PubMed Health⌕ Search

Biomedical subjects

D Greenstein

Publications and source records attributed to D Greenstein.

At least 37 records · Page 2Linked to original sources
PubMed1995

Impaired thermoregulation in Raynaud's phenomenon.

UNLABELLED: In an attempt to examine the role of the thermoregulatory apparatus in the etiology of Raynaud's phenomenon (RP), the authors exposed 15 women with RP and 12 controls to central body cooling and central body warming. Subjects were placed in an environmental chamber at 25 degrees C. Their right hand was placed in an annex of the chamber, which was insulated from the main chamber and maintained at a constant temperature of 25 degrees C throughout the experiment. Blood flow was measured in the digits of the right hand by venous occlusion strain gauge plethysmography and skin thermometry. Body temperature was measured with an oral thermometer. The temperature of the chamber was then increased to 35 degrees C and then reduced to 13 degrees C for twenty-five minutes with measurements repeated. Following this period patients were rewarmed in an ambient temperature of 35 degrees C for twenty minutes. RESULTS: subjects with RP had significantly lower blood flow at all stages of the test; moreover, their digital rewarming response following central cooling was considerably prolonged when compared with controls. Body temperature was lower and dropped significantly more in the RP group following the cold challenge. The authors conclude that subjects with RP have an impaired thermoregulatory mechanism. This may partially explain cold sensitivity.

Adult↗
PubMed1994

Targeted mutations in the Caenorhabditis elegans POU homeo box gene ceh-18 cause defects in oocyte cell cycle arrest, gonad migration, and epidermal differentiation.

We used targeted gene inactivation to analyze the function of a Caenorhabditis elegans POU gene, ceh-18, and to dissect its functional domains in vivo. In ceh-18 mutants, oocytes exhibit an incompletely penetrant failure to arrest in diakinesis of meiotic prophase I and instead undergo multiple rounds of DNA replication without cytokinesis. ceh-18 is expressed in the gonadal sheath cells that signal the oocyte, but not in the oocyte. This suggests that ceh-18 affects, directly or indirectly, a sheath cell signal that causes oocytes to maintain diakinesis arrest. ceh-18 also participates in directing gonad migration and in specifying the differentiated phenotypes of epidermal cells during postembryonic development. Analysis of targeted deletions that disrupt half of the POU domain selectively by deleting either the POUhd or the POUsp alone, indicates that each CEH-18 POU subdomain is sufficient for partial activity in vivo.

Amino Acid Sequence↗
PubMed1994

Multiple DNA conformational changes induced by an initiator protein precede the nicking reaction in a rolling circle replication origin.

The core origin for plus strand DNA replication of filamentous bacteriophage f1 binds the initiator protein (gpII), which subsequently introduces a specific nick in the plus strand. The core origin consists of a nicking region and a binding region. The binding of gpII occurs in two steps, forming a binding intermediate (complex I) and a functional complex for nicking (complex II). Results of gel retardation experiments using circularly permuted DNA fragments and direct visualization by electron microscopy show that gpII induces successive bends within the binding region upon formation of the complexes. We show that gpII binding induces duplex melting in the nicking region using KMnO4 modification of unpaired thymidine residues as a probe for melting. Origin binding occurred in the absence of superhelicity of DNA and Mg2+, whereas duplex melting required superhelical DNA, but not Mg2+. Deletion analyses indicated that hypothetical formation of a cruciform around the nicking site is not necessary for either melting or nicking. A mutation in gpII resulted in stimulation of duplex melting and nicking without showing obvious effects on bending. This suggests that the mechanism of melting involves local interaction between gpII and the nicking region. Furthermore, using synthetic oligonucleotide substrates, we show that the nicking reaction takes place efficiently when the nicking region is single-stranded and the binding region is double-stranded. These results indicate that the nicking reaction is preceded by an ordered series of protein-induced DNA-conformational changes: successive bending of the origin upon gpII binding, followed by duplex melting that requires negative superhelicity.

Base Sequence↗
PubMed1994

Assessment of chemical lumbar sympathectomy in critical limb ischaemia using thermal imaging.

