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Biomedical subjects

R L Brown

Publications and source records attributed to R L Brown.

At least 19 recordsLinked to original sources
PubMed1992

Functional regions of the inhibitory subunit of retinal rod cGMP phosphodiesterase identified by site-specific mutagenesis and fluorescence spectroscopy.

In the dark, the activity of the cGMP phosphodiesterase (PDE) of retinal rod outer segments is held in check by its two inhibitory gamma subunits. Following illumination, gamma is rapidly removed from its inhibitory site by transducin, the G-protein of the visual system. In order to probe the functional roles of specific regions in the PDE gamma primary sequence, 10 variants of PDE gamma have been produced by site-specific mutagenesis and expression in bacteria and their properties compared to those of protein containing the wild-type bovine PDE gamma amino acid sequence. Three questions were asked about each mutant: What is its affinity for the alpha beta catalytic subunit of PDE? Does it inhibit catalytic activity? If so, can transducin relieve this inhibition? Binding to PDE alpha beta was determined directly using fluorescein-labeled gamma by measuring the increase in emission anisotropy that occurs when gamma binds to alpha beta. Inhibition of PDE alpha beta was measured by reconstitution of the gamma variants with gamma-free PDE generated by limited digestion with trypsin or endoproteinase Arg-C. Unlike trypsin, the latter enzyme did not remove PDE's ability to bind membranes and be activated by transducin, so that transducin activation of PDE containing specific gamma variants could be assayed directly. The results indicate that mutations in many regions of gamma affect its binding to alpha beta. A mutant missing the last five carboxy-terminal residues (83-87) was totally lacking in inhibitory activity. However, it still bound to PDE alpha beta tightly, although with a 100-fold lower dissociation constant (approximately 5 nM) than that of wild-type gamma (approximately 50 pM).(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1992

Variation in a medical faculty's decisions to transfuse. Implications for modifying blood product utilization.

Previous studies have identified disconcerting differences in transfusion practices among physicians. This article investigates decisionmaking on transfusion by a medical school faculty. One hundred fourteen physicians indicated their propensity to transfuse 24 hypothetical patients who varied systematically in four clinical cues. Physicians agreed with transfusion for a widely divergent number of these patients (mean, 14.6; standard deviation, 5.5; range, 0 to 24). Although the physicians agreed on the order of importance of the clinical cues, they varied significantly in the importance they empirically attributed to the cues and in their thresholds for transfusion. Aside from a slightly higher propensity to transfuse by general internists, differences in decisionmaking were not attributable to physician-based variables. The wide variability in decisionmaking among physicians in the face of agreement on the order of importance of clinical cues suggests that quality assurance programs, and guidelines that only list the cues that ought to influence transfusion decisions, have low potential to achieve blood-product conservation.

Anemia↗
PubMed1992

Telephone triage by primary care physicians.

To determine if experienced primary care physicians are more likely to reach correct decisions on the telephone than their less experienced colleagues, we asked 31 first-year and 29 third-year residents, 21 faculty, and 36 private practitioners in pediatrics and family practice to evaluate three pediatric patients via a telephone interview with a simulated mother and to decide whether each patient needed to be seen that evening. Compared with first-year residents, the third-year residents, faculty and private practitioners decided less frequently to see children who were not severely ill (P less than .05) or injured (P less than .01); however, less than half obtained histories considered adequate to rule out potential serious illnesses. Faculty did better than either residents or private practitioners in managing a severely dehydrated child; 100% of the faculty, but less than 60% of the residents or private practitioners, chose to see the patient promptly (P less than .001). More than one third of all residents and private practitioners reached inappropriate management decisions despite obtaining information that should have altered their decisions. In these simulations, experience in private practice was not associated with improved telephone management of very sick children. Faculty physicians appeared to be better able to identify severely ill children without inappropriately evaluating those who were less ill. In all three simulations, attainment of the correct decision appeared to be determined not by the number or type of questions asked, but rather by the physician's interpretation of the information collected.

Acute Disease↗
PubMed1991

Aflatoxin production via cross-feeding of pathway intermediates during cofermentation of aflatoxin pathway-blocked Aspergillus parasiticus mutants.

