The stimulatory effect of moderate heat on rat pituitary ACTH cells: histological and hormonal study

Abstract

Pituitary ACTH producing cells are very sensitive towards changes in duration of the heat exposure. The aim of this study was to examine the effects of 4-day continuous exposure of rats to moderate heat on histological and secretory characteristics of ACTH cells in adult male rats. The experimental group was exposed to 35±1°C for 4 days, whereas the control group was kept at room temperature during the same period. ACTH cells were studied using the immunohistochemical and immunofluorescent procedures. The morphometry was conducted using M42 multipurpose test system, while the hormone concentrations were determined by ACTH IMMULITE assay and corticosterone ELISA test. Compared to the controls, a significant (p<0.05) decrease of the body weight by 19.8% and significant (p<0.05) increase of the absolute and relative volumes of the pituitary gland by 23.1% and 36.1% respectively, were registered. It was found that in experimental group neither the localization nor the shape of ACTH cells was significantly changed, but the intensity of immunofluorescence signal was significantly (p<0.05) decreased. The cellular and nuclear volumes of ACTH cells were increased (p<0.05) by 6.9% and 14.3% respectively, while the volume density of ACTH cells was decreased (p<0.05) by 20.0%, in comparison with the corresponding controls. The observed changes were in accordance with increased (p<0.05) values of blood ACTH and corticosterone concentrations by 23.7% and 11.8%, respectively. Based upon the histological and hormonal data, it can be concluded that 4-day continuous exposure to moderate heat causes stimulation of the pituitary ACTH cells in rats.