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Biomedical subjects

M C Johnson

Publications and source records attributed to M C Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1984

Growth, synthesis and regional specialization of the embryonic chicken lens capsule.

The growth, synthesis and regional specialization of the lens capsule has been studied in chicken embryos and compared to adult chickens and mammals. During the final 15 days of embryonic development the surface area of the capsule increased 11-fold. This represents the minimum estimate of capsule growth, since it also increased in thickness during this period. Autoradiographic examination of [3H]proline- or 35SO4-labeled, detergent-cleaned, flat-mounted capsules suggested that all lens cells participated in capsule synthesis. This was supported by the observation that both lens epithelial and fiber cells incorporated [35S]-methionine into collagenase-sensitive proteins with molecular weights similar to type IV collagen. Histochemical staining of detergent-cleaned capsule explants (DCCEs) revealed regional differences in the carbohydrate composition of the capsule. Differences in collagenous proteins were also seen between the anterior and posterior regions of the capsule of the embryonic lenses. Following SDS-PAGE and silver staining a total of six collagenase-sensitive proteins were seen with molecular weights between 150 and 180 K. Three of these polypeptides were common to both anterior and posterior capsules, one was found only in the anterior capsule and the other two were found predominantly in the posterior capsule. No regional differences were seen in the collagenous proteins of capsules from adult chickens, rats or hamsters. The possibility is discussed that the unique pattern of collagenous polypeptides seen in embryonic capsules is related to the rapid growth of the embryonic lens.

Animals↗
PubMed1983

Resistance of wild birds to infection by Chlamydia psittaci of mammalian origin.

Numerous species of birds are natural hosts of C. psittaci and have been implicated as sources of certain strains that cause disease in other vertebrate species, notably those producing psittacosis or ornithosis in humans [1]. Although direct evidence of their involvement in the transmission of chlamydiae to other mammals, especially domesticated ruminants, has not been reported, a careful examination of this possibility is justified [1]. When inoculated parenterally, polyarthritis-producing chlamydiae of ovine origin affected leg joints of turkeys, and abortion-producing chlamydiae of ovine origin was infectious for pigeons and fatal for sparrows [2]. However, several species of small wild birds (three of which were used in the experiments reported here), when inoculated perorally with C. psittaci of turkey origin, seroconverted (36%) and shed the organism (79%) [3]. Therefore, the present study was undertaken to determine whether strains of C. psittaci from domesticated ruminants would infect, multiply in, or be shed by these wild birds. The results indicate that these species of birds are not natural hosts or biologic vectors of these strains. However, considering the heterogeneity of Chlamydia species, certain birds may harbor strains that are associated with naturally occurring infections in some animals. The results also are additional evidence of the more restricted host range of mammalian Chlamydia species as compared to that of avian isolates.

Animals↗
PubMed1983

The role of Schlemm's canal in aqueous outflow from the human eye.

A mathematical model of Schlemm's canal is developed to simulate collapse of the canal and its effect on resistance to flow through the aqueous outflow network. Schlemm's canal is modeled as a porous, compliant channel that is held open by the trabecular meshwork. The trabecular meshwork is modeled as a series of linear springs that allow the inner wall of Schlemm's canal to deform in proportion to the local pressure drop across it. Based on comparisons between the model and results in the literature, the following tentative conclusions are reached: (1) Most of the resistance in the aqueous outflow network occurs in the inner wall of Schlemm's canal. (2) Glaucoma is not caused by a weakening of the trabecular meshwork and a resultant collapse of Schlemm's canal alone. Instead, glaucoma probably results from an increased flow resistance of the inner wall of the canal.

Aqueous Humor↗
PubMed1980

Topical nitrate.

Explore the source record for details and available documents.

Administration, Topical↗
PubMed1980

Comparison of the glucosyltransferases of Streptococcus mutans gs-5 to a non-cariogenic mutant.

