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Biomedical subjects

R Stevens

Publications and source records attributed to R Stevens.

At least 145 records · Page 8Linked to original sources
PubMed1987

The influence of cyproheptadine on immobilization and oestradiol benzoate induced anorexia in ovariectomized rats.

Repeated bodily immobilization significantly reduced the food intake of ovariectomized rats. Additionally, immobilization and oestradiol benzoate were found to produce additive effects in depressing feeding. To determine whether serotonergic mechanisms are involved in the stress- and oestrogen-induced anorexia, the 5-HT antagonist cyproheptadine was given to ovariectomized rats that were immobilized and treated with oestradiol benzoate. Cyproheptadine had no effect on the anorexia produced by oestradiol. The food intake of immobilized rats treated with cyproheptadine was similar to control values, suggesting 5-HT involvement in the stress-induced anorexia. However, cyproheptadine had no ameliorating effects on the changes in body weight following immobilization treatment. The implications of these findings are discussed in relation to a possible neuroendocrine basis for anorexia.

Animals↗
PubMed1987

Effects of cardiotoxin D from Naja naja siamensis snake venom upon murine splenic lymphocytes.

Cardiotoxin D from Naja naja siamensis is cytotoxic to T-lymphocytes above 150 femtomoles/10(6) cells. Equivalent lysis of macrophages or B-lymphocytes requires at least 1000 times more toxin. Reduction and carboxamidomethylation of cardiotoxin D does not effect T cell lysis. At higher toxin concentrations, 50% T-cell lysis occurs within 10 min. Splenocytes cultured with mitogens are up to five times more susceptible to toxin than unstimulated cells. Cardiotoxin D may directly disrupt the plasma membrane, since lysis is unaltered at 4 degrees C.

Animals↗
PubMed1987

Late coding region sequences required for competition by SV40 defectives.

SV40 defectives containing the complete early coding region (E-SV40) or the complete late region (L-SV40) were separately transfected into green monkey cells. They were analyzed for their ability to compete with wtSV40 (introduced by infection) or to undergo replication in the presence of constitutively produced SV40 T-antigen. L-SV40 competed very strongly. It appeared rapidly in infected cells, overgrowing wt genomes by at least 10:1. In addition, it slowed the growth of wt virus and reduced its ability to kill cells. L-SV40 DNA, as expected, replicated continuously in Cosl cells. E-SV40 genomes were poor competitors. They appeared slowly and by themselves did not overgrow wtSV40. When transfected into Cosl cells, E-SV40 genomes replicated efficiently for the first few days and disappeared within a week. Deletion or insertion mutations were introduced into a molecular clone of L-SV40, within the Vp1 gene or the Vp2 gene. All mutants were unable to form infectious virus in two different assays. The mutants were then assayed for competition against wtSV40 and for replication in Cosl cells. The Vp1 mutants competed very poorly with wt genomes and were rapidly lost from coinfected cells. These mutants, like E-SV40, replicated for only a few days in Cosl cells. In contrast, the Vp2 mutant competed with wtSV40 nearly as well as L-SV40. It also replicated continuously rather than transiently in Cosl cells. Next, we determined whether L-SV40 could effectively compete with other evolved SV40 defectives, not containing the late region but containing up to nine SV40 origin regions. We have shown that within five serial passages, L-SV40 became the predominant viral DNA species and the other defectives were lost. Although the Vp1 mutants and E-SV40 were weak competitors, they were shown to recombine with wtSV40 genomes to generate new L-SV40 genomes which again became the predominant species of viral DNA. These results demonstrate that L-SV40 is a potent competitor and that the Vp1 gene or a part of Vp1 plays an important role in this extraordinary competition. We suggest that the Vp1 gene functions to allow L-SV40 genomes to persist rather than generating a product which directly interferes with wtSV40 replication.

Animals↗
PubMed1987

Adolescent self-reports of social activity: assessment of stability and relations to social adjustment.

