EVIDENCE FOR MULTIPLE OPIOID RECEPTORS IN THE HUMAN POSTERIOR PITUITARY

The distribution and quantification of opioid receptor types in post-m ortem human pituitary cryostat sections was determined by quantitative in vitro receptor autoradiography. Highly specific radioligands were used for each opioid receptor type, i.e. [I-125]-FK-33-824 for mu-opio id sites, [I-125][D.Ala(2)]-Deltorphin-I for delta-opioid sites and H- 3-U69,593 for kappa-opioid sites, None of the five specimens tested ex hibited any labelling in the anterior lobe of the pituitary for the th ree radioligands. As for the posterior pituitary, all 5 specimens cont ained both mu and kappa-opioid binding sites whereas none of them show ed delta-binding sites. The presence of both mu- and kappa-opioid bind ing sites in the human posterior pituitary contrasts with previous fin dings in the rat where only re-sites have been found. The present stud y could contribute to understanding of the functional action of opioid s in the human pituitary.