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Biomedical subjects

D P O'Brien

Publications and source records attributed to D P O'Brien.

At least 91 records · Page 5Linked to original sources
PubMed1991

Descending thoracic aorto-bifemoral bypass graft: a safe alternative in the high risk patients.

A fifty-nine year old male presented with disabling intermittent claudication. A Translumbar Aortogram was performed showing ".....total occlusion of the abdominal aorta just distal to the level of the renal arteries". As a direct result of this invasive radiological procedure, he subsequently developed acute pancreatitis and a pancreatic abscess necessitating open surgical drainage. Re-vascularisation of his aortic occlusion was deferred for fifteen months when a Descending Thoracic Aorta Bifemoral (DTAB) bypass was performed--thus avoiding the insertion of foreign, sterile, arterial prosthesis in a previously infect abdominal cavity.

Acute Disease↗
PubMed1990

Fecal incontinence, urinary incontinence, and priapism associated with multifocal distemper encephalomyelitis in a dog.

A 4-year-old castrated mixed-breed dog had atypical signs of chronic distemper encephalomyelitis. The predominant signs were related to visceral rather than somatic dysfunction. The visceral dysfunction was largely attributable to distemper-associated inflammatory lesions in the spinal cord and resulted in fecal incontinence, urinary incontinence, and priapism. Empirical treatment of the dog resulted in transitory improvement prior to euthanasia performed because of the progressive nature of the encephalomyelitis.

Animals↗
PubMed1990

Characterization of a panel of monoclonal antibodies to human coagulation factor XI and detection of factor XI in Hep G2 cell conditioned medium.

We have produced a panel of ten monoclonal antibodies specific to coagulation factor XI. Western blot analysis demonstrates that 9 of these antibodies react with the heavy chain of factor XI and one with the light chain. Seven of these antibodies inhibit factor XI and factor XIa activity. We have used immobilised monoclonal antibody for the production of factor XI deficient plasma and to purify factor XI to homogeneity with high yield in a simple two-step procedure. These monoclonal antibodies were used to develop highly sensitive immunoassays capable of detecting less than 0.01 mu factor XI antigen ml-1. A strong correlation was found between antigen and activity levels in 11 patients with hereditary deficiency indicating that none was cross-reacting material positive. Cultured Hep G2 cells were found to synthesize small amounts of factor XI antigen and this could also be detected by functional assay and by western blot analysis.

Animals↗
PubMed1990

Purification and characterization of factor VIII 372-Cys: a hypofunctional cofactor from a patient with moderately severe hemophilia A.

We have purified factor VIII from a patient with moderately severe hemophilia A (FVIII, 4 U/dL; FVIII:Ag, 110 U/dL) and subjected the protein to Western blot analysis after time course activation with thrombin. The cross reacting material-positive (CRM+) FVIII has the normal distribution of heavy and light chains before thrombin activation, and, after incubation with the enzyme, appropriate cleavages are made at positions 740 and 1689. However, the normal thrombin cleavage at position 372 in the heavy chain of this molecule does not occur. This result is consistent with the demonstration in the patient's leukocyte DNA of a C to T transition in codon 372, leading to the substitution of a cysteine for an arginine residue at the heavy chain internal cleavage site. The severely impaired functional activity of this molecule confirms that the heavy chain of FVIII must be proteolysed in order to effect full cofactor activation in vivo. However, a threefold activation was detected when this protein was incubated with thrombin. No evidence of thrombin-mediated cleavage at position 336 in the heavy chain was detected, in contrast to the variant recombinant B domainless-molecule, FVIII 372-Ile, described by Pittman and Kaufman (Proc Natl Acad Sci USA 85:2429, 1988). Using gel permeation studies of the FVIII/von Willebrand factor (vWF) complex before and after thrombin activation, we have demonstrated that the 40 Kd A2 domain of wild type FVIII dissociates from vWF after cleavage by the enzyme. In contrast, incomplete dissociation was detected in the case of FVIII 372-Cys. We conclude that the functional defect in FVIII 372-Cys is a consequence of the resistance to proteolysis of the internal scissile bond in the heavy chain.

