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Biomedical subjects

L Johnson

Publications and source records attributed to L Johnson.

At least 541 records · Page 30Linked to original sources
PubMedDate not supplied

Age-related variation in seminiferous tubules in men. A stereologic evaluation.

Tubular boundary tissue and seminiferous epithelia were evaluated stereologically in testes from 28 men aged 20 to 48 years and 28 men aged 50 to 90 years. Testes obtained at autopsy within 15 hours of death were perfused with glutaraldehyde, embedded in Epon (Ladd Research Industries, Inc., Burlington, VT), sectioned at 0.5 micron, and stained with toluidine blue. Volume densities (percentage of the testicular parenchyma) of various parameters determined by point counting and diameter measurements were used to calculate total volumes, length of tubules, and number of cells. Electron microscopy was used to determine the volume density of myoid cells in the boundary tissue. Significant (P less than 0.01) age-related reductions occurred in paired testicular weights, paired parenchymal weights, total volume of seminiferous tubules and of seminiferous epithelium, and length of tubules. The volume density and thickness of boundary tissue increased (P less than 0.01) with age. The volume of boundary tissue per man and the volume density of myoid cells in the boundary tissue did not vary with age. Although the number of myoid cells per man tended to be lower in the older group, the number of myoid cells per cross section of seminiferous tubule was increased (P less than 0.01) in older men. The age-related thickening of the boundary tissue was not due to an increase in boundary tissue but resulted from a reduction in the length of the seminiferous tubules.

Adult↗
PubMedDate not supplied

Alcohol abusers' perceptions of the accuracy of their self-reports of drinking: implications for treatment.

Several major literature reviews have concluded that alcohol abusers generally give valid self-reports when interviewed under certain conditions. Nevertheless, across all studies a small proportion of alcohol abusers' self-reports continue to be suspect. Sources of invalidity may relate to subject factors or to circumstances under which data are collected. One novel way of gaining information about conditions possibly affecting the accuracy of alcohol abusers' self-reports is to ask the subjects themselves. In the present study, 208 alcohol abusers were asked about (a) how accurately different people they knew or lived with would report their (i.e., the subjects') drinking at different levels (e.g., abstinent, 1-4 drinks) compared to the subjects' own reports; (b) how accurate their own reports would be at different levels of ethanol consumption; and (c) how accurate their own reports would be when interviewed under different conditions (e.g., by phone, their therapist, a researcher, their employer). The results are largely consistent with studies that have empirically examined the validity of alcohol abusers' self-reports. Suggestions for future research and evaluation are offered.

Adult↗
PubMedDate not supplied

A strategy for obtaining active mammalian enzyme from a fusion protein expressed in bacteria using phospholipase A2 as a model.

An active preparation of human phospholipase A2 (PLA2) was made after expression as an insoluble fusion protein in Escherichia coli. The new key elements required for PLA2 isolation were the maintenance of the fusion protein in solution after the initial solubilization and the use of a tryptophan cleavage procedure for regeneration of native PLA2 from the fusion protein. The fusion protein was composed of a beta-galactosidase leader peptide incorporating six consecutive threonine residues to aid in insoluble inclusion body formation, followed by a tryptophan adjacent to the N-terminus of PLA2. The fusion protein was purified from cell lysates, and the leader peptide was cleaved on the C-terminal side of the tryptophan residue with N-chlorosuccinimide. The released PLA2 was refolded and renatured to produce an enzyme with activity comparable to that of other phospholipases A2.

Amino Acid Sequence↗
PubMedDate not supplied

Cloning and sequence analysis of the cDNA for the rat atrial natriuretic factor precursor.

Atrial extracts contain factors which induce potent natriuresis changes in renal haemodynamics, and relax pre-contracted vascular smooth muscle. Low-molecular-weight peptides which mimic these actions have now been purified by several groups, including ours (see accompanying paper), and higher-molecular-weight proteins with similar but less potent biological activities have also been identified and are presumed to be precursors. If released into the circulation, these peptides, collectively called atrial natriuretic factor (ANF), may play a significant part in blood-pressure homeostasis, regulation of extracellular fluid volume and as antagonists to the hypertensive effects of the renin-angiotensin system and other hormonal and neurotransmitter systems. We describe here the isolation and characterization of rat atrial cDNA clones which encode ANF. Nucleotide sequence analysis shows that auriculin corresponds to the 25 amino acids located close to the C-terminus of a 152-amino acid ANF precursor. Analysis of the in vitro translation products of precursor ANF mRNA suggests that multiple forms of the precursor may exist.

Amino Acid Sequence↗
PubMedDate not supplied

Analysis of deletions in DNA from patients with Becker and Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder for which the biochemical defect is as yet unknown. Recently, two cloned segments of human X-chromosome DNA have been described which detect structural alterations within or near the genetic locus responsible for the disorder. Both of these cloned segments were described as tightly linked to the locus and were capable of detecting deletions in the DNA of boys affected with DMD. In an attempt to determine more precisely the occurrence of these deletions within a large population of DMD patients and the accuracy of one of the segments, DXS164 (pERT87), in determining the inheritance of the DMD X chromosome, the subclones 1, 8 and 15 were made available to many investigators throughout the world. Here we describe the combined results of more than 20 research laboratories with respect to the occurrence of deletions at the DXS164 locus in DNA samples isolated from patients with DMD and Becker muscular dystrophy (BMD). The results indicate that the DXS164 locus apparently recombines with DMD 5% of the time, but is probably located between independent sites of mutation which yield DMD. The breakpoints of some deletions are delineated within the DXS164 locus, and it is evident that the deletions at the DMD locus are frequent and extremely large.

