Section 5 — Mutagenesis 



and rate of radiation. The dynamics of chromo- 

 some changes, induced by radiation, and the 

 mechanism of their occurrence at different 

 phases of the cellular cycle, seems to be a key to 

 new investigations of the protection of the 

 nucleus from the hazard of radiation. In this 

 respect, our first analyses indicate, on the one 

 hand, to the existence of new sites in the chemical 

 protection and, on the other hand, in the 

 mechanism of the occurrence of changes in the 

 nucleus of cells, induced by radiation. 



5.74. On Intracellular ( Chromosomal) and Organismal 

 Mechanisms of Control in Mammalian Radio- 

 sensitivity. J. J. Kerkis (Novosibirsk, 

 U.S.S.R.). 



According to frequency of cells with chromo- 

 somal aberrations appearing for 1 r while irradiat- 

 ing in vitro embryo fibroblasts of human, guinea 

 pigs, mice, rabbits and hamsters with the doses 

 from 5 to 50 r all these mammals arrange 

 according to the decreasing radiosensitivity as 

 follows: guinea pig= man < mouse < rabbit < 

 hamster. These organisms have the same arrange- 

 ment according to increasing LD 50/30 inherent 

 in them and according to chromosome radio- 

 sensitivity of bone marrow cells in vivo. It is 

 doubtful whether these coincidences are acci- 

 dental and appears to indicate the leading role 

 of nuclear structure in the control of general 

 radiosensitivity of organism. This point of view 

 is also confirmed by the data obtained in our 

 laboratory on conformity of cellular and general 

 protection degree by using chemical radio- 

 protectors. 



It is known that adrenalectomy removes 

 strain differences on radiosensitivity in mice. 

 Direct quantitative dependency between the 

 activity of adrenal metabolism and radiore- 

 sistency takes place among mice. We have 

 investigated the influence of adrenalectomy upon 

 chromosomal radiosensitivity. It has been es- 

 tablished that removal of the adrenal metabolism 

 increases the chromosome radiosensitivity ap- 

 proximately for two times. The average level of 

 adrenal activity is genotypically conditioned. On 

 the other hand, the products of chemical metab- 

 olism have an influence upon the radiosensi- 

 tivity of chromosomes themselves. The adrenal- 

 ectomy before and after irradiation has shown 

 that its influence appears to express by creating 

 different conditions for realization initial radi- 

 ation damages. The genetical conditionality 

 of adrenal activity, its effect upon general 

 radiosensitivity of an organism and upon 

 sensitivity of chromosomes of separate cells and, 



at last, higher degree of dependency of adrenal 

 activity itself upon the state of the central 

 nervous system — all these demonstrate compli- 

 cation of interaction of cellular and organismal 

 systems of the control on radiosensitivity and 

 will complicate the estimation of genetical 

 danger degree at different doses of irradiation. 



5.75. The Effects of Protection Against Genetic 

 Damage caused by Ionizing Radiation in 

 Mammalian Sex Cells. N. J. Nuzhdin and 

 G. V. Niznik (Moscow, U.S.S.R.). 



In spite of numerous investigations on the 

 possibility of protection against genetic damage 

 in mammalian germ cells, the evidence available 

 is rather contradictory. This is apparently 

 explained by the fact that owing to physiological 

 barriers the protective drugs used for injection 

 into the organism do not reach sex cells, or 

 while reaching, are incapable of displaying 

 protective action. In this connection we studied 

 the effects of some protective drugs used in 

 irradiation of spermatozoa in vitro on the rate 

 of dominant lethal mutations occurred in them. 



The experiments were carried out on chinchilla 

 rabbits. Spermatozoa were given y-rays Co-60 

 with a dose of 800 r in the saline solution, in the 

 solution of (3-mercaptoethylamine (MEA), S, 

 (3-aminoethylisothiouronium Br. HBr (AET) in 

 corresponding concentrations and also in an 

 atmosphere of CO and N2. 



Females were artificially inseminated after 

 mating with a vasectomized male and sacrificed 

 at 18-20 days of pregnancy. The ratio of the 

 number of live embryos to that of corpora lutea 

 was taken as an index of the rate of dominant 

 lethals. 



The investigations have shown that the 

 insemination of females with unirradiated 

 spermatozoa in both the saline solution and the 

 solutions containing protective drugs ensured a 

 high percentage of embryo survival (83 per cent) 

 in relation to the corpora lutea of pregnancy. 



The insemination of females with spermatozoa 

 irradiated in the absence of protective drugs led 

 to their high mortality rate (84 per cent). The 

 results obtained showed that such protective 

 drugs as MEA and AET, well-known for their 

 good action, did not protect spermatozoa from 

 the appearance of dominant lethals, if introduced 

 into the ejaculate prior to irradiation (15 to 30 

 min). The percentage of viable embryoes in 

 females inseminated with spermatozoa which 

 were irradiated in the presence of the above 

 mentioned protective drugs did not differ from 



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