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Biomedical subjects

S Choi

Publications and source records attributed to S Choi.

At least 235 records · Page 13Linked to original sources
PubMed1984

CT of hepatoma. Dilatation of the intrahepatic bile ducts and intraductal tumour growth.

Computed tomography revealed dilatation of the intrahepatic bile ducts in 25 out of 135 cases of hepatocellular carcinoma. In 6 (4.5%) of these 25 cases the dilatation was generalised, while in the remaining 19 cases (14%) dilatation was localised. In each group 3 cases of intraductal tumour growth was confirmed either at operation or autopsy. With metastatic liver tumour, generalised dilatation was observed in 6 cases (7%) and localised dilatation in 3 (3.5%) out of 85 cases. Localised dilatation was found with higher incidence in hepatocellular carcinoma than in metastatic tumour. This may indicate that the incidence of intraductal infiltration is high in cases of hepatocellular carcinoma. When a relatively small tumour is associated with dilatation of bile ducts, it is more probable that the tumour is a hepatocellular carcinoma than a hepatic metastasis.

Adult↗
PubMed1983

Purification of insulin receptor with full binding activity.

Insulin receptor was purified 2400-fold with an overall yield of 40% from human placental membranes by affinity chromatography on wheat germ agglutinin-Sepharose and insulin-Sepharose. The receptor was eluted from insulin-Sepharose using mild conditions, eliminating urea, so that it was stable and retained full insulin-binding activity. Chromatofocusing and gel filtration analysis indicated that the receptor preparation was apparently pure. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed three high molecular weight protein bands with Mr = 320,000, 300,000, and 270,000 under nonreducing conditions and two major protein bands with Mr = 135,000 and 90,000 under reducing conditions. The purified receptor showed a curvilinear Scatchard plot with maximum insulin binding of 28.5 micrograms per mg of protein. In comparison, the receptor eluted from insulin-Sepharose with previously used conditions in the presence of urea resulted in maximum insulin binding of only 6 micrograms per mg of protein. This indicates that a 4-to 5-fold increase in specific activity can be obtained by using the new elution conditions.

Chromatography, Affinity↗
PubMed1983

The effect of PGF2 alpha on in vivo cerebral arteriolar diameter in cats and rats.

We compared the effect of topical application of PGF2 alpha on cerebral arterioles in cats and rats equipped with an acutely implanted cranial window. Arterial diameter was measured using a microscope and image splitting device. PGF2 alpha in a concentration ranging from 10(-7) to 10(-5) M had no effect on large (greater than or equal to 100 microns) or small (less than 100 microns) cat pial arterioles, but induced a dose dependent constriction of rat pial arterioles with a maximum constriction to 76% of control diameter. Dilation of cat large cerebral arterioles by topically applied PGE2 was not affected by simultaneous application of PGF2 alpha and PGE2 induced dilation of small arterioles was decreased 3% by PGF2 alpha. While we and others have previously shown that both cat and rat brain can synthesize PGF2 alpha, it appears that PGF2 alpha is not likely to normally be a major modulator of cerebral arteriolar resistance in all species.

Animals↗
PubMed1981

Type A components and psychophysiological responses to an attention-demanding performance task.

Although Type A and B individuals appear to differ in psychophysiological responsivity, situations eliciting these differences have not been specified. The current experiment parametrically manipulated response speed in order to examine differences between behavior types in psychophysiological responsivity to this variable. Cardiovascular responses and performance in this paced task were compared to those from a task performed without explicit speed pacing in 24 businessmen classified as Type A or not. Only Type A businessmen showed a well-developed heart rate response in the self-paced task. In the experimenter paced task, the heart rate response of Type A's was most consistent when paced at fast response times; that of non-A's was most consistent when paced at relatively slow response times. Businessmen high in the Speed/Impatience component of Type A initiated anticipatory heart rate slowing later than non-A's and recovered less promptly. Overall relative to non-A's, A's appear to become readily involved and physiologically responsive to a task. Once involved, their responding is altered most by requirements for anticipation and relatively slow controlled response.

Arrhythmias, Cardiac↗
PubMed1981

Nutritional Regulation of Lignin Degradation by Phanerochaete chrysosporium.

Previous studies have shown that a lignin-degrading system appears in cultures of the white rot fungus Phanerochaete chrysosporium in response to nitrogen starvation, apparently as part of secondary metabolism. We examined the influence of limiting carbohydrate, sulfur, or phosphorus and the effect of varying the concentrations of four trace metals, Ca, and Mg. Limitation of carbohydrate or sulfur but not limitation of phosphorus triggered ligninolytic activity. When only carbohydrate was limiting, supplementary carbohydrate caused a transient repression of activity. In carbohydrate-limited cultures, ligninolytic activity appeared when the supplied carbohydrate was depleted, and this activity was associated with a decrease in mycelial dry weight. The amount of lignin degraded depended on the amount of carbohydrate provided, which determined the amount of mycelium produced during primary growth. Carbohydrate-limited cultures synthesized only small amounts of the secondary metabolite veratryl alcohol compared with nitrogen-limited cultures. l-Glutamate sharply repressed ligninolytic activity in carbohydrate-starved cultures, but NH(4) did not. Ligninolytic activity was also triggered in cultures supplied with 37 muM sulfur as the only limiting nutrient. The balance of trace metals, Mg, and Ca was important for lignin degradation.

