Development of an Optimal Model of Combined Radiation and Biological Lesions

Since the search for the effective medication in combined lesions includes the selection of an optimal experimental model for such injuries, there is actually a study aimed at developing an optimal model of combined radiation-biology (Pasteurella) lesions. The pathogen Pasteurella multocida (as one of the most frequent pathogenic agents involved in both isolated and combined radiation-biology lesions of agricultural animals) was used as a model of a biological agent to reproduce experimental biological research. We employed the "Chinchilla" rabbits of 2.5-3.0 kg body weight as a biological model for doing combined radiation Pasteurella lesion. When determining the optimal model of combined radiation-biology (Pasteurella) lesion, we consider that in the joint action of various pathological agents on the organism, there is a synergistic effect of explosion agents, previously specifying minimal doses of external γ-radiation and pasteurellosis pathogen that in the joint action of nonfatal doses would be lethal. The first stage of the experiments determined the minimal doses of gamma rays and pasteurellosis pathogen that in joint action causes combined radiation-biology pathology. We examined 66 rabbits divided into 11 groups of 6 animals each to determine minimal doses of infectious agent-pasteurellosis pathogen. The animals of the first 9 groups were given subcutaneously Pasteurella species at doses 1·10⁹, 1·10⁸, 1·10⁷, 1·10⁶, 1·10⁵, 1·10⁴, 1·10³, 1·10², and 1·10¹ of microbial cells per animal of 0.3 ml suspension in volume; the 10th group of animals were given saline solution; the 11th served as a biological control group. In determining the minimal doses of gamma rays, we conducted experimental tests on 36 rabbits, which have been exposed to external γ-radiation in the "PUMA" system with a ¹³⁷Cs radiation source of the exposure dose of 5.38 R/min at doses 2.0, 4.0, 6.0, 8.0, 10, and 12 Gy. To specify the optimal model of radiation-pasteurellosis lesion, we used the rabbits subjected to a combined radiation-biology effect using minimal doses of gamma rays and pasteurellosis agent, leading to a lethal effect during their complex action. The researches revealed that 50% of the death of rabbits infected with pasteurellosis occurs using Pasteurella at a dose of 3.7·10⁴ microbial cells per kilogram (LD ₅₀ = 3.7∙10⁴ m.c./kg), and 50% of radiation death in rabbits occurs when irradiated their gamma rays at a dose of 8.0 Gy (LD ₅₀ = 8.0 Gy). The combined effect of nonlethal doses of the studied agents in the indicated doses on rabbits led to the aggravation of the course of radiation and pasteurellosis infection, causing the death of animals from combined radiation-pasteurellosis pathology. The model combined radiation-pasteurellosis disease ran its course rapidly, and the animals died 3 to 6 days after the onset. The autopsy of the animals that died from acute radiation-pasteurellosis pathogen had found swelling of the subcutaneous tissue in the pharynx and intermaxillary space of the neck, hyperemia, lymphoid nodular hyperplasia, numerous hemorrhages on the serous and mucous membranes and in the tissues of the parenchymal organs, serous or serous-fibrinous exudate, and in the chest and abdominal regions, pulmonary edema. The research stated that gamma radiation of rabbits at a dose of 8.0 Gy conducted before exposure with Pasteurella at LD ₅₀ (3.7·10⁴ m.c./kg) declined the course of the pasteurellosis process, facilitated its generalization, and fastened the death of animals. Combined radiation-pasteurellosis infection ran its course rapidly, and the animals died within 3 to 6 days after the onset of the disease. The autopsy showed the pathologicoanatomic factors of the acute pasteurellosis: swelling of the subcutaneous tissue, purulent-catarrhal bronchopneumonitis, and pulmonary edema.