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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 253 records · Page 14Linked to original sources
PubMed1990

Pathogenicity of Acanthamoeba and a Corynebacterium in the rat cornea.

Acanthamoeba keratitis is a sight-threatening disease that is difficult to treat. The development of an animal model is necessary for many of the studies required to improve visual outcome in human patients. A rat model is proposed that is dependent on coinoculation of amebae and corynebacteria into the corneal stroma. The infective dose was determined for a virulent Acanthamoeba isolate and was used to screen 17 other isolates, including 7 from the human cornea. A total of 6 were infective in the rat cornea. The model should be useful for controlled in vivo studies of this intractable condition.

Acanthamoeba↗
PubMed1990

Attitudes of at-risk and affected individuals regarding presymptomatic testing for autosomal dominant polycystic kidney disease.

One hundred forty-one individuals with autosomal dominant polycystic kidney disease (ADPKD) and 137 at-risk individuals from 107 kindreds answered a questionnaire to determine knowledge and attitudes about ADPKD and the use of gene linkage analysis for prenatal and postnatal presymptomatic diagnosis. Both groups of individuals displayed a high level of knowledge about the disease. Although 87% of affected individuals considered the recurrence risk of ADPKD high, only 11% of ADPKD did not have children for this reason after diagnosis. Ninety-seven percent of at-risk individuals would utilize gene testing for themselves. Eight-eight percent of ADPKD and 89% of at-risk individuals would test offspring (not significant, NS) and 65% of ADPKD and 50% of at-risk individuals between the ages of 18 and 40 would use prenatal testing (NS). Only 4% of ADPKD and 8% of at-risk individuals between the ages of 18 and 40 would terminate a pregnancy for ADPKD. A greater percentage would terminate a pregnancy for a serious medical problem. The factors influencing presymptomatic testing were analyzed. The data suggest that presymptomatic testing will not substantially modify incidence of ADPKD since it may only occasionally alter reproductive plans.

Adolescent↗
PubMed1990

Risk factors for the development of hepatic cysts in autosomal dominant polycystic kidney disease.

Hepatic cysts are a major manifestation of autosomal dominant polycystic kidney disease. This study examined 239 autosomal dominant polycystic kidney disease patients and 189 unaffected family members to define the factors that influence the presence and severity of hepatic cysts. Autosomal dominant polycystic kidney disease patients with hepatic cysts were older than autosomal dominant polycystic kidney disease patients without such cysts (44.6 +/- 1.1 yr vs. 32.9 +/- 1.1 yr; p less than 0.0001). The number of hepatic cysts increased with age (r = 0.43; p less than 0.0001). Women were more likely to have massive hepatic cystic disease (greater than 15 cysts) than men (p less than 0.04). Women also had larger maximal cyst size (4.2 +/- 0.4 cm vs. 2.7 +/- 0.3 cm; p less than 0.004). Women with hepatic cysts were more likely to have been pregnant (p less than 0.001) and to have had more pregnancies (2.9 +/- 0.3 pregnancies vs. 1.6 +/- 0.2 pregnancies; p less than 0.0009). Kidney volume (p less than 0.0001), number of cysts (p less than 0.004), percentage of cystic parenchyma (p less than 0.001) and predominant cyst size (p less than 0.001) were greater and creatinine clearance was lower (64.5 +/- 3.1 ml/min/1.73 m2 vs. 94.5 +/- 3.4 ml/min/1.73 m2; p less than 0.001) in autosomal dominant polycystic kidney disease patients with hepatic cysts. By logistic regression, the frequency of hepatic cysts was related to increased age, increased severity of renal cystic disease and decreased creatinine clearance. Number and size of hepatic cysts correlated with the occurrence of pregnancy, female gender, increased age and severity of the renal lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Comparison of the classical immunofluorescent antibody tests for Epstein-Barr virus with commercially available test kits.

Twenty reference sera with previously reported titers plus 10 normal seropositive and 10 seronegative sera were used to determine which assay for the detection of antibodies to Epstein-Barr virus should be utilized in our laboratory. By three commercially available test systems and by slides prepared in our laboratory, all techniques detected the same number of samples positive for IgG antibodies to viral capsid antigen (VCA) and Epstein-Barr virus-determined nuclear antigen (EBNA), but the geometric mean titers (GMTs) varied. Major discrepancies arose in the sensitivity of detection of early antigen-diffuse (EA-D) and -diffuse and restricted (EA-DR). Slides prepared in our laboratory gave the best results, detecting 12 of 12 (100%). Slides prepared according to Gull and Hillcrest detected 11 of 12 (92%), and those prepared according to Zeus detected 9 of 12 (75%). From these data, we conclude that all of these methods for detection of VCA and EBNA are adequate. However, in determining antibody levels to EA-D and EA-DR, great care should be taken as to the source of the slide and specificity and sensitivity.

