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Biomedical subjects

S Marshall

Publications and source records attributed to S Marshall.

At least 181 records · Page 10Linked to original sources
PubMed1983

Nonenzymic in vitro isolation of perinatal islets of Langerhans.

We have developed a method to circumvent the use of exogenous proteolytic enzymes in the isolation of islets of Langerhans from the perinatal rodent pancreas. Advantage is taken of the propensity of fibroblastlike cells to attach and migrate on polystyrene at low-serum concentrations (5%). In contrast, at this serum level, rat islet epithelial cells tend not to adhere to the substrate. At 3 d of culture, islets are visible at the edges of the explants. With further fibroblast outgrowth the majority of islets are freefloating by 7 d. Simple agitation of the medium and centrifugation yields approximately 50 micrograms of islet tissue per perinatal pancreas. Further purification of the islets can be obtained by subculture. Rat islets can be maintained in this manner for several months in Medium F12 supplemented with 25% horse serum in an atmosphere of 5% CO2 and air at 37 degrees C. Hormone content of the islet tissue remains constant during prolonged subculture and such islets continue to exhibit appropriate insulin and glucagon responses to glucose and theophylline. The morphological integrity of the endocrine cells within the cultured islets was confirmed by immunocytochemistry and ultrastructural study. Nonendocrine cells are not identifiable within the long-term cultured islets.

Animals↗
PubMed1983

A conservative approach to testicular tumors in children: 12 cases and their management.

During a 34-year period 12 children were seen with testicular tumors. Of 8 benign tumors 7 were treated by orchiectomy and 1 by local excision only. The 4 malignant tumors were managed by orchiectomy and 1 boy also received adjunctive chemotherapy. All patients are alive and have had no recurrent tumors after 1 1/2 to 34 years of followup. Because testicular tumors usually are less aggressive in prepubertal children, the chance of cure by orchiectomy alone in this age group is good. However, the potential of these tumors for metastases makes it imperative that they be observed closely.

Child↗
PubMed1983

Regulation of tyrosinase in human melanocytes grown in culture.

Tyrosinase, the enzyme that controls the synthesis of melanin, is a unique product of melanocytes. Normal and malignant human melanocytes grown in culture were used to study the factors that regulate the expression of tyrosinase. Immunoprecipitation experiments showed that newly synthesized tyrosinase appeared as a protein with an apparent molecular weight of 70,000 that was processed to a protein with an apparent molecular weight of 80,000. Neither tunicamycin nor 2-deoxy-D-glucose inhibited this conversion, suggesting that O-glycosylation is the major biochemical event in the posttranslational modification of tyrosinase. Agents that stimulated the proliferation of normal melanocytes also stimulated tyrosinase activity. Melanocytes with low levels of tyrosinase activity synthesized less tyrosinase, processed the enzyme more slowly, and degraded it more rapidly than melanocytes with high levels of tyrosinase activity. We conclude that tyrosinase activity in cultures of human melanocytes derived from different donors is determined predominantly by its abundance.

Catechol Oxidase↗
PubMed1983

Low pH accelerates dissociation of receptor-bound insulin.

We have examined the effect of pH of the kinetics of [125I]insulin binding in isolated rat adipocytes and found that a lowering of extracellular pH from 7.8 to 7.0 reduced tracer insulin binding (0.2 ng/ml) from 3.3% to 1.0% due to a decrease in receptor affinity. Further studies, performed at 16 C to eliminate the confounding affects of insulin internalization on binding kinetics, revealed that the t1/2 of insulin dissociation was shortened from 44 min at pH 7.8 to 8 min at pH 7.0, while the association rate constant was slightly increased from 1.61 X 10(9) to 2.09 X 10(9) M-1 min-1 at pH 7.8 and 7.0, respectively. Thus, the overall decrease in binding affinity at low pH is due predominantly to an accelerated rate of insulin dissociation. Kinetic studies performed at 37 C also revealed an effect of pH to accelerate insulin dissociation; however, the magnitude of the effect was greatly reduced. This was explained by the observation that when [125I]insulin was prebound to adipocytes at 37 C approximately half of the cell-associated radioactivity resided within the cell at the start of the dissociation experiment. An additional amount of insulin was internalized during the dissociation time course due to endocytotic uptake of cell surface ligand. Consequently, only a small portion of cell-associated [125I]insulin was on the cell surface and susceptible to extracellular pH changes. To assess the effect of low pH (7.0) on receptor-mediated insulin degradation, we prebound [125I]insulin to adipocytes at 16 C, then warmed the cells (37 C) to initiate insulin endocytosis and ligand degradation. Under these conditions, insulin degradation was markedly reduced at the lower pH. These results indicate that 1) low pH reduced insulin binding affinity by accelerating the rate of insulin dissociation, and 2) this is accompanied by a reduction in the rate of receptor-mediated insulin degradation.