Objective assessment of chemical lumbar sympathectomy (CLS) is lacking. Its success is usually judged in terms of the patient's clinical improvement. We have thermographically measured the immediate temperature changes of the lower limb following CLS using a thermal imager (SAN-EI Thermotracer 6T61). Seven patients with critical limb ischaemia and one patient with Raynaud's phenomenon underwent unilateral ablation of the lumbar sympathetic chain using 5% phenol. Four patients were diabetic, two of whom had undergone previous sympathectomy on the same side. Within fifteen minutes of injection, all patients showed a rise in skin temperature in parts of the sock distribution of between 0.8 degrees C and 8.5 degrees C. We conclude that the haemodynamic effects of CLS are immediate and can be objectively measured with thermal imaging.

Aged↗
PubMed1994

Liver hemorrhage: recurrent episodes during pregnancy complicated by preeclampsia.

Intrahepatic hemorrhage with rupture is the most serious and potentially life-threatening liver complication of pregnancy. With improved management, more patients are surviving this complication, and therefore, a number of patients are at risk of a recurrence should they again become pregnant. This case describes a patient who suffered two episodes of intrahepatic hemorrhage in two different pregnancies. Each episode was associated with mild preeclampsia. The first hemorrhage was limited by the liver capsule and treated conservatively, whereas with the second hemorrhage, the subcapsular hematoma ruptured, requiring arterial embolization followed by surgery. An arteriogram performed during the second episode of hemorrhage showed numerous pseudoaneurysms in the area of bleeding, suggesting that a vasculopathy plays a primary role in the pathogenesis of the intrahepatic hemorrhage associated with pregnancy. This case shows that intrahepatic hemorrhage may recur with future pregnancies, and individuals who suffer this complication of pregnancy and again become pregnant should be carefully monitored for the development of preeclampsia.

Adult↗
PubMed1994

Systemic heparinization during peripheral vascular surgery: thromboelastographic, activated coagulation time, and heparin titration monitoring.

Fifteen patients (9 male, 6 female) undergoing peripheral vascular surgery were monitored during surgery for evidence of subclinical anticoagulation using the activated coagulation time (ACT), thromboelastography (TEG), and heparin titration monitoring. Assessments were made at 30-minute intervals before and after the occlusion clamp. Mean (+/- SD) ACT values preoperatively were 111 (17) seconds, and 10 minutes after 5,000 IU of heparin, the ACT was 264 (57) seconds (P < 0.001). Intraoperatively, there was a significant decline in ACT values at 30 minutes (ACT 228 [50] sec, P < 0.005) and 60 minutes (200 [46] sec, P < 0.001) postheparin. No significant difference in ACT was observed between samples drawn distally and proximally to the clamp. TEG profiles were abolished in all patients immediately following heparinization. However, in 2 patients nearly complete return of the TEG coagulation profile was observed prior to the termination of the procedure and was associated with ACT values less than 160 seconds. The heparin device was unable to accurately monitor heparin elimination at these low doses. Variability of patient response to heparinization necessitates the use of intraoperative monitoring of anticoagulation during peripheral vascular surgery.

Aged↗
PubMed1994

The cold hemiplegic arm.

BACKGROUND AND PURPOSE: Vasomotor changes occur in the arm after hemiplegic stroke. Previous studies have provided conflicting results, with most showing an increase in skin temperature of the hemiplegic arm. However, a number of patients complain of distressing coldness of the hemiplegic arm. METHODS: Eleven patients with symptomatic coldness and 10 patients with hemiplegia but no coldness were recruited. The severity of the symptom of coldness was compared by questionnaire with other common symptoms after stroke. A thermographic camera was used to record the finger skin temperature response to cold stress. Blood flow to both hands was also measured simultaneously by means of two plethysmographs. In all patients there were no symptoms in the unaffected arm, and this was used as a control. RESULTS: The symptom of coldness rated highly compared with other symptoms. In the symptomatic group the finger temperature on the hemiplegic side was lower at rest (median difference at rest, 0.65 degrees C; P < .0001) and at all times after cold stress. In the asymptomatic group the fingers on the hemiplegic side were colder at rest and after initial cooling (median temperature difference, 0.2 degrees C) but at no other time. Hand blood flow on the hemiplegic side was also decreased in the symptomatic group by 35%. This was not seen in the asymptomatic group. CONCLUSIONS: Coldness of the hand may be a severe and distressing symptom in some patients after hemiplegia. Symptomatic patients have lower finger skin temperatures at rest and after standard cold stress. These symptomatic patients also had reduced blood flow to the hemiplegic hand.

