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Biomedical subjects

R A Morgan

Publications and source records attributed to R A Morgan.

At least 109 records · Page 6Linked to original sources
PubMed1987

Post-transcriptional regulation and DNA undermethylation of intracisternal A particle genes in embryonal carcinoma cell lines.

Northern blot analysis and in vitro nuclear transcription assays were performed in order to clarify conflicting reports on the expression of intracisternal A particle (IAP) genes in embryonal carcinoma (EC) cell lines. Results demonstrate that post-transcriptional mechanisms control the final steady-state levels of IAP RNA in EC cells. IAP genes were further found to be undermethylated in IAP-expressing EC cell lines.

Animals↗
PubMed1987

Experience with the straight endorectal pullthrough for the management of ulcerative colitis and familial polyposis in children and adults.

The first significant experience with the straight endorectal pullthrough for the management of ulcerative colitis was presented before the American Surgical Association in 1977 by Lester Martin. Since then the operation with or without modification has been used extensively. High stool frequencies in some series led to disenchantment with the straight anastomosis and to the development of various reservoir procedures to increase rectal capacity and thereby reduce frequency. As a result, no large series of straight pullthroughs is available for comparison with the reservoir modifications. Between September 1977 and September 1986, 72 children and adults, 61 with ulcerative colitis and 11 with familial polyposis, underwent endorectal pullthrough (ERPT) and straight ileoanal anastomosis under the overall direction of a single surgeon (AGC). Sixty patients have undergone ileostomy closure and form the basis of this study. Mean age at operation was 22.7 years (range 4-48 yr), and duration of active disease averaged 6 years. One-half of the patients underwent total abdominal colectomy with ERPT as a primary procedure. There were 11 cases of adhesive bowel obstruction following ERPT, and in six patients in the series permanent revision to a Brooke ileostomy was required. One patient died of hepatic failure in the late postoperative period. Follow-up has ranged from 3 months to 9 years. Mean stool frequency for the group as a whole at 3, 6, 12, 24, and 36 months was 11.8, 11.2, 9.6, 9.0, and 8.3 per 24 hours, respectively. Daytime continence was achieved in all patients. Occasional nocturnal soiling occurred in 11.1% of patients at 1 year. Stool frequency and continence were also analyzed by age group above and below 18 years and above and below 30 years. There were no statistically significant differences between these groups. The authors conclude from this study that ERPT with straight ileoanal anastomosis remains an appropriate alternative for children and adults with ulcerative colitis or familial polyposis and compares favorably with the more complicated ERPT involving a reservoir.

Adenomatous Polyposis Coli↗
PubMed1986

Fifty years' experience with esophageal atresia and tracheoesophageal fistula. Beginning with Cameron Haight's first operation in 1935.

Four hundred twenty-six patients with esophageal atresia with or without tracheoesophageal fistula have been primarily cared for at the University of Michigan Medical Center since Cameron Haight's initial experience with this entity. Over the period of observation, the incidence of new cases as well as the number of associated anomalies has remained constant. The long-term survival of these patients has steadily improved over the past half-century from 36% in the pre-1950 era to 84% during the most recent 20 years. Conversely, operative mortality has shown a progressive decline from 56% early in the authors' series to 6.9% more recently, despite a steady increase in the proportion of high-risk neonates seen at the University of Michigan Medical Center during this time span. In the last 9 years, there have been no postoperative deaths in group A or B risk infants (36 patients), while the rate has been 18.2% in group C risk babies (27 patients); almost all of these deaths were due to severe associated anomalies. During the last 10 years, the authors have changed their technique of anastomosis from a two- to a one-layer method while still advocating a primary repair via an extrapleural approach. Although this change has resulted in a modest increase in the rate of anastomotic leak (17% vs. 6.2%, p less than 0.03), the leaks have been small and asymptomatic because of the extrapleural approach and, as a result, have been managed conservatively without any untoward sequelae. Conversely, there has been a significant decrease in the rate of stricture formation with the one-layer anastomosis (4.3% vs. 23.3%, p less than 0.002). While this may in part be explained by the change in anastomotic technique, it is felt that the more aggressive diagnosis and surgical management of gastroesophageal reflux (seen in 37.9% of our recent group) have contributed greatly to this decrease. The steady improvement in survival over this 50-year period, in spite of the increasing number of high-risk infants, is attributable to major improvements in neonatal care before, during, and after operation.

Esophageal Atresia↗
PubMed1986

Sub-ambient aggregometry: a tool for examining platelet storage at any temperature between 4-22 degrees C.