Antibodies, Viral↗
PubMed1990

Comparison of dinucleotide frequency and codon usage in Toxoplasma and Plasmodium: evolutionary implications.

The weight-averaged observed/expected dinucleotide frequencies for the sum total of the coding regions of five Toxoplasma genes were compared with the same parameters previously determined for the coding regions of 21 Plasmodium genes. In addition, codon usage in the five Toxoplasma genes was compared with that in the 21 Plasmodium genes, and the percent distribution of amino acids in the Toxoplasma protein pool and the Plasmodium protein pool were compared with that in a general protein pool of 314 proteins. The results are consistent with the hypothesis that, contrary to currently held opinion, the genera Toxoplasma and Plasmodium are not especially closely related.

Animals↗
PubMed1990

Uric acid handling in autosomal dominant polycystic kidney disease with normal filtration rates.

PURPOSE: Patients with autosomal dominant polycystic kidney disease (ADPKD) are alleged to have more frequent or more pronounced alterations of uric acid homeostasis than are seen in most other types of chronic renal diseases. We performed this study to examine the hypothesis that individuals with ADPKD have abnormal uric acid homeostasis that is manifest before the development of renal insufficiency. PATIENTS AND METHODS: We studied 301 subjects, 163 with ADPKD and 138 relatives without ADPKD (NADPKD), by ultrasonography. The subjects were interviewed and examined. Venous blood and two 24-hour urine collections were obtained for uric acid and creatinine determinations. RESULTS: Presence of hyperuricemia, serum uric acid levels, uric acid clearance, and fractional excretion of uric acid did not differ between ADPKD and NADPKD subjects with normal renal function (creatinine clearance greater than 80 mL/minute/1.73 m2). Clearance of uric acid decreased and fractional excretion increased in subjects with decreased renal function in both groups. Female gender enhanced renal excretion of uric acid in both groups and hypertension depressed it except in men with ADPKD, who had higher fractional excretions of uric acid than did hypertensive NADPKD men. CONCLUSIONS: Uric acid homeostasis is preserved in individuals with ADPKD with normal renal function when compared to unaffected family members. Hyperuricemia and decreased renal excretion of uric acid develop as renal function worsens in ADPKD, similar to that in control subjects. The expected depressing effect of hypertension on renal handling of uric acid was not seen in men with ADPKD, speculatively due to an effect of atrial natriuretic factor.

Female↗
PubMed1990

Maternal serum alpha-fetoprotein levels in pregnancies among black and white women with fetal open spina bifida: a United States collaborative study.

In the present study second-trimester maternal serum alpha-fetoprotein levels were analyzed from 146 pregnancies associated with fetal open spina bifida to identify whether affected pregnancies from the black population were associated with higher maternal serum alpha-fetoprotein levels than their white counterparts. Pregnancies in black women not affected by open spina bifida are already known to have higher maternal serum alpha-fetoprotein levels. All of the cases were analyzed with gestational ages assigned by last menstrual period, and all maternal serum alpha-fetoprotein values were expressed as multiples of the median, to correct for differences in gestational age and assay among the 15 centers reporting data. The levels from affected pregnancies in white and black women fit log Gaussian distributions, with medians of 3.10 and 4.37 multiples of the median, respectively, on the basis of singleton, unaffected, white pregnancy medians. These results support adjustment of maternal serum alpha-fetoprotein values for race in black women; in addition, if a screening program's policy is to screen at a comparable risk in the two races, a higher maternal serum alpha-fetoprotein multiple of the median cutoff would be justified for black women.

Black People↗
PubMed1990

Decreased vascular compliance after reimplantation of the left lower lobe in young pigs.

