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Biomedical subjects

K L Jackson

Publications and source records attributed to K L Jackson.

At least 73 records · Page 4Linked to original sources
PubMed1985

The intestinal radiation syndrome: sepsis and endotoxin.

Rats were whole-body irradiated with 8-MeV cyclotron-produced neutrons and 137Cs gamma rays to study the role of enteric bacteria and endotoxin in the intestinal radiation syndrome. Decrease in intestinal weight was used as an index of radiation-induced breakdown of the mucosa. Neutron and gamma-ray doses that were sublethal for intestinal death resulted in a dose-dependent decrease in intestinal weight, reaching minimal values 2 to 3 days after exposure, followed by recovery within 5 days after irradiation. Neutron and photon doses that caused intestinal death resulted in greater mucosal breakdown with little or no evidence of mucosal recovery. The presence of fluid in the intestine and diarrhea, but not bacteremia or endotoxemia, were related to mucosal breakdown and recovery. Neither sepsis nor endotoxin could be detected in liver samples taken at autopsy from animals which died a short time earlier from intestinal injury. These results suggest that overt sepsis and endotoxemia do not play a significant role in the intestinal radiation syndrome.

Animals↗
PubMed1985

Hepatic injury after whole-liver irradiation in the rat.

Radiation-induced hepatic injury in rats, which is characterized by marked ascites accompanied by liver necrosis, fibrosis, and vein lesions, is described in this study. These adverse sequelae are produced within 30 days after irradiation if there is surgical removal of two-thirds of the liver immediately after whole-liver irradiation. The LD50/30 day and median survival time after liver irradiation and two-thirds partial hepatectomy is 24 Gy and 17 days, respectively. Death is preceded by reduction in liver function as measured by [131I]-labeled rose bengal clearance. Prior to death, liver sepsis and endotoxemia were detected in most irradiated, partially hepatectomized animals. Pretreatment of the animals with endotoxin and/or antibiotic decontamination of the GI tract, which increase the host resistance to infection and endotoxemia, resulted in increased survival time, but no irradiated, partially hepatectomized animal survived beyond 63 days. The combination of these treatments resulted in additive effects leading to 38% survival at 100 days. These treatments did not, however, prevent the eventual development of radiation-induced liver pathology. This suggests that sepsis and endotoxemia resulting from the bacteria in the intestine are the immediate cause of death after 30-Gy liver irradiation and partial hepatectomy. It is concluded that the hepatectomized rat model is an economical and scientifically manageable experimental system to study a form of radiation hepatitis that occurs in compromised human livers.

Animals↗
PubMed1985

Effect of Pseudomonas contamination or antibiotic decontamination of the GI tract on acute radiation lethality after neutron or gamma irradiation.

The influence of antibiotic decontamination of Pseudomonas contamination of the GI tract prior to whole-body neutron or gamma irradiation was studied. It was observed that for fission neutron doses greater than 5.5 Gy, cyclotron-produced neutron doses greater than 6.7 Gy, and 137Cs gamma-ray doses greater than 14.4 Gy, the median survival time of untreated rats was relatively constant at 4.2 to 4.5 days, indicating death was due to intestinal injury. Within the dose range of 3.5 to 5.5 Gy of fission neutrons, 4.9 to 6.7 Gy of cyclotron-produced neutrons, and 9.6 to 14.4 Gy of gamma rays, median survival time of these animals was inversely related to dose and varied from 12 to 4.6 days. This change in survival time with dose reflects a transition in the mechanisms of acute radiation death from pure hematopoietic, to a combination of intestinal and hematopoietic, to pure intestinal death. Decontamination of the GI tract with antibiotics prior to irradiation increased median survival time 1 to 5 days in this transitional dose range. Contamination of the intestinal flora with Pseudomonas aeruginosa prior to irradiation reduced median survival time 1 to 5 days in the same radiation dose range. Pseudomonas-contaminated animals irradiated within this transitional dose range had maximum concentrations of total bacteria and Pseudomonas in their livers at the time of death. However, liver bacteria concentration was usually higher in gamma-irradiated animals, due to a smaller contribution of hematopoietic injury in neutron-irradiated animals. The effects of both decontamination of the GI tract and Pseudomonas contamination of the GI tract were negligible in the range of doses in which median survival time was dose independent, i.e., in the pure "intestinal death" dose range. Finally, despite the marked changes in survival time produced by decontamination or Pseudomonas contamination in the "transitional dose range," these treatments had little effect on ultimate survival after irradiation as measured by the LD50/5 day and the LD50/30 day end points. The implications of these results with respect to treatment of acute radiation injury after whole-body irradiation are discussed.

