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Biomedical subjects

L Johnson

Publications and source records attributed to L Johnson.

At least 73 records · Page 4Linked to original sources
PubMed2000

Efficiency of spermatogenesis: a comparative approach.

Efficiency of spermatogenesis is the estimated number of spermatozoa produced per day per gram of testicular parenchyma. Spermatogenesis is the process of cell division and cell differentiation by which spermatozoa are produced in testes. Efficiency of spermatogenesis is influenced by species differences in the numerical density of germ cell nuclei and in the life span of these cells. Activities of spermatogonia, spermatocytes, and spermatids partition spermatogenesis into three major divisions (spermatocytogenesis, meiosis, and spermiogenesis, respectively). Spermatocytogenesis involves mitotic germ cell division to produce stem cells and primary spermatocytes. Meiosis involves duplication of chromosomes, exchange of genetic material, and two cell divisions that reduce the chromosome number and yield four spermatids. In spermiogenesis, spherical spermatids differentiate into mature spermatids which are released in the lumen of seminiferous tubules as spermatozoa. Spermatogenesis and germ cell degeneration can be quantified from numbers of germ cells in various developmental steps throughout spermatogenesis. Germ cell degeneration occurs throughout spermatogenesis; however, the greatest impact occurs during spermatocytogenesis and meiosis. There are species and seasonal influences on the developmental steps in spermatogenesis at which germ cell degeneration occurs. Number of Sertoli cells, amount of smooth endoplasmic reticulum of Leydig cells, and the number of missing generations of germ cells within the spermatogenic stage of the cycle influence efficiency of spermatogenesis. Efficiency of spermatogenesis is influenced to the amount of germ cell degeneration, pubertal development, season of the year, and aging of humans and animals.

Aging↗
PubMed2000

Techniques for evaluating selected reproductive disorders of stallions.

Numerous techniques may be used for evaluation of the different reproductive disorders of the stallion. Approaches may vary from real-time ultrasonography and biopsy for evaluating testicular tumors to use of special assays for evaluating sperm or plasma for presence of antisperm antibodies. This communication addresses techniques used to evaluate five relatively uncommon, but perplexing, disorders of breeding stallions: (1) seminal vesiculitis, (2) hemospermia associated with idiopathic urethral defects, (3) acrosomal dysfunction, (4) abnormal spermatozoal chromatin, and (5) azoospermia.

Animals↗
PubMed2000

Liver transplantation improves cirrhosis-associated impaired oral glucose tolerance.

BACKGROUND: Thirty-five percent to 80% of cirrhotic patients have impaired glucose tolerance (IGT) or diabetes mellitus (DM). Diabetic cirrhotics have higher morbidity and mortality than nondiabetics. Therefore, it would be worthwhile to determine whether liver transplantation improves glucose homeostasis in these patients. METHOD: A total of 26 patients awaiting liver transplantation were evaluated for impaired glucose homeostasis by fasting blood glucose and/or oral glucose tolerance tests (OGTT). Five patients underwent transplant surgery within 1 year of OGTT and had a repeat OGTT 3-6 months after transplantation. RESULTS: Sixty-five percent (17/26) of the patients had abnormal glucose homeostasis. Twenty-three percent (6/26) met American Diabetes Association criteria for DM, and another 42.3% (11/26) had IGT. All patients had normal HbA1C levels. After transplantation, the 2-hr blood glucose improved in four patients and the mean 2-hr glucose level was reduced (204 +/- 94 vs. 132 +/- 53 mg/dl [mean +/- SD, P=0.051]). CONCLUSION: Liver transplantation can reverse cirrhosis-associated impaired glucose tolerance.

Adult↗
PubMed2000

Age of onset in affective disorder: its correlation with hereditary and psychosocial factors.

