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Biomedical subjects

T D Allen

Publications and source records attributed to T D Allen.

At least 73 records · Page 4Linked to original sources
PubMed1993

Salvaging the obstructed ureterosigmoidostomy using an ileal interposition technique.

Ureterointestinal obstruction is a major complication of ureterosigmoidostomy and one that usually forces a flight to other forms of urinary diversion. Many patients, however, are reluctant to give up the life-style that ureterosigmoidostomy offers and prefer an alternative that permits retention of the basic features of the procedure. To satisfy these demands a technique has been developed in which an intussuscepted segment of small bowel is interposed between the colon and the ureters. This operation has allowed salvage of an obstructed ureterosigmoidostomy in 6 patients and has given such good results that it has been done as a primary procedure in 1. In addition to its use for the salvage of existing ureterosigmoidostomies, the operation permits primary ureterosigmoidostomy to be done in patients with dilated ureters, and it may even lessen the risk of colon cancer by separating the urothelium from the colonic mucosa.

Adolescent↗
PubMed1993

Continence in the myelodysplastic patient following enterocystoplasty.

To evaluate the ability of augmentation cystoplasty alone to provide a low pressure bladder and an adequate degree of continence in the myelodysplastic patient, the clinical records and urodynamic data of the last 18 consecutive such patients undergoing augmentation cytoplasty at our institution were reviewed. Two patients underwent colocystoplasty and 16 underwent ileocystoplasty. No patient underwent any procedure on the bladder neck or urethra. The 2 colocystoplasty patients exhibited episodic dampness attributed to contractions of the augmentation but all of the ileocystoplasty patients were dry during the day except 1 who had a urethral resistance of only 19 to 22 cm. water. On the basis of this review, ileocystoplasty alone appears to be sufficient for satisfactory continence in patients with a neurogenic bladder undergoing vesical augmentation if bladder outlet resistance exceeds 25 to 30 cm. water.

Adolescent↗
PubMed1993

Lymphocyte migration across high endothelium is associated with increases in alpha 4 beta 1 integrin (VLA-4) affinity.

The constitutive recirculation of lymphocytes between the widely distributed organs of the immune system is essential for host defence. We have developed an in vitro model of lymphocyte migration from the blood into lymph nodes which employs primary cultures of high endothelial cells (HEC). HEC-adherent lymphocytes adopt one of two distinct morphologies which correlates with their position in the endothelial layer; type I cells are bound to the surface of HEC and type II cells are underneath the endothelial layer. In a previous study we reported that the numbers of type I and type II cells are independently regulated, however the relationship between these two lymphocyte populations was not determined. In this study we have carried out detailed kinetic, phenotypic and functional analyses of type I and type II lymphocytes and determined their relationship. Using allotype marked lymphocytes from the PVG.RT7a and PVG.RT7b rat strains in a pulse-chase analysis, type I and type II lymphocytes were found to represent the same population of lymphocytes at different stages of interaction with the endothelial layer, rather than representing two independent lymphocyte populations. Migration was an irreversible event and the efficiency of migration (i.e. transition from type I to type II) was related to the concentration of lymphocytes plated on to the HEC layer. Following transmigration lymphocytes showed an increased ability to migrate across HEC layers and to bind to immobilised CS1 peptide. The increased binding to CS1 peptide was transient and fell to control levels over a 3 hour time period. The expression of alpha 4 integrin subunit on lymphocytes was unchanged following migration which suggests that the affinity of the CS1 receptor, alpha 4 beta 1, is upregulated by interaction with HEC. Together these results suggest that transendothelial migration is regulated by increases in the affinity of alpha 4 beta 1 integrin on lymphocytes following contact with HEC.

Animals↗
PubMed1993

The nuclear pore complex: three-dimensional surface structure revealed by field emission, in-lens scanning electron microscopy, with underlying structure uncovered by proteolysis.

