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Biomedical subjects

S J Foster

Publications and source records attributed to S J Foster.

At least 127 records · Page 7Linked to original sources
PubMed1982

Injured vitreous stimulates DNA synthesis in retinal pigment epithelial cells in culture and within the vitreous.

Cultures of rabbit retinal pigment epithelium (RPE) were exposed to normal vitreous and to vitreous injured by intravitreal injection of foreign particles. Counts of labeled RPE nuclei after incubation with 3H-thymidine in vitro indicated an increase in DNA synthesis with exposure to normal vitreous and an even greater increase with exposure to injured vitreous. Fractionation of injured vitreous demonstrated that the apparent proliferation stimulus resided in the cell-free supernate. The data suggest that normal vitreous contains a humoral factor that stimulates RPE proliferation and that levels of an active agent increase after vitreal injury. RPE injected into the vitreous also responds by increased DNA synthesis to subsequent vitreal injury. This observation implies that foreign substances in the vitreous, as after vitreal hemorrhage, promote development of extraretinopathies involving RPE by stimulating intravitreal proliferation of invasive RPE cells.

Animals↗
PubMed1982

Age-associated lesions in barrier-reared male Sprague-Dawley rats: a comparison between Hap: (SD) and Crl:COBS[R]CD[R](SD) stocks.

Age-associated lesions were characterized in two outbred stocks of barrier-reared male Sprague-Dawley rats. Seventy-two virgin Hap:(SD) between 6-29 months of age and 113 retired breeder Crl:COBS[R]CD[R]CDR(SD) between 12-38 months of age were evaluated for the presence of lesions in all major organ systems. Rats of both stocks developed a spectrum of neoplastic, inflammatory and degenerative diseases with highest prevalence in the oldest age groups. In general, the shorter-lived Hap:(SD) rats had greater incidences and severity of lesions when compared to Crl:COBS[R]CD[R]SD of similar ages. Many of these differences were not apparent when the two stocks were compared over their respective life spans. The study provides baseline pathology data relevant to the use of these rats in gerontologic research.

Adenoma↗
PubMed1982

Ultrastructural demonstration of transretinal migration by vitreal macrophages marked with latex particles.

The injection of 1.1-micrometer latex particles into the rabbit vitreous elicits an intravitral invasion of macrophages. The particle-filled macrophages are initially restricted to the vitreous, are later found at the vitreoretinal interface, and by 6 weeks are distributed throughout the inner layers of the retina. The phagocytes appear to lyse in the outer retinal layers, and the released particles are found between and within the cells of the photoreceptor region. The observations indicate that latex-marked macrophages from the vitreous can penetrate and migrate within the retina.

Animals↗
PubMed1980

Cyclic nucleotides, possible intracellular mediators of macrophage activation and secretory processes.

Macrophages from various sources can be stimulated by a variety of substances to secrete a range of inflammatory mediators and degradative enzymes. The mechanisms involved in the activation and secretory processes are unknown, However, recent evidence suggests that cyclic AMP may play a role in the regulation of neutral protease secretion. Thus, it has been shown that agents known to increase intracellular cyclic AMP levels (cyclic AMP analogues, phosphodiesterase inhibitors, prostaglandin E1 and E2, catecholamines, cholera toxin and, indirectly, glucocorticosteroids) inhibit the secretion of the neutral protease plasminogen activator. It is speculated that macrophage activation may also initiated by changes in the steady-state levels of cyclic nucleotides. A decrease in intracellular cyclic AMP and/or an increase in cyclic GMP levels would favour secretion. It is possible that these changes could be brought about by the action of various stimuli to modify the capacity of the macrophage to synthetize or degrade cyclic nucleotides.

Animals↗
PubMed1977

Glucocorticoids increase the responsiveness of cells in culture to prostaglandin E1.

The influence of steroid hormones on the response of human astrocytoma cells (1321N1) to prostaglandin E(1) (PGE(1)) has been investigated. Responsiveness to PGE(1) was determined by measuring the conversion of [(3)H]ATP to cyclic [(3)H]AMP in cells prelabeled with [(3)H]adenine. After incubation of the cells with dexamethasone, a marked increase in both the maximal effect (2- to 3-fold) and the potency (5-fold) of PGE(1) was observed. The effect was specific for the action of PGE(1) in that no change in the response of the cells to isoproterenol was observed. The EC(50) for dexamethasone was 0.001 muM and the effect was dependent on the presence of serum. The effect of dexamethasone was first observed after a 30- to 60-min lag and was maximal by 6-8 hr. Preconfluent cultures (3 days after seeding) exhibited optimal responsiveness to glucocorticoids. Both hydrocortisone and corticosterone mimicked the effect of dexamethasone but both were less potent. The action of dexamethasone was blocked by progesterone, testosterone, and 17alpha-methyltestosterone. Cycloheximide, at a concentration (1.0 mug/ml) that blocked protein synthesis (>90%) in 1321N1 cells, totally prevented the effect of dexamethasone on the response of the cells to PGE(1). Upon removal of dexamethasone from cells treated for 16 hr, responsiveness to PGE(1) returned to control levels with a half-time of 4 hr. Dexamethasone also was found to increase the response to PGE(1) of a Rous sarcoma virus-transformed human astrocytoma cell line and the WI-38 human fibroblast line. The most obvious interpretation of our findings is that glucocorticoids induce the synthesis of a protein that selectively modifies the sensitivity of adenylate cyclase to PGE(1).

Cells, Cultured↗
PubMed1977

Pathological changes during aging in barrier-reared Fischer 344 male rats.

Pathology, microbiology, and selected serum chemistries were evaluated in 144 male Fischer rats from 4 to 33 mo of age. The rats were reared and maintained under barrier conditions, which successfully excluded the introduction of major infectious disease agents throughout the entire study, including Mycoplasma pulmonis. A wide variety of pathology was found and tabulated, and many lesions were found to increase in severity and incidence with age. There was a high correlation of renal disease severity with increasing age, while alpha-1 globulin and cholesterol increased.

Adenoma, Chromophobe↗
PubMed1971

Effect of osmotic shock on tetracycline resistance in Escherichia coli bearing an R-factor.

1. Escherichia coli with an R-factor conferring resistance to tetracycline was induced to high-degree resistance by pre-exposure to the antibiotic. The degree of resistance was drastically lowered by subjecting the cells to osmotic shock. 2. Resistance to tetracycline was rapidly restored by incubating the shocked cells in a glucose-salts medium containing shock proteins prepared from tetracycline-sensitive and -resistant cells. Resistance was also restored by incubating the cells in a complex medium without shock protein. 3. The initial recovery of resistance was followed by a secondary fall in resistance when the cells were cultured in complex medium; this secondary fall was largely prevented by the addition of a low concentration (10mug/ml) of tetracycline to cells. The secondary fall was significantly less in shocked E. coli cells harbouring a mutant R-factor in which tetracycline resistance is largely constitutive. 4. Tetracycline resistance was also transiently depressed by treating R-factor-bearing cells with EDTA in tris buffer. 5. The significance of these results in relation to the mechanism of tetracycline resistance in R-factor-bearing cells is discussed.

Buffers↗