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Biomedical subjects

A Watkinson

Publications and source records attributed to A Watkinson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Self-expanding metal stents for the palliation of dysphagia due to inoperable oesophageal carcinoma.

Adequate palliation of dysphagia due to inoperable oesophageal carcinoma is difficult to achieve with low morbidity. Thirty-three patients (21 men and 12 women of mean(s.e.m.) age 69(2) years) with inoperable carcinoma of the oesophagus underwent insertion of self-expanding metal stents. In 22 patients the tumours were in the lower third of the oesophagus, in eight in the middle third and in three in the upper third. A stent was inserted as primary palliative therapy in 14 patients, after failed laser therapy in 13 and after oesophageal perforation following other treatments in six. Patients presented with dysphagia of grade 3 or 4. Three types of stent were used: Wallstent, Strecker and Gianturco; stents were inserted under fluoroscopic guidance after balloon dilatation of the stricture. All attempted insertions of metal stents were successful. Dysphagia reduced from grade 3 or 4 to 0 or 1. There were no perforations related to insertion. Patients who had stents inserted to seal previous perforations left hospital a median 7 days later. Dysphagia recurred in six patients, due to migration of the stent (three), blockage by food bolus (one) and tumour overgrowth (two). These problems were easily treated. Self-expanding metal stents seem to offer excellent palliation with minimal morbidity for patients with inoperable carcinoma of the oesophagus.

Adenocarcinoma↗
PubMed1995

The effect of glycerol and humidity on desmosome degradation in stratum corneum.

Moisturizers are known to have occlusive, emollient and humectant properties, all of which help to alleviate the symptoms of skin xerosis. Although the biological mode of action of moisturizers is poorly understood, the recent observation that skin xerosis is associated with incomplete desmosome digestion suggests that moisturizers improve the desquamation process in such conditions. To examine the possibility that certain moisturizers act by facilitating desmosomal digestion, we investigated the ability of glycerol, a common humectant, to influence this process in stratum corneum in vitro. Examining desmosome morphology in isolated stratum corneum by electron microscopy, it was observed that the desmosomes were in more advanced stages of degradation in glycerol-treated tissue compared with control tissue. This enhanced desmosomal degradation in glycerol-treated tissue was confirmed by significant decreases in the levels of immunoreactive desmoglein 1, a marker of desmosome integrity. Desmosomal degradation was also shown to be a humidity-dependent event, being significantly reduced at low relative humidity. The effect of glycerol on desmosome digestion was emphasized further in two in vitro model systems. Firstly, glycerol increased the rate of corneocyte loss from the superficial surface of human skin biopsies in a simple desquamation assay. Secondly, measurement of the mechanical strength of sheets of stratum corneum, using an extensiometer, indicated a dramatic reduction in the intercorneocyte forces following glycerol treatment. These studies demonstrated the ability of glycerol to facilitate desmosome digestion in vitro. Extrapolating from these results, we believe that one of the major actions of moisturizers in vivo is to aid the digestion of desmosomes which are abnormally retained in the superficial layers of xerotic stratum corneum.

Cytoskeletal Proteins↗
PubMed1995

Plastic-covered metallic endoprostheses in the management of oesophageal perforation in patients with oesophageal carcinoma.

OBJECTIVE: To evaluate the role of plastic-covered self-expanding metallic endoprostheses in patients with oesophageal perforation occurring during endoscopically guided dilatation prior to laser treatment for malignant obstruction. SUBJECTS AND METHODS: Six patients with oesophageal perforation following laser treatment for malignant obstruction were treated. Four patients received the polyurethane-covered Wallstent endoprosthesis (Schneider SA, Bulach, Switzerland) and two patients the barbed polyethylene-covered Gianturco stent (William Cook, Europe). RESULTS: All patients had successful stent placement under intravenous sedation and fluoroscopic guidance with immediate relief of dysphagia and sealing of the perforation. Following the procedure all patients could eat either a normal diet or soft food and five patients were discharged within 3-4 days. None of the serious sequelae usually associated with oesophageal perforation were observed. Two patients required second overlapping stents to be inserted within 1 week because of minor migration of the initial endoprostheses. In one patient two stents were necessary because the carcinoma extended over 17 cm. Five patients died after stent insertion (mean survival time = 49 days, range 16-80; median survival time = 37 days, range 16-80) due to a general deterioration in their condition, although all could swallow normally until death. The remaining patient was well and tolerating a light diet at 1 month. CONCLUSION: This technique is quick, safe and cost-effective and is now our preferred method of managing malignant oesophageal obstruction associated with perforation.