Adipose Tissue↗
PubMed1983

Varicocele in youth.

Thirty boys 8 to 18 years of age seen in a general urologic practice with emphasis on pediatrics had palpable varicoceles. A concomitant finding was that 77 percent of these patients had a smaller testis on the left side. Because the small testis is present before maturity, its size appears due to arrest of testicular growth rather than to atrophy. Surgical correction is advisable when the varicocele is pronounced, the involved testis is distinctly smaller or there is scrotal pain.

Adolescent↗
PubMed1983

Coagulum pyelolithotomy.

Stones in the kidney can be a source of both challenge and frustration to the surgeon. A stone seemingly easily accessible at the start of surgery can move into the depths of a renal calix during the procedure. The intraoperative injection of certain coagulation factors into the renal pelvis will produce a gelled substance (coagulum), which can encase the free-lying stones within the collecting system, thereby expediting their removal.

Adult↗
PubMed1982

Varicocele in childhood and adolescence: implication in adulthood infertility?

Thirty boys eight to eighteen years of age had a clearly palpable left varicocele. The presenting complaint usually was either an asymptomatic scrotal mass or a scrotal ache after physical exercise. In 77 per cent of the patients the left testis was smaller than its male. All but one of the 17 boys between ages eight and fifteen had a smaller left testis. When the varicocele is symptomatic, presents as a prominent mass, or where growth of the left testicle lags behind that of its mate, surgical correction of the varicocele is recommended.

Adolescent↗
PubMed1981

The transfer of platelet factor 4 from its proteoglycan carrier to natural and synthetic polymers.

1. Transfer of dansyl-platelet factor 4 complexed with a series of glycosaminoglycans to heparin has been detected and studied by measuring changes in the anisotropy of the dansyl fluorescence. The protein was most easily transferred from chondroitin sulphate and least easily from heparan sulphate. 2. The transfer of the dye-labelled protein from its biological chondroitin 4-sulphate proteoglycan carrier to natural and synthetic anionic polymers was similarily followed. The transfer to heparin and dermatan sulphate was shown to be the same whether 3 mM Ca2+ or 8 mM EGTA was present in the solution. 3. The shapes of the binding curves of the dansyl-factor to the polymers have been compared at I = 0.4M. 4. The observed changes in anisotropy of dye fluorescence have been correlated with the charge density and the stereochemistry of the charged groups of the natural polymers. Large complexes are observed with polymers of high negative charge/weight ratios. Less charged polymers containing disaccharide units of iduronic acid and glucosamine N-sulphate will also from large complexes at I = 0.15 M. 5. It is demonstrated that the release of a platelet factor 4 proteoglycan complex in vivo would result in the transfer of the protein to heparin, moderate quantities of either dermatan or heparan sulphates would not prevent this transfer.

Blood Coagulation Factors↗
PubMed1981

The sites of deposition of newly synthesized histone.

The chromosomal fragments produced by nuclease digestion of freshly replicated chromatin migrate more rapidly relative to bulk chromatin when analyzed in nucleoprotein gels. The cause of the anomalous migration has been studied and the evidence indicates that rather than reflecting a shorter nucleosomal repeat in vivo that it may be a consequence of nucleosome sliding during the digestion itself. The distinct electrophoretic characteristics of nucleosomal material containing newly replicated DNA have enabled us to examine their histone composition by two dimensional electrophoresis. We find that nucleosomes containing new DNA also contain newly synthesized histones H3 and H4. In contrast more than 50% of newly synthesized H2A and H2B, and essentially all of new H1, are deposited at sites on the bulk chromatin distinct from that material containing newly replicated DNA. In addition we show that newly synthesized histones H3 and H4 are bound unusually weakly when they first become associated with the chromatin.

Animals↗
PubMed1981

Urethral diverticula in young girls.

Five cases of urethral diverticulum in young girls are herein presented. None of these children had associated local infections, unlike what is generally the case in adult women with a similar lesion. Three girls experienced spontaneous regression of the diverticulum. Therefore, unless the diverticulum causes clinical problems, postponement of surgical intervention is advised.

Adolescent↗
PubMed1981

Simplified approach to cryoprecipitate coagulum pyelolithotomy.

A simplified approach to coagulum pyelolithotomy, utilizing ureteral catheters for injection of the coagulum, is advantageous for small intrarenal pelves, or when it is difficult to mobilize the kidney because of a previous operation. The approach is technically easy and straight-forward. We highly recommend its use in selected cases.

Adult↗