ABSTRACT
The substances displacing labelled ligands from opiate receptors of the rat brain membrane fraction were found in the thymosin fraction 3 and acetoacid extract of the thymus by the radioreceptor assay. Comparison of the displacing activity of acetoacid extracts of perfused and non-perfused thymus and peripheral blood as well as an estimation of the blood content in the thymus allowed to conclude that blood does not participate in the ability of thymus preparations to bind to opiate receptors. On the basis of the enzymatic treatment data one can conclude that opiate receptor ligands present in thymus preparations are of peptide nature. The value of their sodium shift suggests that those peptides are partial agonists of morphine. The possible role of opioid peptides in the thymic endocrine function is discussed.
