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Biomedical subjects

C Kent

Publications and source records attributed to C Kent.

At least 199 records · Page 11Linked to original sources
PubMed1990

Extracranial carotid arteries: evaluation with "black blood" MR angiography.

The authors evaluated the accuracy of "black blood" magnetic resonance (MR) angiography for depicting disease involving the extracranial carotid arteries. Two- and three-dimensional flow-compensated gradient-echo sequences were employed to create "bright blood" images. A thin-section spin-echo sequence with flow presaturation allowed the creation of black blood images. Projection angiograms were made from bright and black blood images with application of a maximum- or minimum-intensity projection algorithm, respectively. These methods were used in 13 healthy volunteers and 17 patients, and a prospective blinded comparison of MR angiography and conventional angiography was performed. Normal carotid arteries were well shown with both bright and black blood methods; in patients, both methods were sensitive for detecting carotid disease. However, bright blood angiography exaggerated the severity of carotid lesions in 13 of 33 arteries, mostly in severe disease; this problem was not encountered with black blood angiography. The authors conclude that bright blood angiography is a sensitive method for screening carotid disease; when a significant abnormality is found, black blood angiography should be performed for more precise delineation of the lesion.

Adult↗
PubMed1989

Localization of the membrane-associated CTP:phosphocholine cytidylyltransferase in Chinese hamster ovary cells with an altered membrane composition.

The subcellular localization of the membrane-associated CTP:phosphocholine cytidylyltransferase was determined in Chinese hamster ovary cells in which the phospholipid composition had been altered by growth in the presence of N-methylethanolamine or treatment with phospholipase C. Cell homogenates were fractionated on Percoll density gradients, and marker enzyme activities were used to determine the location of the cellular membrane fractions. The peak of cytidylyltransferase activity occurred in the gradient at a density intermediate to that of the peaks of endoplasmic reticulum and plasma membrane markers. The profile of cytidylyltransferase activity most closely resembled that of the Golgi membrane marker; however, upon sucrose gradient centrifugation, the profile of the Golgi apparatus was very different from that of cytidylyltransferase. Differential centrifugation suggested a nuclear membrane association of the enzyme. Cytidylyltransferase was associated with a membrane fraction that sedimented when subjected to very low speed centrifugation (65 x g, 5 min). From Percoll gradient fractions, nuclei were identified by microscopy, and they migrated with cytidylyltransferase activity. The data are consistent with a localization of cytidylyltransferase in the nuclear membrane.

Animals↗
PubMed1989

The effect of polycyclic aromatic hydrocarbons on choline kinase activity in mouse hepatoma cells.

Choline kinase catalyzes the first rate-limiting step in the pathway of biosynthesis of phosphatidylcholine. This enzyme was shown previously to be induced in liver by treatment of rats with polycyclic aromatic hydrocarbons (Ishidate et al. (1980) Biochem. Biophys. Res. Commun. 96, 946-952). The present study was undertaken to determine whether choline kinase in the murine hepatoma cell line, Hepa 1c1c7, is inducible by aromatic hydrocarbons and, if so, whether this induction is mediated by the aromatic hydrocarbon receptor. Treatment of Hepa 1c1c7 cells with 10 microM beta-naphthoflavone resulted in a 1.6-fold increase of choline kinase activity, but no response was seen when the cells were exposed to either 5.0 microM benzo[a]pyrene or 1.0 nM 2.3,7,8-tetrachlorodibenzo-p-doxin, both potent inducers of aryl hydrocarbon hydroxylase. Cell line variants with either deficient or elevated aromatic hydrocarbon receptors showed no increase in choline kinase activity following treatment with any of the polycyclic aromatic hydrocarbons. These results are not consistent with a role for the aromatic hydrocarbon receptor in increased choline kinase activity in Hepa 1c1c7 cells.

Animals↗
PubMed1989

Comparing tobacco cigarette dependence with other drug dependencies. Greater or equal 'difficulty quitting' and 'urges to use,' but less 'pleasure' from cigarettes.

About 1000 persons seeking treatment for alcohol or drug dependence were asked, relative to cigarettes, about the difficulty of quitting the use of the substance for which they were seeking treatment, the strength of their strongest urges to use, and the pleasure they derived from use. Fifty-seven percent said that cigarettes would be harder to quit using than their problem substance. These ratings were related to the level of cigarette dependence and the perceived difficulty of quitting the use of the problem substance. The alcohol-dependent persons were about four times more likely than the drug-dependent persons to say that their strongest urges for cigarettes were at least as great as their strongest urges for their problem substance. Cigarettes were generally rated as less pleasurable than alcohol or other drugs. Thus, experiential experts on dependence judge cigarette dependence as at least as "addictive" as other drug use, but not as pleasurable, indicating important similarities and differences between cigarette dependence and other forms of dependence on psychoactive substances.