The effects of chronic denervation on pulmonary vasculature are not well understood. Three groups of young pigs were prepared: (1) those receiving sham thoracotomy, (2) those having left upper lobectomy alone (innervated left lower lobe), and (3) those receiving left pneumonectomy followed by reimplantation of the left lower lobe (denervated left lower lobe). At 10 weeks after operation, animals were anesthetized and instrumented for study. No changes in baseline pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, or pulmonary vascular resistance were observed. With diversion of the entire cardiac output to the left lung or lobe, however, the group with reimplanted lobes had a significantly higher pulmonary artery pressure and pulmonary vascular resistance than the other groups. This may result from chronic denervation of the pulmonary vasculature and receptor upregulation.

Animals↗
PubMed1990

Phylogenetic relationships of Cryptosporidium determined by ribosomal RNA sequence comparison.

Reverse transcription of total cellular RNA was used to obtain a partial sequence of the small subunit ribosomal RNA of Cryptosporidium, a protist currently placed in the phylum Apicomplexa. The semi-conserved regions were aligned with homologous sequences in a range of other eukaryotes, and the evolutionary relationships of Cryptosporidium were determined by two different methods of phylogenetic analysis. The prokaryotes Escherichia coli and Halobacterium cuti were included as outgroups. The results do not show an especially close relationship of Cryptosporidium to other members of the phylum Apicomplexa.

Animals↗
PubMed1990

Effect of prolonged 5-hydroxytryptamine uptake inhibition by paroxetine on cortical beta 1 and beta 2-adrenoceptors in rat brain.

The effects of prolonged (21 day) oral administration of the antidepressants paroxetine (0.9 to 8.9 mg/kg/day) and amitriptyline (2.7 to 27 mg/kg/day), on rat brain cortical beta 1- and beta 2-adrenoceptor numbers and affinities were investigated using [3H]-CGP 12177. Although amitriptyline, 27 mg/kg, caused a significant (p less than 0.05) 20% reduction in the number of beta 1-adrenoceptors, paroxetine, at doses up to 8.9 mg/kg p.o., did not influence binding of [3H]-CGP 12177 to cortical beta 1- or beta 2-adrenoceptors. This study with paroxetine provides further evidence that the down-regulation of central beta 1-adrenoceptors in rat brain after repeated administration is not a property of all antidepressant drugs.

Adrenergic beta-Antagonists↗
PubMed1990

The effect of adjusting maternal serum alpha-fetoprotein levels for maternal weight in pregnancies with fetal open spina bifida. A United States collaborative study.

The effect of adjustment of maternal serum alpha-fetoprotein levels for maternal weight was evaluated in 143 pregnancies associated with fetal open spina bifida. The cases were analyzed with gestational dates as initially assigned either by last menstrual period (73%) or by ultrasonography (27%). The weights of women with pregnancies affected by open spina bifida were found not to be different from unaffected pregnancies. Adjustment resulted in a net increase in detected cases at two commonly used cutoff points: 2.0 and 2.5 multiples of the median. At 2.0 multiples of the median, the detection rate increased from 80% to 84%, whereas at 2.5 multiples of the median the rate rose from 68% to 69%. Adjustment for maternal weight has previously been shown to reduce the false-positive rate in maternal serum alpha-fetoprotein screening for fetal open spina bifida by reducing variance in unaffected pregnancies; our data provide further support for consideration of maternal weight when interpreting material serum alpha-fetoprotein measurements.

Body Weight↗
PubMed1990

Renal structure and hypertension in autosomal dominant polycystic kidney disease.

Hypertension has been reported to occur in 50 to 75 percent of subjects with autosomal dominant polycystic kidney disease (ADPKD) prior to the onset of marked renal insufficiency but concurrent with cystic deformation of the renal parenchyma. The present study was undertaken to examine whether the renal structural abnormalities are greater in hypertensive (HBP) versus normotensive (NBP) male and female patients with ADPKD who were matched within gender groups for age, body surface area, serum creatinine concentration (males HBP 1.2 +/- 0.02 vs. NBP 1.1 +/- 0.03 mg/dl. NS: females HBP 0.9 +/- 0.03 vs. NBP 0.9 +/- 0.02 mg/dl, NS) and creatinine clearance (males HBP 100 +/- 3 vs. NBP 108 +/- 3 ml/min/1.73 m2, NS: females HBP 97 +/- 3 vs. NBP 96 +/- 2 ml/min/1.73 m2, NS). Renal volume was significantly greater in the HBP compared to the NBP group (males HBP 624 +/- 47 vs. NBP 390 +/- 43 cm3, P less than 0.0005; females HBP 446 +/- 32 vs. NBP 338 +/- 24 cm3, P less than 0.002). Since increased renal volume is due to increased cysts, the results indicate that the early high incidence of hypertension in ADPKD correlates with the renal structural abnormalities in this disorder.

