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Biomedical subjects

L R Brown

Publications and source records attributed to L R Brown.

At least 109 records · Page 6Linked to original sources
PubMed1982

Primary mediastinal carcinoid tumors.

A study of 15 cases of carcinoid tumor of the thymus, diagnosed and treated at the Mayo Clinic, revealed histopathologic features of the neoplasm that might cause it to be confused with other mediastinal tumors, both primary and secondary. The tumor was associated with ectopic ACTH production in six patients, of whom five had Cushing's syndrome. Metastasis, which occurred in 11 patients (73%), was delayed for as long as 8 years after initial diagnosis. Eleven patients underwent surgical resection of their primary thymic neoplasms, and nine of these received postoperative radiotherapy or chemotherapy or both. One patient was treated with chemotherapy alone, and three had no treatment for their neoplasms, which were discovered at autopsy. Eight patients are still alive. Of these, five have developed metastases, and only one is free of metastatic disease more than 5 years after diagnosis. In the two remaining cases, the discovery of the thymic tumor was recent and follow-up is not yet meaningful. Overall, four of the seven patients who died had proven metastatic disease. The mean survival after the appearance of extrathymic tumor in this group was 3 years. Of the five patients who are still alive with metastasis, all have survived at least 2 years since that spread of their disease.

Adolescent↗
PubMed1982

Roentgenologic diagnosis of primary corticotropin-producing carcinoid tumors of the mediastinum.

A study was undertaken of five patients with Cushing syndrome due to adrenocorticotropin (ACTH) production by thymic carcinoid tumor (primary mediastinal APUDomas), including two recent patients examined by computed tomography (CT) of the chest. Plain roentgenography of the chest initially failed to detect tumor in four of the five patients, while CT of the chest yielded definitive diagnostic information in both patients in whom it was employed. For one of these patients, a mediastinal tumor could be seen retrospectively on plain roentgenograms of the chest, although it had been missed on the first examination. One of the tumors appeared to be partially calcified on CT scan, a finding not previously reported. Blastic osseous metastasis, which is common when malignant carcinoid tumors spread to bone, was seen in one patient. Our data suggest that in patients with suspected ectopic ACTH production, CT scanning of the mediastinum should be performed early in order to avoid delay in diagnosis of an ACTH-secreting carcinoid tumor of the mediastinum.

Adolescent↗
PubMed1981

Melittin bound to dodecylphosphocholine micelles. H-NMR assignments and global conformational features.

Assignments have been obtained for most of the H-NMR lines of melittin bound to fully deuterated dodecylphosphocholine micelles by combined use of two-dimensional spin echo correlated spectroscopy and one-dimensional NMR methods. Nuclear Overhauser enhancement measurements showed that the mobility of the entire polypeptide chain is reduced by binding of melittin to the detergent micelle and that the amino-terminal and carboxy-terminal halves of the primary structure constitute separate, compact domains within the conformation of micelle-bound melittin. p2H titration experiments showed that the presence of positive charges on the four amino groups of melittin had little influence on the conformation of the micelle-bound polypeptide. Titration of tetrameric melittin with detergent provided evidence that melittin assumes similar conformations as a self-aggregated tetramer and as a monomer bound to micelles.

Bee Venoms↗
PubMed1981

Location and orientation relative to the micelle surface for glucagon in mixed micelles with dodecylphosphocholine: EPR and NMR studies.

The spin labels, 5-doxylstearate, 12-doxylstearate, 16-doxylstearate and 1-oxyl-2,2,6,6-tetramethyl-4-dodecylphosphopiperidine, have been incorporated into dodecylphosphocholine micelles and mixed dodecylphosphocholine glucagon micelles. The EPR spectral parameters for the different spin labels and the 1H- and 13C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles. Furthermore, the location and environment of the spin labels in the dodecylphosphocholine micelles were not noticeably affected by the addition of glucagon and the 1H-NMR spectra observed for glucagon in mixed spin label/deuterated dodecylphosphocholine/glucagon micelles showed that the different spin labels had essentially no effect on the conformation of glucagon. Approximate spatial locations within the micelle for the nitroxide moieties of the different spin labels were determined from the NMR relaxation rates observed for different nuclei of dodecylphosphocholine. On this basis, the line broadening of individually assigned glucagon 1H-NMR lines by the different spin labels was used to determine the approximate orientation of the polypeptide chain with respect to the micelle surface. Overall, the data indicate that the glucagon backbone runs roughly parallel to the micelle surface, with the depth of immersion adjusted so that polar and apolar side chains can be oriented towards the surface or interior of the micelle, respectively.

