-(alpha, alpha, beta, beta-tetrafluorophenethyl) benzylamine (MK-251).

Alpha,alpha-Dimethyl-4-(alpha,alpha,beta,beta-tetrafluorophenethyl)benzylamine (MK-251) has been found to prevent certain types of experimentally induced ventricular arrhythmias and at maximally effective doses possesses substantial hemodynamic safety in contrast to standard antiarrhythmic agents. MK-251 prevented or modified ventricular arrhythmias produced by injection of tetrafluorohexachlorobutane into the coronary artery of dogs and baboons. In dogs, the dose estimated to prevent 80% of the arrhythmic impulses (ED80) was 0.5 mg/kg i.v. and 5.0 mg/kg p.o. The duration of action after oral administration of 5.0 mg/kg to the dog or baboon exceeded 5 to 6 hours. MK-251 delayed the onset of arrhythmias resulting from coronary artery ligation, reduced their severity and permitted a conversion back to normal sinus rhythm earlier than in control dogs. In cats, the doses of digoxin required to induce ventricular ectopic activity, ventricular tachycardia and ventricular fibrillation were elevated by MK-251. In anesthetized dogs, 4 times the i.v. ED80 produced no change in blood pressure, cardiac contractility or output, or in ventricular conduction. The only effect after 8 times the ED80 was a slight decrease in contractility. In contrast. lidocaine at its ED80 (0.21 mg/kg/min), decreased blood pressure and contractility; there was no change in ventricular conduction. Quinidine at the ED80 (8.8 mg/kg i.v.) and above produced hypotension, decreased contractility and prolonged conduction in a dose-related manner.

Amines↗
PubMed1974

Acquisition of new DNA sequences after infection of chicken cells with avian myeloblastosis virus.

DNA-RNA hybridization studies between 70S RNA from avian myeloblastosis virus (AMV) and an excess of DNA from (i) AMV-induced leukemic chicken myeloblasts or (ii) a mixture of normal and of congenitally infected K-137 chicken embryos producing avian leukosis viruses revealed the presence of fast- and slow-hybridizing virus-specific DNA sequences. However, the leukemic cells contained twice the level of AMV-specific DNA sequences observed in normal chicken embryonic cells. The fast-reacting sequences were two to three times more numerous in leukemic DNA than in DNA from the mixed embryos. The slow-reacting sequences had a reiteration frequency of approximately 9 and 6, in the two respective systems. Both the fast- and the slow-reacting DNA sequences in leukemic cells exhibited a higher T(m) (2 C) than the respective DNA sequences in normal cells. In normal and leukemic cells the slow hybrid sequences appeared to have a T(m) which was 2 C higher than that of the fast hybrid sequences. Individual non-virus-producing chicken embryos, either group-specific antigen positive or negative, contained 40 to 100 copies of the fast sequences and 2 to 6 copies of the slowly hybridizing sequences per cell genome. Normal rat cells did not contain DNA that hybridized with AMV RNA, whereas non-virus-producing rat cells transformed by B-77 avian sarcoma virus contained only the slowly reacting sequences. The results demonstrate that leukemic cells transformed by AMV contain new AMV-specific DNA sequences which were not present before infection.

Journal Article↗
PubMed1974

Cell-mediated immune response of ragweed-sensitive patients to ragweed antigen E. In vitro lymphocyte transformation and elaboration of lymphocyte mediators.

The in vivo and in vitro responses to ragweed antigen E were evaluated in 28 untreated atopic patients with ragweed hayfever. The methods employed included direct skin testing, measurement of total serum IgE, measurement of specific IgE anti-ragweed antibodies, leukocyte histamine release, lymphocyte transformation, and release of lymphocyte mediators (migration inhibitory factor and mitogenic factor). The patients could be divided into sensitive and insensitive groups on the basis of their in vitro reactivity to antigen E. 20 patients in the sensitive group had statistically higher levels of total serum IgE, higher levels of specific IgE anti-ragweed antibodies, and greater leukocyte sensitivity as measured by antigen-induced histamine release than did eight patients in the insensitive group. Lymphocytes from sensitive patients produced greater amounts of migration inhibitory factor and mitogenic factor when challenged by antigen E than did lymphocytes from insensitive patients. A possible role for the lymphocyte in this allergic disease is discussed. The results of this study indicate that the immune response to ragweed antigen is complex and involves components of both immediate and delayed hypersensitivity.

Adolescent↗
PubMed1972

Thymus-derived lymphocytes produce an immunologically specific macrophage-arming factor.

Spleen cells from mice immunized with an allogeneic tumor when cultured with the specific tumor cells release into the supernatant a specific macrophage-arming factor(s) (SMAF) which binds nonspecifically to macrophages from both mice and rats and renders these cytotoxic to the specific tumor cells. SMAF also binds in an immunologically specific way to the target cells. SMAF-treated target cells grow normally in the absence of macrophages but are killed in the presence of normal macrophages. Thymus-derived cells are necessary for the production of SMAF since (a) after treatment with anti-theta serum immune spleen cells fail to release SMAF; (b) spleen cells from immunized T cell-deprived mice (thymectomized as adults followed by whole body irradiation and restored with bone marrow) fail to produce SMAF on stimulation with the specific target cells. While SMAF has the properties of a cytophilic antibody, it does not belong to one of the established classes of immunoglobulin since high activity is found after column separation in a fraction having a molecular weight between 50,000-60,000 daltons.

Animals↗