BACKGROUND: Affective disorders probably have a multifactorial aetiology, both biological and psychosocial factors may be of importance at onset as well as at relapses. The aim of the study was to investigate how the age of onset of bipolar and unipolar disorder relates to family history of affective disorder, early parental separation and life events. A second purpose of this study was to analyze the importance of life events preceding the first and subsequent episodes of affective disorder. METHODS: The case records of 282 patients (161 females/121 males; mean age 56) were investigated. They all had a DSM-IV based diagnosis of either bipolar I/II (67%) or unipolar (33%) disorder. Variables, such as family history, early parental loss and life events according to Paykel life events scale, were examined. RESULTS: We found a significantly lower age of onset in bipolar patients with a family history of affective disorder (28.9 vs. 33.9 years). Bipolar patients with preceding life events had a higher age of onset (33.1 vs. 28.3 years). Moreover, bipolar patients with heredity, had less life events at onset. For the bipolar, as well as the unipolar group, life stressors more frequently preceded the first episode of affective disorder than the subsequent episodes. LIMITATIONS: The major limitation of this study is the retrospective approach, with e.g. difficulties to decide whether a life event plays a role in aetiology of affective disorder or is its consequence. CONCLUSIONS: Bipolar patients with high constitutional vulnerability have an earlier age of onset and need less stress factors to become ill. Better knowledge about the stress- and the vulnerability-factors in affective disorder might contribute to development of individually tailored therapeutic strategies in future.

Adult↗
PubMed2000

Tracheal collapse. Diagnosis and medical and surgical treatment.

Tracheal collapse remains a common clinical problem in middle-aged, small-breed dogs. Clinical signs are characteristic, and the diagnostic work-up serves to identify predisposing triggers of disease and to allow optimization of therapy for individual animals. Bronchoscopic confirmation of airway collapse aids in characterizing the extent of airway damage and allows collection of airway samples to rule out infectious or inflammatory airway disease. Once coincident diseases have been managed, cough suppressants are used to control signs and reduce chronic airway injury.

Animals↗
PubMed2000

An adenovirus E1A mutant that demonstrates potent and selective systemic anti-tumoral efficacy.

Replication-selective oncolytic viruses constitute a rapidly evolving and new treatment platform for cancer. Gene-deleted viruses have been engineered for tumor selectivity, but these gene deletions also reduce the anti-cancer potency of the viruses. We have identified an E1A mutant adenovirus, dl922-947, that replicates in and lyses a broad range of cancer cells with abnormalities in cell-cycle checkpoints. This mutant demonstrated reduced S-phase induction and replication in non-proliferating normal cells, and superior in vivo potency relative to other gene-deleted adenoviruses. In some cancers, its potency was superior to even wild-type adenovirus. Intravenous administration reduced the incidence of metastases in a breast tumor xenograft model. dl922-947 holds promise as a potent, replication-selective virus for the local and systemic treatment of cancer.

Adenoviridae↗
PubMed2000

What is heartburn worth? A cost-utility analysis of management strategies.

OBJECTIVE: To determine the best treatment strategy for the management of patients presenting with symptoms consistent with uncomplicated heartburn. METHODS: We performed a cost-utility analysis of 4 alternatives: empirical proton pump inhibitor, empirical histamine2-receptor antagonist, and diagnostic strategies consisting of either esophagogastroduodenoscopy (EGD) or an upper gastrointestinal series before treatment. The time horizon of the model was 1 year. The base case analysis assumed a cohort of otherwise healthy 45-year-old individuals in a primary care practice. MAIN RESULTS: Empirical treatment with a proton pump inhibitor was projected to provide the greatest quality-adjusted survival for the cohort. Empirical treatment with a histamine2 receptor antagonist was projected to be the least costly of the alternatives. The marginal cost-effectiveness of using a proton pump inhibitor over a histamine2-receptor antagonist was approximately $10,400 per quality-adjusted life year (QALY) gained in the base case analysis and was less than $50,000 per QALY as long as the utility for heartburn was less than 0.95. Both diagnostic strategies were dominated by proton pump inhibitor alternative. CONCLUSIONS: Empirical treatment seems to be the optimal initial management strategy for patients with heartburn, but the choice between a proton pump inhibitor or histamine2-receptor antagonist depends on the impact of heartburn on quality of life.

Anti-Ulcer Agents↗
PubMed2000

Cloning and characterization of a cyclic peptide synthetase gene from Alternaria alternata apple pathotype whose product is involved in AM-toxin synthesis and pathogenicity.