Choline↗
PubMed1981

Combined use of proton-proton Overhauser enhancements and a distance geometry algorithm for determination of polypeptide conformations. Application to micelle-bound glucagon.

In a new approach for the determination of polypeptide conformation, experimental data on intramolecular distances between pairs of hydrogen atoms obtained from nuclear Overhauser enhancement studies are used as input for a distance geometry algorithm. The algorithm determines the limits of the conformation space occupied by the polypeptide chain. The experimental data are used in such a way that the real conformation should in all cases be within these limits. Two important features of the method are that the results do not depend critically on the accuracy of the distance measurements by nuclear Overhauser enhancement studies and that internal mobility of the polypeptide conformation is explicitly taken into consideration. The use of this new procedure is illustrated with a structural study of the region 19-27 of glucagon bound to perdeuterated dodecylphosphocholine micelles.

Amino Acid Sequence↗
PubMed1981

Corneal edema with hydrogel lenses and eye closure: time course.

Central corneal thickness changes during the wearing of hydrogel lenses under closed-eye conditions were measured for two subjects. Each wore an investigational ultrathin Bausch & Lomb Soflens contact lens (series X-176) on one eye only under closed-eye conditions for periods ranging from 30 min to 6 hr. The other eye served as a control. Corneal thickness of the control eyes increased gradually and reached a maximum increase of about 4% at the end of the 4-hr wearing trial. Corneal thickness in the experimental eyes also increased with wearing time during the first 4 hr and then remained fairly constant up to a wearing time of 6 hr. The maximum thickness increases for the two subjects were 9.8 and 9.1%, respectively. About 80% of the maximum corneal thickness change was present after 3 hr of closed-eye contact lens wear. The corneal thickness in the control eye returned to baseline 80 min after removal of the contact lens. Corneal thickness of one experimental eye returned to baseline 2 hr after the contact lens was removed.

Adult↗
PubMed1981

Effect of nitrogen source on end products of naphthalene degradation.

Soil cultures, enrichment cultures, and pure culture isolates produced substantial quantities of salicylic acid from naphthalene in a mineral salts medium containing NH(4)Cl as the nitrogen source. However, when KNO(3) was substituted for NH(4)Cl, these same cultures failed to accumulate detectable quantities of salicylic acid but did turn the medium yellow. When an isolate identified as a Pseudomonas species was used, viable cell numbers were much greater in the medium containing KNO(3), but up to 94% of the naphthalene was utilized in both media. After 48 h of incubation in a 0.1% naphthalene-mineral salts medium, the cultures containing NH(4)Cl showed irregular clumped cells, a pH of 4.7, 42 mug of salicylic acid per ml, and the production of 4.4 ml of CO(2). Under the same conditions, the cultures in the medium containing KNO(3) showed uniform cellular morphology, a pH of 7.3, no salicylic acid, the production of 29.7 ml of CO(2), and a distinct yellow coloration of the medium. The differences between nitrogen sources could not be accounted for by pH alone since results obtained using buffered media were similar. Growth with NH(4)NO(3) displayed a pattern similar to that obtained when NH(4)Cl was used. The yellow coloration in the medium containing KNO(3) was apparently due to more than one compound, none of which were 1,2-naphthoquinone or acidic in nature, as suggested by other investigators. Further attempts to identify the yellow compounds by high-pressure liquid chromatography, infrared analysis, and gas chromatography-mass spectrometry have been unsuccessful thus far.

Journal Article↗
PubMed1981

Transcriptional inhibition and production of guanosine polyphosphates in Bacillus subtilis.

