[Interaction of various tetrahydroisoquinoline alkaloids with opiate receptors in the rat hypothalamus and midbrain].

Using the method of competitive displacement of 3H-labelled naloxone, (D-ala2)-met enkephalinamide or (D-ala2)-D-leu-enkephalin by salsolinol, 1-methyl-6-hydroxy-1, 2, 3, 4-tetrahydro-beta-carboline or 1-methyl-6-methoxy-1, 2, 3, 4-tetrahydro-beta-carboline from opiate receptors, it was shown that the alkaloids studied were capable to cause specific interactions with rat hypothalamus and midbrain however, exhibiting distinctly less affinity as compared with morphine or its analogs. The sodium ratios, determined from the effective doses of the tetrahydroisoquinoline alkaloids corresponding to the alkaloid concentrations, which induce 50% displacement of 3H-naloxone from the opiate receptors in the presence or absence of 100 mM NaCl, have been found to be 0.75 for salsolinol and 3.6 for beta-carbolines studied. The data obtained suggest that salsolinol, similar to naloxone, is a "pure" morphine antagonist, whereas the beta-carbolines studied may be classified with the agonist-antagonist type. A considerable decrease in the affinity of mu-type opiate receptors has been found in presence of salsolinol in the incubation medium. The possible mechanisms of pharmacological action of the alkaloids and their relation to development of alcohol dependence and tolerance are discussed.