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Biomedical subjects

M Hicks

Publications and source records attributed to M Hicks.

At least 37 records · Page 2Linked to original sources
PubMed1993

Laparoscopic partial nephrectomy in the pig model.

In an effort to further evaluate the potential application of laparoscopy to urologic surgery, we explored the feasibility of using this minimally invasive approach for performing a partial nephrectomy. Nine female pigs underwent laparoscopic partial nephrectomy (LPN) utilizing a plastic cable tie (15 mm. x 4 mm. x 1 mm.) to achieve renal ischemia and an Argon Beam Coagulator probe (ABC) (Birtcher Medical Systems) to fulgurate the transected surface. Six weeks after LPN, 6 pigs underwent creatinine clearance, renin level, arteriography, BP samples and were then killed. The renal remnants were weighed and sectioned for histological studies. These studies revealed excellent function of the renal remnant, no AV fistula, and no evidence of renovascular hypertension. LPN is a feasible, repeatable procedure in the pig. Control of the renal hilum, transient parenchymal compression with a plastic cable, and use of the argon beam coagulator are key elements in performing this procedure.

Animals↗
PubMed1993

Continuous measurement of oxygen consumption by linoleic acid membranes exposed to free radicals generated by gamma-radiation.

Vesicles enclosed by membranes prepared from linoleic acid were exposed in the chamber of an oxygen electrode to free radicals generated by 60Co gamma-rays. Oxidation was observed by oxygen consumption, conjugated diene formation, and tri-iodide assay for hydroperoxides. There was a dose-dependent lag period before the onset of rapid peroxidation. The radiation chemical yields (G-values) ranged from 4.45 to 19.37 mu-mol J-1 for maximum rates of oxygen consumption and from 2.18 to 16.37 mumol J-1 for maximum rates of hydroperoxide production when the radiation dose-rate was varied between 5.39 and 0.14 Gy min-1. The magnitudes of these G-values and the linear relationship between yield of hydroperoxide and (dose-rate)1/2 were indicative of a chain mechanism for peroxidation operating in membranes. The lack of congruence between the amount of oxygen consumed and hydroperoxide formed suggested that the oxygen consumed in membrane oxidation led to the formation of oxidized derivatives of linoleic acid additional to the hydroperoxides.

Dose-Response Relationship, Radiation↗
PubMed1993

Identification of products from oxidation of uric acid induced by hydroxyl radicals.

The aim of the present study was to separate and characterise products formed by oxidation of uric acid by hydroxyl radicals with a view to probing for these products in vivo in clinical contexts. Aerated solutions of 200 microM uric acid, or its oxidation products, allantoin or parabanic acid, were exposed to gamma radiolysis, (52.0 Gy/min), as a source of HO. radicals, at pH 3.4 and 7.4. Aliquots were taken every 5 minutes for 20 minutes and oxidation products were separated by HPLC and analysed with a diode array detector. Identities of oxidation products were confirmed on the basis of similarity of retention times and absorbance spectra and peak purity parameters of known standards. Hydroperoxides were measured by tri-iodide formation in the 20 minute sample. Exposure of uric acid to such HO.fluxes produced a net loss of the parent compound with formation of a complex mixture of products with allantoin and parabanic acid being the predominant products at pH 3.4. The rate of uric acid degradation at physiological pH was slower and the distribution of oxidation products was different. A small but significant amount of uric acid hydroperoxide was detected at both pHs. A mechanism for uric acid oxidation under these conditions is presented.

Chromatography, High Pressure Liquid↗
PubMed1993

A feature of alcoholic Wernicke's encephalopathy favourable to the maintenance of memory function: vomiting.

Outcome in terms of progression of Korsakoff's psychosis is known to be unlikely when the preceding thiamin deficiency syndrome, Wernicke's encephalopathy, does not follow heavy alcohol use. There is evidence that alcohol potentiates thiamin-related brain damage. It is argued here that in heavy drinkers, if vomiting precedes the onset of the encephalopathy, then the latter might develop at a time when tissue alcohol levels are close to zero. Any progression to Korsakoff's psychosis could then be associated with less or even no impairment. This outcome would not be expected if ingestion of alcohol continued during the vomiting stage. In a follow-up study of 61 cases of alcoholic Wernicke's encephalopathy, these concepts are given some support by the results obtained.

Aged↗
PubMed1993

Intrahepatic portosystemic vascular stents: a bridge to hepatic transplantation.

Refractory esophageal variceal hemorrhage (EVH) remains a formidable problem in patients awaiting liver transplantations. Transjugular intrahepatic portosystemic shunts (TIPS) have provided an alternative approach for managing EVH that may obviate the need for portosystemic shunt surgery. Experience with TIPS placement and subsequent successful hepatic transplantation in patients without previous portosystemic shunt surgery has not been previously reported. Two patients are reported who underwent TIPS placement and subsequent successful hepatic transplantation without previous portosystemic shunt surgery. This experience indicates that (1) TIPS can provide effective control of EVH for at least several weeks, (2) TIPS placement decreases portal hypertension, thus facilitating technical performance of the transplant procedure and minimizing blood loss, (3) TIPS may undergo vascular incorporation, thus requiring that they be accurately positioned so that the lengths of suprahepatic inferior vena cava and portal vein are not compromised at the time of transplantation, (4) TIPS thrombosis can be effectively treated and prolonged patency may be observed, and (5) deterioration in hepatic function and exacerbation of hepatic encephalopathy were not observed after TIPS placement. In summary, TIPS provide an attractive, effective means for managing refractory EVH in patients awaiting liver transplantation.

