Patterns of radiation damage. Effects of radiation exposure

Patterns of radiation damage. Effects of radiation exposure

A characteristic feature of the defeat by radioactive radiation is the presence of a hidden period during which no violations can be detected in the body. It is often called the period of imaginary well-being (incubation period).

During the incubation period, of course, a number of phenomena occur. However, the changes that occur after irradiation are so insignificant that they cannot be detected by both biochemical and physiological methods. The duration of this latent period is inversely proportional to the radiation dose.

Fractional radiation exposure.

With fractional irradiation with small doses, the duration of the incubation period can be very long. For example, if radioactive products that create a lethal dose enter the body, the incubation period can last more than a year.

Usually, with massive irradiation, when a lethal dose is created in a short period of time, the incubation period in higher animals lasts from several hours to 30-40 days, and in lower multicellular organisms (mollusks, crustaceans, plants) it can last several months.

Generally speaking, the duration of the incubation period for the body depends on the radiation dose (Fig. 20). After the incubation period, the lesion phenomena develop very quickly; the increase in hematological, biochemical and physico-chemical changes leads either to death or to subsequent normalization.

The nature of the course of the lesion over time indicates that at the very beginning a primary reaction occurs in the body, which then continues to develop independently (without exposure to radiation) and, in the same way as with autocatalytic processes, more and more molecules are involved in the reaction;

Fig. 20. Dependence of the incubation period for rats on the radiation dose.

in the end, this leads to prominent defeats. The general course of development of radioactive radiation damage can be considered as a self-accelerating process resembling the development of autocatalytic chemical reactions. The increase in various indicators characteristic of the lesion will be depicted by an aex curve. Depending on the dose, the steepness of the curve will change, but its shape will remain the same.

Opinion of other experts on the effects of radiation.

Many foreign researchers note that this pattern does not apply to a group of protozoa (infusoria, bacteria) that die only during irradiation from very large doses of radiation, equal to about hundreds of thousands of X-rays. However, other researchers have observed an incubation period in protozoa after exposure to lethal doses. Medvedev, Mansel, Shekhtman found that amoebas after irradiation with a dose of about 105r do not die immediately, but after a certain period of time.

It was also found that the phage of the coli bacterium is not immediately inactivated after irradiation. Thus, the simplest ones are not an exception to the general rule. (see page 20), they also have an incubation period after irradiation, but under certain conditions created in the environment, it can last for a very short period of time (see page 94).

The latent period is revealed most characteristically when irradiated with relatively small threshold lethal doses. Sometimes, when exposed to large doses, it is possible to detect a number of changes immediately after irradiation. Immediately after irradiation with lethal doses, opalescence is detected in the blood of animals [95]; very quickly after irradiation, even with relatively small doses, the appearance of leukocytosis can be noticed.

Dependence of the reactions of organisms on the dose.

Some authors have noticed that toxicity appears in the blood immediately after irradiation (Fig.21). Studies of the process of cell division in cultures have shown [134] that the percentage of dividing cells decreases significantly immediately after irradiation; some researchers have detected changes in the electronic activity of nerve cells, etc. (fig. 22).

However, if the doses are not too large, these changes disappear relatively quickly (see Fig.22). After irradiation, along with others, an increase in capillary permeability is primarily observed, and if the doses are not very large, the permeability returns to normal. After irradiation, along with an increase in the permeability of capillaries, their fragility also increases [98,40].

However, even these changes when irradiated with not very large doses disappear for a while, after which they reappear when the disease becomes apparent. These early changes manifest themselves differently in different animals. To the greatest extent, shock phenomena are manifested in rabbits and to a much lesser extent in dogs, monkeys and other animals.

Such changes cannot be considered primary reactions of radiation damage.

Other reactions to the effects of radiation.

The appearance of the above reactions immediately after irradiation and the return to normal indicate that these reactions do not play a role in the development of radiation damage. Currently, it is believed that they are the result of a primary shock.

The effect of radioactive radiation is not selectively directed at any system; radiation affects a variety of molecules, so a wide variety of reactions can occur as a result. Some of them, arising, develop and fade like the above pseudo-primary reactions, others cause an excitation reaction.

Fig.21. The nature of the increase in signs of radiation damage over time when irradiated with different doses.

At the same time, the development of the lesion over time shows that there must be reactions or groups of reactions that continuously develop during the latent period or during the period of time when everything seems to be returning to normal.

