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Biomedical subjects

R A Johnson

Publications and source records attributed to R A Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1989

Cation and structural requirements for P site-mediated inhibition of adenylate cyclase.

The cation and structural requirements of the intracellular inhibitory "P" site of adenylate cyclase were investigated in human platelet membranes, bovine sperm particles, and detergent-solubilized and purified preparations from rat and bovine brain. Sensitivity of adenylate cyclase to P site-mediated inhibition was enhanced by reversible and irreversible activators of the enzyme. The most effective sensitization of the platelet and brain adenylate cyclases was observed with Mn2+ and upon proteolysis with inhibin in the presence of guanosine 5'-O-(3-thiotriphosphate). These resulted in IC50 values for (2',5'dideoxy-adenosine (2',5'-dd-Ado) and 2'-deoxy-3'-AMP of approximately 1-2 microM. The data were consistent with the ideas that P site-mediated inhibition of adenylate cyclase is dependent on divalent cation and is a function of enzyme activity. A number of nucleosides and nucleotides were synthesized and used to define structural requirements for P site-mediated inhibition of a detergent-solubilized adenylate cyclase from rat brain. The data suggest a strict requirement for an intact adenine moiety and a beta-glycosidic linkage for the ribosyl moiety. 2'-Deoxy-and especially 2',5'-dideoxy-ribosyl moieties enhanced sensitivity and a strong preference for phosphate at the 3'-position was exhibited. Substitutions at the 5'-ribose position impaired sensitivity. The order of potency and IC50 values of the more potent adenosine analogs were 2',5'-dideoxy-3'-AMP (congruent to 0.1 microM) greater than 2'-deoxy-3'-AMP (congruent to 1 microM) greater than 2',5'-dd-Ado (congruent to 3 microM) greater than 3'-AMP (congruent to 9 microM) greater than 2'-deoxy-adenosine (congruent to 15 microM) greater than adenosine (congruent to 80 microM). Large substitutions at the 3'-ribose position were tolerated, e.g., dApdN di- and dAp(dN)4 penta-nucleotides and succinyl- and p-fluoro-sulfonyl-benzoyl- moieties. The purified adenylate cyclase from bovine brain was inhibited by P site agonists with IC50 values of 34 and 45 microM for 2'-deoxy-3'-AMP and 2',5'-dd-Ado, respectively. The data imply, first, that the locus of the P site is the catalytic subunit of adenylate cyclase and, second, that the increased sensitivity observed with Mn2+ is due to an effect of the cation on the catalytic subunit. In contrast with adenylate cyclases from other mammalian tissues, the enzyme from bovine sperm exhibited only weak sensitivity to P site agonists; 2'-deoxy-3'-AMP congruent to 2',5'-dd-Ado greater than adenosine, each with IC50 values greater than 1000 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine↗
PubMed1989

Production of recombinant human serum albumin from Saccharomyces cerevisiae.

Human serum albumin has been constitutively expressed in a Saccharomyces cerevisiae brewing yeast. After cell growth and disruption the product was associated with the insoluble fraction and represented approximately 1% of total cell protein. After the cell debris was extensively washed, the albumin was solubilized with 8 M urea and 28 mM 2-mercaptoethanol in 50 mM sodium carbonate buffer, pH 10. The denatured albumin was refolded by dialysis and further purified by anion exchange and gel filtration chromatography. Losses of renatured material could be reduced, or higher protein concentrations used during refolding, if the denatured product was purified by cation-exchange chromatography in urea prior to refolding. Apart from an additional N-terminal N-acetyl methionine, the refolded product proved identical to human serum albumin derived from plasma when compared by a variety of physical, chemical, and biological analytical methods.

Chromatography, Gel↗
PubMed1989

Chronic exposure to tumor necrosis factor in vivo preferentially inhibits erythropoiesis in nude mice.