The structure of the nuclear pore complex (NPC) has been previously studied by many different electron microscopic techniques. Recently, scanning electron microscopes have been developed that can visualise biologically relevant structural detail at the same level of resolution as transmission electron microscopes and have been used to study NPC structure. We have used such an instrument to visualise directly the structure of both cytoplasmic and nucleoplasmic surfaces of the NPC of manually isolated amphibian oocyte nuclear envelopes that have been spread, fixed, critical point dried and coated with a thin fine-grained film of chromium or tantalum. We present images that directly show features of the NPC that are visible at each surface, including coaxial rings, cytoplasmic particles, plug/spoke complexes and the nucleoplasmic basket or fishtrap. Some cytoplasmic particles are rod-shaped or possibly "T"-shaped, can be quite long structures extending into the cytoplasm and may be joined to the coaxial ring at a position between each subunit. Both coaxial rings, which are proud of the membranes, can be exposed by light proteolytic digestion, revealing eight equal subunits each of which may be bipartite. We have determined that the nucleoplasmic filaments that make up the baskets are attached to the outer periphery of the coaxial ring at a position between each of its subunits. These filaments extend into the nucleoplasm and insert at the distal end to the smaller basket ring. The space left between adjacent basket filaments would exclude particles bigger than about 25 nm, which is consistent with the exclusion limit previously found for NPC-transported molecules.

Actin Cytoskeleton↗
PubMed1992

Unilateral post-obstructive diuresis in the neonate.

A total of 3 neonates exhibited severe post-obstructive diuresis after relief of unilateral ureteral obstruction. Of the neonates 2 had normal kidneys contralaterally while 1 had a contralateral kidney that was dysplastic. Urinary output exceeded oral intake initially in all 3 patients necessitating intravenous supplementation for up to 10 days. Stabilization resulted from an increase in oral intake rather than a decrease in diuresis. Unilateral post-obstructive diuresis is extremely uncommon but it may occur in the neonate because of the unique features of the renal physiology encountered in this age patient.

Diuresis↗
PubMed1992

Exstrophy of the bladder: primary closure after iliac osteotomies without external or internal fixation.

A total of 6 consecutive infants with exstrophy of the bladder underwent iliac osteotomy in association with primary closure of the bladder without internal or external fixation of the bony pelvis. Hospitalization time was short and there were no resulting problems with healing, bony deformities or subsequent ambulation. Fixation of the bony pelvis after iliac osteotomy does not appear to be necessary in nonambulatory patients undergoing primary closure for bladder exstrophy.

Bladder Exstrophy↗
PubMed1992

High resolution scanning electron microscopy of the nuclear envelope: demonstration of a new, regular, fibrous lattice attached to the baskets of the nucleoplasmic face of the nuclear pores.

The nuclear envelope (NE) of amphibian oocytes can be readily isolated in relatively structurally intact and pure form and has been used extensively for structural studies. Using high resolution scanning electron microscopy (HRSEM), both surfaces of the NE can be visualized in detail. Here, we demonstrate the use of HRSEM to obtain high resolution information of NE structure, confirming previous data and providing some new information. NEs, manually isolated from Triturus cristatus oocytes, have been mounted on conductive silicon chips, fixed, critical point dried and coated with a thin, continuous film of chromium or tantalum and viewed at relatively high accelerating voltage in a field emission scanning electron microscope with the sample within the objective lens. Both nucleoplasmic and cytoplasmic surfaces of the nuclear pore complexes (NPC) have been visualized, revealing the cytoplasmic coaxial ring, associated particles, central plug/transporter and spokes. The nucleoplasmic face is dominated by the previously described basketlike structure attached to the nucleoplasmic coaxial ring. In Triturus, a novel, highly regular flat sheet of fibers, termed the NE lattice (NEL) has been observed attached to the distal ring of the NPC basket. The NEL appears to be distinct from the nuclear lamina. Evidence for the NEL is also presented in thin TEM sections from Triturus oocytes and GVs and in spread NEs from Xenopus. A model is presented for NEL structure and its interaction with the NPCs is discussed.

Amphibians↗
PubMed1992

Transforming growth factor beta 1 promotes the differentiation of endothelial cells into smooth muscle-like cells in vitro.