When exponentially growing cells of Bacillus subtilis were treated with rifampin or lipiarmycin, both inhibitors of the initiation of ribonucleic acid synthesis, large amounts of (p)ppGpp accumulated. This accumulation appears to be independent of the ribosome-dependent stringent factor reaction because both relA and relC mutants responded in a manner similar to that of the wild type. The possibility that ribonucleic acid polymerase is directly involved in (p)ppGpp metabolism is discussed.

Aminoglycosides↗
PubMed1981

Relationship between saliva and serum agglutination titers and post-irradiation caries activity in cancer patients.

Agglutination titers in 444 saliva and 481 serum samples from 36 head and neck cancer patients and 16 control subjects were determined against formalinized cellular antigens of Streptococcus and Lactobacillus species. Saliva agglutination titers were significantly higher in cancer patients before radiotherapy than in control subjects. Changes in specific saliva agglutination titers to oral isolates following radiotherapy reflected changes in saliva IgA and post-irradiation caries activity. Patients with no post-irradiation caries activity had significantly higher saliva agglutination titers to S. mutans, S. sanguis, and L. fermenti, lower plaque S. mutans counts, and higher saliva IgA levels than those with post-irradiation caries activity. Serum agglutination titers were unrelated to either serum immunoglobulin levels, microbial counts, or caries activity.

Adolescent↗
PubMed1981

Effects of a single application of sodium fluoride gel on dental plaque acidogenesis.

Quantitative comparisons of the lactate and acetate produced by human dental plaque in vitro and in situ were made before and after five-minute exposures to 1% NaF gel. Assays included total ionic plaque fluoride by a fluoride electrode, L(+)- and D(-)-lactate by an enzyme method, and acetate by a standard GLC procedure. A single topical application of NaF gel increased plaque fluoride about eight-fold. Six hours after gel use, plaque fluoride had declined to about 20% above pretreatment levels. Plaque fluoride baseline levels and variation between and within subjects were greater than expected. This may have been due largely to non-standardized oral hygiene practice and/or the routine use of fluoride dentifrices and the wide variation in the natural fluoride content of drinking water. Fluoride gel use significantly reduced L(+)-lactate in vitro, but D(-)-lactate and acetate were virtually unaffected. Conversely, gel use significantly inhibited the in situ production of each of these acids. The findings of this study indicate that topically applied fluoride gel impairs plaque acidogenesis to an extent that could be meaningful in preventing dental caries.

Acetates↗
PubMed1981

Immunoglobulin class of agglutinins to oral microorganisms in post-irradiation cancer patients.

Fractionation of serum samples from head and neck cancer patients and their assay for agglutination activity toward oral microorganisms showed that the activity was derived from IgG, 7S IgA, 10S (dimeric) IgA, and IgM, with considerable activity in the 10S IgA region. These findings probably account for the lack of a significant relationship among levels of individual serum immunoglobulins, agglutination titers, and caries activity presented in an earlier study. Conversely, most of the agglutinating activity in fractionated saliva was attributed to 11S IgA, presumably secretory IgA, with some activity from a 19S substance and, in the caries-active patients, from a higher molecular weight factor. These data correspond to positive correlations between saliva IgA levels, agglutination titers, and absence of caries in these patients.

Agglutination Tests↗
PubMed1981

Comparative effect of SnF2, NaF, and SnCl2 on the growth of Streptococcus mutans.

The inhibitory effects of NaF, SnF2, and SnCl2 were compared in vitro on the growth of Streptococcus mutans NCTC No. 10449. Sodium fluoride arrested growth at 300 and 600 ppm F (while SnF2 suppressed the rate of growth at 75 ppm F), showed some bactericidal activity at 150 and 300 ppm F, and was totally bactericidal at 600 ppm F. The greater inhibition by SnF2 suggests an additive effect of SN2+. As a measure of a fluoride-free Sn2+ solution, SnCl2 was inappropriate since most of the tin present, at a neutral pH, was Sn4+. The influence of pH was particularly noteworthy with SnF2 at 600 ppm F, where a total bactericidal effect was observed within four h at pH 5.9, while viable cells were still recoverable from four to 40 h with SnF2 at pH 7.2.