Adolescents' self-reports of peer social activity were examined with regard to short-term stability and in relation to social adjustment. Two separate periods of data collection are reported; year 1 with 74 grade nine students and year 2 with 76 grade nine students. On both occasions, four administrations of a self-report questionnaire were undertaken. As well, in year 2, social adjustment ratings, indices of perceived competence and self-efficacy, and IQ were collected. The analyses of the measure's consistency indicated acceptable stability of the self reports across two weeks and high internal consistency. These findings indicate the potential utility of this methodology for studying peer activity. Zero-order and multiple correlation analyses between social activity, self-evaluations and social adjustment were computed. The analyses suggest that peer social activity is correlated with social self-esteem, enhanced social self-efficacy and teacher's ratings of social engagement. Social isolation appeared to be an independent dimension and was related to lowered self-esteem and teacher ratings of social withdrawal. Overall, the results of the study add to our understanding of the components of social adjustment in adolescence.

Adolescent↗
PubMed1987

Reliability of continuous-wave Doppler probes.

Small-diameter, thin-walled latex tubes, through which a blood-simulating agent (0.1% suspension of simethicone in 0.9% sodium chloride) flowed at controlled rates, were embedded at varying depths in a tissue-mimicking matrix of powered graphite suspended in 4% agar. A continuous-wave (CW) Doppler probe was mounted at a 45-degree angle to the flow and passed transversely over the tube by a motorized drive mechanism at a rate of 0.42 mm/sec. Flow rates through the tubes were monitored with electromagnetic flow probes. The maximum depth from which quantitatively reliable signals could be obtained was 1.2 cm for 10 MHz probes and 3.3 cm for 5 MHz probes. Qualitative detection of flow was possible to a depth of 3.1 cm for 10 MHz probes and 7.0 cm for 5 MHz probes. The distances from the tube center for obtaining quantitatively reliable signals were limited to +/- 0.9 mm with a 10 MHz probe and +/- 1.8 mm with a 5 MHz probe. Qualitatively useful signals could be detected +/- 2.9 mm from the beam center by the 10 MHz probes and +/- 4.4 mm by the 5 MHz probes indicating a need for cautious interpretation as an interfering signal might be generated by any vessel within that range. Twenty percent of the randomly tested CW probes were considered unsuitable for use in quantitating blood flow, which underscores the importance of probe characterization before use.

Blood Flow Velocity↗
PubMed1987

Intimal integrity and fibrinolytic potential of reversed and in situ vein grafts.

The improved patency rates of in situ vein grafts are attributed to better flow characteristics, anastomotic "fit," and intimal preservation. This study compared the early changes in intimal morphology and fibrinolytic activity of in situ and reversed vein bypass grafts from mongrel dogs. Four to six centimeter in situ and reversed vein segments were used to bypass left and right femoral and internal carotid arteries, respectively. Heparin (100 U/kg) was administered before arterial clamping. Anastomoses were fashioned end to side and the intervening artery was ligated. Fifty-two grafts were harvested at day 1 (12 grafts), day 7 (16 grafts), day 14 (12 grafts), and 12 weeks (12 grafts). The veins were analyzed for histologic changes by light microscopy and scanning electron microscopy. The fibrinolytic activity of the grafts was assayed by the fibrin slide and fibrin plate techniques. There were no significant differences in morphology or fibrinolytic activity between the reversed and in situ grafts at any time period. These findings indicate that the improved patency rates associated with in situ grafts are not dependent on improved preservation of intimal structure or fibrinolytic activity.

Animals↗
PubMed1987

Seventh-grade students at-risk for school failure.

This study was designed to assess the effects of failure on the subsequent test performance in school of young adolescents. Fifty-one seventh-grade students, identified as at-risk for future school failure, were compared to 51 randomly selected classmates on individually administered measures of intelligence, self-concept, problem-solving ability, coping ability, attribution, and locus of control. Teachers' ratings, mathematics ability, and grades of the two groups were also compared. Students with a history of school failure, although of normal intelligence, were found to be significantly less intellectually, academically, and affectively competent than their more successful peers and were rated by their teachers as significantly less able to deal adaptively with normal school stress. A discriminant analysis separated the groups with 93% accuracy. On two equivalent mathematics tests, one given under relaxed conditions, and the other under normal school test-like conditions, approximately thirty percent of both the at-risk and the otherwise normal students got lower scores when they thought they were taking a test. Implications of these results for the understanding and remediation of stress-depressed school performance are discussed.

Achievement↗
PubMed1986

Complementation between SV40 and RFV defectives and acquisition of SV40 origins by late RFV genomes.

