Abstract
AbstractIn areas with moderate continental climate, increased average ambient temperature during the summer represents a stressogenic factor that affects the hypothalamo-pituitaryadrenocortical axis in mammals. Therefore, we wanted to examine the effects of 4 days of constant exposure to moderately elevated ambient temperature (35 ± 1oC) on the histomorphometric and immunofl uorescent characteristics, as well as on the hormonal secretion of pituitary corticotropes (ACTH) cells in adult male rats. In comparison with the controls kept at 20 ± 2oC, a signifi cant increase (p<0.05) of the absolute and relative pituitary weight (23.1% and 36.1%, respectively) was registered after exposure to heat. The localization, as well as the shape of the ACTH cells in the heat exposed group was not signifi cantly altered, but their immunopositivity was weaker. After 4 days of heat exposure, a weaker signal confi rmed the relative fl uorescence intensity of the ACTH cells (15.3%, p<0.05). In heat exposed rats, an increase of the cellular and nuclear volumes of immunolabelled ACTH cells and decrease of their volume density (6.9%, 14.3% and 20.0%, respectively; p<0.05) was registered. Observed histomorphometric and immunofl uorescent features of the pituitary ACTH cells were in accordance with the increased (p<0.05) value of plasma adrenocorticotropic hormone (ACTH) by 23.7% compared to the control rats. It can be concluded that the 4-day exposure to moderately elevated ambient temperature intensifi es pituitary ACTH secretion in adult male rats.
Highlights
One of the physical stressors that strongly influences animal homeostasis, besides cold and immobilization stress, is high ambient temperature [1,2]
The areas with moderate continental climate are characterized by prolonged periods with high ambient temperature during the summer months, representing a persistent stressogenic factor, which is very conducive to our research
The decreased body mass of our rats after 4-day exposure to elevated ambient temperature is in line with data observed by other authors in rats [25] and pigs [26], chronically exposed to high ambient temperatures (33-36oC)
Summary
One of the physical stressors that strongly influences animal homeostasis, besides cold and immobilization stress, is high ambient temperature [1,2]. Like other stressors which аre recognized as threatening factors for the survival of an individual [3], elevated ambient temperature provokes many different stress responses in a living organism, one of the first of which is the neuroendocrine response. It is well-known that the first reaction to a thermal stressor is activation of the sympatho-adrenomedullary system, but if the stimulus persists, in an attempt to regain and maintain homeostasis, the stimulation of the hypothalamic-pituitaryadrenal (HPA) axis occurs [4]. Acting in the hypothalamus and pituitary gland, these hormones have a crucial regulatory part in the HPA axis activity resulting in a termination of the animal response to an external stressor [6]
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