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R Downing

Publications and source records attributed to R Downing.

At least 91 records · Page 5Linked to original sources
PubMed1980

Isolating the elusive islet.

The lack of a technique that allows mass isolation of intact, viable human islets is part of the reason that islet transplantation has not become available to the human diabetic. This report outlines the history of islet isolation and presents two new technical modifications that have been developed in the dog. Many of the current problems in islet isolation are presented, including the difficulty in obtaining enough human pancreatic tissue with minimal warm-ischemia time; inadequate distention of the pancreas to provide sufficient disruption for maximal enzymatic reaction to release intact islets; inefficient chopping methods; the use of collagenase of variable composition; different digestion methods for obtaining isolated islets; and inefficient methods for separating and purifying the islets from the ductal, acinar, and fibrous components. The first new modification involves distention of the dog pancreas through the venous system of the gland rather than the ductal system. This results in improved intralobular disruption, which improved the yield of isolated dog islets by permitting more efficient collagenase digestion. The second new modification eliminates the concept of isolating intact islets: the dog pancreas is digested by trypsin to a single-cell preparation that is partially purified by Ficoll gradients; further purification of the endocrine cells results from selective aggregation using rotational culture. This process produces pseudoislets that contain all the islet cell types and can be kept in culture for up to 4 wk, releasing their hormones in response to appropriate stimuli. These modifications may assist in the struggle to isolate the elusive human islet for safe and effective islet transplantation in the diabetic patient.

Animals↗
PubMed1979

Whole gut irrigation: a survey of patient opinion.

Patients' assessment of whole gut irrigation via a nasogastric tube has been obtained by a questionnaire answered by 79 of 99 patients who received this method of bowel preparation before operation on the large bowel or colonoscopy. Abdominal pain during the irrigation was experienced by 13 patients (17 per cent) and nausea and vomiting occurred in 24 (30 per cent). Intubation with a nasogastric tube and the discomfort of prolonged sitting on a commode were considered the most disagreeable aspects of the procedure. Fifty-six patients (71 per cent) would have agreed to the irrigation being repeated if necessary and many patients preferred whole gut irrigation to previous 'orthodox' bowel preparations that they had experienced.

Aged↗
PubMed1979

A cleavage map of the TOL plasmid of Pseudomonas putida mt-2.

A cleavage map of the TOL plasmid pWWO has been determined for the restriction endonucleases HindIII and XhoI. A number of techniques were employed including (i) digestion of purified cleavage products with a second enzyme; (ii) hybridisation of purified XhoI fragments to Southern blots of HindIII digest products and (iii) analysis of a number of deletion mutants.

Chromosome Mapping↗
PubMed1978

Double-blind trial of thiothixene and chlorpromazine in acute schizophrenia.

In a double-blind trial of chlorpromazine and thiothixene conducted with 79 acutely ill, newly hospitalized schizophrenic patients, chlorpromazine and thiothixene were shown to be equally effective in producing meaningful symptomatic improvment over an average period of approximately 3 weeks, as measured by Global Assessments (CGI), BPRS, and NOSIE.

Acute Disease↗
PubMed1976

A comparison of two psychiatric screening tests.

A comparison is made between the General Health Questionnaire (GHQ) and the Symptom Checklist (SCL) as psychiatric screening tests in community-based research projects. Both are shown to correlate equally well with independent clinical assessment, and the differences between them mainly reside in the form of their response scales. The GHQ works best as a screening test, since it has fewer false positives associated with its use, but it may miss those with long-standing disorders. The SCL tends not to miss long-standing disorders and furnishes diagnostic sub-scales if these are required. Both tests function better with men than with women and with whites than with blacks, but neither is affected by social class or age of the respondent. The study revealed high correlations between the symptoms of anxiety and depression, and indicated some possible differences between the symptom clusters seen in whites and in blacks.

Age Factors↗
PubMedDate not supplied

Assessment of the reproducibility of alginate encapsulation of pancreatic islets using the MTT colorimetric assay.

Radioisotope diffusion experiments demonstrate that alginate/polyaminoacid encapsulation can prevent antibody and cytotoxic cell contact in vitro. The unpredictable outcome of xenotransplantation of encapsulated islets may reflect incomplete encapsulation. We have assessed a cytotoxic/MTT (tetrazolium) assay to test antibody permeability of capsules. Samples of free porcine islet tissue, and islet tissue encapsulated in alginate/poly-L-lysine/alginate microspheres were incubated with fresh autologous pig serum or normal human serum overnight. Cell metabolism was assessed by the MTT assay. Data from eight experiments (10 replicates/experiment) were analyzed using the Mann-Whitney U-test. Values were deemed significant when p < 0.05. Free islets cultured in human serum showed a significant reduction in metabolism when compared with islets cultured in pig serum: percentage reduction 52 +/- 23% (mean +/- SD). The differences in formazan production were significant in all experiments (p < 0.05). Alginate encapsulation of islets or removal of xenoreactive antibodies in human serum by adsorption was shown to prevent the effects of complement-mediated lysis. However, in one of the eight experiments, there was a significant reduction in islet metabolism after exposure of encapsulated porcine islets to human serum. In conclusion, it has been shown that alginate encapsulation can prevent complement-mediated lysis. However, the encapsulation process employed was imperfect and did not prevent complement-mediated lysis of porcine islets in all experiments. The cytotoxicity/MTT assay allows investigation of the permeability of capsules to serum antibodies and could be performed to determine the viability of the islets and the integrity of microcapsules prior to transplantation.

Alginates↗