Esophageal and Gastric Varices↗
PubMed1992

Antioxidant activity of propylthiouracil.

Propylthiouracil (PTU) has been demonstrated to reduce alcohol-induced hepatocyte damage and severe alcoholic liver disease. Although the mechanism by which the drug operates is yet to be elucidated, there is evidence that PTU may act as an antioxidant. The present study examines the reaction of PTU with oxygen free radicals and the ability of PTU to directly inhibit peroxidation of a model membrane system. PTU reacted directly with hydroxyl radicals produced by gamma-radiolysis. The rate constant for the PTU/hydroxyl radical reaction as determined by steady state competition kinetics with p-nitrosodimethylaniline was 8 x 10(9) L/mol/sec. PTU was less reactive towards superoxide generated by the xanthine/xanthine oxidase system, having a small but significant inhibitory effect on superoxide-induced reduction of cytochrome c only at a concentration of 200 microM. The ability of PTU to protect lipids from peroxidative changes was tested in membranes prepared from linoleic acid. The rate of peroxidation induced by 40 degrees heat decreased from 0.078 to 0.024 mM hydroperoxide/hr in the presence of 0-50 microM PTU. However, this trend was reversed at PTU concentrations above 50 microM. These data suggest that the protective effects of PTU against liver damage may be due to scavenging reactions with hydroxyl radicals in particular and/or its antioxidant potential.

Animals↗
PubMed1992

Technical problems associated with placement of the Bird's Nest inferior vena cava filter.

Technical problems encountered during percutaneous placement of 165 Bird's Nest filters over 16 months are described. Filter deployment was successful in all patients. Although frequent, the technical problems were all minor with no long-term sequelae. Several problems were inherent to the design of the filter. Other problems related to the patient's anatomy were seen as well. Because deployment of the Bird's Nest filter is more operator-dependent than is deployment of other types of inferior vena cava filters, knowledge of pitfalls and means to avoid problems are particularly important.

Humans↗
PubMed1991

Alcoholic beverage consumption prior to the onset of Wernicke's encephalopathy.

Alcoholic beverage consumption prior to the onset of Wernicke's encephalopathy is shown to be, primarily, full strength beer, although not always in large quantity, by 91% of 80 patients. Secondly, in order of frequency of consumption, was white wine sold in casks and consumed by 30% of patients. These findings have implications when decisions have to be made regarding which alcoholic beverages could be fortified with thiamine as a measure designed to prevent the development of the Wernicke-Korsakoff syndrome.

Journal Article↗
PubMed1991

A canine model of paired graft thrombosis.

A novel canine model for reliably producing graft thrombosis is described. Two unilateral aortoiliac bypasses are performed while preserving the integrity of the native vascular tree. These grafts are briefly mechanically occluded at the time of the initial operation, and they remain occluded postoperatively because flow is preferentially directed through the larger-caliber, thrombo-resistant native circulation. Percutaneous temporary intra-arterial balloon occlusion of the native vessels redirects flow into the occluded graft segments, which can be used in experimental protocols. This new model for studying graft thrombosis requires only a single, simple operative procedure, and easily allows secondary percutaneous graft manipulation.

Animals↗
PubMed1990

'Hairpin' catalytic RNA model: evidence for helices and sequence requirement for substrate RNA.

We have identified the catalytic domain within the sequence of the negative strand of the satellite RNA of tobacco ringspot virus. Minimum energy RNA folding calculations predict a two dimensional model with four major helical regions which are supported by mutagenesis experiments. This model for the catalytic complex consists of a 50 base catalytic RNA and a 14 base substrate RNA folded together in a type of hairpin two dimensional structure. Part of the recognition region between the catalyst and substrate is two helices of 6 bases and 4 bases respectively. Catalytic activity remains when the bases in these two helices are changed but base pairing is maintained. Thus an appropriately engineered 'hairpin' catalyst is capable of cleaving heterologous RNA.

Base Sequence↗
PubMed1989

Increase in crosslinking of nonenzymatically glycosylated collagen induced by products of lipid peroxidation.

The increase in crosslinking in normal and nonenzymatically glycosylated rat tail tendon collagen after treatment with decomposing lipid hydroperoxides was assessed by measuring the breaking time of tendons immersed in 7 M urea under a 3 g weight at 40 degrees C (thermal rupture time). The incubation of tendons in 200 mM glucose for 43 h at 40 degrees C increased thermal rupture times from 5.15 to 26.38 min, (P less than 0.001) with no significant corresponding increase in tendons incubated in buffer alone. After incubation of the glycosylated tendons in the presence of peroxidized linoleic/arachidonic acid vesicles for about 20 h, their thermal rupture time increased to 3360 min (P less than 0.001). The rupture time for normal tendons after the same treatment was 206 min. These apparent crosslinking increases cannot be fully accounted for by reactions involving malondialdehyde, as incubation of both glycosylated and normal tendons in enzymatically produced malondialdehyde resulted in a modest two- to threefold increase in thermal rupture time.

Animals↗
PubMed1988

Catalysis of lipid peroxidation by glucose and glycosylated collagen.

Peroxidation of membranes of linoleic/arachadonic acid vesicles at 40 degrees C was catalysed by glucose or glycosylated collagen. Kinetics of hydroperoxide production were similar in both cases. There was a kinetic lag, the duration of which was inversely proportional to the amount of glucose or glycosylated collagen used to initiate the peroxidation. This was followed by a rapid increase in the rate of oxidation. The final rate was independent of the amount of catalyst added. Vesicle lysis accompanied the increases in peroxidation. Addition of desferrioxamine, an iron chelator, only partially inhibited the oxidative process.

Animals↗