Involvement of α2-adrenergic agents in the effects of Tyr-W-MIF-1 and Tyr-K-MIF-1 after three models of stress

The endogenous peptides Tyr-W-MIF-1 and Tyr-K-MIF-1 are members of Tyr-MIF-1 family isolated from bovine hypothalamus and human parietal cortex. They have opioid-like and antiopioid-like properties. Noradrenaline is involved in various CNS functions, including modulation of pain and it is considered as a transmitter of the antinociceptive effects of mu-selective opioids. Literature data showed that stress elicits antinociceptive effects. This phenomenon is named stress-induced analgesia (SIA). It has been categorized into opioid and nonopioid. It is known that both peptides are able to inhibit the expression of some forms of SIA. The aim was to examine whether alpha(2)-adrenergic agents (alpha(2)-adrenoceptor agonist clonidine, alpha(2)-blocker yohimbine, noradrenaline reuptake inhibitor desipramine) are involved in the effects of Tyr-W-MIF-1 and Tyr-K-MIF-1 after 1 h immobilization (IS), cold (CS) or hot (HS) stress. All drugs were injected intraperitoneally (i.p.) in male Wistar rats. The nociception. was measured by paw pressure (PP) test. The results suggest that alpha(2)-adrenergic agents are involved in the antinociceptive effects of Tyr-W-MIF-1 and Tyr-K-MIF-1. The effects are probably due to different interaction between mu- and alpha(2)-receptors on presynaptic level, interactions of Tyr-W-MIF-1 and Tyr-K-MIF-1 with opioid p-receptors and involvement of opioid and nonopioid component in immobilization, cold or hot stresses.