Aged↗
PubMed1993

Post-translational processing of chromogranin A: differential distribution of phosphorylated variants of pancreastatin and fragments 248-313 and 297-313 in bovine pancreas and ileum.

Chromogranin A is a secretory protein expressed widely in neuroendocrine cells. It is known to be phosphorylated but the precise sites of phosphorylation are not known. We have isolated, from bovine pancreas and ileum, chromogranin A fragments corresponding to a region giving rise to a biologically active product, pancreastatin. Phosphorylation patterns were determined by fast atom bombardment mass spectrometry and alkaline phosphatase digestion followed by ion-exchange chromatography and radioimmunoassay. In the pancreas, there were unmodified, mono- and di-phosphorylated forms of the fragment chromogranin A(248-313) with Arg and Glu at positions 293 and 301 respectively; in addition, there were small amounts of monophosphorylated peptide with an alternative primary sequence of His and Lys at 293 and 301 respectively. Two products of cleavage, pancreastatin and the fragment 297-313, were also found in unmodified and monophosphorylated forms. In the ileum, peptides with both alternative primary sequences were found, pancreastatin was absent, and phosphorylation was generally less than in the pancreas. Chromogranin A-derived peptides therefore exhibit tissue-specific patterns of phosphorylation and cleavage, and at least two phosphorylation sites occur in the region giving rise to a biologically active product.

Alkaline Phosphatase↗
PubMed1992

Functional control of chromogranin A and B concentrations in the body of the rat stomach.

The chromogranins are soluble, acidic, proteins which are frequently co-stored in neuroendocrine cells with biogenic amines. In the gastric mucosa chromogranin A is localized to enterochromaffin-like cells which are the main source of histamine, and which are known to be regulated by circulating gastrin. We have used radioimmunoassays selective for the extreme C-terminal regions of chromogranin A and B to examine changes in gastric extracts following modulation of the gastric luminal contents. There were decreased concentrations of the two chromogranins in tissue extracts of rats after food withdrawal (which lowered plasma gastrin concentrations); inhibition of acid secretion with the H+/K(+)-ATPase inhibitor, omeprazole (which increased plasma gastrin concentrations) raised chromogranin A and B concentrations both in fasted rats, and in rats fed ad libitum. There was no evidence for altered patterns of posttranslational cleavage of chromogranin A or B with these treatments. The data indicate that chromogranin A and B concentrations in gastric ECL cells are regulated in parallel with histamine production, and are consistent with the idea that the chromogranins play a role in the formation and stabilization of the secretory granule involved in amine storage.

Amino Acid Sequence↗
PubMed1992

Reserpine-induced processing of chromogranin A in cultured bovine adrenal chromaffin cells.

The effect of reserpine on the processing of the secretory granule protein chromogranin A (CgA) in isolated bovine adrenal chromaffin cells was investigated using two radioimmunoassays employing site-specific antisera. The two antisera were directed against closely associated regions of the CgA molecule which would be exposed by specific processing: antiserum L331 was raised against the C-terminus of the regulatory peptide pancreastatin, and the second antiserum, L300, was raised against the synthetic peptide [Tyr0]CgA306-313 (YLSKEWEDA), a sequence that lies immediately C-terminal to pancreastatin and adjacent to a dibasic amino acid cleavage site. Chronic reserpine treatment of chromaffin cells produced a time- and dose-dependent increase in processing, as demonstrated by an increase in pancreastatin- and YLSKEWEDA-immunoreactivity (ir). The reserpine-induced rise in pancreastatin-ir was due predominantly to an increase in pancreastatin 1-47, whereas the rise in YLSKEWEDA-ir was due to increases in three polypeptides: a 51-kDa YLSKEWEDA-ir polypeptide, CgA297-313, and CgA248-313. The latter predominated. The action of reserpine on both pancreastatin- and YLSKEWEDA-ir was found to be largely inhibited by the protein synthesis inhibitor cycloheximide. The results show that treatment of isolated chromaffin cells with reserpine induces both the selective proteolytic processing and peptidyl-glycine amidation of CgA and its derived fragments. As reserpine has a similar effect on proenkephalin in chromaffin cells, the results suggest that reserpine induces a general increase in the activity of the processing enzymes, partially by an increase in protein synthesis.