Fig.22. The time change in the rate of cell division in chicken embryos after irradiation with different doses.

Indirect data, along with the general dynamics of the lesion development, support the assumption that the primary reaction that occurs during irradiation develops in the body.

Side shock changes, if the main incubation period is long, have time to return to normal. If the dose is large and the incubation period is small, then all reactions, merging with the main action of the lesion, develop continuously until the moment of death of the organism. When irradiated with small doses that are not capable of causing an intense shock reaction, signs of damage appear only in the long term.

The fact that two non-specific effects do not occur simultaneously indicates that the phenomenon of primary shock cannot be confused with the primary mechanisms of radiation damage.

Mechanisms that slow down/weaken the effects of radiation damage.

As a result of exposure to radiation , the following processes occur sequentially:

  1. absorption of radiation energy by matter.
  2. exchange of physical energy for chemical energy.
  3. physico-chemical reactions of aftereffect.

The study of the kinetics of the course of radiation damage shows that during the development of radiation sickness in the last period (physico-chemical processes), two different reactions or groups of reactions occur.

The first of them is a photochemical reaction that takes place during a very short period of time of direct interaction of secondary electrons with matter. Its output determines the number of initially formed active molecules that give rise to a secondary reaction.

Substances that help to combat the effects of radiation.

The correctness of this assumption is confirmed by numerous studies where the preventive effect has been studied [92]. As is known, a large group of substances introduced during irradiation has the ability to significantly weaken the toxic effect of radiation. These include the following substances:

  1. compounds containing a sulfhydryl group—glutathione, thiourea, thiomercaptan;
  2. substances that reduce oxidative processes are cyanides, even carbon monoxide, azides, etc. [20].

These substances have an effect only at the time of irradiation and are completely ineffective after irradiation. It is clear that the lack of oxygen and preventive substances inhibit the development of a rapid reaction, which lasts for an extremely short period of time and during irradiation.

As already indicated (see page 41), the effect of these preventive substances can only extend to the reaction associated with the interaction of radicals with chemical components of protoplasm, since radicals cannot exist for a long time in the presence of reactive molecules and their lifetime is measured in millionths of a second.

The lack of effectiveness of these substances after irradiation shows that immediately after the first short-term reaction, a qualitatively completely new physicochemical reaction occurs in cells and tissues.

Dependence of radiation reactions on temperature.

A characteristic feature of these two reactions is their dependence on temperature. Studies conducted on cold-blooded animals show that temperature practically does not affect the development of the lesion at the time of irradiation, but it has a strong effect on the reaction of the aftereffect.

It has been repeatedly noted that when the temperature decreases, the sensitivity of various tissues and organisms to radioactive radiation decreases.

It was found that the deadly effect in fruit flies it decreases if they are kept at low temperatures all the time. Observations have shown that the skin of newborn rats with prolonged cooling has significantly greater radioresistance. The content of irradiated frogs at a reduced temperature significantly increases their survival rate [129] (Table 11).

Table 11

Survival rate (in percent) of frogs kept after irradiation at various temperatures.

The data indicated in Table 11 indicate that the reaction rate of the lesion is significantly delayed when the temperature decreases; at the same time, the temperature coefficient of acceleration of the reaction is 6-7.

In cases where frogs irradiated with a dose of 3000 r are transferred to a higher temperature after being in the cold for several days, the lesion begins to develop rapidly and, most notably, at the same rate as those frogs that were kept at a high temperature (Fig. 23, 24).

Fig.23. Survival curves for frogs irradiated at different temperature conditions.

  1. at a temperature of 20-23 degrees Celsius during irradiation.
  2. at a temperature of 1-3 degrees Celsius during irradiation.
  3. at a temperature of 6 degrees Celsius in the first two hours after irradiation.
  4. 1-3 degrees Celsius during irradiation, during the first 24 hours after irradiation, the temperature was 6 degrees Celsius.
  5. at a temperature of 6 degrees Celsius for 8 weeks after irradiation and further at a temperature of 21-23 degrees Celsius.

Fig.24. Survival curves for frogs irradiated at different temperature conditions.

it is noteworthy, with the same speed as those frogs that were kept at high temperature (Fig. 23, 24).

This means that the reaction was suspended when the temperature changed, but its active centers remained unchanged.

 

From the book:

The continuation in the next article:  https://radiation-info.com/en/2022/05/14/radiation-damage-effects-of-radiation-exposure-part-2/

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