Alpha-smooth muscle actin is considered a reliable marker for distinguishing between arterial smooth muscle and endothelial cells. Several authors have reported heterogeneity in the expression of this actin isoform in atherosclerotic lesions. Such heterogeneity appears to result from the presence of different smooth muscle cell phenotypes (contractile and synthetic) in these lesions. In the present study, we show that bovine aortic endothelial cells, which are characterised by the presence of Factor VIII-related antigen (FVIII) and by the absence of alpha-smooth muscle actin (alpha-SM actin) may be induced to express the latter when exposed to TGF-beta 1. FVIII was detected by immunofluorescence, alpha-SM actin was detected by immunofluorescence and immunoblotting. The number of cells expressing alpha-SM actin increased with time of incubation with TGF-beta 1, and this increase occurred concomitantly with a decrease in the expression of FVIII. Double immunofluorescence demonstrated the presence of cells that expressed both FVIII and alpha-SM actin after 5 days of incubation with TGF-beta 1. With longer incubation times (10-20 days) the loss of FVIII expression was complete and over 90% of the cells expressed alpha-SM actin. Ultrastructurally, cells in control cultures showed the typical features of endothelial cells. In the TGF-beta 1-treated cultures, cells which appeared indistinguishable from contractile and synthetic smooth muscle cells were observed. Withdrawal of TGF-beta 1 after 10 days incubation resulted in the re-appearance of polygonal cells which were FVIII-positive and alpha-SM actin-negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1991

ATP dependent histone phosphorylation and nucleosome assembly in a human cell free extract.

Physiologically spaced nucleosome formation in HeLa cell extracts is ATP dependent. ATP hydrolysis is required for chromatin assembly on both linear and covalently closed circular DNA. The link between the phosphorylation state of histones and nucleosome formation has been examined and we demonstrate that in the absence of histone phosphorylation no stable and regularly spaced nucleosomes are formed. Phosphorylated H3 stabilizes the nucleosome core; while phosphorylation of histone H2a is necessary to increase the linker length between nucleosomes from 0 to approximately 45 bp. Histone H1 alone, whether phosphorylated or unphosphorylated, does not increase the nucleosome repeat length in the absence of core histone phosphorylation. Phosphorylations of H1 and H3 correlate with condensation of chromatin. Maximum ATP hydrolysis which is necessary to increase the periodicity of nucleosomes from approximately 150 to approximately 185 bp, not only inhibits H1 and H3 phosphorylation but facilitates their dephosphorylation.

Adenosine Triphosphate↗
PubMed1991

Identification of amino acids in lac repressor protein cross-linked to operator DNA specifically substituted with bromodeoxyuridine.

Amino acids in lac repressor protein which form cross-links to lac operator DNA specifically substituted with bromodeoxyuridine (BrdU) have been identified. Five sites of cross-linking in BrdU-substituted operator DNA were found at positions +3, +4, +14, +18, and +19 relative to the initiation site for transcription (Wick, K.L., and Matthews, K.S. (1991) J. Biol. Chem. 266, 6106-6112). Irradiation of complexes of repressor and each of these five singly substituted operator DNAs was executed under large scale conditions to generate sufficient complex for proteolysis, separation of the peptide-DNA, and peptide sequencing. The DNAs substituted with BrdU for thymidine at positions +3, +18, and +19 yielded cross-links to the peptide spanning residues 23-33, with the cross-link identified at His-29. Substitution at position +14 resulted in a cross-link to Tyr-17 within the peptide containing amino acids 13-22. These results are consistent with the structure determined by NMR and molecular dynamics calculations of the NH2-terminal headpiece-symmetric operator complex (Lamerichs, R.M.J.N., Boelens, R., van der Marel, G.A., van Boom, J.H., Kaptein, R., Buck, F., Fera, B., and Rüterjans, H. (1989) Biochemistry 28, 2895-2991; de Vlieg, J., Berendsen, H.J.C., and van Gunsteren, W.F. (1989) Proteins 6, 104-127). This structure indicates proximity of His-29 in the major groove to thymidines at positions +3 and +4. Since base pairs at positions +18 and +19 occupy symmetrical positions to +3 and +4 in the promoter distal region of the operator, it would be anticipated that cross-links similar to the +3 and +4 positions would form at these sites; this prediction is not borne out by the behavior at +4/+18, as no peptide could be identified cross-linked to DNA substituted at +4. Molecular dynamics simulations and the NMR data indicate that Tyr-17 interacts with the thymine at position +8, which is symmetrically related to position +14. Although BrdU-associated strand scission at +8 is protected, this site does not cross-link with bound lac repressor; inversely, DNA substituted with BrdU at +14 cross-links to repressor, but is not protected from strand scission by the presence of the protein. These differences at symmetrically related nucleotide positions (+4 versus +18, +8 versus +14) reflect the inherent asymmetry in the interaction. The identification of amino acids in proximity to specifically substituted sites confirms that positions of several amino acids in the intact protein-operator complex correspond to those in the structure of the NH2-terminal headpiece-operator DNA complex.