The extracellular glucosyltransferase (GTF) enzymes of Streptococcus mutans GS-5 and avirulent mutant GS-511 were fractionated using agarose and DEAE-cellulose columns. GTF of GS-5 produced both water-soluble and -insoluble glucans, while those of GS-511 made soluble products almost exclusively. Nearly all (98%) of the small amount of insoluble GTF enzyme made by GS-511 was bound to the cell wall.

Carbohydrates↗
PubMed1979

Powder mixing in direct compression formulation by ordered and random processes.

The mixing processes taking place in a two component system involving a cohesive drug, tetracycline and a direct compression vehicle, spray dried lactose (SDL), have been studied by chemical analysis of powder samples and fluorescence microscopy. At a drug concentration level of 0.25% w/w, both random and ordered mixing is taking place. Mixture quality is better (Cv = 1%) using a fine grade of crystalline lactose (CL) than with SDL (Cv = 4%). Using fractionated material, it was found that SDL between 106 and 300 micron gave Cv values up to 12%, whereas with SDL below 106 micron values of 2% were obtained. The poor quality of the SDL mixtures is attributed to ordered unit segregation.

Chemistry, Pharmaceutical↗
PubMed1979

Diagnosis of tuberculosis: routine cultures of bronchial washings are not indicated.

During a five-year period, cultures of bronchial washings for Mycobacterium tuberculosis were obtained almost routinely (859 of 1,012 bronchoscopic examinations.). This practice proved costly, and the diagnostic yield was extremely low. Only three cases were diagnosed solely by this method (0.35 percent). Five other cases were false-positive. Additionally, 39 patients with known active pulmonary tuberculosis had false-negative cultures of bronchial washings; 13 of these 39 patients were receiving antituberculosis drugs at the time of their bronchoscopic examinations. The inhibitory effect of local anesthetics upon the growth of M tuberculosis is the possible cause for the remaining 26 false-negative cultures. We conclude that bronchoscopic examination and culture of bronchial washings are not the best sources for diagnosis of pulmonary tuberculosis and that cultures of sputum and/or gastric washings are usually sufficient. The practice of obtaining routine cultures of bronchial washings in known pulmonary tuberculosis is of questionable value, when nearly two-thirds may be false-negative.

Aged↗
PubMed1979

Effect of inhibitors of arachidonic acid metabolism on mitogenesis in human lymphocytes: possible role of thromboxanes and products of the lipoxygenase pathway.

Although it is already known that prostaglandins inhibit lymphocyte responses to mitogens the role of other products of arachidonic acid (AA) metabolism has not previously been investigated. Various inhibitors of AA metabolism were studied for their effects on mitogenesis in human lymphocytes, including imidazole, benzylimidazole, N-0164, L-8027, 5, 8, 11, 14 eicosatetraynoic acid, nordihydroguaiaretic acid, indomethacin, and aspirin. Selective or partially selective inhibitors of thromboxane synthesis, such as imidazole, benzylimidazole, N-0164, and L-8027 inhibited the mitogenic response at concentrations that also substantially affect thromboxane B2 synthesis in platelet-free lymphocyte preparations. Since indomethacin failed to reverse the inhibition by imidazole or N-0164, it is probably due to decreased thromboxane synthesis per se rather than secondary increases in prostaglandin synthesis. Eicosatetraynoic acid and nordihydroguaiaretic acid were more effective inhibitors of mitogenesis than of thromboxane synthesis. Since these agents also affect the lipoxygenase pathway, it is possible that part of their action is at this level. Thus, in addition to the inhibitory effects of prostaglandins on mitogenesis, other products of AA metabolism may promote the response.

Antilymphocyte Serum↗
PubMed1978

Radioisotope scanning in the initial staging of bronchogenic carcinoma.