Adult↗
PubMed1990

Human antibody response to the nucleoside triphosphate hydrolase of Toxoplasma gondii.

An enzyme-linked immunosorbent assay (ELISA) that uses a recombinant protein of Toxoplasma gondii as antigen was used for the detection of specific antibodies in human sera. An antigenic portion of the T. gondii nucleoside triphosphate hydrolase (NTPase) was expressed in Escherichia coli as a glutathione S-transferase fusion protein with an apparent molecular mass of about 5000. A total of 118 T. gondii positive and 63 negative sera were examined. Seven % of the T. gondii positive sera, but none of the negative sera, reacted with the recombinant NTPase. Advantages and disadvantages that are associated with the use of fusion proteins as antigens in ELISA are discussed.

Animals↗
PubMed1990

Clinical comparison of two assays for rapid detection of cytomegalovirus early nuclear antigen.

Three methods for detection of cytomegalovirus (CMV) in 218 clinical specimens were compared: (1) shell vial assay to detect the early nuclear antigen after incubation for 16 hours and 40 hours (Syva Company); (2) 24-well plate assay to detect the early nuclear antigen after incubation for 16 hours (DuPont); and (3) convention tissue cell culture. CMV was detected in 26 specimens (12%) by one or more of these methods. With the shell vial assay, 12 (46%) and 15 (58%) specimens were positive after incubation for 16 hours and 40 hours, respectively. CMV was detected in 17 specimens (65%) by the 24-well plate assay. There was no significant difference in the detection of CMV between these assays. CMV was identified by conventional tissue culture in 15 of 22 (68%) evaluable cultures after an average of 14.2 days. More specimens were positive by conventional culture than by the 16-hour shell vial assay (P = 0.035). For optimal detection of CMV in clinical specimens, both conventional tissue cell culture and an early antigen assay should be performed. The two early antigen assays evaluated in this study yielded comparable results. However, the 24-well plates are more easily manipulated, and the 24-well plate assay, as performed, was easier to interpret and more cost efficient.

Antibodies, Monoclonal↗
PubMed1990

Transformation of chloroplast ribosomal RNA genes in Chlamydomonas: molecular and genetic characterization of integration events.

Transformation of chloroplast ribosomal RNA (rRNA) genes in Chlamydomonas has been achieved by the biolistic process using cloned chloroplast DNA fragments carrying mutations that confer antibiotic resistance. The sites of exchange employed during the integration of the donor DNA into the recipient genome have been localized using a combination of antibiotic resistance mutations in the 16S and 23S rRNA genes and restriction fragment length polymorphisms that flank these genes. Complete or nearly complete replacement of a region of the chloroplast genome in the recipient cell by the corresponding sequence from the donor plasmid was the most common integration event. Exchange events between the homologous donor and recipient sequences occurred preferentially near the vector:insert junctions. Insertion of the donor rRNA genes and flanking sequences into one inverted repeat of the recipient genome was followed by intramolecular copy correction so that both copies of the inverted repeat acquired identical sequences. Increased frequencies of rRNA gene transformants were achieved by reducing the copy number of the chloroplast genome in the recipient cells and by decreasing the heterology between donor and recipient DNA sequences flanking the selectable markers. In addition to producing bona fide chloroplast rRNA transformants, the biolistic process induced mutants resistant to low levels of streptomycin, typical of nuclear mutations in Chlamydomonas.

Chlamydomonas↗
PubMed1990

Small subunit ribosomal RNA evolution in the genus Acanthamoeba.

Reverse transcription of small subunit ribosomal RNA (srRNA) was used to determine the partial nucleotide sequences of the srRNA of seven isolates of Acanthamoeba. These seven sequences and the sequence of the corresponding region in an A. castellanii previously totally sequenced were compared in order to investigate evolution of the srRNA gene in Acanthamoeba. The results of the comparisons were consistent with the hypotheses that the genus is monophyletic, that the Pussard and Pons grouping system is valid, that the Acanthamoeba expansion segments in the srRNA gene evolve at a much faster rate than the rest of the gene, and that the extent of nucleotide sequence divergence in the genus Acanthamoeba is roughly similar to that differentiating vertebrates and invertebrates.

Acanthamoeba↗