Effect of different types of stress on adrenal gland parameters and adrenal hormones in the blood serum of male Wistar rats

In the present study, we examined gross changes in the mass of whole adrenal glands and that of the adrenal cortex and medulla in mature male Wistar rats subjected to three different stress types: acute, chronic, and combined, i.e., chronic followed by acute stress. These parameters were correlated with adrenal activity as judged from serum levels of corticosterone and catecholamine, respectively, as well as with serum levels of ACTH and glucose. Under all three conditions, we observed bilaterally asymmetric and stress-type-independent hypertrophy of whole adrenals, as well as adrenal cortices and medullas. Under acute and combined stress, adrenal hypertrophy was followed by increase of adrenal hormones in the blood serum. However, under chronic stress, both cortical and medullar activities as judged from low or unaltered levels of the respective hormones and glucose were compromised and disconnected from the input signal of ACTH. Since all of the studied adrenal activities could be restored by subsequent acute stress, it is concluded that chronic isolation can be viewed as partly maladaptive stress with characteristics resembling stress resistance rather than the stress exhaustion stage of the general adaptation syndrome