Cofermentation of Aspergillus parasiticus strains (SRRC 163 and SRRC 2043) blocked at different steps in the aflatoxin B1 (AFB1) biosynthetic pathway in a synthetic liquid medium or on seeds (cottonseed, corn kernels, and peanuts) resulted in production of AFB1. Strain SRRC 2043 accumulated O-methylsterigmatocystin (OMST), a late precursor in AFB1 biosynthesis, whereas SRRC 163 accumulated averantin, an early precursor in the pathway. Strain SRRC 2043 secreted large amounts of OMST in culture relative to the amounts of several other pathway intermediates secreted into media (by other AFB1 pathway-blocked strains). AFB1 production occurred even when colonies of SRRC 163 and SRRC 2043 strains (producing no detectable AFB1) were grown together on an agar medium while physically separated from each other by a filter membrane (0.22-micron pore size). In addition, when mycelia of strain SRRC 163 were added to culture filtrates (containing no mycelia but containing secreted OMST) of strain SRRC 2043, AFB1 production occurred. The results suggested a chemical (rather than genetic) mechanism of complementation for AFB1 production between AFB1 pathway-blocked strains, since no mycelial contact was required between these strains for AFB1 production. The mechanism for chemical complementation involves secretion of OMST by SRRC 2043 and subsequent absorption and conversion of OMST to AFB1 by mycelia of strain SRRC 163.

Aflatoxin B1↗
PubMed1991

Successful treatment of primary amebic meningoencephalitis.

The fourth documented survivor of primary amebic meningoencephalitis, a young man with a history of waterskiing in a stagnant freshwater lake in northeastern Pennsylvania, is presented. Early consideration of this unusual diagnosis, based on historical factors (recent contact with warm fresh water), coupled with prompt aggressive therapy with high-dose amphotericin B is emphasized in achieving a successful outcome.

Adult↗
PubMed1990

Race, nutritional status, and survival from breast cancer.

The effects of nutritional status on differences in the survival of black and white women with breast cancer were studied in a cohort of 1,960 Georgia women diagnosed during 1975-1979. After data were adjusted for stage of disease, socioeconomic status, and other prognostic factors, poorer survival rates were shown in black women. Within each stage classification, lower levels of serum albumin and hemoglobin and higher relative body weight were more common among blacks and were independently associated with poorer survival. Among women with stage 3 disease, adjustment for these variables substantially reduced the excess mortality rate among blacks, suggesting that racial differences in survival may be partly explained by differences in nutritional status or extent of disease within stage.

Aged↗
PubMed1990

Early diagnosis of substance abuse: evaluation of a course of computer-assisted instruction.

A computer-assisted, experiential course of instruction on early diagnosis of substance abuse was developed and compared to three existing substance abuse curricula for third-year medical students on family medicine clerkships. The experimental course, requiring 2 hours of teacher contact, consisted of three computer-assisted instruction modules, active discussion, role play, opportunities for applying new knowledge and clinical skills, and modelling of clinical interest by a family doctor. The three comparison educational programmes were a one-week immersion experience on a substance abuse in-patient unit, 1-4 hours of lecture, and no formal teaching. For 6 months, all third-year medical students at Jefferson Medical College were exposed to one of these courses, and to the same required readings on substance abuse, on their required family medicine rotations at different clerkship sites. They completed end-of-rotation questionnaires assessing their knowledge, satisfaction with substance abuse teaching, and motivation for continued learning. Groups were similar with regard to demographic variables, academic performance, and previous curricular and extra-curricular exposure to substance abuse. Despite a possible selection bias favouring the immersion experience, the computer-assisted course resulted in higher levels of knowledge on early diagnosis, but similar attitudes and satisfaction. The computer-assisted and immersion courses produced more favourable outcomes than lecture-based teaching and no formal teaching. Compared to no formal teaching, lecture did not produce measurable effect. The results suggest that a computer-assisted, experiential substance abuse course, based on relevant and practical goals, can efficiently augment knowledge and motivation for further learning of third-year medical students.

Adult↗
PubMed1990

Variation in polygalacturonase production among Aspergillus flavus isolates.

Pectinase production by Aspergillus flavus was determined by measuring clear zones formed around colonies stained with ruthenium red. Several isolates produced red zones instead of clear zones. Red zones were reproduced with pectinesterase and correlated with absence of specific polygalacturonases. Of 87 isolates tested, 15 produced red zones.

Aflatoxins↗
PubMed1990

Suicide and schizophrenia: data from a prospective community treatment study.

This article reports the analysis of prospectively gathered data on eight young adults who committed suicide during an ongoing longitudinal study of long-term treatment of schizophrenia in the community. Young adult men with an early onset of psychiatric illness were identified as a high-risk subgroup. At the time of admission to the study, the subjects who eventually committed suicide reported significantly more distress and tended to be less satisfied with their lives than the other subjects. Specifically, baseline measures of self-reported subjective distress were consistently predictive of later suicide, whereas interviewer-rated measures and postbaseline assessments were not.

Adolescent↗
PubMed1990

Physicians' role in managing emotionally distressed patients already in psychotherapy.