The anemia of chronic disease (ACD) is associated with conditions in which macrophage activation occurs. Activated marrow macrophages suppress erythropoiesis in vitro and produce tumor necrosis factor (TNF). Therefore, we tested the effects of chronic in vivo exposure to TNF to determine if it was a candidate for a mediator of ACD. Nude mice were inoculated with Chinese hamster ovary (CHO) cells expressing the human TNF gene or with control cells containing the transfection vector alone. The TNF mice promptly became reticulocytopenic, and after 3 weeks their corrected reticulocytes were 2.6% +/- 0.7% as compared with 7.3% +/- 4% in control mice. The hematocrit at 3 weeks was 28.4% +/- 1.7% in TNF mice as compared with 46% +/- 0.8% in control mice. This anemia was also associated with low serum iron and normal iron stores and increased erythropoietin (Epo) levels. The TNF mice showed an absolute monocytosis with twice the number of circulating monocytes as control mice and had M-colony-stimulating factor (CSF) activity in their serum. The TNF mice also became mildly thrombocytopenic. Marrow CFU-E and BFU-E were profoundly decreased (1.2 +/- 0.2 x 10(3) v 8.6 +/- 0.2 x 10(4) CFU-E per femur, and 6.5 +/- 1 x 10(2) v 8.5 +/- 0.2 x 10(4) BFU-E per femur). Splenic CFU-E and BFU-E were similarly depressed. In contrast, marrow CFU-GM and CFU-GEMM were not affected. The residual BFU-E in TNF mice were relatively resistant to TNF as compared with control mice. These data demonstrate that TNF preferentially inhibits erythropoiesis in vivo and may be important in the pathogenesis of ACD.

Anemia↗
PubMed1988

Are double translocations double trouble?

Double translocation heterozygotes are rare, but need not necessarily pose more of a counselling problem than single reciprocal translocation heterozygotes. Nine cases of double translocation are presented, together with a review of the few reports published to date. An attempt is made to provide simple counselling guidelines in the assessment of the risk of producing a liveborn abnormal child. This is not based on theoretical considerations of segregation patterns, but extrapolated from what is known empirically about the viable segregation patterns in carriers of single reciprocal translocations. It assumes that there is no interference with the independent assortment of the two separate exchanges, unless a common participating chromosome is involved. The possibility of an interchromosomal effect has not been taken into consideration.

Congenital Abnormalities↗
PubMed1988

Quantitative and functional change in T cells of primiparous mice following injection of benzo(a)pyrene at the second trimester of pregnancy.

Progeny from benzo(a)pyrene (BP) exposed (150 micrograms/g body weight) primiparous mothers, injected during the second trimester of pregnancy, are severely compromised immunologically. In view of maternal-fetal associations, we studied, during pregnancy and postpartum, the quantitative and functional status of the maternal T cell population in the thymus and/or spleen. In the thymus, there is an exacerbated depression in the amounts of thymocytes, (theta +, Lyt 1+, Lyt 2+ cells) during pregnancy relative to the corn oil-injected controls, which is sustained postpartum. In the spleen, while there are inconsistencies in the level of theta + cells, The Lyt 1+ are depressed postpartum relative to virgins, but the Lyt 2+ are enhanced during pregnancy and postpartum, reaching levels greater than 700-fold of controls. In controls, while the number of Lyt 1+ cells was higher than BP-exposed mice or virgins during pregnancy, they virtually disappeared postpartum. A similar but reversed image is mirrored by the Lyt 2+ cells, i.e., they were virtually absent during pregnancy but increased postpartum. Splenic allogeneic and syngeneic mixed lymphocyte responses were subnormal. The data show that BP disrupts the maternal T cell repertoire, leading to an accumulation of Lyt 1-2+ cells, and suggest that splenic disruption may be due to changes in the differentiation potential of T precursor cells. These changes not only are most likely to affect maternal defenses, but also may have a direct bearing on the establishment of progeny immune status.

Animals↗
PubMed1988

Variations in content of care in a family medicine residency relating to types of insurance coverage.

