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Biomedical subjects

M Risk

Publications and source records attributed to M Risk.

At least 19 recordsLinked to original sources
PubMed2001

Heart rate variability measurement in diabetic neuropathy: review of methods.

Heart rate variability (HRV) is an important tool to analyze the autonomic function. It therefore has a special interest for early detection and ensuing treatment of autonomic neuropathy in diabetic patients. The aim of this work is to present a brief historical review of HRV, as well as a technical review of the most common methods to measure it. In this work is presented a system that performs three measurements of HRV. An overview of methodologies developed to quantify HRV is presented; this technical review covers the most common time and frequency domain techniques, for short and long periods of time, with comments about clinical utility of these tests. A system performing three standard tests of HRV, Anscore Health Management System, is presented. This system performs metronomic breathing (MT), the Valsalva Test (VT), and the Stand Test (ST). A normal range study with 212 healthy subjects in three centers (ages 20-80 years, with even age distribution, and even male and female distribution) was conducted. A subset of 45 subjects from the total number of subjects was selected for the reproducibility study, consisting of three measurements of each test. The normal range study showed a decrease in all the ratios with age and, for the Valsalva test, a difference among genders; 5th percentiles were calculated. The reproducibility study results, expressed as mean CV%, were 4.30% for the MT, 6.26% for the VT, and 6.66% for the ST. HRV is the most reliable measurement of autonomic function; when controlled maneuvers like MT, VT, and ST are performed, high reproducibility is obtained, with results comparable to that observed for nerve conduction studies. Such reproducibility makes autonomic function testing more feasible as a test component in multicenter studies of different neurological disorders.

Adult↗
PubMed1998

Establishment and characterization of a simian virus 40-transformed temperature-sensitive rat luteal cell line.

The primary culture of rat luteal cells and their long-term maintenance have been difficult. Low cellular yields have limited the possibility for the study of gene regulation in luteal cells. The goal of this study was to develop a cell line to serve as a model by which to study the expression and regulation of various genes specific to luteal cells. We attempted to develop a luteal cell line by transformation of large luteal cells through infection with a temperature-sensitive simian virus (SV-40 tsA209) mutant that has a temperature-sensitive mutation required for the maintenance of cell transformation. We report here the successful establishment of such a cell line, designated GG-CL cells. Large luteal cells were purified to homogeneity by flow cytometry from corpora lutea of day 14 pregnant rats, cultured for 24 h, and then infected with the SV-40 tsA209 mutant virus. Transformed cells were maintained at the permissive temperature (33 C) until colonies were identified. Several colonies of transformed cells were isolated and passaged. They multiplied at 33 C and formed multilayers. At the nonpermissive temperature (40 C), cells reverted to the normal differentiated phenotype similar to the primary luteal cells in culture. To determine whether GG-CL cells express the genes found in normal luteal cells, messenger RNA (mRNA) expression was examined by either Northern analysis or RT-PCR with primers specific to each mRNA. GG-CL cells were found to express receptors for interleukin-6 and glucocorticoid, as well as the newly discovered estrogen receptor-beta (ER-beta) and the orphan nuclear receptor nur 77. No receptors for ER-alpha, progesterone, LH, or PRL could be detected. This cell line also expressed 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), but not cholesterol side-chain cleavage cytochrome P450 (P450scc), 3beta-hydroxysteroid dehydrogenase, or aromatase cytochrome P450 (P450arom). Although the cells did not express the PRL receptor, they did express Janus kinase (JAK2) and signal transducers and activators of transcription (Stat5b), and, when transfected with the PRL receptor, they responded to PRL with a marked inhibition in 20alpha-HSD mRNA expression. In addition, estradiol enhanced ER-beta expression in a dose-dependent manner whereas cAMP stimulation caused a marked and rapid increase in the expression of the orphan receptor nur 77. In summary, a temperature-sensitive cell line was successfully established from the large luteal cells of rat corpora lutea. These cells express key genes encoding enzymes and receptors inherent to this defined luteal cell population and respond to stimulation by PRL, estradiol, and cAMP.