The use of routine radioisotope scanning to screen for subclinical metastatic disease in the initial staging of bronchogenic carcinoma was studied. To define the value of scans, liver, brain, and bone scans were studied prospectively in 111 patients and retrospectively in 114 patients. Among patients with clinical findings suggesting metastatic disease, 14.4 per cent of the liver scans, 12.3 per cent of the brain scans, and 35.7 per cent of the bone scans were positive. All patients free of clinical findings had negative liver and brain scans. Positive bone scans occurred in 8 per cent of the patients without clinical abnormalities. True-positive bone scans occurred in less than 4 per cent of the patients free of clinical abnormalities. The clinical findings noted in the patients pointed to the organ involved in only 76 per cent of the abnormal liver scans, 62 per cent of the abnormal brain scans, and 75 per cent of the abnormal bone scans. Clinical findings associated with positive liver and brain scans were multiple and significant, whereas findings with the positive bone scans could be few or subtle. Routine scanning failed to identify a significant number of patients with clinically unsuspected metastatic disease. Liver, brain, and bone scanning is indicated only in patients suspected of having metastatic disease.

Adult↗
PubMed1978

Quantitative thyroid fluorescent scanning: technique and clinical experience.

A method for quantifying thyroid gland iodine content using a modified fluorescence scanning system is described. The technique does not require a computer. Two single channel analyzers and digital scalers are used to determine net counts from iodine k-alpha x-rays and system response in counts per milligram is calibrated from studies of known quantities of iodine placed in thyroid phantoms. Fluorescence quantification of thyroid gland iodine content was performed in 250 patients with a wide variety of thyroid disorders. Thirty euthyroid patients judged to have no evidence of thyroid disease averaged 10.1 +/- 3.9 mg glandular iodine. Results for several major diagnostic categories were: untreated Graves' disease, 28 patients, 24.4 +/- 9.9 mg; diffuse euthyroid goiter, 14 patients, 16.1 +/- 7.4 mg; primary hypothyroidism, seven patients, 0.5 mg; and nontoxic multinodular goiter, 28 patients, 7.3 +/- 4.1 mg. Follow-up studies on patients treated for Graves' disease both medically and with 131I generally revealed elevated iodine contents in persistently hyperthyroid patients, lower than normal average amounts in euthyroid patients, and only trace amounts in hypothyroid patients. Although the clinical role of fluorescence iodine quantification remains to be fully established, the technique provides information not otherwise available on an important parameter of thyroid status.

Fluorescence↗
PubMed1977

Ultrastructural localization of sucrases in Streptococcus mutans GS-5 and an extracellular polysaccharide mutant: a comparative cytochemical and immunocytochemical study.

Electron microscopy and cytochemical and immunocytochemical procedures were used to study the ultrastructural distribution of sucrase enzymes in two strains of Streptococcus mutans. In a strongly adherent and virulent parent strain, GS-5, most of the invertase and fructosyltransferase activities were demonstrated extracellularly or bound to the cell surfaces. Intracellularly, enzymatic sites were detected near the plasma membrane on the periphery of the nucleoid and central mesosome. In GS-511, a mutant of diminished virulence and adherence, most of the enzymatic activity was not located on the cell surfaces, but was found away from the cell walls and associated with extracellular polysaccharides. Intracellularly, GS-511 manifested the same distribution of invertase and fructosyltransferase as did GS-5; however, the close association of these enzymes with the plasma membrane was not shown in GS-511. In both strains, extracellular areas near regions associated with cross wall formation appeared to show localized concentrations of these sucrases. Antibodies against partially purified glucosyltransferase (GTF) enzymes from GS-5 were used to localize GTF by immunocytochemical techniques. Indirect ferritin localization procedures showed that the extracellular and cell-bound GTF enzymes were distributed in similar locations as the fructosyltransferase and invertase enzymes. By absorption of the antiserum with whole GS-511 cells, the location of extracellular GTF and surface antigens unique to GS-5 was demonstrated. The dramatically reduced levels of cell-bound sucrase activity in GS-511 indicates the significant role of these enzymes in adherence and cariogenicity.

Cell Membrane↗