Chromosome Deletion↗
PubMedDate not supplied

A new mechanism for induced vitamin D deficiency in calcium deprivation.

Synthesis of vitamin D in the skin in response to ultraviolet light is the main determinant of vitamin D status in man and it is therefore surprising that rickets and osteomalacia, clinical signs of vitamin D deficiency, remain common in tropical and subtropical countries. Skin pigmentation can reduce vitamin D formation but this is a negligible limitation in people exposed to abundant ultraviolet light. Earlier studies in animals and man suggested that another environmental factor, the low calcium/high cereal diet typical of susceptible populations, might affect the efficiency of vitamin D utilization. We show here in rats that the rate of inactivation of vitamin D in the liver is increased by calcium deprivation. The effect is mediated by 1,25-dihydroxyvitamin D, produced in response to secondary hyperparathyroidism, which promotes hepatic conversion of vitamin D to polar inactivation products that are excreted in bile. This finding has widespread implications both for understanding the pathogenesis of endemic rickets and in that it provides a unifying mechanism for the development of vitamin D deficiency in many clinical disorders.

Animals↗
PubMedDate not supplied

Evaluation of zinc salt based fixatives for preserving antigenic determinants for immunohistochemical demonstration of murine immune system cell markers.

Conventional aldehyde based fixatives produce good morphological preservation. However, owing to their cross-linking mechanism of action, epitope loss may occur during fixation compromising the tissue for subsequent immunohistochemical (IHC) analysis. IHC is an important tool for characterizing antigen, cytokine and cytomorphological markers. The increasing use of mouse models for study of pathogenesis has highlighted the need to investigate alternative fixatives. In the study reported here, tissue samples from RIII mice with immune mediated lesions, Mycobacterium bovis infected mice, and uninfected control mice were fixed in either zinc salt fixative or buffered formalin, then tested for IHC using a panel of antibodies (CD3, CD4, CD8, CD45, CD54, F4/80, Interferon-gamma and MIP2). Zinc salt fixation preserved processing-sensitive murine cell markers (CD4, CD8 and CD54) and improved the intensity of immunolabeling for CD45, F4/80 and CD3. Buffered formalin failed to preserve any of the processing-sensitive murine epitopes for demonstration by subsequent IHC.

Animals↗
PubMedDate not supplied

Data standards are back seat drivers! Methodology for incorporating information quality into quality assurance project plans.

Quality assurance project plans for environmental data collections consider user requirements for the measurements and express these in the form of data quality objectives. User requirements now may include capture of measurements and associated information in prescribed formats to facilitate entry into computerized information systems. Establishing ahead of time that the data requirements may be an important "back seat driver" for an environmental collection effort can save considerable resources for an organization. Also, the planning may need to accommodate unique requirements associated with the entry of data into data collection systems.

Data Collection↗
PubMedDate not supplied

Improving knowledge of the prostate cancer screening dilemma among African American men: an academic-community partnership in Washington, DC.

OBJECTIVE: Studies have shown that African American men are at greater risk than other men for prostate cancer in terms of both incidence and mortality. At the same time, the utility of screening asymptomatic men for prostate cancer remains controversial. The combination of high incidence and high mortality with the uncertain benefits of screening poses a difficult problem for African American men. This study was part of an ongoing project that sought to develop and evaluate health education materials designed to help African American men make an informed decision about prostate cancer screening. The project represented a collaboration between the Most Worshipful Prince Hall Grand Lodge of the District of Columbia and the Lombardi Cancer Center of Georgetown University. METHODS: The authors conducted eight focus groups with 44 members of the Prince Hall Masons. The focus groups covered men's understanding of prostate cancer screening and their preferences for methods of health education. RESULTS: Participants demonstrated a high level of awareness of the availability of prostate cancer screening, a low awareness of the screening controversy, and a desire for detailed epidemiologic information and information about the benefits and limitations of screening. The preferred forms of educational materials were video and print-based materials, which the research team has recently developed. CONCLUSIONS: These findings demonstrate the feasibility of developing an academic-community collaboration with the goal of improving a health-related problem in the African American community. A randomized trial is underway to evaluate the impact of the video and print education materials.

Academic Medical Centers↗
PubMedDate not supplied

Operative management of unstable pelvic fractures.

With the high incidence of pelvic fractures in trauma cases, nurses need to understand these injuries and their complications. Accurate assessment determines the type of fracture management; open reduction and internal fixation (ORIF) is often the treatment of choice, since it allows earlier mobility and fewer complications.

Fracture Fixation, Internal↗
PubMedDate not supplied

The diagnosis of major depression in renal dialysis patients.

Controversy exists regarding the frequency of depression in renal dialysis patients. We have assessed an unselected sample of 99 dialysis patients using the Diagnostic Interview Schedule (DIS). A current Major Depressive Episode (MDE) was diagnosed in 8.1% of the sample, one-half of whom had a past history of MDE. An additional 12.1% had only a past history of depression. In contrast to patients with no affective disorder, characteristics of patients with a current MDE included the following: a history of previous MDE; female sex; duration of dialysis less than or equal to 24 months; a younger mean age; solitary living arrangements; and unemployment. The following DSM-III criteria distinguished patients with MDE from those with no affective disorder: depressed mood or loss of interest; feelings of worthlessness or excessive guilt; anorexia and weight loss; and slowed or mixed-up thoughts. DSM-III criteria that were common in the entire sample but not useful in distinguishing patients with MDE included loss of energy, insomnia, and decreased sexual interest. These results indicate that some DSM-III criteria are common in dialysis patients and therefore do not distinguish major depression, whereas other DSM-III criteria are more specific for MDE. Further, it is possible that the prevalence of MDE is greater in dialysis patients than in the general population.

Adult↗