Animals↗
PubMed1997

Glutamine study in hepatic schistosomiasis and effect of conventional medical therapy.

The liver plays a major role in urea and glutamine metabolism where it maintains ammonia and bicarbonate homeostasis under physiological and pathological conditions. Glutamine assessment in different liver diseases showed deviations from normal serum values. In the present study, glutamine level in serum [serum glutamate values] (SGV) and liver tissue homogenates (liver homogenate glutamine values] (LHGV) in patients with schistosomal hepatic fibrosis with and without conventional supportive medical therapy and anti-schistosomal therapy were correlated. LHGV in liver tissue homogenates from cases were higher than those of matched controls. SGV of patients with late hepatic schistosomiasis were greater than those with early stages of the disease. All patients, whether in early or late schistosomal hepatic fibrosis, showed reduction of SGV after treatment. We came to the conclusion that in patients with schistosomal hepatic fibrosis, whether early or late, there is a derangement of glutamine metabolism which could be corrected partially by the conventional supportive medical therapy. Again, estimation of glutamine in serum could be considered an early and reliable parameter for the assessment of liver function in patients with schistosomal hepatic fibrosis.

Animals↗
PubMed1991

Chronic arsenicalism suspected from arsine exposure: a case report and literature review.

This report describes an unusual case of long-term arsenic exposure, apparently of industrial origin. The afflicted worker suffered from a complex of medical problems of sudden onset. Chemical (atomic absorption spectrometry, AAS) and physical (electron dispersion spectrometry, EDS) examination of the work environment showed long-term deposition of high levels of arsenic in a cleaning bath. When a new acidic cleaning solution was employed, elemental arsenic was apparently volatilized as arsine gas, resulting in sudden toxicity. Periodic reoccurrences of debilitation were explained by repeated use of the acid cleaning solution; each new application released a deeper layer of the metallic arsenic previously deposited on the bath walls electrolytically. The original source of the arsenic appears to have been prior cleaning of arsenic-contaminated agricultural spray equipment.

Adult↗
PubMed1988

[Surgery of the thoracic aorta. Value of tissucol].

The techniques for sealing with the Tissucol fibrin glue, used in repair of aortic dissections and aneurysms, are described. We applied this method to 24 patients operated upon for acute (9 cases) or chronic (15 cases) lesions of the thoracic aorta. No patients died of haemorrhage, and post-operative bleeding was only 500 ml on average. Provided strict precautions are taken, this adjuvant haemostatic method considerably improves the immediate prognosis of acquired aortic lesions. Other operations of cardiac surgery may benefit from these sealing techniques the cost of which must be weighed against the blood transfusion units that are saved.

Aortic Dissection↗
PubMed1986

Determination of aldosterone secretion rate utilizing mixed mode and high performance liquid chromatography.

A simpler method for determining aldosterone secretion rate (ASR) has several applications. High performance liquid chromatography (HPLC) has several advantages over traditional chromatographic methods for purification to constant specific activity of aldosterone liberated from its 18-glucuronide by acid hydrolysis. We found it necessary to introduce several modifications to remove urochromes before HPLC. Two methods for determining ASR were developed. With Method A a more traditional initial procedure was followed, and Sephadex LH-20 chromatography allowed removal of considerable urochromes before HPLC. However, aldosterone recovery was improved with Method B, which employed several bonded phase silica derivatives (Sepralytes) and a PBE 94 column to remove urochromes before HPLC. With this procedure the Sephadex LH-20 chromatography was not required. Aldosterone purification to constant specific activity was achieved by HPLC on a diol column with a normal phase system, and quantification was performed by RIA. ASR determinations were equivalent with both methods. This methodology should be applicable to other steroid secretory rate determinations and to applications involving purification of steroid conjugates.

Aldosterone↗
PubMed1984

Determination of urinary and plasma dihydroxyphenylalanine by coupled-column high-performance liquid chromatography with C8 and C18 stationary phases.