Amino Acid Sequence↗
PubMed1990

The warm knee sign--an evaluation.

The presence of an area of warmth at the knee has been described in cases of arterial occlusion at the popliteal fossa. A study was carried out to evaluate the significance of this sign by comparing clinical and thermographic findings with arteriographic results in a group of 30 patients. The clinical and thermographic findings were described with reference to the symptomatic limb. Clinically, 14/30 (47%) and thermographically, 16/30 (53%) had "positive" warm knee signs. The overall agreement between clinical impressions and thermographic findings was 28/30 (93%). The commonest arteriographic finding in patients with a positive warm knee sign was that the occlusion or stenosis ended at the adductor hiatus. Comparing this arteriographic finding with a positive warm knee sign, sensitivity, specificity, positive and negative predictive values of 73%, 75%, 79% and 69% respectively were obtained suggesting that this is a useful sign, is of proven value and deserves its place in the initial screening of patients with peripheral vascular disease.

Aged↗
PubMed1989

Purification of recombinant human tissue factor.

Tissue factor (TF) is a 263 amino acid membrane-bound procoagulant protein that serves as a cofactor for the serine protease factor VII (fVII). Recombinant human TF (rTF) produced in both human kidney 293 cells and Escherichia coli has been immunoaffinity purified by using a TF-specific monoclonal antibody. Recombinant TF produced in 293 cells is glycosylated and migrates on reducing SDS-PAGE with an apparent molecular weight (Mr) of 45K. Some interchain disulfide-bonded rTF dimers are observed under nonreducing conditions. The E. coli produced rTF has a molecular weight of 33K and 35K, with the 33K band missing nine amino acids at the carboxy terminus. Although the E. coli produced rTF does not contain any carbohydrate, it is fully functional in both a chromogenic assay and a one-stage prothrombin time assay. A variant has been constructed wherein the cytoplasmic cysteine (residue 245) has been mutagenized to a serine residue. The amount of disulfide-linked aggregates is dramatically reduced following immunoaffinity purification of this four-cysteine variant (C2455), which is active in the chromogenic and prothrombin time assays.

Amino Acid Sequence↗
PubMed1989

Reasoning about conditional sentences: development of understanding of cues to quantification.

The previous literature has reported that when children are asked to judge the truth or falsity of universally quantified conditional sentences of the form If a thing is P then it is Q they typically give responses, e.g., responding "true" whenever there is a case of P and Q even if there are also cases of P and not-Q. Three experiments are reported that address possible sources of this error. Experiment 1 shows that the error survives on sentences that refer to particular things as well as to things of a particular kind, and further shows that articulating the necessity of the consequent (... then it has to be Q) eliminates the error for adults and reduces it for fifth graders, although it does not affect second grade performance. Experiment 2 shows that for second and fifth graders the error survives to problems that are not universally quantified and for second graders to problems that are not conditionals although are otherwise structurally similar. Experiment 3 compares various verbal formulations of such universally quantified conditionals: Second and fifth graders do not make the error when the quantification is expressed with the surface structure that makes its universality most explicit (all things ...); the error tendency is greatest when the indefinite article is used (if a thing ...); and formulations using any fall in between. We argue that such erroneous evaluations of universally quantified conditionals have more to do with the quantificational aspect than the conditional aspect of the problems; children interpret the indefinite article as existential, although they resist the error when the cue to universal quantification is completely clear. The error appears to result more from the surface-structure form of the stimuli than from an inability of children to appreciate the logic of universally quantified conditionals.

Adolescent↗
PubMed1989

Use of limited retroperitoneal lymphadenectomy in nonseminomatous germ cell tumors.

In an attempt to prevent ejaculatory dysfunction associated with retroperitoneal lymphadenectomy, the dissection has been modified to stay above the inferior mesenteric artery. Using this approach, there has been no adverse impact on survival (at least 18 months follow-up) in 18 patients with nonseminomatous germ cell tumors.

Ejaculation↗
PubMed1989

The molecular biology and biochemistry of tissue factor.

