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Biomedical subjects

A T Davis

Publications and source records attributed to A T Davis.

At least 127 records · Page 7Linked to original sources
PubMed1977

Group B streptococcal meningitis: delayed response to treatment.

Four infants with group B streptococcal meningitis had a delayed response to antibiotic therapy. Resolution of cerebrospinal fluid infection and/or pleocytosis occurred only after prolonged and intensive antimicrobial management. In this respect, these infants were similar to infants with gram-negative enteric meningitis. It is suggested that infants with group B streptococcal meningitis be closely monitored to insure adequate response to therapy.

Chloramphenicol↗
PubMed1975

Phosvitin phosphate content. Implications for protein kinase assay.

The maximal rates of the protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) reaction studied with chicken egg yolk phosvitin as substrate are dependent on the level of dephosphorylation of phosvitin. 30 per cent dephospho-phosvitin gives the optimal initial rates. With varying levels of dephosphorylation, the apparent Km for the substrate also changes in a biphasic manner. If this factor is taken into account, and a suitable adjustment is made for the concentration of dephospho-phosvitin in the reaction it is possible to achieve maximal rates for the kinase reaction with phosvitin preparations of varying levels of dephosphorylation. Such a consideration is important for comparing the results of protein kinase studies using phosvitin as the substrate.

Adenosine Triphosphate↗
PubMedDate not supplied

Studies of prostatic cytosol protein kinases of the aging ACI rat.

Changes in prostatic cytosolic cyclic AMP (cAMP)-dependent and independent protein kinases associated with aging in ACI rats were determined. A decrease in prostatic weight and tissue protein content (but not DNA) with age was noted. The cytosolic cAMP-dependent protein kinase was present predominantly as the type II isozyme. Total content of this enzyme per prostate declined by 37% in 12-month-old rats but remained relatively stable thereafter. However, the activity ratio (+cAMP/-cAMP) increased with aging, indicating an elevation in the amount of the holoenzyme or a decrease in the amount of the free catalytic subunit. Concomitantly the specific activity (activity/unit protein in the cytosol) of this enzyme was found to be increased; this is most likely due to the loss of bulk proteins in the cytosol, and may indicate a slower loss of this enzyme protein in relation to other cytosolic proteins. By comparison, the cAMP-independent protein kinase demonstrated a marked and progressive decline in amount as well as in specific activity with aging, e.g. 80-90% decline at 12 months of age. The above changes in these enzymes did not appear to be due to low circulating androgen in the animals, since they were not reversed on administration of 3.0 mg of testosterone propionate per rat daily for four consecutive days. It is therefore suggested that the above-described changes in prostatic cytosolic protein kinases are primarily associated with cellular senescence in this organ.

Aging↗
PubMedDate not supplied

Effects of thyroid hormone deprivation on immunity in postmetamorphic frogs.

Previously, we showed that sodium perchlorate treatment of larval frogs (Xenopus laevis) interferes with the normal expansion of T and B lymphocytes and development of an adult-type T-cell population. It was unclear whether these effects resulted from preventing metamorphosis or from long-term thyroid hormone (TH) deprivation. To try to distinguish between these possibilities, we have now studied the effects of perchlorate treatment beginning immediately after metamorphosis. After 5 months, treated animals, but not untreated controls, had large thyroid goiters, were significantly smaller, and had significantly fewer erythrocytes, thymocytes, and splenocytes. Although the number of IgM- splenocytes and thymocytes was reduced, the estimated percent of major histocompatibility complex (MHC) class II+ cells within this subset was not significantly different from that of controls. Furthermore, splenocytes from perchlorate-treated frogs could respond normally by [3H]TdR incorporation to the T-cell mitogens, phytohemagglutinin-P (PHA) and concanavalin A (Con A). Thus, unlike perchlorate-treated larvae, perchlorate-treated juveniles appear to be able to develop T cells with an adult phenotype competent to respond to activation and proliferation signals.

Animals↗
PubMedDate not supplied

Late thymectomy in Xenopus tadpoles reveals a population of T cells that persists through metamorphosis.

To investigate the persistence of larval T lymphocytes in the adult period, tadpoles of the South African clawed frog, Xenopus laevis, were allowed to develop to prometamorphic stages 57-58 and thymectomized (Tx). Thymectomy at this stage allows for maximal expansion of the larval T cell population but prevents emergence of the adult T cell population. Using a T cell-specific monoclonal antibody (mAb) which recognizes the XTLA-1 determinant, we examined the absolute numbers of thymic and splenic T cells expressing XTLA-1 in normal tadpoles, postmetamorphic Tx frogs, and intact age-matched adult frogs. A small, but measurable, number of larvally-derived XTLA-1+ cells persists through metamorphosis. By simultaneously staining with a mAb specific for class II major histocompatibility (MHC) antigens, we determined the phenotype of the persisting XTLA-1+ cells in the Tx frogs. Like XTLA-1+ splenocytes in intact adult controls which are predominantly class II+, most XTLA-1+ cells in Tx adults also express class II. In contrast, most XTLA-1+ cells in the tadpole are class II-. This suggests that a small population of class II+ larval T cells survives metamorphic transition to become a long-lived population in the adult. Alternatively, some class II- larval T cells may express class II in the adult period.

Animals↗
PubMedDate not supplied

Group C beta-hemolytic streptococcal infections in children: nine pediatric cases and review.

Streptococci of Lancefield group C colonize healthy individuals but infrequently cause invasive disease. Eight pediatric cases of infection due to group C streptococci were identified in a retrospective survey of a recent 6-year period at a children's hospital. An additional case of group C meningitis diagnosed in 1975 was included. These nine cases and 22 pediatric cases from the literature are presented to illustrate important points with respect to clinical presentations and complications and to show that these organisms can cause serious, sometimes fatal infection: pneumonitis, sinusitis, septicemia, endocarditis, osteomyelitis, and meningitis. Group C streptococci are described in terms of their biochemical properties, the infections they cause in animals, and their tendency to produce disease in humans. With increasingly frequent serologic grouping of non-group A beta-hemolytic streptococci, recognition of the role of specific non-group A streptococci is likely to increase. The antimicrobial agent of choice for infections due to group C streptococci is penicillin G. The minimum inhibitory and minimum bactericidal concentrations for the organism should be determined since penicillin tolerance may occur and may be responsible for the slow response to penicillin therapy in some cases.

Adolescent↗