This paper describes a rapid, simple and sensitive method for measurement of L-dihydroxyphenylalanine (DOPA) in biological fluids. The method uses a two step frontal-chromatographic clean-up, followed by coupled minibore HPLC with electrochemical detection. The use of phenylboronate removes the peaks that interfere with the detection of DOPA. Inclusion of [14C]DOPA corrects for any variability in recovery.

Adult↗
PubMed1984

Rapid chromatographic purification of urinary steroid glucuronates for determination of aldosterone secretion rate.

Aldosterone secretion rate (ASR) is utilized as a rapid screening procedure to detect subtle forms of hypertension. A rapid and robust chromatographic method has been developed, based on easily prepared, rigid matrices, which permit the flow of urine by suction through sequential purification columns. Both major metabolites, aldosterone glucuronate and tetrahydroaldosterone glucuronate, are isolated in ca. 75% yield. They are hydrolyzed and quantitated by high-performance liquid chromatography-radioimmunoassay (HPLC-RIA) or, for bulk preparation, further purified by preparative chromatofocusing. These two polar conjugates are isolated in nearly pure form by HPLC on a C2 column with a two-step gradient. An ASR determination can be completed in one to two working days; preparative-scale work takes somewhat longer.

Aldosterone↗
PubMed1983

Nuclear magnetic resonance studies of Ba1 bacterium and some model systems.

Lithium NMR relaxation times of some model systems and E. coli cells in high LiCl concentration were measured. The lithium NMR relaxation times were compared to the relaxation times in the holotolerant bacterium Ba1 (Goldberg, M., Risk, M. and Gilboa, H. (1983) Biochim. Biophys. Acta 763, 35-40). Complementary studies of the water protons NMR relaxation times were carried out. It is suggested that the lithium in the H.S. Ba1 bacterium is occulated in small pores of the cell envelope.

Chlorides↗
PubMed1982

Actions of Ptychodiscus brevis red tide toxin on metabolic and transmitter-releasing properties of synaptosomes.

A pure toxin isolated from Ptychodiscus brevis stimulated differential release of amino acid neurotransmitters from mammalian cortical synaptosomes together with loss of K+ content and respiratory stimulation at 40 ng/ml. The effect was blocked by tetrodotoxin and by verapamil, implicating Na+ channel activation and possibly Ca2+ influx as necessary for the response, although the response did not change upon omission of Ca2+. Verapamil was therefore likely to be acting as a Na+ channel blocker in this instance. The toxin at 40 ng/ml caused acetylcholine release from guinea pig ileum, which is consistent with the proposed depolarising action for the toxin.

Acetylcholine↗
PubMed1981

Crystallization and preliminary X-ray diffraction studies of methemoglobin Bart's.

Methemoglobin Bart's (gamma 4) purified from the blood of an alpha thalassemic neonate has been crystallized in a crystal form unique for hemoglobins. The space group is trigonal, P3121, or the enantiomorph P3221, a = b = 55.85 A, c = 159.10 A. There are three tetrameric molecules in the unit cell with two gamma-chains per asymmetric unit.

Crystallization↗
PubMed1979

High pressure liquid chromatographic separation of two major toxic compounds from Gymnodinium breve davis.

Cultured Gymnodinium breve cells were extracted in acidified ether and fractionated by a new, convenient procedure utilizing thin layer chromatography or elution dry column chromatography. The most toxic fraction was further separated either directly by analytical high pressure liquid chromatography (HPLC) or in subsequent work by preparative, followed by analytical HPLC. Two toxic compounds, designated T46 and T47, were isolated; purity of each was demonstrated by rechromatography in analytical HPLC with both adsorptive and reverse phase packings. Both the single pass and recycle modes of operation were used with two detector systems in each to demonstrate a single entity. UV, fluorescence, and stability data differentiated these compounds from previously described, less toxic components from G. breve.

Animals↗