ECOLOGO-MORPHOLOGICAL ANALYSIS OF SMALL MAMMALS
PERIPHERAL ENDOCRINE GLANDS INHABITING AREAS WITH HIGH
RADIOACTIVITY
O.V. Ermakova
Institute of Biology, Komi Scientific Centre, Ural division of RAS, Syktyvkar,
Russia
Colossal problems related to exposure to low_dose ionizing radiation (IR) have
Occurred on the territories polluted as a result of nuclear tests at the Semipalatinsk and
Novozemel’sk proving grounds and failures at the South_Ural and Chernobyl nuclear
power plants (NPP). Such problems also exist in the Komi Republic because its territory
includes areas with increased background radiation of natural and technogenic origin. In
the present paper, data are given which were obtained both in the course of multiyear
experiments on murine rodents inhabiting areas with increased levels of radioactive
pollution (the Ukhta district, Komi Republic and the 30_km zone of the Chernobyl NPP)
and in laboratory trials aimed at estimating the chronic effect of IR in low doses. The goal
of the research was to study the regularities of structural and functional changes in the
peripheral endocrine glands of murine rodents under longterm exposure to IR in the
environment and under conditions modeling chronic exposure to external irradiation.
MATERIALS AND METHODS
Given the radiation situation on the territory of the Radium station and the data of
dosimetric and radiochemical analysis, the animals dwelling there have been exposed to
dose loads of external irradiation in the range of 0.3–3 cGy/year; from incorporated
radionuclides, 1.2–4 cGy/year; and from gaseous emanations of radon and thoron, 1.3
cGy/year.
The absorbed dose from external γ irradiation computed for a group of adult voles
from the Chernobyl zone as of September 1986 was equal to 110 and 2 cGy at the two
surveyed plots. Over the studied period, under conditions of radioactive pollution of the
environment by heavy natural radionuclides (HNR), more than 1000 root voles (Microtis
oeconomus Pall.) were harvested and studied within the Ukhta Radium station (Komi
Republic) and a total of 147 root voles were taken from the 30 km zone of the Chernobyl
NPP. Study of the action of radiation and chemical factors was conducted on pubescent
root voles, white nonpedigree mice, and Wistar rats. To experimentally assess the
contribution of external irradiation to the biological effects revealed in the endocrine
organs, several series of experiments were conducted (within the same range of doses that
is observed in natural biocenoses) on various species of murine rodents.
1) Assessment of morphological changes in the peripheral endocrine organs of root voles
during phases of long total irradiation at constant dose rate (20–25 μGy/h; duration of
irradiation—14, 60, and 120 days).
2) Morphological analysis of endocrine organs under external 30_day irradiation of Wistar
rats at varying dose rate. The dose rate in one case was 20–25 μGy/h, and in another 400–
450 μGy/h (over 30 days the total absorbed dose constituted 1.4–1.8 and 28.8–32.4 cGy,
respectively).
3) Analysis of hormonal content in homogenates of adrenal gland tissue of white
nonpedigree mice at low_dose chromic irradiation (20.0–22.6 cGy; dose rate 400 μGy/h).
Two steel_coated ampules containing 0.474 Ч 106 and 0.451 Ч 106 kBq 226Ra,
located at a distance 2.5 m from one another, were the sources of γ radiation. The
irradiation levels used in the experiment simulated the conditions of the external
γ_radiation background at the trial plots. The thyroid gland, adrenal glands, and ovaries
were fixed in 10% formol solution, Buen liquid, and glutar aldehyde with subsequent
paraffin or epon araldite embedding using generally accepted techniques. The state of the
surveyed organs was assessed according to the following criteria: relative mass of the
organ; width of adrenal cortex and its zones; volume of nuclei in each zone (AG); ratio of
main structural components; average diameter of follicles; height of thyroid epithelium
(TG); and estimate of the number of follicles according to degree of maturity, atretic
follicles, and corpus luteum (OV). Stereological indicators were determined with the aid of
a standard planimetric grid with 100 nodes in the ocular nozzle. To study the processes of
folliculogenesis, we analyzed a spectrum of the distribution of follicles by diameter. As
integral indicators of the functional activity of the thyroidal parenchyma, the index of
activity of the thyroid gland and the functional index were calculated.