EL SV40 and RFV are variants of SV40 and BKV which contain bipartite or dual genomes. One molecule contains all the early viral sequences (E-SV40, E-RFV) and the other all the late viral sequences (L-SV40, L-RFV). Early and late genomes complement one another during productive infection. Experiments were designed to determine if E-genomes of one virus could complement L-genomes of another virus. If complementation did occur, intermolecular recombination events which lead to a more efficient infection or an altered host range might occur, and the sequences involved could than be identified. Two combinations were generated by direct transfection of BSC-1 green monkey cells. E-RFV and L-SV40 DNA complementation resulted in hybrid virus growth and cell killing. The hybrid demonstrated a narrow host range. Following serial passage, some E-RFV genomes contained SV40 origin region sequences but these recombinants did not overgrow prototype E-RFV genomes, even after many virus passages. In addition, no significant alterations in host range could be detected. Complementation between E-SV40 and L-RFV yielded a virus with a relatively wider host range. Virus growth and cell killing appeared very slowly at first. However, with each passage of E-SV40/L-RFV, cell killing occurred progressively more rapidly, until passage 7 when it became extensive in 7 days rather than 6-8 weeks. Infected cells contained 10-20 times more E-SV40 than L-RFV DNA during the first passage. However, by passage 7, both genomes were equally represented. During serial passage, L-RFV DNA acquired SV40 sequences from around the origin and the terminus of replication, such that recombinant (r) L-RFV genomes contained three SV40 origins [corrected] (including the 72-bp repeat) and 2 termini, and prototype L-RFV DNA was lost. E-SV40/rL-RFV demonstrated an altered host range propagating in some cell lines which did not support E-SV40/L-RFV growth. Both the host range change and the increased growth of rL-RFV genomes were shown to be at least partly caused by the acquisition of the SV40 sequences.

Animals↗
PubMed1986

Past is prologue.

Explore the source record for details and available documents.

History, Modern 1601-↗
PubMed1986

Designed transfer of specific immune responses with bone marrow transplantation.

Bone marrow transplant donors were immunized with tetanus/diphtheria toxoids 6-7 d before bone marrow donation to investigate the role of B cell subpopulations in reconstitution of humoral immunity. Lymphoblastoid B cells spontaneously producing IgG antitetanus and/or antidiphtheria toxoid were detected in the donor marrows at the time of transplantation. Recipients rapidly demonstrated 3-90-fold increases in serum IgG antitetanus and antidiphtheria toxoid levels. Antidiphtheria fragment A antibody in three donor/recipient pairs demonstrated spectrotypic identity indicating transfer of the donors' response. Reimmunization of three recipients 64-154 d after transplant revealed an IgG antibody response associated with reappearance of spontaneous antibody-producing B cells and an antidiphtheria fragment A response characteristics of the donor's immune response. These observations extend the understanding of the role of B cell subpopulations and provide a basis for specific modulation of immunity in the setting of bone marrow transplantation.

Adult↗
PubMed1986

Issues for American internal medicine through the last century.

The content, role, and purpose of internal medicine, organized as an American specialty 100 years ago, have been marked by ambivalence from the beginning. Nevertheless, molded to a large extent by external events, including the strategic and symbolic importance of surgery in American medicine, the rise of university medical schools, development of other specialties, and, more recently, the demand for primary care and the incentives built into reimbursement schemes and organized health care systems, internal medicine has become a powerful entity in American medicine. Its role in the future is likely to be more influential than in the past, both in policy and substantive areas. Continuing tensions in internal medicine include uncertainties about the relation between generalism and specialism, primary care and subspecialties, and internal medicine and general medicine.

Certification↗
PubMed1985

The effect of 6-mercaptopurine on natural killer-cell activities in Crohn's disease.

