DIRECT EFFECTS OF STRESS ON ADRENOCORTICAL FUNCTION

The adrenal gland plays a pivotal role in the stress response since th is response involves the hypothalamic-pituitary-adrenal axis (HPAA) an d the sympatho-adrenomedullary system (SAMS) as its two principal comp onents. An important relation between the immune system and the other stress response systems is also centered on the adrenal gland. It is w ell known that the cortex secretes glucocorticoids while the medulla s ecretes epinephrine, two of the major effects of the stress response. Some other aspects, however, also deserve special consideration: The p aracrine effects of the cortical secretion on the medullary cells thro ugh the special irrigation system of the gland and reciprocally the in fluence of the medulla upon the cortex, either by direct close contact or by local innervation. The influence of vascular events also needs to be considered as well as the existence of some local hormonal axis such as those resulting from the local production of renin or CRH in a drenal cells. Some other cells such as mast cells, macrophages and end othelial cells seem to play a role in the regulation of the adrenal co rtex and hence in the tuning of the stress response. Stressors stimula te the release of CRH from the hypothalamic paraventricular nucleus in ducing the secretion of ACTH from the pituitary and that of corticoste roids from the adrenal cortex. Through the activation of the sympathet ic system the adrenal can be stimulated even before adequate levels of ACTH are reached. In conditions of chronic stress the adrenal cortex undergoes an adaptation that allows the hypersecretion of glucocortico ids to occur even without the increment of ACTH.