Adult↗
PubMed1989

Prospects for smoking treatment in individuals seeking treatment for alcohol and other drug problems.

Alcohol and drug using clients of the Addiction Research Foundation were asked about their interest in receiving treatment for cigarette smoking. Forty-six percent said that they were "moderately" to "very much" interested in attending a treatment program if it were available. Despite a consistent preference for receiving smoking treatment after their alcohol or drug problem was treated, there was moderate interest in receiving smoking treatment during the alcohol or drug treatment among those who were very interested in receiving smoking treatment in general. Seventy-one percent reported that it would be "as difficult" or "more difficult" to give up cigarettes than the drug or alcohol which brought them to the hospital for treatment. The importance of treating smoking in alcohol and drug using clients is discussed.

Adolescent↗
PubMed1989

Localisation of chromogranin A and B, met-enkephalin-arg6-gly7-leu8 and PGP9.5-like immunoreactivity in the developing and adult rat adrenal medulla and extra-adrenal chromaffin tissue.

The localisation of chromogranins A and B, met-enkephalin-arg6-gly7-leu8 (met-enk 8) and protein gene product 9.5 (PGP 9.5) in the adrenal medulla and extra-adrenal chromaffin tissue has been studied in the developing rat by immunogold-silver staining. In the adult rat adrenal the cytoplasm of all medullary chromaffin cells showed a positive response with chromogranin A and B; in each case occasional groups of cells with a low reactivity that may have been NA cells were seen. Chromogranin A was first detected in adrenal medullary and extra-adrenal chromaffin cells at 18 days of gestation whilst chromogranin B was not detected in animals younger than 7 days. In 15 days old animals the adrenal medullary response to A and B was of the same intensity as that seen in the adult. Less than 1% of adult medullary chromaffin cells were responsive to met-enk 8 staining and medullary cells were unreactive in the fetus, with only extra-adrenal chromaffin tissue responding prenatally. During the first postnatal week immunoreactive cells appeared in the adrenal medulla in considerably greater proportions than in the adult gland. In contrast, positively stained nerve terminals associated with chromaffin cells and abundant in the adult adrenal were not detected during the first week of life. Immunoreactive nerve terminals were first seen early in the second week of life at a time when positive chromaffin cells were becoming less common. PGP 9.5 was located in all chromaffin cells of the adult adrenal and was readily detected in chromaffin cells in the adrenal and in extra-adrenal locations of the earliest stage examined (E16). Our findings suggest that the ontogenesis of the chromogranin-like immunostaining reflects the maturation of chromaffin granules and the PGP 9.5 immunostaining detected a protein common to cells of neuronal origin and expressed at an early stage of differentiation. The reciprocal relationship between the presence of enkephalins in chromaffin cells and in their presynaptic terminals merits further investigation.

Adrenal Medulla↗
PubMed1988

The membrane domain of 3-hydroxy-3-methylglutaryl-coenzyme A reductase confers endoplasmic reticulum localization and sterol-regulated degradation onto beta-galactosidase.

A hybrid gene has been constructed consisting of coding sequence for the membrane domain of the endoplasmic reticulum protein 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase linked to the coding sequence for the soluble enzyme Escherichia coli beta-galactosidase. Expression of the hybrid gene in transfected Chinese hamster ovary cells results in the production of a fusion protein (HMGal) which is localized in the endoplasmic reticulum. The fusion protein contains the high-mannose oligosaccharides characteristic of HMG-CoA reductase. Importantly the beta-galactosidase activity of HMGal decreases when low density lipoprotein is added to the culture media. Therefore, the membrane domain of HMG-CoA reductase is sufficient to determine both correct intracellular localization and sterol-regulation of degradation. Mutant fusion proteins which lack 64, 85, or 98 amino acid residues from within the membrane domain of HMG-CoA reductase are found to be localized in the endoplasmic reticulum and to retain beta-galactosidase activity. However, sterol-regulation of degradation is abolished.

Animals↗
PubMed1987

Maternal narcotic addiction: pregnancy outcome in patients managed by a specialized drug-dependency antenatal clinic.

A retrospective analysis has been made of the outcome of pregnancy in 174 women abusing narcotics, managed by a specialist team from a drug-dependency antenatal clinic. These women were cared for through 182 pregnancies of greater than 20 weeks' gestation, resulting in 183 live and 5 stillbirths. The majority of patients were enrolled in a methadone programme and stabilized on the drug before the third trimester. The group was characterized by a high prevalence of previous obstetric and medical problems. The most common antenatal complications were preterm labour (24%) and anaemia (12%). Preterm delivery and small-for-gestational-age each occurred in a quarter of pregnancies. The mean birth-weight for the group was 2,746 g +/- 721 g; mean +/- S.D. Eight perinatal deaths occurred (5 stillbirths, 3 neonatal deaths), giving a perinatal mortality rate of 43/1,000. The data on narcotic abusers have been compared with similar data obtained from randomly selected public antenatal clinic patients who delivered during the same period.

