EFFECT OF ACUTE STRESS ON CIRCULATORY LEVELS OF ADRENOCORTICOTROPIC HORMONE IN RATS LOCALLY HEAD-IRRADIATED WITH X-RAYS

In order to study the effects of ionizing radiation on the pituitary gland before and after an acute stress attack, rats aged 8 days were locally head-irradiated with a single dose of 9.6 Gy of X-rays. One group of animals was irradiated under hypothermia (rectal temp. 5.96 °C). At the age of 46 days, the animals were sacrificed and circulatory adrenocorticotropic hormone levels were measured by the RIA method. Basal ACTH levels were lower in the irradiated animals when compared to the non-irradiated controls (p<0.05). After an acute stress attack, the irradiated animals showed significantly lower ACTH levels compared to the non-irradiated controls (p<0.001). Animals subjected to hypothermia during irradiation, after an acute stress attack, showed significantly higher ACTH levels in comparison to animals irradiated under normal body temperature (p<0.001). It may be concluded that a dose of 9.6 Gy of X-rays reduces the post-stress response of the pituitary gland and that hypothermia effectively protects the pituitary gland when ionizing radiation is concerned.