The content of care in a family practice residency program was analyzed using a microcomputer information system. The distribution of recorded diagnoses in the training program was found to be very similar to results of two national studies of family medicine. Despite this overall similarity, important differences were found when distributions for patients with six types of insurance coverages were analyzed separately. This study demonstrates the potential effect of insurance coverage on the clinical content of family medicine. As the health care system changes, residency programs will need to remain adaptable to maintain patient bases reflecting the broad content of family medicine.

Adolescent↗
PubMed1988

Demographic, clinical, and financial factors relating to the completion rate of screening mammography.

A retrospective analysis of the UCLA Family Health Center Research Data Base was performed to determine the relationship between completion rates of screening mammography and various patient demographic, clinical, and financial factors. Data from a 16-month period, from July 1984 through October 1985, were analyzed. Eight hundred twenty-seven women over 50 years of age were seen in the UCLA Family Health Center at least once during the study period. One hundred thirty-six (16.4%) of these women had screening mammography performed. Health insurance coverage was an important determinant of mammography completion. Patients covered by a health maintenance organization were 2.5 (P less than .05) times more likely to receive screening mammography. Uninsured patients were only 0.5 times as likely to have this procedure performed. The completion rate for screening mammography increased significantly with increasing number of visits during the study period (P less than .001). The age groups analyzed were significantly associated with completion rate. Marital status had a significant relationship to completion rate, but this was due to a lower completion rate in the group of patients whose marital status could not be determined. The employment status could not be evaluated due to the high rate of missing data. Race, smoking status, alcohol consumption, and the sex and training level of the primary provider were not found to be significantly associated with screening mammogram completion rates.

Aged↗
PubMed1988

Documenting patients' end-of-life decisions.

The anguish families experience when they are asked to make health care decisions for incompetent members has stimulated the search for an adequate procedure to document patients' end-of-life decisions. This study explores a method of recording competent patients' wishes via a "value history," a questionnaire that can guide families and the health care team during an incompetent person's terminal illness. Questions addressed were these: Can a primary care physician gather information from competent patients about their care before they become incompetent? Can a nurse practitioner gather the information as efficiently as a physician? Do patients want this information recorded in their charts? and, Is the primary care office as well as the patient's home an appropriate location to obtain a value history? Four hundred patients were invited to record their wishes for future care. Patients expressed that they wanted to be told the truth about their health and their health care, and they wanted to participate in decision-making, even while dying. The majority did not want to be maintained indefinitely on life-support systems. Patient responses were similar regardless of whether the NP or physician conducted the interview. A primary care office or patient's home are both suitable for filling out the value history. Because of the enthusiastic patient responses, the authors recommend that value histories become a routine part of a patient's medical record.

Adolescent↗
PubMed1987

Dissociation of the ribulosebisphosphate-carboxylase large-subunit binding protein into dissimilar subunits.

The ribulosebisphosphate-carboxylase large-subunit binding protein from Pisum sativum chloroplasts is an oligomer of two types of subunit with the composition alpha 6 beta 6. These two subunits are immunologically distinct, show different partial protease digestion patterns and have different amino-terminal sequences. Leaves of Hordeum vulgare also contain an oligomeric binding protein composed of equal amounts of two types of subunit. Treatment of either P. sativum stromal extracts or purified binding protein with ATP and Mg2+ ions causes the dissociation of the oligomeric form of the binding protein to the monomeric subunits. This effect is highly specific for ATP since CTP, UTP, GTP, ADP, AMP, cyclic AMP, NADPH and pyrophosphate do not cause dissociation.

Adenosine Triphosphate↗
PubMed1987

Nephropathic cystinosis with central nervous system involvement.