Journal Article↗
PubMed1980

Metabolic effects of large fructose loads in different parts of the rat nephron.

Rats were given large parenteral loads of fructose and the different segments of single nephrons then analyzed for fructose metabolites, fructose metabolizing enzymes, and nucleotide high energy phosphates. Fructokinase and fructose-1-P aldolase activities, and all the major metabolite and nucleotide effects, were confined to the proximal tubule. The proximal straight segment had the highest fructokinase and suffered the greatest changes. In this segment, fructose-1-P rose to 60 mmol/kg (dry weight basis) and glycerol-3-P and glucose-6-P reached 8 and 12 mmol/kg, respectively. ATP fell 80% and GTP (judging from the changes in GTP plus GDP) fell by the same percentage, but UTP was less affected. Total adenylate decreased 50%. In the proximal convoluted tubule, where fructokinase was lower and fructose-1-P aldolase higher than in the straight segment, fructose-1-P rose ony one-fourth as much and glucose-6-P was almost unchanged. In contrast, glycerol-3-P rose more, reaching 16 mmol/kg. Other substances measured along the nephron were glycerol-3-P dehydrogenase, fructose-1,6-bisphosphate aldolase, fructose, glucose, fructose bisphosphate, triose phosphate, and 6-P-gluconate. Control ATP levels were found to be highest in the distal tubule.

Adenine Nucleotides↗
PubMed1979

Blood pressure in a high school population. II. Clinical profile of the juvenile hypertensive.

One-hundred-fourteen hypertensive high school students were evaluated to determine whether a distinctive clinical profile could be identified; 71 normotensive students served as controls. Selected blood chemistry determinations, urinalysis, and chest roentgenograms were done to help rule out secondary causes of hypertension. Left ventricular function was assessed by echocardiography and systolic time intervals. The hemodynamic response to exercise was also evaluated. A significant number of the subjects 14 to 18 years of age with persistent systolic and/or diastolic pressure 1.65 SD above the mean for age and sex showed the following: obesity; elevated serum triglyceride concentration; basilar hypertrophy by electrocardiogram/vectorcardiogram; electromechanical systole and pre-ejection period shorter, and the ratio of the pre-ejection period over the left ventricular ejection time lower, than mean for age and sex as determined by systolic time intervals; volume indices depressed and cardiac contractile functions elevated as determined by echocardiography; higher blood pressure at start of exercise stress test and higher peak systolic and diastolic pressures during test, and a slower return of heart rate to base line level after the test. The above findings should be useful in following the course of a young individual with essential hypertension and may provide a means of evaluating therapeutic intervention.

Adolescent↗
PubMed1979

Synthesis of 5-selenium-substituted uracil derivatives. Inhibition of thymidylate synthetase by 5-hydroseleno-2'-deoxyuridylate.

5-Selenium-substituted derivatives (diselenides) or uracil, 2'-deoxyuridine, and 2'-deoxyuridylic acid were synthesized via the addition of methyl hypobromite to the 5,6 double bond, followed by reaction of the adducts with sodium diselenide. The physical and chemical properties of these compounds (including their facile reduction by dithiothreitol and rapid reoxidation) were similar to those of the corresponding 5-sulfur analogues. 5-Hydroseleno-2'-deoxyuridylic acid was as potent as 5-mercapto-2'-deoxyuridylate in inhibiting thymidylate synthetase from L. casei (ki approximately 6 X 10(-8) M) but the nucleoside III was considerably less active than 5-mercapto-2'-deoxyuridine in the inhibition of growth of the leukemia L1210 cell in culture.

Animals↗
PubMed1978

Angiographic features in tubular-papillary adenocarcinoma of the kidney.

Angiography and nephrotomography are essential in evaluation of avascular or hypovascular space occupying lesions of the kidney. Ultrasound adds another dimension in differentiating solid from cystic masses. Two cases of tubular-papillary adenocarcinoma were reported. Their angiographic findings consisted of a few neovascularities. Nephrotomography and ultrasonography in the second case showed a solid mass.

Adenocarcinoma, Papillary↗
PubMed1978

Distribution along the rat nephron of three enzymes of gluconeogenesis in acidosis and starvation.

Methods were devised or modified which made it possible to measure phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase in seven defined parts of single nephrons and in patches from thin limb and papilla areas dissected from freeze-dried microtome sections of rat kidney. All three enzymes were essentially confined to the proximal tubule. In normal kidneys, the levels were highest in the proximal convoluted tubule. Glucose-6-phosphatase was 20 times higher in the early part of the convoluted segment than in the late part of the straight segment. With one exception, in acidosis, only phosphoenolpyruvate carboxykinase increased (fourfold in the proximal convoluted segment but much less in the straight portion). In starvation, phosphoenolpyruvate carboxykinase increased about as much as in acidosis in the proximal straight tubule, but not as much in convoluted portions, whereas glucose-6-phosphatase rose modestly in both parts of the proximal tubule and fructose bisphosphatase rose only in the straight tubule, especially the early segment. It is suggested that ammoniagenesis can accompany gluconeogenesis in the proximal convoluted tubule but not in the straight segment.

Acidosis↗