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  • 1985-1989  (2)
  • 1985  (2)
  • 1
    ISSN: 1432-1335
    Keywords: Regenerating liver ; Cell cycle ; O6-Methylguanine DNA transferase ; DNA alkylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary O6-Methylguanine DNA transferase activity was investigated in liver proteins obtained at various intervals after partial hepatectomy and/or after hydroxyurea-induced synchronization of the liver cell cycle. Liver proteins were incubated with 3H-methylated calf thymus DNA as previously described by Pegg et al. (1981). The loss of O6-methylguanine was measured by radiochromatography of DNA hydrolysates. The extent of O6-methylguanine repair differed during the cell cycle: the activity increased in late G1, reached a maximum in early S phase and declined in late S phase and G2M. These results indicate that hepatocytes are endowed with an increased DNA repair capacity for this promutagenic lesion during the period of highest transformation sensitivity in the cell cycle. Though increased, however, this repair potential does not, because of its exhaustibility, appear to be sufficient to prevent initiation of transformation after high doses of alkylating carcinogens.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2072
    Keywords: Rhesus monkey ; Morphine dependence ; Naloxone ; Nalorphine ; Postdependent sensitization ; Abstinence ; Schedule-controlled responding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of morphine, naloxone, and nalorphine on responding maintained under a variable-interval schedule of food presentation were assessed in rhesus monkeys before and after successive periods of daily morphine maintenance (15.0 mg/kg/day SC). Withdrawal from morphine dependence was accomplished gradually following the first two maintenance periods and abruptly following the third period. Schedule-controlled responding was disrupted when morphine maintenance was abruptly discontinued but not when the maintenance dosage was gradually reduced to zero. Tolerance to the acute effects of IV morphine on responding developed during morphine maintenance and dissipated after daily injections were discontinued. The effects of IV naloxone and IV nalorphine following each period of morphine maintenance were generally similar to their effects in initial determinations. These data indicate that tolerance-producing regimens of repeated daily injections with morphine do not necessarily produce enduring changes in the effects of opiate antagonists on schedule-controlled behavior. Additionally, gradual withdrawal from morphine maintenance can minimize the behavioral disruptions that attend abrupt abstinence.
    Type of Medium: Electronic Resource
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