Adolescent↗
PubMed1986

A one-step technique for the subcellular fractionation of total cell homogenates.

A procedure was developed for the rapid, analytical subcellular fractionation of entire homogenates from the Chinese hamster ovary and HeLa cell lines. The procedure avoids a nuclear sedimentation step and the losses that accompany such a step. A key to the development of this procedure was the addition to homogenates of either micrococcal nuclease or DNase I. Nuclease-treated homogenates were fractionated on self-forming Percoll gradients. The entire procedure from cell harvesting through collecting gradient fractions took only 2.5 h. The position of marker enzymes in the gradient fractions indicated clear resolution of plasma membranes, Golgi apparatus, endoplasmic reticulum, and lysosomes. This procedure should facilitate many studies requiring subcellular fractionation of cultured cells.

Animals↗
PubMed1986

Diacylglycerol metabolism in phospholipase C-treated mammalian cells.

Treatment of cultured cells with phospholipase C causes increased rates of hydrolysis of cellular phosphatidylcholine and increased rates of incorporation of choline into phosphatidylcholine. The fate of the diacylglycerol produced by the phospholipase C hydrolysis was examined in two cell lines, Chinese hamster ovary and HeLa. In the former cells, turnover of the glycerol moiety of phosphatidylcholine was not enhanced by phospholipase C treatment, indicating that the phospholipase C-generated diacylglycerol was recycled into new phosphatidylcholine. In HeLa cells, turnover of the glycerol backbone of phosphatidylcholine was enhanced by phospholipase C treatment, and the increased rate of turnover of the glycerol moiety was similar to that of the phosphate moiety. Thus, the fate of diacylglycerol generated at the plasma membrane was demonstrated to differ in these two cell lines. Incorporation of precursors of diacylglycerol into phosphatidylcholine was not enhanced by phospholipase C treatment in either cell line.

Cell Line↗
PubMed1986

Characterization of the pathways for phosphatidylethanolamine biosynthesis in Chinese hamster ovary mutant and parental cell lines.

A tritium suicide procedure was devised to facilitate the isolation of Chinese hamster ovary cell mutants defective in phosphatidylethanolamine biosynthesis. One mutant with a 20-50% reduction in [3H]ethanolamine incorporation was chosen for further analysis and was shown to have reduced activity of CTP: phosphoethanolamine cytidylyltransferase. Levels of phosphatidylethanolamine and rates of its biosynthesis were compared in the mutant and parent cell lines. Despite the reduced activity of the CDP-ethanolamine pathway in the mutant, levels of phosphatidylethanolamine were the same in mutant and parent cells. Rates of phosphatidylethanolamine synthesis de novo, as measured by incorporation of 32PO4 into phosphatidylethanolamine, were also the same in mutant and parent cells, as was the rate of incorporation of [3H]serine into both phosphatidylserine and phosphatidylethanolamine. After a long term labeling with [3H]serine, the specific radioactivity of phosphatidylserine was the same as that of phosphatidylethanolamine, and there was no difference in the specific radioactivities of the two lipids between mutant and parent cells. These results implicate decarboxylation of phosphatidylserine as the sole route for synthesis of phosphatidylethanolamine under normal culture conditions.

Animals↗
PubMed1986

Chinese hamster ovary cells depend on exogenous lipids to survive phospholipase C treatment.

Chinese hamster ovary cells were maintained in culture medium supplemented with delipidated serum to make them dependent on nonlipid components for lipid synthesis. Growth in lipid-free medium resulted in an increased flux through the CDP-choline pathway for phosphatidylcholine synthesis. The increased flux appeared to be mediated by the CTP:phosphocholine cytidylyltransferase because cellular phosphocholine levels decreased in cells grown in lipid-free medium, and both cell-free cytidylyltransferase activity and membrane-associated cytidylyltransferase activity increased in cells grown in lipid-free medium. Chinese hamster ovary cells maintained in culture medium supplemented with complete serum can grow at nearly normal rates in the presence of phospholipase C for many generations, even though the treatment enhances turnover of cellular phosphatidylcholine (R. Sleight and C. Kent (1983) J. Biol. Chem. 258, 824-830). The phospholipase C treatment, however, was toxic to cells maintained in medium supplemented with delipidated serum. Lysophosphatidylcholine protected cells from phospholipase toxicity, but did not support growth. The rate of utilization of lysophosphatidylcholine for phosphatidylcholine synthesis was about 8% of the turnover rate for phosphatidylcholine, and was not increased by phospholipase C treatment. Reconstitution of the medium with fractionated serum lipids showed that the cells required specific neutral lipids, namely, fatty acids plus cholesterol, in order to grow in the presence of phospholipase C. Either oleate or cholesterol (up to 80 microM) alone did not allow growth in phospholipase C, but a combination of these two lipids supported growth effectively.