The cloning of tissue factor (TF) cDNAs has recently been carried out which has allowed the characterization of this cellular receptor for factor VII. The predicted primary structure indicates that it is a multidomain protein comprised of a hydrophilic extracellular domain, a membrane spanning structure and a cytoplasmic region. Post-translational modifications include four potential N-linked glycosylation sites of which three are occupied. There is evidence that the intracellular cysteine residue is thioester-linked to palmitic acid, and that this could enhance the anchoring of the receptor to the membrane. The four remaining cysteine residues are located in the putative extracellular domain and appear to form two intramolecular disulphide bonds. There is no significant homology between TF and any other published protein sequence in current databases. There is evidence that TF is the primary initiator of the coagulation cascade. Early models of coagulation tended to assign TF to a subordinate role, but now it is widely accepted that the extrinsic pathway is critical as TF/FVIIa activates both FX and FIX. It has been reported that zymogen FVII has catalytic activity and this would indicate that the simple complexing of FVII and TF is sufficient to initiate coagulation without an infinite regression of proteolytic events. Many cell types synthesize TF constitutively but, significantly, endothelial cells do not normally express TF on their surfaces, consistent with a quiescent haemostatic system. Recently a number of agonists known to be thrombogenic in vivo have been shown to induce de novo synthesis of TF by endothelial cells. TF thus operates at two levels: exposure of the subendothelium to blood results in the binding of FVII to TF and consequently to clot formation, and induction of TF synthesis by a variety of agonists results in the intact endothelium becoming procoagulant. In concert with TF expressed by monocytes and macrophages this endothelial cell procoagulant activity may play a role in the pathogenesis of thrombotic disease.

Amino Acid Sequence↗
PubMed1989

Purification and characterization of factor VIII 1,689-Cys: a nonfunctional cofactor occurring in a patient with severe hemophilia A.

We have purified the factor VIII from a CRM+ Hemophilia A plasma (90 U/dL VIII:Ag but 0 U/dL VIII:C) and analyzed the protein before and after thrombin activation by Western blotting with monoclonal antibodies (MoAbs). Normal or patient citrated plasma was ultracentrifuged, cryo-ethanol-precipitated and chromatographed on Sepharose 6B. The void volume fractions were reduced and subjected to ion exchange chromatography yielding material of specific activity approximately 1,000 U/mg protein (VIII:C or VIII:Ag). Factor VIII purified in this way from normal plasma is fully activatable by thrombin with proteolytic fragmentation as previously described by F. Rotblat et al (Biochemistry 24: 4294, 1985). Factor VIII 1,689-Cys has the normal distribution of factor VIII light and heavy chains prior to thrombin activation. After exposure to thrombin the heavy chain polypeptides were fully proteolysed but the light chain was totally resistant to cleavage. This is consistent with the demonstration in the patient's leucocyte DNA of a C to T transition in codon 1,689 converting Arg to Cys at the light chain thrombin cleavage site as previously described by J. Gitschier et al (Blood 72:1022, 1988). Uncleaved light chain of Factor VIII 1,689-Cys is not released from von Willebrand factor (vWF) by thrombin, but this is not the sole cause of the functional defect since the protein purified free of vWF has no coagulant activity. We conclude that the functional defect in factor VIII 1,689-Cys is a consequence of failure to release the acidic peptide from the light chain upon thrombin activation.

Antibodies, Monoclonal↗
PubMed1988

Diagnosis of dysautonomia in a cat by autonomic nervous system function testing.

Clinical signs of dysautonomia, including dilated pupils, dry mucous membranes, and megaesophagus, were observed in a cat. The diagnosis was confirmed by use of autonomic nervous system function testing including 0.1% pilocarpine and physostigmine ocular response tests, plasma catecholamine assays, and cardiovascular responses to various perturbations intended to elicit autonomic responses. The cause of the autonomic dysfunction was not ascertained, and the cat was euthanatized after 5 weeks of unsuccessful treatment with pilocarpine, metoclopramide, prochlorperazine, and parenteral nutrition.

Animals↗
PubMed1988

Escalation of feline predation along a gradient from avoidance through "play" to killing.

