Studies, using a wide variety of stressors, have clearly indicated that the pattern of neuroendocrine response is dependent upon the stress stimulus applied. 2. The Tyr-MIF-1 family of peptides (Tyr-MIF-1s) includes MIF-1, Tyr-MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1. These neuropeptides, neuromodulators are able to inhibit the expression of some forms of stress-induced analgesia. 3. The aim of this study was to compare changes in ACTH and corticosterone (CORT) concentration after various stressors (immobilization, cold and heat), as well as after injection of investigated Tyr-MIF-1s peptides. 4. According to our results, hypothalamic-pituitary-adrenal (HPA) system was activated by all the stressors applied. Heat and immobilization are stronger stressors, as the exposure of animals to a high ambient temperature and immobilization resulted in the highest rise of plasma ACTH and CORT concentration when compared with cold stress. Moreover, all the investigated peptides from Tyr-MIF-1 family, administered after application of stressors, inhibited the elevations in adrenocorticotropic hormone (ACTH) and corticosterone (CORT) plasma concentrations significantly. 5. In conclusion, the various stressors applied seem to induce a different response of the HPA system as judged by quantitative changes in ACTH and CORT release. We suggest that Tyr-MIF-1 peptides may possess anti-stressor effects, as they inhibited stress-induced rising in two hormones that were investigated.