Adrenal Glands↗
PubMed1991

Heterogeneity of chromogranin A-derived peptides in bovine gut, pancreas and adrenal medulla.

Chromogranin A is produced in many endocrine cell types, and is widely used as a marker in endocrine-cell pathology and secretory-cell biology. There is some evidence that it may be proteolytically processed to yield the putative pancreatic regulatory peptide, pancreastatin, and, in order to characterize the relevant pathways in gastrointestinal and pancreatic endocrine cells, we have used, in radioimmunoassay, site-directed antibodies to pancreastatin itself (L331) and to a sequence of chromogranin A immediately C-terminal to pancreastatin (L300). The latter antibody revealed three major forms of immunoreactivity of 8 kDa and five peptides of approx. 3 kDa in bovine pancreas and gut extracts. The 8 kDa peptides were characterized as chromogranin A-(248-313)-peptides, i.e. C-terminally extended forms of pancreastatin; two of the 8 kDa variants differed in two positions, confirming a polymorphism predicted from cDNA sequencing. One of the 3 kDa peptides was characterized as chromogranin A-(297-313)-peptide, i.e. the C-terminal heptadecapeptide of the 8 kDa peptide that would be liberated after cleavage to yield pancreastatin. On the basis of chromatographic studies, immunohistochemistry and the stoichiometry of different immunoreactive peptides, three different pathways of chromogranin A processing were identified: in adrenal chromaffin cells chromogranin A existed mainly as the unmodified intact protein, in pancreatic islet and gastric antral endocrine cells pancreastatin and the 3 kDa peptides were major products, but in small intestine and gastric corpus endocrine cells there was little nor no pancreastatin and the 8 kDa cleavage product predominated. There are therefore important differences in the distribution of chromogranin A-derived peptides between quite closely related populations of endocrine cells that are attributable not only to variable post-translational cleavage but also to the expression of different primary sequences. It seems possible that in different cell types chromogranin A-derived peptides might subserve a variety of different functions.

Adrenal Medulla↗
PubMed1991

Prognostic factors in soft tissue injuries of the cervical spine.

A series of 35 patients presenting with soft tissue injuries of the cervical spine were reviewed clinically and radiographically after an average of 10.8 years. Symptoms persisted in 86 per cent and were intrusive or worse in 23 per cent. On presentation, paraesthesia, thoracolumbar back pain and multiple symptoms were predictive of continuing symptoms and their severity. Degenerative changes of the cervical spine were present in 68 per cent of the patients, of whom 87 per cent were symptomatic. Of those with normal radiographs, 80 per cent were symptom-free. Degenerative changes occurred significantly more frequently in patients who had sustained soft tissue injuries than in a control population.

Adult↗
PubMed1990

Dental manpower.

Explore the source record for details and available documents.

Dental Assistants↗
PubMed1989

The isolation and chemical characterization of phosphorylated enkephalin-containing peptides from bovine adrenal medulla.

There is increasing evidence that the opioid peptide precursor, proenkephalin A, and its products undergo extensive post-translational modification, in addition to the cleavage at dibasic amino acid sites. We have used an antiserum directed toward the C terminus of Met-enkephalin Arg6-Phe7 in a radioimmunoassay to monitor the purification to homogeneity of four peptide B variants from bovine adrenal medulla, using gel filtration, anion exchange chromatography, and reverse phase high performance liquid chromatography. Amino acid sequence analysis, together with immunochemical data, confirmed that each comprised the primary sequence, proenkephalin A-(209-239). In addition, three of the four variants were shown to be phosphorylated by alkaline phosphatase digestion, microphosphate analysis, and ethanethiol derivatization coupled with amino acid sequence analysis; these variants were shown to have 1, 2, or 3 phosphate groups per peptide chain, which corresponded to their increasing acidic nature. The phosphorylation sites were clustered together at positions Ser7, Ser13, and Ser15 and were in close association with acidic residues. The clustering of phosphorylated residues is unique among regulatory peptide precursors. This region of proenkephalin A is well conserved, which suggests that it constitutes an important novel functional domain.