Much has been written on how physicians should manage patients in emotional distress, including recommendations for making successful referrals to mental health providers. Little has been written, however, on the management of distressed patients who are already in psychotherapy. This article, drawing on three cases, a review of the literature, and systems theory, presents recommendations for managing these patients. Physicians are encouraged to assess these patients for risk of suicide or homicide, substance abuse, and indications for psychotropic medication. They are advised to seek a patient's permission to speak to his or her therapist when the patient may be in immediate danger, when psychotropic medications, hospitalization, or psychiatric consultation is considered, and when the patient fails to respond to ongoing treatment. For patients whose therapists are not psychiatrists, psychiatric consultation is recommended when there are questions about psychotropic medications, when psychiatric and substance abuse disorders coexist, and when hospitalization is considered. Therapists skilled in applying systems theory should be consulted when the patient, psychotherapist, and physician agree that the patient is not making sufficient progress. In most cases, however, physicians should reassure patients about distressing symptoms, avoid expressing opinions about the therapist and psychosocial issues, and encourage patients to renew or to expand their commitment to their psychotherapy.

Adult↗
PubMed1989

Heparin cofactor II-proteinase reaction products exhibit neutrophil chemoattractant activity.

The physiologic function of the plasma glycoprotein heparin cofactor II (HCII) is not well understood. An in vivo role for thrombin (IIa) inhibition by HCII in the presence of certain glycosaminoglycans (dermatan sulfate and heparin) can be proposed. Many proteins, such as complement components, can be proteolyzed to generate secondary bioactive molecules. HCII is a substrate for the human neutrophil (PMN) proteinases cathepsin G (CG) and elastase (LE). We found that degradation of HCII by CG or LE generated products with potent PMN chemotactic activity, which did not stimulate the PMN oxidative burst. Our results suggest that HCII may be a physiologic regulator of the acute inflammatory response.

Cathepsin G↗
PubMed1989

Expression in bacteria of functional inhibitory subunit of retinal rod cGMP phosphodiesterase.

The cGMP phosphodiesterase of vertebrate retinal rod outer segments plays a key role in visual transduction. A functionally active form of the inhibitory gamma subunit of the phosphodiesterase, which keeps the enzyme inactive in the dark, has been obtained in high yield from a synthetic gene expressed in Escherichia coli. A DNA sequence encoding the 87-residue bovine gamma subunit was chemically synthesized and assembled from 10 oligonucleotides. The synthetic gene was cloned into an expression vector that uses the promoter PL of lambda phage. E. coli was transformed with this vector, which encodes a fusion protein consisting of the first 31 residues of the lambda cII protein, a 7-residue joining sequence that is specifically cleaved at its C-terminal end by clotting protease factor Xa, and the 87-residue gamma subunit. The fusion protein was solubilized in 6 M urea and purified by ion-exchange chromatography on a CM-Sephadex column. The typical yield was 1 mg of fusion protein per liter of bacterial culture, which corresponds to the amount of gamma in about 2500 bovine retinas. Proteolytic cleavage of the fusion protein by factor Xa released a synthetic gamma with the same amino acid sequence as that of native gamma. Both fusion protein and synthetic gamma inhibited trypsin-activated phosphodiesterase with high affinity (Kd less than 100 pM). Likewise, both were as effective as native gamma in inhibiting transducin-activated phosphodiesterase in rod outer segment membranes. This inhibition was reversed by the activation of additional transducin. Thus, the N terminus of gamma is not intimately involved in interactions with either the catalytic subunits of the phosphodiesterase or the activated form of transducin. In contrast, a C-terminal deletion mutant terminating at residue 74 of gamma stimulated rather than inhibited the trypsin-activated enzyme. Thus, the C-terminal region of gamma is critical for inhibition of the phosphodiesterase.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1978

Countercurrent immunoelectrophoresis in the diagnosis of viral infections of the central nervous system.

Countercurrent immunoelectrophoresis was utilized in the study of 621 specimens of cerebrospinal fluid to determine the correlation of detection of viral antigens with the clinical diagnosis of aseptic meningitis and related viral infections. A panel of viral antisera was immunoelectrophoresed against 119 specimens from patients with suspected viral infections of the central nervous system (group I), 32 from patients with bacterial meningitis (group 2), and 470 from patients with no suspected infection of the nervous system (group 3). One or more precipitin bands were detected in 79% of specimens from group 1, 19% from group 2, and 4% from group 3. Paired acute- and convalescent-phase sera from 32 (78%) of 41 patients with precipitin bands detected by countercurrent immunoelectrophoresis demonstrated a fourfold or greater change in complement-fixing antibodies to the detected antigen. With refinements in antisera, countercurrent immunoelectrophoresis may become useful in the rapid laboratory diagnosis of viral infection of the central nervous system.

Acute Disease↗