RESULTS AND DISCUSSION
Comparative morphological analysis of field and experimental materials showed that
chronic irradiation at low doses leads to the development of unspecific reactions in the
endocrine organs, expressed in alteration of their structural organization at the cell,
tissue, and organ levels (see figure).
In the experiment on irradiation of Wistar rats with doses of 5 and 50 cGy (dose rate
2.5 and 40.0 μGy/h), lesion of the genetic system of follicle thyrocytes, expressed in rein_
forcement of the processes of the formation of cells with micronuclei, was observed.
Homotypic morphological changes appeared in the adrenal glands of laboratory and
wild animals after prolonged exposure to radiation. For instance, microadenoma of the
adrenal cortex, which is a benign enlargement of cell clones, was observed under model
experimental conditions in white nonpedigree mice, as well as in root voles under
environmental conditions of increased background radiation (in the “Ukhta” population
19% and in the “Chernobyl” population 27% of mature individuals had sites of hyperplasia
in the adrenal cortex).
Both in laboratory animals, in various experiments on the effect of external radiation
(absorbed dose 1.8–5.4 and 50.0 cGy), and in animals taken from natural populations
(dose burden of external irradiation in the range of 0.3–3 cGy/year), structural
transformations in the thyroid parenchyma were single_type and gave evidence for the
stimulating impact of chronic exposure to γ radiation on the processes of folliculogenesis
in the TG. Diffused foci of inflammatory reaction, i.e., leucocyte infiltrates and local
necrotic changes in zona fasciculata were often observed in the adrenal cortex, and
boundary cancellation between the zones of the adrenal cortex (zona glomerulosa, zona
fasciculata, and reticular zone), along with disorganization of the cortex, sites of local
destruction, and atrophy of parenchyma, were noted. The most pronounced signs of
alteration were observed against the background of the increased functional activity of the
organ, when the impact of the radiation factor overlapped population effects (e.g., high
population density).
In the experiment with chronic outer irradiation of white nonpedigree mice (absorbed
doses were 20.6–22.6 cGy), a reliable increase in the volume of the zona fasciculata and
decrease in the volume of the zona glomerulosa of the adrenal cortex, as well as an
increase in the glucocorticoid level in the AG tissue, were observed.
Comparison of the results of the experiment and radioecological monitoring showed
that the chronic influence of IR caused a homotypic reaction of hyperactivity of the adrenal
cortex in voles. The number of follicles of various types—primordial, primary, growing,
and cavitary—were counted in the ovaries. In the voles from polluted territories, the
number of growing follicles reliably exceeded that in the controls. The number of cavitary
follicles was not changed, but the number of more mature graafian follicles in the voles
from the radionuclide polluted site was reliably higher than in the controls. These findings
demonstrate the increased rate of maturation of the follicles in the animals exposed to
irradiation. Meanwhile, the supply of primordial follicles in them appeared to be lower
than the control level . This decrease in the OV reserve capabilities, on the one hand, and
accelerated maturation of follicles, on the other hand, is a peculiar way of adaptation of the
rodents to the unfavorable impact of the environment.
Intensity of proliferation (IP) and embryonic mortality are important features of
population viability. These indicators were reliably different in the control and
experimental animals. The greatest intensity of proliferation was characteristic of the voles
taken from the trial plots (82%) and the lowest was found in the controls (55%). At the
same time, embryonic mortality indicators were higher in the voles from the polluted plot.
Thus, the observed variations of the morphological parameters of the studied organs reflect
regular changes in their functional activity in the physiological range; they are directed at
the maintenance of homeostasis under altered conditions and are compensatory and
adaptive in nature. Sometimes it is hard to define the effects observed after the action of IR
in low doses; but in combination with other agents, they may facilitate cell_tissue
reactions. The greatest frequency of the processes of tissue alteration occurs with the
combined action of radiation and chemical factors both under the conditions of the
animals' natural environment and under experimental conditions.