Donald J. Pizzarello

Repair and Latent Injury in Rat Liver After X-Irradiation

Abstract Young male rats were given single x-ray doses of 100, 250, or 500 rads to the liver, then partially hepatectomized at time intervals up to 12 weeks to study persistence of mitotic inhibition and chromosome aberrations. Mitotic inhibition was greater as the dose increased and animals took longer to return to control levels. Initial levels of chromosome bridges appeared to vary linearly with dose and to persist at these levels for time intervals related to the dose (3 weeks after 500 rads). After this time, the level of bridges fell to approximately one-half that initially seen with no further change observed.

Regenerating Rat Liver: A Good System for Radiobiological Studies?

Abstract After partial hepatectomy, regeneration of Charles River male albino rat liver provides large numbers of nearly synchronously dividing cells. However there is such variability in levels of DNA synthesis and mitosis among untreated hepatectomized animals that demonstration of treatment effects is difficult. Mitosis is more radiosensitive than DNA synthesis and is completely inhibited after 500 rads during the early phases of maximum mitotic activity, which makes variability among control animals less important. A dose of 250 rads did not completely inhibit mitosis.

EFFECT OF MODERATE DEGREES OF HYPOTHERMIA ON THE SENSITIVITY TO WHOLE-BODY IRRADIATION IN ADULT RATS.

Adult female CFN/sup 3/ rats were cooled to a body temperature of 25 deg C by immersion in a water bath. The animals were maintained in a hypothermic state for eight hours before irradiation. A lethal dose of 900 r of x radiation was administered at room temperature after whlch body temperature was gradually returned to normal. All animals that were hypothermic when irradiated survived at least five months, whereas those not hypothermic when irradiated were all dead within 13 days. Animals subjected to hypothermia alone showed no ill effects. Possible mecharrisms of hypothermic protection are discussed. (H.M.G.)

Loss of chromosomal aberrations as a result of growth of irradiated rat liver.

Newly weaned and young adult rats were given single doses of 250 rads to the hepatic region and partially hepatectomized at various intervals up to seven weeks later. Levels of chromosomal bridges persisted undiminished in larger animals, whereas in smaller animals they decreased to approximately half of the initial number during the first three weeks, with no further change observed. Measurements of liver weight, total DNA, and mitotic levels after irradiation established that growth of the liver is more rapid in young animals. These aberrations are apparently lost during cell division related to cell growth.

Biological detection of reduction in dose at the surface of volume sources containing beta emitters

Dosimetry theory related to volume sources containing uniformly distributed beta-emitting radionuclides predicts a rapid drop in dose at the outer surface to approximately one half of the maximum dose within the volume. The purpose of this study was to determine if this reduction in surface dose could be observed using a measurable biological endpoint. In this study rats were injected with radiocolloids of either 198Au, 113In-m or 99Tc-m, to produce liver irradiation from their decay, or their livers were treated with external X-irradiation. After irradiation, a portion of the liver was surgically removed to stimulate cell division in the liver remnant revealing radiation damage in the form of chromosomal aberrations. The percentages of dividing cells with bridges were scored in the outer edges (0.45 mm) of the tissue sections and were compared to levels obtained from the central portion of the liver lobe. No significant difference was observed with X-irradiation or from 99Tc-m irradiation. However, irradiation with 198-Au and 113In-m (which emit large numbers of energetic electrons) produced significantly fewer aberrations in the outer layer when compared to the central portion. These differences in the distribution of biological damage allowed us to detect the predicted dose reduction at the surface of volume sources containing beta emitters.