Nephropathic cystinosis is associated with end-stage renal failure, retinal damage, and hypothyroidism. Patients may now survive past the first decade of life with the use of dialysis and renal transplantation. Examination of a 24-year-old woman with this disorder revealed ovarian failure, mildly abnormal results on a glucose tolerance test, intermittent confusion, short-term memory loss, and cerebral atrophy on computerized axial tomography. Autopsy examination at age 25 years revealed cystine storage in multiple tissues including the atrophic ovaries, pancreatic islet cells, the aorta, and the brain. Dysfunction of multiple organ systems may develop in patients with cystinosis who survive into adulthood. This emphasizes the need for a systemic therapy for cystinosis.

Adult↗
PubMed1987

Early changes in T lymphocytes and subsets of mouse progeny defective as adults in controlling growth of a syngeneic tumor after in utero insult with benzo(a)pyrene.

Benzo(a)pyrene, a potent carcinogen, severely suppresses the anti-SRBC plaque-forming cell response, the mixed lymphocyte response (afferent T cell function), and an in vivo graft-vs.-host response (efferent T cell function) of mouse progeny exposed to the carcinogen during gestation (11 to 13 days). Immunodeficiency occurs early after birth (1 week) and persists for 18 months. The abnormalities in the T cell-mediated responses led us to examine the quantitative profile of T cells and subsets (Lyt 1+, Lyt 2+) present in the lymphoid organs during fetogenesis (15 to 19 days) and postnatally. In addition, we examined the ability of 3- to 8-month-old progeny and their spleen cells to resist the in vivo growth of cells from a syngeneic fibrosarcoma (a tumor that had been induced by benzo(a)pyrene). Our observations included: (1) Depletion of T cells and subsets in the thymus late (19 days) in gestation and postnatally. (2) Depleted T and Lyt 1+ cells in the spleen during gestation, while postnatally the former were enhanced and the effect on the latter was variable (enhancement and reduction). (3) In the fetal liver, the T cells were reduced, but the Lyt 1+ cells were unchanged. (4) The Lyt 2+ cells were strikingly enhanced in the fetal liver and spleen, but most dramatically for the former. (5) The Lyt 1/Lyt 2 ratio was less than 1.00 or controls in the fetal liver and spleen, a condition which persisted for 30 days postnatally in the latter organ. (6) Benzo(a)pyrene-exposed progeny or their spleen cells were relatively ineffective in resisting in vivo growth of transferred tumor cells. These results show that this carcinogenic pollutant induces a marked disorientation of T cells and subsets which can persist for at least 4 weeks postnatally. This suggests disruption of T cell differentiation during ontogenesis which may have profound implications on the ability to resist induction and growth of neoplasias after in utero exposure to the carcinogen.

Animals↗
PubMed1987

Evaluating census data quality using intensive reinterviews: a comparison of U.S. Census Bureau methods and Rasch methods.

"In this paper, we consider Rasch measurement methodology as an alternative to conventional U.S. Census Bureau methodology for evaluating the quality of data obtained using different measurements of the same characteristic. Rather than assuming, like the Census approach, that respondents have true states corresponding to the categories of a questionnaire item, the Rasch approach assumes that measuring instruments and survey respondents vary continuously on one or more common dimensions called latent traits. Unlike the Census approach, the Rasch approach requires that the properties of measuring instruments be invariant across different subclasses of respondents, generating parameter estimates that are sufficient statistics for elementary discrete sampling models. The different conclusions that can be drawn from the Census and Rasch approaches are illustrated by an evaluation of questionnaire items designed to measure the limitation or prevention of work because of physical or mental disability."

Americas↗
PubMed1987

Noninvasive evaluation of right ventricular function.