Adrenal Medulla↗
PubMed1989

Identification and characterization of N-glycosylated and phosphorylated variants of proenkephalin A-derived peptides in bovine adrenal medulla, spinal cord and ileum.

Recent studies have shown that during its biosynthesis in bovine adrenal medulla, the opioid precursor proenkephalin A, may be both N-glycosylated and phosphorylated. To investigate whether these chemical modifications were common to proenkephalin A processing in other tissues, we have sought to characterize enkephalin-containing peptides from bovine adrenal medulla, spinal cord and ileum. The peptides were identified using antiserum L189, specific for the C-terminus of Met-enkephalin Arg6Gly7Leu8 (MERGL), and L152, specific for the C-terminus of Met-enkephalin Arg6Phe7 (MERF). Glycosylated MERGL-immunoreactive peptides of 23, 20, 16 and 13 kDa were identified in adrenal medulla using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and concanavalin A-Sepharose affinity chromatography. Sephadex G50 gel filtration fractionated the glycosylated peptides into two immunoreactive peaks. Similar peaks of concanavalin A-binding MERGL immunoreactivity were detected in extracts of spinal cord and ileum, although there were differences in relative proportions of the two peaks. Antiserum L152 identified phosphorylated N-terminally extended variants of MERF when boiling water extracts of adrenal medulla, spinal cord and ileum were separated by anion exchange chromatography. In adrenal medulla these peptides were more than 99% phosphorylated, whereas in both ileum and spinal cord there was a relatively higher proportion of the unphosphorylated peptide. The results indicate that N-glycosylation and phosphorylation of proenkephalin A occurs in adrenal medulla, spinal cord and ileum, although there are tissue-specific differences in the relative proportions of the modified and unmodified peptides.

Adrenal Medulla↗
PubMed1988

Characterisation of N-terminally extended met-enkephalin Arg6Gly7Leu8 variants in the porcine upper digestive tract.

Proenkephalin A-derived peptides are known to occur in the gut, but their precise identity is uncertain. We report here the isolation of N-terminally extended forms of Met-enkephalin Arg6Gly7Leu8 from porcine upper digestive tract monitored by radioimmunoassay. A single major form was identified in pyloric antral muscle and mucosa, but in the duodenum two major forms were detected. Microsequence analysis together with immunological data revealed that the antral mucosal peptide and the most acidic duodenal peptide had identical amino-acid sequences, corresponding to a 5.3 kDa peptide terminating in Met-enkephalin Arg6Gly7Leu8. The data indicate that high-molecular-weight peptides may constitute a major proportion of gut opioid peptide immunoactivity.

Amino Acid Sequence↗
PubMed1988

N-linked glycosylation of a proenkephalin A-derived peptide. Evidence for the glycosylation of an NH2-terminally extended Met-enkephalin Arg6-Gly7-Leu8 variant.

To investigate the possibility that the opioid peptide precursor proenkephalin A was glycosylated, we utilized an antiserum raised against the COOH terminus of Met-enkephalin Arg6-Gly7-Leu8 (MERGL) to identify and characterize enkephalin-containing peptides from extracts of bovine adrenal medulla. Sephadex G-50 gel filtration separated two immunoreactive peaks which had apparent masses of 9 and 6 kDa. Anion-exchange chromatography and reverse-phase high pressure liquid chromatography (HPLC) revealed that the 9-kDa material was a heterogenous mixture of immunoreactive peptides, of which one (9K-MERGL Ia) was purified to homogeneity. The 6-kDa material separated into two major immunoreactive peaks (6K-MERGL I and 6K-MERGL II) on anion-exchange chromatography, and these were obtained in an homogenous form after reverse-phase HPLC. Amino acid sequencing, together with immunological characterization, indicated that the three peptides were identical in chain length, and corresponded to proenkephalin A 116-165. They contained the sequence Asn-Ser-Ser which is a potential N-glycosylation site. In 9K-MERGL Ia, but not the others, automated Edman amino acid sequencing was unable to detect the relevant asparagine residue, suggesting that this residue has been chemically modified. Further investigation of the 9K-MERGL material using lectin affinity chromatography provided direct evidence of glycosylation. Verification of this result was obtained using the specific enzyme glycopeptidase F (glycopeptide-N-glycosidase) which demonstrated that 9K-MERGL contained, in part, N-linked oligosaccharide chains. These results show that an NH2 terminally extended Met-enkephalin Arg6-Gly7-Leu8 variant was N-glycosylated, and hence indicate that the precursor polypeptide proenkephalin A can be glycosylated during translation in the rough endoplasmic reticulum.