Animals↗
PubMed1984

Intent to participate in worksite health promotion activities: a model of risk factors and psychosocial variables.

A model of risk factors and psychosocial variables that should enhance the prediction of participation in worksite health promotion programs was evaluated by a sample survey (10% random sample) of approximately 13,000 State employees in South Carolina. The response rate for the survey was 66.3%, n = 854. A split sample strategy was employed to develop and then validate the psychosocial model. Degree of satisfaction with one's current status and intent to change it were assessed in six health areas: weight, nutrition, exercise, cigarette smoking, alcohol consumption, and the handling of stress and tension. In each area, a known risk factor was used to predict degree of satisfaction and intent to change. Variables from the psychosocial model were added in a step-wise regression procedure. The key variables in the psychosocial model were Personal Efficacy (specific to each of five areas), Job Stress, Trait Anxiety, and Health Knowledge. Risk factors contribute significantly to the prediction of dissatisfaction and intent to change in all areas except cigarette smoking and nutrition. The model of psychosocial factors contributed significantly to the prediction of dissatisfaction and intent to change in all areas. Personal Efficacy was significantly related both to dissatisfaction and intent to change, whereas the Job Stress and Anxiety variables were more effective in predicting dissatisfaction than intent to change. Health Knowledge had little direct or interactive effects on dissatisfaction or intent to participate. The implications of these findings for health promotion programs were examined.

Adolescent↗
PubMed1982

An estimate of the radiation-induced cancer risk from the whole-body stray radiation exposure in neutron radiotherapy.

The 1980 BEIR III risk factors have been used to estimate the secondary cancer risks from the whole-body stray radiation exposures which occur in neutron radiotherapy. The cancer risks have been calculated using the linear, linear-quadratic and quadratic dose-response models for the gamma component of the stray radiation. The linear dose-response model has been used to calculate the risk for the neutron component of the stray radiation. These risk estimates take into consideration for the first time the age and sex distribution of cancer patients undergoing neutron therapy. Changes in the cancer risk as a function of the RBE (10-100) assigned to the stray neutron radiation component have also been assessed. The excess risks in neutron-treated patients have been compared to the excess cancer risks for photon-treated patients and with the expected incidence of cancer in a normal population having the same age and sex distribution. These risk estimates clearly indicate that it will be necessary to tolerate a higher incidence of secondary cancers in patients undergoing fast neutron neutron therapy than is the case with conventional photon therapy. However, for neutron RBEs of less than 50 the increased cancer risk is only a fraction of the normal expected incidence of cancer in this population. Moreover, comparison of the radiation-induced cancer risk with reported normal tissue complication rates in the treatment volume indicates that the excess cancer risk is substantially lower than the risk from other late normal tissue effects.

Adolescent↗
PubMed1976

Single dose fast neutron RBE for pulmonary and esophageal damage in mice.

Mice whose thoraxes were exposed to cyclotron neutrons or x rays died from esophagus damage 10 to 70 days after exposure, and from pulmonary damage 70 days to 6 months after exposure. The single exposure RBE for esophagus lethality was 1.9 at at a neutron dose of 1,475 rads and 1.6 for pulmonary lethality at a neutron dose of 950 rads. The significance of these values for neutron radiotherapy of the thorax is discussed.

Animals↗
PubMed1975

Cyclotron fast neutron RBE for various normal tissues.

The relative biological effectiveness (RBE) values of fast neutrons as a function of dose in the range of dose per fraction being used clinically are reported for effects on several normal mouse tissues. The specific tissues examined were: thymus, spleen, white blood cells (WBC), testes, and small intestine. The RBE values for damage to the thymus (1.2), spleen (1.2), WBC (1.0), and testes (3.0) were independent of neutron dose size. In contrast, the RBE for the small intestine varied between 2.7 and 3.4 and was dependent on the size of the neutron dose. The RBE for intestinal death (2.4) and hematopoietic death (1.1) also is reported.

Animals↗