Adaptation to Cold Affects the Dimensions of Adrenal Gland Zones in Hibernating and Non-Hibernating Animals

Надійшла 23.01.2018 Прийнята до друку 19.02.2018 Received January, 23, 2018 Accepted February, 19, 2018 Согласно современным представлениям адаптация к холоду у человека может развиваться по метаболическому, инсулятивному (изоляционному), гипотермическому типу или их комбинации и определяться параметрами окружающей среды (интенсивность, характер, вид воздействия и др.), индивидуальными факторами (генетические, расовые, половые, возрастные, конституционные и др.) [3, 12]. Подобной классификации стратегий адаптации у других млекопитающих в доступной нам литературе обнаружить не удалось. Кроме того, в природе существует еще одна стратегия адаптации, не свойственная человеку, – гибернация. Для приспособления к колебаниям температуры окружающей среды (ТОС) млекопитающие используют определенный набор поведенческих реакций, физиологических изменений и морфологических приспособлений, степень вовлечения которых у негибернирующих и гибернирующих животных может отличаться [4]. При этом разнообразные поведенческие и физиологические ответы, инициируемые стрессовыми воздействиями, обусловлены активацией двух основных систем – гипоталамо-гипофизарнонадпочечниковой и симпато-медулло-адреналовой, конечным звеном которых являются надпочечники [1]. При хронических воздействиях существует определенная взаимосвязь между устойчивой активацией центральных механизмов, регулирующих секрецию гипофизарного адренокортикотропного гормона, и экстрагипофизарных механизмов, регулирующих размер надпочечников [9, цит. по 14]. According to current notions, based particularly on population studies depending on the environmental parameters (intensity, nature and type of particular impact) and individual factors (genetic, racial, sexual, age, constitutional, etc.) the adaptation to cold in humans can develop by metabolic, insulation, hypothermic types or their combinations. [3, 12]. The available publications do not contain any classification of adaptation strategies for other mammals. Moreover, some mammalian species are characterized by one more adaptation strategy, the hibernation, which is not peculiar to a human. To adapt to the fluctuations in ambient temperature, the mammals use a specific set of behavioral responses, physiological adjustment and morphological changes. At the same time it is believed that the extent of their involvement in non-hibernating and hibernating animals may differ [4]. There are various behavioral and physiological responses initiated by stressors, nevertheless all they are resulted from an activation of two main systems, i. e. the hypothalamic-pituitary-adrenal and sympatheticmedulla-adrenal, and the final actors of them are the adrenal glands [1]. Chronic effects are often characterized by an existence of certain relationship between the steady activation of the central mechanisms regulating the secretion of pituitary adrenocorticotropic hormone, and extrahypophysis mechanisms regulating the size of the adrenal glands [9, cited by 14]. Since the adrenal glands can be involved into the mechanisms, implementing different types of body adaptation УДК 612.592:591.445:[591.128.1+591.128.2 А.В. Шило*, Д.Г. Луценко, И.М. Карибян, В.В. Ломако Изменения величины зон надпочечников гибернирующих и негибернирующих животных при адаптации к холоду

According to current notions, based particularly on population studies depending on the environmental parameters (intensity, nature and type of particular impact) and individual factors (genetic, racial, sexual, age, constitutional, etc.) the adaptation to cold in humans can develop by metabolic, insulation, hypothermic types or their combinations.[3,12].The available publications do not contain any classification of adaptation strategies for other mammals.Moreover, some mammalian species are characterized by one more adaptation strategy, the hibernation, which is not peculiar to a human.
To adapt to the fluctuations in ambient temperature, the mammals use a specific set of behavioral responses, physiological adjustment and morphological changes.At the same time it is believed that the extent of their involvement in non-hibernating and hibernating animals may differ [4].
Серийные срезы надпочечников толщиною 6-12 мкм получали на криомикротоме «SLEE Mainz Сryostat» («SLEE Medical GmbH», Германия) и окрашивали гематоксилином и эозином.Светооптическое исследование проводили на универсальном микроскопе «AmScope IN300T-FL» («Amscope», США), оснащенном цифровой фотокамерой «Tucsen TCC-5OICE» («Tucsen», Великобритания).Стереологические показатели (общая площадь над-to the cold, to various degree, and the data on the effect of short-term rhythmic cold influences on the structural and functional state of adrenal glands are scanty, we performed the investigation of the stereological changes in the adrenal gland with rhythmic cold and constant cold effects in homoio -and heterothermic animals. The experiments were carried out in accordance with the Law of Ukraine On the Protection of Animals Against Cruelty (№ 3447-IV of 21.02.2006), and in compliance with the requirements of the Bioethics Committee of the IPC&C of the NAS of Ukraine, agreed with the statements of the European Convention for the Protection of Vertebrates, for Experimental and Other Scientific Purposes (Strasbourg, 1986).
