Effect of acute heat stress on rat adrenal cortex — a morphological and ultrastructural study

The Effects of Long-Term Exposure to Moderate Heat on Rat Pituitary ACTH Cells: Histological and Hormonal Study

Global warming causes an increased ambient temperature and prolonged heatwaves during the summer, which represent stressogenic factors affecting the hypothalamo-pituitary-adrenocortical (HPA) axis in mammals. The aim of this study was to investigate the effects of long-term (7-60 days) exposure to moderately elevated ambient temperature (35 ± 1°C) on the histological aspect and secretory ability of pituitary adrenocorticotropic (ACTH) cells, as well as on the corticosterone output, in adult rats. Stereological parameters of ACTH cells were estimated upon immunohistochemistry. The blood concentrations of ACTH and corticosterone were determined by immunoassays. The volume of ACTH cells in rats exposed to moderately high temperature for 7, 14, 21, 30 and 60 days decreased (p<0.05) by 18.1%, 14.5%, 13.5%, 8.6% and 14.2% respectively, compared to the same parameter in the controls. The volume density of ACTH cells in the groups exposed to elevated temperature for 7, 14, 21, 30 and 60 days decreased (p<0.05) by 40.0%, 33.3%, 26.7%, 13.3% and 26.7% respectively, in comparison with control rats. The plasma concentration of ACTH varied differently (p<0.05) with the duration of exposure to the elevated temperature. The serum concentration of corticosterone was decreased (p<0.05) by 54.9%, 24.4%, 29.9%, 21.1% and 24.4% in groups subjected to moderately high temperature for 7, 14, 21, 30 and 60 days respectively, all compared to the control value. Despite some signs of functional recovery of ACTH cells during the treatment, the impression is that the long-term character of this stressor overcomes the capacity of the HPA axis for resistance.

The Effect of Moderate Heat on Rat Pituitary ACTH Cells: Histomorphometric, Immunofluorescent and Hormonal Study

In 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.