Adrenal Medulla↗
PubMed1988

Proenkephalin A-derived peptides in the human gut.

The intramural distribution of the proenkephalin A-derived peptides Leu5-enkephalin, Met5-enkephalin, Met5-enkephalin-Arg6-Phe7, and Met5-enkephalin-Arg6-Gly7-Leu8 was studied throughout the human gastrointestinal tract. A parallel distribution was found of Leu5/Met5-enkephalin, measured with a Leu5-enkephalin antiserum that cross-reacts about 30% with Met5-enkephalin, and of Met5-enkephalin-Arg6-Phe7-immunoreactivity and Met5-enkephalin-Arg6-Gly7-Leu8-immunoreactivity. In each case, high tissue concentrations were present in the submucosa and muscularis corresponding to the pyloric sphincter. Taking all different regions together, a high correlation was revealed between tissue levels of Leu5/Met5-enkephalinlike peptides and Met5-enkephalin-Arg6-Gly7-Leu8-like peptides (r = 0.89), as well as between Met5-enkephalin-Arg6-Gly7-Leu8-like peptides and Met5-enkephalin-Arg6-Phe7-like peptides (r = 0.75). Met5-enkephalin-Arg6-Phe7 immunoreactivity was accounted for by a major peak (87% +/- 3% of total immunoreactivity) coeluting with the standard peptide in Sephadex G-50 chromatography and largely composed of the authentic heptapeptide, as shown by reverse-phase high-performance liquid chromatography. Leu5/Met5-enkephalin immunoreactivity was separated by high-performance liquid chromatography into peaks composed of Leu5-enkephalin and Met5-enkephalin. Allowing for Met5-enkephalin immunoreactivity in the assay used, the apparent Leu5/Met5-enkephalin molecular ratio was approximately 1:4. The high concentration of all peptides studied at the pyloric junction suggests a rich enkephalin-containing innervation at this level, in keeping with the proposed involvement of an enkephalinergic mechanism in the control of pyloric function.

Chromatography, High Pressure Liquid↗
PubMed1988

Proenkephalin A processing in the upper digestive tract: isolation and characterisation of phosphorylated N-terminally extended Met-enkephalin Arg6Phe7 variants.

Previous studies suggest the processing of proenkephalin A in the porcine upper digestive tract might differ from that in the brain. To characterise more precisely some of the products, we have used antibodies to Met-enkephalin Arg6Phe7 (MERF) in radioimmunoassay to monitor the isolation of immunoreactive peptides from extracts of porcine pyloric antral muscle, antral mucosa, and duodenum. Sephadex G50 gel filtration of each extract produced a single broad peak of high-molecular-weight MERF-immunoreactivity. On anion-exchange chromatography the antral muscle MERF-immunoreactivity fractionated into two major peaks, and that from the antral mucosa and duodenum each into four major peaks, suggesting tissue specific processing of proenkephalin A within the porcine gut. Reverse-phase HPLC and Edman degradation analysis revealed that the least acidic antral muscle peptide was a 31-residue N-terminally extended form of MERF that is equivalent to proenkephalin A 209-239. Alkaline phosphatase digestion of the N-terminally extended MERF variants indicated that some of these peptides were modified by phosphorylation. We conclude that there are complex patterns of proenkephalin A processing in the porcine gut, which in part are due to phosphorylation.

Alkaline Phosphatase↗