Animals↗
PubMed1985

Regulation of phosphatidylcholine biosynthesis in Chinese hamster ovary cells by reversible membrane association of CTP: phosphocholine cytidylyltransferase.

Treatment of Chinese hamster ovary cells with phospholipase C was previously shown to stimulate the CDP-choline pathway for phosphatidylcholine biosynthesis, and to cause activation of the CTP:phosphocholine cytidylyltransferase with a concomitant change in subcellular location of the enzyme (Sleight, R., and Kent, C. (1983) J. Biol. Chem. 258, 831-835). This paper presents a detailed analysis of the early events in the phospholipase C treatment, and provides evidence that the increased cytidylyltransferase activity causes the increased flux through the pathway. The time courses for the increase in cytidylyltransferase activity, increase in amount of membrane-associated enzyme, decrease in phosphocholine levels, and increase in phosphatidylcholine synthesis were similar, with all changes occurring within 30 min after addition of phospholipase C. These events preceded a decrease in cellular choline levels which correlated with a decreased capacity for choline uptake. The rate at which radioactive label was lost from pulse-labeled phosphocholine was the same as the rate at which label was incorporated into phosphatidylcholine, and these rates were stimulated 2.2-fold by phospholipase C treatment. We have also shown that the association of cytidylyltransferase with membranes was rapidly reversible when phospholipase C was removed from the cultures, and that the rate of decrease in phosphatidylcholine synthesis paralleled the rate of decrease in cytidylyltransferase activity. Cytidylyltransferase became reassociated with membranes when phospholipase C was added back to cultures from which it was previously removed. These results represent the first detailed account of the time frame involved in regulating phosphatidylcholine synthesis by the reversible association of cytidylyltransferase with cellular membranes.

Animals↗
PubMed1985

Nuclear magnetic resonance imaging--a new look at the fetus.

A new form of obstetric imaging using nuclear magnetic resonance (NMR) has been assessed for use in pregnancy. A total of 92 examinations were performed in 62 women during the second and third trimesters in both normal and complicated pregnancies including 14 with diabetes, six with pre-eclampsia and four with intrauterine growth retardation. Our experience has shown that NMR imaging gives excellent differentiation of both maternal and fetal tissues, and because of complete penetration both superficial and deep structures have been clearly identified. The best fetal images were obtained most consistently in the third trimester providing good detail of brain, lungs, liver, heart, bladder, subcutaneous fat, placenta and umbilical cord while maternal tissues were clearly seen at all gestations. As this form of imaging uses no ionizing radiation it offers an alternative means with unique capabilities for investigating pregnancy.

Biometry↗
PubMed1984

Separation of choline- and ethanolamine-labeled metabolites by ion-exchange high-pressure liquid chromatography.

Two methods utilizing ion-exchange high-performance liquid chromatography have been developed for the separation of choline- and ethanolamine-containing metabolic precursors for phosphatidylcholine and phosphatidylethanolamine. Both methods employ an analytical anion-exchange column supplemented with a cation-exchange column; the latter is required only to separate betaine from choline. Complete separation of choline- and ethanolamine-labeled metabolites from extracts of Chinese hamster ovary cells can be achieved in 20 min.

Animals↗
PubMed1984

On the uptake and storage of 5-hydroxytryptamine, 5-hydroxytryptophan and catecholamines by adrenal chromaffin cells and nerve endings.

Light-microscopic autoradiographs of the adrenal medulla at various intervals after the intravenous injection of [3H] 5-HTP, [3H] 5-HT, [3H] noradrenaline and [3H] adrenaline have been studied. The distribution of silver grains following [3H] 5-HTP uptake was found to be uniform over each of the two main cell populations, adrenaline-storing (A) cells and noradrenaline-storing (NA) cells in the adrenal medulla, but A cells were twice as active as NA cells in incorporating the isotope, a situation very similar to that found after [3H] dopa uptake. 5-HT administration resulted in a pattern resembling the distribution of [3H] noradrenaline uptake, with A cells being 4 or 5 times more active than NA cells and a gradient of activity from the periphery of the medulla inwards. However, the time-course for the loss of radioactivity was not the same for both amines: levels of 5-HT activity were not significantly reduced after one week whereas the degree of [3H] noradrenaline labelling after one week was less than 10% of that at one hour. Thus 5-HT may be bound to sites in the adrenal medulla normally occupied by noradrenaline but it would appear that the release mechanism is different. There was no evidence of 5-HT uptake by adrenal nerve endings.

5-Hydroxytryptophan↗