Fluorides↗
PubMed1981

Comparison of Streptococcus mutans concentrations in non-banded and banded orthodontic patients.

The effect of orthodontic banding on the prevalence of Streptococcus mutans in plaque was evaluated by comparisons between patients wearing bands and patients just prior to banding on the basis of treatment and/or dental caries history. Banded patients had significantly higher levels of S. mutans in plaque and greater numbers of S. mutans-infected sites than did caries-free patients. Caries-free banded patients had more S. mutans-infected sample sites than did the caries-free non-banded group.

Adolescent↗
PubMed1981

Characterization of calcifiable proteolipid from Streptococcus mutans.

Proteolipid is known to initiate calcification in vitro. Apoprotein and phospholipid components of proteolipid from five of 14 calcifiable S. mutans specimens were characterized. The apoproteins contained 16 amino acids with calculated percent polarities ranging from 32.0 to 45.2. The acidic phospholipids were cardiolipin, mono- and diphosphoinositides, and phosphatidylserine. Neutral lipids, phosphatidylethanolamine and phosphatidylcholine, were also found. The latter were the most abundant in all isolates. Appropriate hydrophobic proteins and acidic phospholipids in the proteolipids accounted for S. mutans calcifiability.

Amino Acids↗
PubMed1981

World food resources and population: the narrowing margin.

This bulletin examines the narrowing margin between global food production and population growth. Between 1950 and 1971, world grain production nearly doubled and per capita production increased 31%. During the 1970s, gains in output barely kept pace with population growth, consumption/person declined in sub-Saharan Africa and parts of Asia, food prices were volatile, and over 100 food deficit countries came to depend on the exportable surplus of North America, now the only major grain exporting region. The world fish catch levelled off in the early 1970s and beef production, still dependent mainly on grassland grazing, levelled off in the mid-1970s. With little new land left to plow, satisfying increased food demand now depends on sharp increases in yields on existing crop land. Worldwide, this effort is hampered by loss of topsoil and irrigated land, conversion of cropland to nonfarm uses, rising energy costs, inefficient agrarian structures, particularly in the Soviet Union, the falling yield response to chemical fertilizers in agriculturally advanced countries, and the emerging competition between food and agriculturally based energy crops. Green Revolution successes in some developing countries deomonstrate that, given the right inputs, 3rd world farmers can increase crop yields dramatically. Feeding the world's poor also requires more equitable income and food distribution, including a reduction in the proportion of grain and fish consumed indirectly as livestock products by the affluent. Most important in meeting food needs on a finite planet is braking population growth. The author concludes that every effort should be made to stabilize world production at abour 6 billion by 2020, rather than 10.5 billion by 2110, as is now projected by the UN.

Agriculture↗
PubMed1981

Spectrophotometric and liquid-chromatographic studies of thymolphthalein monophosphate. Specifications for high-quality substrate for the measurement of prostatic acid phosphatase activity.

Fourteen lots of thymolphthalein monophosphate (TMP), disodium salt, obtained from 10 commercial suppliers were compared spectrophotometrically at 445 and 595 nm, liquid-chromatographically with monitoring at 254 nm, and enzymically by measurements of activity of prostatic acid phosphatase in human serum. Eight lots were classified as "unacceptable," six as "acceptable." Spectrophotometric testing revealed four lots with excessive thymolphthalein and three lots with grossly deficient amounts of TMP. In general, the chromatographic results paralleled those obtained by spectrophotometry, and both results correlated well with enzymic activity. Changing water content in this hygroscopic salt was a major problem, which resulted in great uncertainty as to the formula weight and therefore as to the moles of TMP actually taken. From these studies, specifications for high-quality TMP were determined. The critical importance of simultaneous enzymic activity measurements in comparisons with other "acceptable" lots in defining an adequate TMP substrate is stressed. Use of these specifications for selecting TMP for acid phosphatase activity measurements should improve intra- and inter-laboratory analytical performance.

Acid Phosphatase↗