[Anti-stress effect of D-Ala2-Leu5-Arg6-enkephalin]

In experiments on white rats and mice, stress was induced by suspending the animals by the neck fold. The evaluation of the degree of the stress and antistressor properties of a hexapeptide arginine-containing analog of leu-enkephalin was performed according to the changes in the weight of the thymus, spleen, adrenals, and appearance of ulceration in the gastric mucosa. At the same time the level of immunoreactive cortisol was measured in the rat blood by radioimmunoassay, whereas the content of 11-hydroxycorticosteroids by fluorometry. It has been demonstrated that the leu-enkephalin analog possesses marked antistressor properties comparing very favourably with the action of adaptogens obtained from eleutherococcus extract.