Afternaria afternata apple pathotype causes Alternaria blotch of susceptible apple cultivars through the production of a cyclic peptide host-specific toxin, AM-toxin. PCR (polymerase chain reaction), with primers designed to conserved domains of peptide synthetase genes, amplified several products from A. alternata apple pathotype that showed high similarity to other fungal peptide synthetases and were specific to the apple pathotype. Screening of a Lambda Zap genomic library with these PCR-generated probes identified overlapping clones containing a complete cyclic peptide synthetase gene of 13.1 kb in length with no introns. Disruption of this gene, designated AM-toxin synthetase (AMT), by transformation of wild-type A. afternata apple pathotype with disruption vectors resulted in toxin-minus mutants, which were also unable to cause disease symptoms on susceptible apple cultivars. AM-toxin synthetase is therefore a primary determinant of virulence and specificity in the A. alternata apple pathotype/apple interaction.

Alternaria↗
PubMed2000

Management and outcomes of delayed sternal closure after cardiac surgery in neonates and infants.

OBJECTIVES: To investigate the efficacy, safety, and patterns of management of open sternotomy and delayed sternal closure in infants who were left with an open sternum after cardiac surgery and to assess these patterns for possible correlation with outcome. DESIGN: Retrospective chart review with statistical analysis. SETTING: Pediatric cardiac surgery service at a regional referral center based in an urban university teaching hospital. PATIENTS: All 128 patients <1 yr of age who were left with an open sternum after cardiac surgery with cardiopulmonary bypass during the 4-yr period from July, 1992 to June, 1996. INTERVENTIONS: Procedures for managing open sternotomy and delayed sternal closure were analyzed retrospectively. No interventions were undertaken for the study. MEASUREMENTS AND RESULTS: Of the 128 patients, 14 (11%) died before sternal closure; delayed sternal closure was performed in the remaining 114. Of these 114, 13 died in the early postoperative period. During sternal closure, significant increases were noted in pulmonary arterial (from 21.1+/-7.6 mm Hg to 26.1+/-6.5 mm Hg; p = .006), left atrial (from 8.4+/-3.4 mm Hg to 11.5+/-3.7 mm Hg; p < .001), and right atrial pressures (from 7.3+/-2.5 mm Hg to 9.8+/-2.5 mm Hg; p < .001). In addition, mean airway pressure (from 7.4+/-2.0 mm Hg to 8.6+/-2.4 mm Hg; p < .001) and peak inspiratory pressure (from 29.3+/-5.4 mm Hg to 31.3+/-5.6 mm Hg; p = .004) increased. Sternal wound infection occurred in one patient. CONCLUSIONS: Delayed sternal closure is an effective approach to the management of neonates and infants at risk for hemodynamic, respiratory, or hemostatic instability early after cardiac surgery. Significant changes in hemodynamics and respiratory variables occur during sternal closure, often requiring adjustment of inotropic and ventilatory management. (Crit Care Med 2000; 28: 1180-1184)

Cardiac Surgical Procedures↗
PubMed2000

The effect of locally delivered controlled-release doxycycline or scaling and root planing on periodontal maintenance patients over 9 months.

BACKGROUND: This research report evaluates clinical changes resulting from local delivery of doxycycline hyclate (DH) or traditional scaling and root planing (SRP) in a group of patients undergoing supportive periodontal therapy (SPT). METHODS: In all, 141 patients received either DH (67) or SRP (74) treatment in sites > or =5 mm on one-half of their dentition at baseline and month 4. RESULTS: Clinical results were determined at month 9. Baseline mean probing depth recordings were similar between the two groups (DH = 5.9 mm; SRP = 5.9 mm). Mean month 9 results showed similar clinical results for attachment level gain (DH 0.7 mm; SRP 0.8 mm) and probing depth reduction (DH 1.3 mm; SRP 1.1 mm). Percentage of sites showing > or =2 mm attachment level gain at month 9 was 24.7% in the DH group and 21.2% in the SRP group. Thirty-nine percent (39%) of DH sites and 38% of SRP sites showed > or =2 mm probing depth reduction. When treated sides of the dentition were compared to untreated sides, DH showed a difference in disease activity (> or =2 mm attachment loss) from 19.3% (untreated) to 7.2% (treated); and SRP from 14.3% (untreated) to 8.1% (treated). CONCLUSIONS: Results show that both DH without concomitant mechanical instrumentation and SRP were equally effective as SPT in this patient group over the 9-month study period.