In this article, we show that feline predation involves a continuous gradient of activation between defense and attack and that predatory "play" results from an interaction of the two. Benzodiazepines (oxazepam, diazepam) escalated attack toward killing, so that cats that had avoided mice prior to the drug now played with them, cats that had originally played now killed, and cats that killed mice now did so with less preliminary contact. In such shifts, no sharp demarcation between play and predation was evident. Lateral hypothalamic lesions disrupted the escalation of attack. During recovery, attack was escalated once again along the gradient toward killing, but in the absence of both defense and play. A similar result was obtained in intact killers and nonkillers by the application of mild tail pinch. These results suggest that play with prey is a misnomer for predatory behavior that fails to escalate along the gradient between defense and attack. Movement notation analysis revealed that playful movements are adaptive in that they protect the cat from injury.

Aggression↗
PubMed1988

Factor VIII-bypassing activity of bovine tissue factor using the canine hemophilic model.

The bleeding disorder of hemophilia A currently treated by replacement therapy of the missing coagulation factor, factor VIII, is frequently complicated by the development of neutralizing antibodies. The therapeutic potential of attenuated forms of the lipid-associated glycoprotein tissue factor, a known initiator of coagulation, was investigated as a factor VIII-by-passing activity. The protein moiety of tissue factor (Apo-TF) was partially purified and exhibited minimal procoagulant activity before relipidation in vitro. In pilot studies, Apo-TF injection into rabbits previously anticoagulated with an antibody to factor VIII was found to have a procoagulant effect. The efficacy of the material was further demonstrated when injection of Apo-TF in hemophilic dogs resulted in a normalization of the cuticle bleeding time. Little or no change in the blood parameters associated with disseminated intravascular coagulation was observed at lower doses, although mild to moderate effects were seen at higher doses. These data suggest a novel role for Apo-TF preparations as a potential therapeutic agent for hemophiliacs with antibodies to factor VIII once the potential thrombogenicity of such materials is evaluated.

Animals↗
PubMed1987

Inhibition of non-dopamine cells in the ventral tegmental area by benzodiazepines: relationship to A10 dopamine cell activity.

Previous electrophysiological studies have demonstrated that non-dopaminergic (non-DA) neurons within the substantia nigra pars reticulata (SNR) are extremely sensitive to the inhibitory effects of GABA and GABA-mimetic drugs, including benzodiazepines, whereas dopaminergic (DA) neurons in the substantia nigra pars compacta (SNC) are less sensitive to these compounds and may be influenced indirectly by SNR neurons. The interactions between A10 DA and non-DA neurons within the adjacent ventral tegmental area (VTA) are not as well characterized. In the present experiments, single unit recording and microiontophoretic techniques were used to determine the effects of benzodiazepines on DA and non-DA neurons in the VTA of chloral hydrate anesthetized rats. Diazepam, administered intravenously (i.v.), potently inhibited non-DA, SNR-like cells within the VTA. The effects of diazepam on A10 DA cells were more variable than those observed on non-DA, SNR-like cells in this region, but 77% of such cells showed moderate to marked excitation. Both of these effects were reversed by the benzodiazepine antagonist Ro 15-1788; on many cells, this agent produced marked rebound effects beyond the original basal firing rates. However, when administered alone, Ro 15-1788 exerted no effect on either cell population. Microiontophoretic administration of the benzodiazepines chlordiazepoxide and flurazepam resulted in marked inhibition of non-DA SNR-like cells, but produced either mild inhibition or no effect on A10 DA cells; excitation of DA cells was never observed even though the same neuron was excited by i.v. diazepam. These findings suggest that benzodiazepines act directly upon non-DA, SNR-like cells in the VTA to produce inhibition of activity and a disinhibition of A10 DA cells. This relationship makes it unlikely that benzodiazepines would enhance feedback inhibition of DA cells following neuroleptic administration. In fact, when administered following haloperidol, i.v. diazepam failed to reverse haloperidol-induced increases of A10 DA cell firing; if anything, diazepam further depolarized the cell. If antipsychotic drugs produce their clinical effects, in part, by inducing depolarization inactivation of DA cells, then benzodiazepines might be a useful adjunctive therapy in the treatment of schizophrenia.

Animals↗