Amino Acid Sequence↗
PubMed1991

Resolution of vesicoureteral reflux in completely duplicated systems: fact or fiction?

A total of 60 patients (71 renal units) with grade 2/5 vesicoureteral reflux into the lower pole moiety of a completely duplicated system was managed by medical surveillance and is compared to an identically managed age, race and sex matched control population with a similar degree of reflux into a single collecting system. During a median 2-year observation period reflux ceased spontaneously in 10% of the patients with duplication compared to 35% of the control population (p less than 0.01). Comparisons between the 2 study groups failed to reveal a difference in the incidence of break-through urinary tract infections, advancing degrees of reflux and/or the development or progression of renal scarring (p greater than 0.5). Despite the fact that the resolution rate in duplex systems is significantly lower than that of a single system, it is apparent that cessation of grade 2/5 reflux into a duplicated ureter will occur and that a trial of medical management is an appropriate initial method of therapy.

Actuarial Analysis↗
PubMed1991

Cloacal anomalies and other urorectal septal defects in female patients: a spectrum of anatomical abnormalities.

The anatomy and management of 16 female patients with urorectal septal defects have been reviewed. The diagnosis was often confused by the anomalous appearance of the external genitalia, and the internal arrangements of the urinary tract, genital tract and lower intestinal tract were frequently bizarre and unpredictable. Because of the potential of these patients for secondary infection and sepsis, a prompt and thorough anatomical evaluation in such cases is essential. Initial treatment should be directed toward decompression of the involved organ systems and definitive reconstruction should be deferred until the child is older, at which time the emphasis should be upon a simultaneous multisystem repair performed, whenever possible, in 1 stage.

Abnormalities, Multiple↗
PubMed1991

Ultrastructural and morphometric alterations in bone marrow stromal tissue after 7 Gy irradiation.

To evaluate the response of marrow stroma to 7 Gy irradiation, femoral bone marrow was fixed by vascular perfusion (so as to avoid the artificial destruction of sinus endothelia), and was examined using light and electron microscopy with morphometric methods. The radiation caused a marked decrease in hematopoietic cell number (NHC) within 3 days post-irradiation, followed by total recovery of hematopoiesis, which occurred gradually over 28 days. An increased number of fat cells was seen by 7 days. During the whole course of hypoplasia and recovery, the continuity of sinus wall, three-dimensional reticular mesh work in hematopoietic parenchyma, gap junctions (GJ) between stromal cells, the adventitial cell cover of sinus wall (ACC), and the stromal cell numbers of reticular cells (RC), sinus endothelia (SE), and macrophages (MP) were maintained. The cellularity of stromal components of RC, SE, and MP seemed passively increased in contrast to a reduction in numbers of NHC. A similar tendency was observed (1) between NHC and ACC and (2) between GJ and the cellularity of fat cells, which had a statistical significant correlation (p less than 0.05; t-test). The mechanism of radio resistance in bone marrow stroma and the possible functional adaptation and cellular coordination after irradiation are discussed.

Adipose Tissue↗