Aged↗
PubMed1994

Perfusion defects in vibration white finger: a clinical assessment using isotope limb blood flow.

Vibration white finger is a vasospastic disorder caused by long-term exposure to vibration tools. In an attempt to assess the extent of obliterative vessel disease in this disorder, hyperaemic hand blood flow was measured using technetium-labelled human albumin and a gamma camera. This method quantitates blood flow in ml/100 ml of tissue per min in addition to providing a perfusion image used to assess vessel disease. A perfusion score is then given to this image to reflect the extent of disease. The results of this study demonstrate that 78% of patients with vibration white finger had evidence of organic vessel disease. Moreover, patients with advanced disease tend to be bilaterally affected. The use of this simple method is advocated to aid in the diagnosis of vibration white finger; this may be particularly important for medicolegal purposes.

Adult↗
PubMed1993

Spontaneous and induced differentiation of human melanoma cells.

Malignant melanoma cells can differentiate spontaneously in vivo and in vitro into cells with a finite lifespan. Analysis of differentiating cells from primary melanomas in culture revealed a flat, fibroblast-like morphology and expression of the fibroblast-associated marker leucine aminopeptidase (LAP). Differentiation was also observed in a minor sub-population of permanent cell lines derived from metastatic lesions. An experimental model of melanoma cell differentiation was then developed, using the pyrimidine analog bromodeoxyuridine (BUdR). BUdR-treated cells had a flat morphology, were contact-inhibited, had up to 20-fold increased surface area, expressed LAP, no longer proliferated anchorage-independently in soft agar, and 3 out of 4 cell lines were non-tumorigenic in athymic nude mice. Our results show that models of differentiation of melanoma cells can be established that help to define pathways of differentiation.

Animals↗
PubMed1992

A single amino acid substitution reduces the superhelicity requirement of a replication initiator protein.

The origin of rolling circle replication in filamentous coliphage consists of a core origin that is absolutely required and an adjacent replication enhancer sequence that increases in vivo replication 30 to 100-fold. The core origin binds the initiator protein (gpII) which either nicks or relaxes negatively superhelical replicative form DNA (RFI). Nicking at the origin, but not relaxation, leads to initiation of DNA replication. Our results indicate that the ratio of nicking to relaxation (nicking-closing) in vitro depends on the superhelical density of the substrate. We have studied the effect of a single amino acid substitution in gpII, which allows wild-type levels of replication in the absence of the enhancer, on origin nicking and binding. The enhancer-independent mutation yields more nicking and less relaxation of RFI, compared to the wild-type protein. The mutant gpII also shows a reduced requirement for superhelicity of the substrate in the nicking reaction. At the same time, the mutant gpII increases the cooperativity of protein-protein interactions in origin binding. We propose that the relaxation activity of gpII negatively regulates replication initiation, and that both increase in the negative superhelicity of the substrate and action of the replication enhancer may antagonize the relaxation activity.

Amino Acid Sequence↗
PubMed1992

Growth-factor-independence and invasive properties of colorectal carcinoma cells.

During serial passage of the colorectal carcinoma cell line SW1116 in athymic nude mice, we selected 2 variants that metastasized to the lungs and liver. The metastatic capacity of these in vivo variant cell lines was associated with their ability to (1) grow under growth-factor-deprived conditions, (2) invade and transgress a reconstructed basement membrane with high effectiveness, and (3) produce higher activities of the substrate-degrading enzymes collagenase and plasminogen activator as compared to parental cells. To assess the relative contribution of growth-factor-independence and high levels of invasiveness/motility to the metastatic phenotype, variants of 6 colorectal carcinomas were selected in vitro by adaptation to a growth-factor-free culture medium followed by selection of highly invasive cells in chemoinvasion assays. Four out of 6 cell lines selected for growth-factor-independence showed significantly higher levels of invasiveness through reconstructed membranes, suggesting co-segregation of growth-factor-independence and high levels of invasiveness in vitro. Using an in vitro chemoinvasion assay, 2 poorly and 1 highly invasive cell line were further selected for invasiveness. After 6 selection passages, all cell lines were highly invasive and showed high motility rates. However, when injected s.c. into athymic nude mice to test their metastatic capacity in vivo, double-selected variant cell lines did not form spontaneous metastases. Our results indicate that growth-factor-independence and high levels of invasiveness, although associated with the metastatic phenotype, are not sufficient for experimental metastasis formation of colorectal carcinoma cells in vivo.