A specifically modified commercially available aggregometer, referred to as a sub-ambient aggregometer, was used to measure certain parameters of platelet function throughout the temperature range of 4-37 degrees C. Platelet aggregation responses to ADP and stirring (spontaneous aggregation) were found to be maximal at room temperature. The possible relevance of this to routine platelet storage is discussed. Shear-induced light transmission change (SILTC) as a quick, repeatable, non-invasive index of platelet morphology was used to monitor small-sample platelet storage at 4 degrees C and during its subsequent resuscitation at 37 degrees C. This confirmed the combined usefulness of the sub-ambient aggregometer and SILTC measurements for monitoring platelets during storage. Further application of this approach should enable the optimum temperature for the liquid storage of platelets to be defined, which may not necessarily be 22 degrees C as usually employed.

Adenosine Diphosphate↗
PubMed1984

Transcription of intracisternal A-particle genes in mouse myeloma and Ltk- cells.

In vivo- and in vitro-synthesized RNA from the murine plasmacytoma MOPC-315 was found to hybridize to all regions of a 7.2-kilobase-pair intracisternal A-particle (IAP) gene. IAP-specific transcripts were also detected in mouse Ltk- cells, but not in cells derived from normal tissues (kidney, liver, spleen) of 6-week-old BALB/c mice. Three RNA species of 7.2, 5.3, and 3.8 kilobases were identified by Northern blot analysis of MOPC-315 polyadenylated RNA. The 7.2- and 5.3-kilobase transcripts were found in greater levels in nuclear as compared with whole cell RNA, suggesting the involvement of one or more of the following mechanisms: RNA processing, preferential nuclear transport, or differential RNA stability. We show that the primary IAP transcript is initiated within the long terminal repeat by hybridization analysis with restriction digests of cloned IAP DNA and [gamma-S]pppApNp ... RNA synthesized in nuclei with [gamma-S]ATP as the RNA initiating probe. Low concentrations of alpha-amanitin (2 micrograms/ml) inhibited IAP RNA synthesis by greater than 90%, suggesting that RNA polymerase II is responsible for IAP transcription.

Animals↗
PubMed1984

Correlation of undermethylation of intracisternal A-particle genes with expression in murine plasmacytomas but not in NIH/3T3 embryo fibroblasts.

We report here comparative studies of DNA methylation and expression of intracisternal A-particle (IAP) genes in murine plasmacytomas, TEPC-15 and MOPC-315, in NIH/3T3 embryo fibroblasts, and in normal liver from young adult BALB/c mice. In Southern blot analysis using methylation-sensitive restriction enzymes, we observed hypomethylation of 4.7- and 5.3-kilobase pair IAP proviruses, and partial undermethylation of other IAP DNA fragments in TEPC-15, MOPC-315, and 3T3 cells, while most of these DNA fragments were hypermethylated in liver. The extent of undermethylation at 12 different sites including the long terminal repeat sequence region and 5'-flanking sequence within one specific IAP gene was found to be similar between 3T3 cells and plasmacytomas. Little or no undermethylation of these sites was found in liver. Hypomethylation of IAP genes, however, is not correlated with their expression in 3T3 cells (as it is found for plasmacytomas), since 3T3 cells, like liver cells, have no detectable transcripts. We also observed hypomethylation of the kappa-light chain gene in 3T3 cells, suggesting that undermethylation may be a generalized phenomenon in these cells. The relationships between gene undermethylation and the control of gene expression in 3T3 cells is discussed.

Animals↗
PubMed1981

Localization and characterization of N-ethylmaleimide sensitive inhibitor(s) of thiol cathepsin activity from cultured nil and polyoma virus-transformed nil hamster cells.

Exposure of cultured Nil (a stable line of fibroblast cells from Syrian hamsters) or polyoma virus-transformed (PyNil) hamster fibroblasts to 0.5 mM N-ethylmaleimide for 5 minutes resulted in striking increases in thiol cathepsin activity in unfractionated cell-free lysates. The paradoxical increase in activity of the normally N-ethylmaleimide-sensitive cathepsins apparently occurred as the result of the protective compartmentalization of the cathepsins in the lysosomes (20,000 X g sedimented fraction) and the unprotected localization of an inhibitor(s) in the soluble cytoplasm (175,000 X g supernatant fraction). Under continuous exposure of the cells to N-ethylmaleimide, a rapid increase in cathepsin activity (seen in the first 5 minutes) was followed by a steady decrease in activity (half inactivation time, 90 minutes). The relative difference in rates of N-ethylmaleimide inactivation of thiol cathepsins and thiol cathepsin inhibitors provides a means for estimating lysosomal cathepsin activity in whole cell extracts without the need for more time-consuming fractionation procedure. In reciprocal inhibition tests, it was found that, regardless of the source of cathepsins, the Nil and PyNil cathepsin inhibitor(s) inactivated the cathepsins to approximately the same extent. The inhibitors were heat stable (90-100 degrees C for 15 minutes) at pH 4, but were totally inactivated when boiled at pH 8.5. On a calibrated Sephadex G-100 column, the relative molecular weight (Mr) of the inhibitor(s) was 13,000 daltons. On the same column, the Mr of the cathepsins was 24,000 daltons. Compared with the cathepsin activity from Nil cells, there was about five times less cathepsin activity recoverable from the PyNil cells.