Crohn's disease patients on long-term 6-mercaptopurine therapy (more than 4 months) were evaluated for activity of peripheral blood natural killer cells. Natural killer-cell cytolytic activity against K-562 tumor-cell targets was examined, as was natural killer-cell suppression of lymphoblastoid B-cell antibody production. In addition, these patients were studied for their ability to generate antitetanus-specific IgG-antibody-producing lymphoblastoid B cells following in vivo booster immunization. Crohn's disease patients on 6-mercaptopurine therapy had significant reductions in peripheral blood natural killer-cell activity against K-562 targets compared to normals, disease controls, and Crohn's disease patients not on 6-mercaptopurine. Natural killer-cell suppression of lymphoblastoid B-cell antibody production was likewise decreased in 6-mercaptopurine-treated patients compared to normal controls. In contrast, the in vivo generated lymphoblastoid B-cell antibody responses of Crohn's disease patients on 6-mercaptopurine therapy were not decreased compared to normal, while Crohn's disease patients not on 6-mercaptopurine therapy had significantly impaired IgG antitetanus antibody responses. These findings suggest that 6-mercaptopurine therapy in Crohn's disease affects several lymphoid subpopulations, resulting in a decreased natural killer-cell cytotoxic activity against K-562 target cells and a decreased natural killer-cell ability to suppress lymphoblastoid B-cell antibody production, as well as an improved humoral immune response following tetanus toxoid booster immunization.

Adult↗
PubMed1985

Defective generation of tetanus-specific antibody-producing B cells after in vivo immunization of Crohn's disease and ulcerative colitis patients.

In vivo booster immunization with tetanus toxoid normally results in the temporal development of circulating populations of B cells that secrete antibody after in vitro culture. In assessing the humoral immunoregulatory status in patients with inflammatory bowel disease, we found that the antibody production by the B cells that spontaneously secrete tetanus-specific immunoglobulin G in vitro, and which occur in the circulation 7 days postimmunization, was highly variable and below normal in the majority of Crohn's disease and ulcerative colitis patients. The decreased in vitro antibody responses correlated with the lack of an increase in the serum antitetanus immunoglobulin G titers, but did not correlate with disease activity, location, or steroid therapy. The majority of patients who did not produce an immunoglobulin G-antitetanus toxoid antibody response similarly failed to produce an immunoglobulin G-antidiphtheria antibody response after immunization. Lymphocytes from the patients who failed to produce normal levels of antitetanus toxoid antibody did, however, proliferate normally when stimulated by tetanus toxoid in vitro. These results suggest there are in vivo humoral immune defects in inflammatory bowel disease.

Adult↗
PubMed1985

Release of immunoreactive beta-endorphin in vitro from pituitaries of young and old male rats.

The release of immunoreactive beta-endorphin (IR-BE) in vitro from the anterior pituitary (AP) and the neurointermediate lobe of the pituitary (NIL) from old male rats was significantly greater than from the AP and NIL from young male rats. In addition, the content and concentration of IR-BE in the AP and NIL was significantly greater in old than in young male rats, as was the concentration of IR-BE in the plasma. Chromatographic analysis revealed that in old male rats, the increase in IR-BE contained in and released by the AP and NIL, and found in the plasma, represented an increase in a peptide which coeluted with beta-endorphin rather than beta-lipotropin. These data suggest that both the AP and the NIL contribute to the elevation in plasma levels of IR-BE observed in old male rats, and that the increase in pituitary and plasma IR-BE in old male rats represents an increase in beta-endorphin.

Aging↗
PubMed1985

Diabetes induced by streptozocin results in a decrease in immunoreactive beta-endorphin levels in the pituitary and hypothalamus of female rats.

Immunoreactive beta-endorphin (IR-BE) was measured by radioimmunoassay in the anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL), and hypothalamus of female rats 4 wk after being made diabetic by a single injection of streptozocin (STZ). STZ-induced diabetes resulted in a significant reduction in the content and concentration of IR-BE in the AP and the content of IR-BE in the hypothalamus. Total hypothalamic protein was also significantly diminished. IR-BE levels in the NIL were unchanged. Column chromatography indicated that the reduction in IR-BE in the AP of the diabetic female rats represented a decrease in peptides that co-eluted with beta-endorphin and beta-lipotropin. In the hypothalamus, the reduction in IR-BE was represented solely by a decrease in a peptide co-eluting with beta-endorphin. Beta-lipotropin was not detectable in the hypothalami of control or diabetic female rats. These results suggest that, in the rat, diabetes may produce alterations in the mechanism(s) that regulate endogenous opiate levels in the pituitary and hypothalamus.

Animals↗