Administration, Topical↗
PubMed2000

Cocaine-associated ischemic colitis.

Cocaine use can result in various gastrointestinal complications, including gastric ulcerations, retroperitoneal fibrosis, visceral infarction, intestinal ischemia, and gastrointestinal tract perforation. We report cocaine-associated colonic ischemia in three patients and review the literature. Including ours, 28 cases have been reported, with a mean patient age of 32.6 years (range, 23 to 47 years); 53.5% were men and 46.5% were women. The interval between drug ingestion and onset of symptoms varied from 1 hour to 2 days. Cocaine is a potentially life-threatening cause of ischemic colitis and should be included in the differential diagnosis of any young adult or middle-aged patient with abdominal pain and bloody diarrhea, especially in the absence of estrogen use or systemic disorders that can cause thromboembolic events, such as atrial fibrillation.

Abdominal Pain↗
PubMed2000

An initial evaluation of the Iowa Dental Surgical Simulator.

The University of Iowa colleges of dentistry and engineering are collaborating to build an effective but low-cost surgical simulator that uses force feedback to teach and assess the tactile skills of dentistry. A prototype simulator was built, and a formative evaluation examined the realism of the haptics and identified directions for future work. Using a cross-over design, twelve experienced practitioners probed two virtual teeth using two instruments attached to the force feedback device. The session was videotaped, the forces recorded, and a standardized questionnaire completed. Two analyses were conducted: an ANOVA examined practitioners' questionnaire responses, and a t-test analyzed the probing forces. Significant tooth order by instrument order interaction and instrument effects were found. Practitioners were generally satisfied. They preferred a standard joystick to an explorer, felt that two-dimensional graphics were sufficient, and emphasized that the existing vibration be eliminated. Random placement of caries should help teach generalized skills.

Analysis of Variance↗
PubMed1999

RNA binding characteristics and overall topology of the vaccinia poly(A) polymerase-processivity factor-primer complex.

The vaccinia virus-encoded heterodimer responsible for poly(A) tail elongation comprises a polyadenylylation catalytic subunit (VP55) and associated processivity factor (VP39). We show that monomeric VP39's affinity for RNA homopolymers follows the hierarchy poly(I) >poly(U) >>poly(G) >poly(A) >poly(C), that the heterodimer interacts stably with 40-45 nucleotide nucleic acid segments, and that its homopolymer preference for polyadenylylation priming is comparable to the VP39 affinity hierarchy (above). For oligonucleotide ligands possessing the previously-identified (rU)2-(N)25-rU heterodimer-binding motif, the heterodimer's affinity and base-type preference are mediated via both the (rU)2and rU portions, with the greater contribution coming from (rU)2. VP39's R107 sidechain contributes to specificity at the downstream rU. Substitution of each ribouridylate of the motif with either ribothymidine or 4-thiodeoxythymidine indicated that the downstream rU interacts with both heterodimer subunits, whereas the upstream (rU)2interacts only with VP55. A 'crosslinking SELEX' approach indicated VP39-base proximity around position -10 of a 4-thioribouridine/deoxycytidine ligand pool. Upon incubating the heterodimer with a panel of identical-sequence oligonucleotides derivatized with azidophenacyl bromide at various phosphate positions, those derivatized at positions -11 to -21 photocrosslinked to both subunits in a coordinated manner. This region may therefore pass through a 'cleft' or enclosed 'channel' at the subunit interface.

Binding Sites↗
PubMed1999

Long-term care. Wait 'til your dad gets home.

Patients and carers were unaware of eligibility criteria for long-term care. Many patients interviewed in a qualitative study were not aware they had been assessed for services. Delays in providing rehabilitation services and mobility restrict independence.

Aged↗