الفهرس 
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Abstract
Acute exposure to different types of stress and changes of stress hormones leads to different physiological and behavioral disturbances in humans and animals.
The present study aimed to investigate the effects of prolonged exposure to two different types of stress (heat stress and water immersion restraint stress) and repeated injection of adrenaline and dexamethasone ( which is a synthetic hormone instead of cortisol) – as representatives of most changeable hormones during exposure to different stressors – and evaluating their effects on some physiological and biochemical alterations.
The study was carried out on male albino rats, of Spraggue strain, weighing 120 – 150 gram. They were divided into 5 equal groups, of six animals each as follows:
Group (1), which served as control group.
Group (2), in which rats were injected with 100 ug / Kg of adrenaline for 28 consecutive days.
Group (3): in which rats were injected daily with dexamethasone (160 ug / Kg ) for 28 days.
Group (4), in which animals were exposed to heat stress by incubating at 38 ºC ( one hour daily ) for 28 days.
Group (5) in which animals were exposed to water immersion restraint stress by restraining animals in wire cages put in glass tank and immersed with water ( 23 ºC ) for one hour in 28 consecutive days.
At the end of experimental period a spatial working memory test was applied on control and all treated animals, and then rats were sacrificed to obtain blood samples for preparing serum and plasma and other samples for hematological investigations. Serum was used for determination of concentrations of blood glucose, triglycerides, total cholesterol and total proteins. Plasma was used for assaying levels of chorticosterone and adrenocorticotrophic hormone (ACTH) in all treated groups and statistically compared to those of control group.
The results of the present study showed the following:
1- Adrenaline treatment led to a significant increase in glucose, triglyceride and total cholesterol levels. It increased the concentrations of plasma corticosterone and ACTH, but did not induce significant change in spatial working memory. The hormone caused also nonsignificant change in white blood cells and increase of monocytes and neutrophils.
2-Dexamethasone injection significantly increased the levels of blood glucose and triglycerides but nonsignificant decrease in total proteins. It caused a very highly significant decrease in corticosterone and ACTH levels. Moreover, it increased the time of spatial working memory and induced changes in total and differential leukocyte count. of which a decrease of eosinophils and lymphocytes.
3- Chronic exposure of rats to heat stress induced a significant increase in triglycerides and cholesterol levels, while no significant change in glucose and protein levels was observed. Heat stress induced also a very highly significant increase in both corticosterone an ACTH levels. Similarly, an increase in latency of spatial working memory was recorded. A nonsignificant decrease in leucocytes and monocytes was also observed.
4- Water immersion restraint stress led to significant rise in glucose level but not significant increase in corticosterone and ACTH concentrations. Impairment of working memory was also observed through the increasing time necessary for spatial working memory of rats under the stress. Nonsignificant increase in leucocytes and neutrophils was observed. However these results may indicate other effective pathways rather than hypothalamo – pituitary – adrenal axis in such type of stress.
from the results of the present study, it could be concluded that chronic exposure to stressors and prolonged increase of stress hormones resulted from long period repeated treatments or as a response to stress on animals may lead to disturbances in some metabolic parameters and neuo-hormonal homeostasis and probable incidence of some diseases like diabetes or memory disorders. The results also support the idea that stress hormones, particularly the adrenal hormones, respond to stress in different ways depending on variability of stressors its acute effect and duration exposure. The study recommend also for curing about precautions of use of such hormones in long- term treatments.