Aminopeptidases↗
PubMed1981

Radioimmunoassay of the leukotrienes of slow reacting substance of anaphylaxis.

A rabbit immunized with a conjugate of leukotriene D4 (LTD4) and bovine albumin via the icosanoid carboxyl produced antibodies with comparable affinities for leukotrienes C4, D4, and E4 (LTC4, LTD4, and LTE4) and their 11-trans stereoisomers. The antibodies bound 3H-labeled 11-trans-LTC4 and 11-trans-LTC4 with the same average association constant (Ka) of 2.8 x 10(9) M-1 at 37 degrees C and were present at a concentration of 0.32 microgram/ml of the immune rabbit plasma. When 9.5 microliter of anti-LTD4 and 108 pmol of 11-trans-[3H]LTC4 (40 Ci/mmol) were incubated in a volume of 300 microliter with LTC4, LTD4, LTE4, or their 11-trans stereoisomers, 50% inhibition of 11-trans-[3H]LTC4 binding was achieved at levels varying between 0.3 and 0.7 ng. As assessed with synthetic analogs of the natural leukotrienes, the antibodies recognized neither those changes within the 6-sulfidopeptide unit of LTD4 produced by deamination or modest peptide lengthening nor the specific stereochemistry of the delta 14-cis double bond. However, the antibodies did recognize the triene lipid domain and the position and spatial orientation of the glutathione or cysteinylglycine function. Binding of 11-trans-[3H]LTC4 by anti-LTD4 was not inhibited by glutathione, cystinylbisglycine, arachidonic acid, or 5-hydroxy-6,8,11,14-icosatetraenoic acid, and leukotriene B4 (LTB4) was about 1/1000th as active as LTC4, LTD4, or LTE4. Mouse lymphoma (WEHI-5) and rat basophil leukemia (RBL-1) cells, when stimulated with calcium ionophore A23187, each produced immunoreactive leukotrienes; and LTC4, LTD4, and LTE4 from RBL-1 cells were individually quantitated by radioimmunoassay after resolution by high-performance liquid chromatography.

Animals↗
PubMed1981

Are lysosomes involved in hexose transport regulation? Turnover of hexose carriers and the activity of thiol cathepsins are arrested by cyanate and ammonia.

The cycloheximide-related loss of transport activity (manifested as a decrease in Vmax for transport) in cultured Nil hamster fibroblasts was blocked by the addition of carbamoyl phosphate, cyanate (a product of spontaneous phosphate elimination from carbamoyl phosphate), or ammonium salts to the culture medium. Acid proteases capable of hydrolyzing alpha-N-benzoyl-D,L-arginine-beta-naphthylamine (cathepsins B1, H, and L) were also inhibited in situ by ammonia and cyanate. The inactivation of these cathepsins by ammonia was irreversible and probably was related to the increase in the intralysosomal pH known to be caused by an accumulation of ammonia in the lysosomes. The inhibition of the cathepsin activity by cyanate in situ (and in cell-free extracts) was completely reversible and blocked irreversible inhibition of the cathepsin(s) by N-ethylmaleimide. The inactivation of the cathepsins caused by cyanate was deduced to be the result of reversible blocking of sulfhydryl groups essential to the thiol cathepsin activity. The concomitant inhibition of thiol cathepsins and hexose carrier inactivation provided further evidence for the involvement of lysosomal proteases in at least part of the mechanism that regulates the rate of hexose transport in animal cells.

Ammonia↗
PubMed1980

Development of seamless tri-leaflet valves.

In terms of their hydrodynamic characteristics at physiologically-relevant flows, the tri-leaflet valves show remarkable in vitro performance in comparison with similarly sized or even larger prosthetic valves. The ongoing in vivo studies confirmed the importance of adequate fluid mechanical design criteria, surface smoothness and rigorously clean fabrication procedures to minimize thrombo-embolic phenomena in the absence of anticoagulant therapies. Results from ongoing in vitro and in vivo durability studies suggest these are promising prostheses for valve replacement.

Animals↗