Numerous technologic advances have greatly facilitated the noninvasive analysis of right ventricular function. Nevertheless, important clues continue to be available to the astute clinician by physical examination. The chest x-ray is of rather limited utility. The electrocardiogram can show evidence of right atrial enlargement or right ventricular hypertrophy. Unfortunately, both sensitivity and specificity are deficient. Echocardiography is a widely available and potentially very accurate source of information concerning right ventricular dysfunction. Careful temporal analysis of the M-mode echocardiogram can give information beyond chamber size and wall thickness. Two-dimensional echocardiography allows more accurate determination of chamber size and wall thickness and also permits analysis of segmental wall motion and chamber contour. Doppler echocardiography allows measurement of pressure differences and flow kinetics. Preliminary data indicate that one can accurately assess pulmonary artery pressure and possibly right ventricular diastolic function. Color-flow mapping allows for accurate determination of valvular regurgitation and enhances the accuracy of standard Doppler echocardiographic techniques. Radionuclide analysis of the right ventricle by blood-pool imaging allows accurate determination of ejection fraction and wall motion. In addition, it may be possible to estimate pulmonary artery pressure. Use of short-acting radionuclides allows for serial imaging of the right ventricle after pharmacologic intervention or exercise. Perfusion scanning can show evidence of exercise-induced ischemia, although applicability to the right ventricle is somewhat limited. Avid scanning allows localizing of myocardial injury to the right ventricle. CT scanning of the heart is of limited clinical utility, because cardiac motion occurs too rapidly for accurate imaging. The advent of the cine-CT may overcome this problem and allow evaluation of right ventricular volumes and wall motion. Digital subtraction imaging allows for accurate video densitometric calculation of ejection fractions, but offers no advantage over other currently available techniques. Magnetic resonance imaging may prove to be the methodology of choice for analysis of right ventricular function, because it can give accurate measurement of right ventricular wall motion, ejection fraction, and (similar to Doppler flow studies) some indication of flow within the right-sided chambers. It will soon be possible to generate information concerning the biochemical content of the right ventricular myocardium, perhaps providing early evidence of hypertrophy or myopathy.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac Output↗
PubMed1987

Potent adenosine receptor antagonists that are selective for the A1 receptor subtype.

The xanthines currently represent the most potent class of adenosine receptor antagonists. However, known derivatives of xanthine show little difference in antagonist potency between the two putative adenosine receptor subtypes, A1 and A2. We conducted a systematic study of xanthine structure-activity relationships that compared antagonist potency at the A1 receptor of adipocytes with potency at the A2 receptor of platelets. Since adenosine receptors are coupled to adenylate cyclase in these tissues, inhibition of adenylate cyclase via A1 receptors and stimulation via A2 receptors were used as models of receptor activation. Antagonist potency was quantitated by Schild analysis, which yields an estimate of affinity (Ki) for the drug-receptor interaction. Ki values of a series of xanthine analogues enabled us to identify structural modifications than enhanced antagonist selectivity for one receptor subtype over the other. We found that changes in the substituent at position 8 of the xanthine nucleus influenced antagonist potency at the A1 adenosine receptor more than at the A2 receptor. In particular, an 8-cyclohexyl or 8-cyclopentyl substituent promoted antagonist selectivity for the A1 receptor subtype. Thus, 1,3-dipropyl-8-cyclopentylxanthine had comparatively high affinity (Ki = 0.47 +/- 2 nM) at the A1 receptor, and was roughly 150-fold more potent as an antagonist of the A1- than of the A2-adenosine receptor subtype. In addition, the cycloalkylxanthines were relatively ineffective as inhibitors of cyclic nucleotide phosphodiesterases when used at concentrations that produced marked adenosine receptor antagonism.

Adenosine↗
PubMed1987

Two-sample rank tests for detecting changes that occur in a small proportion of the treated population.

In the course of studying a biological phenomenon thought to be a precursor to chromosome breakage, researchers have found that treatments sometimes produce a higher proportion of "outliers" than do controls. Our examples pertain to smokers and patients undergoing chemotherapy, although the statistical methods developed here would apply to subjects exposed to any other health hazard. We formulate the problem in a nonparametric setting. Locally most powerful rank tests are obtained for mixture alternatives. In one instance, the approximate scores test has the simple form of counting the number of treatment responses above a combined sample percentile. Our test statistics are compared to the Wilcoxon and normal scores tests using empirical power studies and asymptotic efficiencies.

Biometry↗