Animals↗
PubMed1992

Acute vibration--its effect on digital blood flow by central and local mechanisms.

In order to establish underlying mechanisms responsible for the vasospastic disorder vibration white finger (VWF), the acute effect of vibration on digital blood flow was assessed. Thirteen patients with primary Raynaud's phenomenon (RP), 15 patients with WVF and 13 controls were exposed to acute vibration in the middle digit of one hand for 1 and 3 minutes. Blood flow was measured in that digit and in the middle finger of the contralateral hand using strain gauge plethysmography before and after vibration. The measurements were then repeated following digital nerve blockade using 2% Lignocaine in the vibrated digit. The results demonstrate that vibration affects digital blood flow through two independent mechanisms. Vibration appears to cause both an axonal vasoconstrictor reflex and an active local vasodilation phenomenon. In patients with established vasospastic disorders this vasoconstrictor reflex is exaggerated.

Adult↗
PubMed1992

Is antibiotic penetration compromised in the ischaemic tissues of patients undergoing amputation?

Antibiotic prophylaxis is indicated for patients undergoing amputation for severe ischaemia or gangrene. However, the adequacy of tissue levels of antibiotics in ischaemic tissue is not known. In this study the serum and tissue antibiotic levels were measured after intravenous administration of metronidazole (15 mg/kg body weight) and cephradine (20 mg/kg body weight). In 11 patients, venous samples were taken at time 0 (induction of anaesthesia) 10, 30 and 60 min. Samples of 2 g each of fat and muscle were collected from the amputation site and three distal sites. Metronidazole and cephradine levels were measured and the degree of limb ischaemia estimated preoperatively by an isotope limb blood flow method. Our results indicate that both metronidazole and cephradine penetrate ischaemic tissues to levels equivalent of a Mean Inhibitory Concentration (MIC) 50 for most organisms encountered in vascular surgery, and that the degree of ischaemia does not alter this.

Aged↗
PubMed1991

The assembly of functional preinitiation complexes and transcription of 5S RNA-encoding genes containing point mutations.

The transcription of several Syrian hamster 5S RNA-encoding genes (5S genes) containing single and multiple point mutations in and around the intragenic control region has been analyzed in a HeLa cell-free system. Although most genes with point mutations displayed normal levels of transcription, several exhibited a three- to fivefold reduction in transcription. These mutations interfere with the interaction between the 5S genes and the soluble factors. The above studies help to establish the importance of specific nucleotides within the 5S gene for productive interactions of individual transcription factors in vitro.

Animals↗
PubMed1990

Replication enhancer-independent mutation increases the co-operativity with which an initiator protein binds its origin.

The plus-strand replication origin of bacteriophage fl has a bipartite structure consisting of a required core origin region and an adjacent A + T-rich enhancer sequence that potentiates replication approximately 100-fold. The core origin binds the initiator protein (gpII) and the enhancer binds the Escherichia coli integration host factor (IHF). gpII binds the core origin in two steps, forming a binding intermediate (complex I) and a functional complex for nicking (complex II). We have used a double-label gel binding assay to determine the stoichiometry of the gpII-origin interaction. The results indicate that complex I contains two gpII molecules per origin, and complex II contains four gpII molecules per origin. Enhancer-independent mutations in gpII allow wild-type levels of replication in the absence of either the enhancer or IHF. We have examined the binding of an enhancer-independent gpII mutant (mp1) protein to the replication origin. The mp1 mutation in gpII (Met40----Ile) increases the co-operativity with which the protein binds to form complex II. In addition, the mutant gpII forms both complexes with a DNA fragment containing only two (beta-gamma) of the three repeats from the core origin sequence, while the wild-type protein forms only complex I with this fragment. We discuss how a mutation that increases the co-operativity of binding of an initiator protein might stimulate DNA replication.

Base Sequence↗