The work was performed during the autumn-winter period in male golden hamsters (Mesocricetus auratus) (of 85-95 g weight; n = 20) and males of breedless white rats (Rattus norvegicus) (of 200-300 g weight; n = 20).Before the experiment, the animals were kept in cages by 4-5 individuals in each at a controlled light: dark regime (12 hrs : 12 hrs), at an ambient temperature of 22…24°C and on a standard diet ad libitum.
The hamsters entered hibernation after 10-14 days of exposure at (5 ± 2)°C.The average duration of the bout was (3 ± 0.5) days.Constant cold exposure (CCE) was performed by keeping a group of rats (n = 4) under the conditions of varying ambient temperatures from 1 to 7°C for 5 weeks under free-running light conditions and hamsters (one animal each) in a dark cold chamber at an ambient temperature of 4°C for 3-4 weeks with free access to water and food.
Rhythmic cold exposure (RCE) was performed for 2 days with different intensity of the cold stimulus (-12°C and 10°C) according to the following protocol [10]: first 15 min of each hour (day-light hours), the animals were exposed to cold, the following 45 minutes they were kept at 22…24°C (total of 9 exposures per day).The animals were divided into the following groups: 1 -control; 2 -after CCE; 3 -after RCE (-12°C), 4 -after after RCE (10°C), 5 -hibernation and 6 -2 hrs after arounsd from hibernation (only hamsters).
Serial sections of 6-12 µm were obtained by means of the cryomicrotome SLEE Mainz Cryostat (SLEE Medical GmbH, Germany) and stained with hematoxylineosin.Microscopical study was carried out by means of the AmScope IN300T-FL universal microscope (Amscope , USA) equipped with a digital camera Tucsen TCC-5OICE (Tucsen, Great Britain).Stereological indices (total area of adrenal gland, cortical and medullary zones) were obtained using the image analysis software Aim-Image Examiner (Carl Zeiss, Germany).
Полученные ранее данные [10] о повышении уровня тиреоидных гормонов в крови и отсутствие значимых изменений в надпочечниках (таблица) после ПХВ в целом согласуются с результатами O. Heroux [5] и могут свидетельствовать об адаптации крыс к The cold exposures used in the study had no significant effect on the stereological parameters of adrenal glands of rats (Table ).However in hamsters (Table ) the RCE (-12°C) resulted in a significant increase in the total area of adrenal gland and the area of cortical zone.Constant cold exposure (CCE) on the contrary resulted in a strong decrease in the total area of adrenal gland and the area of cortical zone, the area of the medulla layer was not changed.Hibernation caused a reduction in the cortical layer and hypertrophy of the adrenal glands after rewarming of hamsters.
of the cortical zones, having its own specific regulatory mechanism, responds to the stimulation of adrenocorticotropic hormone [15].
Numerous studies indicate the perturbations in the structure and function of the adrenal gland in response to acute and chronic effects of various stress factors, moreover structural disturbances can occur due the changes in the relative dimensions of any of the zones.In particular, chronic exposure to cold or isolation leads to a temporary activation of the pituitary-adrenal system and an increase in the dimensions of the adrenal glands and level of corticosterone in the plasma in rats [cited by 14].The animals with obesity, having an increased steroidogenesis, represent a hyperplasia of the cortical layer of adrenal glands [11].Heat exposure induced a decrease in the cortical layer dimensions (zone fasciculata) [6,9].Various physical loads led to hypertrophy of the cortical and medullar structures of adrenal gland, which indicated an increase in functional activity of the gland [2].The effect of chronic noise on rats resulted in a significant decrease in the volume of the fasciculate and reticular zones [8].After immobilization a high correlation was found between plasma levels of corticosterone and the relative weight of adrenal glands [7].
The absence of significant changes in the adrenal glands of rats after CCE (Table ) along with the our previous data on an increased level of thyroid hormones in blood [10], is generally consistent with the data of O. Heroux [5] and may indicate the development of adaptation to cold.For the RCE (10°C) group, the cold stimulus was apparently insignificant, and the absence of significant changes with RCE (-12°C) may be due to the development of a habitation to cold stimulus, i. e. the most common response of a body, developing in response to the repeated effects [3].
The hamsters were more susceptible both to RCE and to CCE: either the increase/decrease in total area and cortical layer (with a constant area of the medullary layer) was noted (Table ).
The observed differences in the responses of hamsters to cold influences (Table) can be related either to just a difference in mass between hamsters and rats (at least 2 times the weight of the latter is higher), and to the various mechanisms of cold adaptation in non-hibernating and hibernating animals [4].It should also be noted that M. Trefna et al. [13] reported that keeping the hamsters in the cold to initiate hibernation in 50% of cases resulted in the death of animals.These authors believe that, this might result from the loss of hibernation phenotype due to the long term breeding in captivity of laboratory Syrian hamsters.This fact should also be taken into account in future to conduct such studies.