Opiate receptors in rat pituitary are confined to the neural lobe and are exclusively kappa

The distribution and density of opiate receptor subtypes in rat pituitary were examined by quantitative autoradiography of tritiated ligand-binding to slide-mounted sections under conditions optimized to label mu, delta, or kappa opiate receptors. Mu and delta receptor-binding was virtually undetectable in the pituitary. Kappa receptor-binding was confined to the neural lobe where it was densest in the external rim. Autoradiographic silver grains in emulsion-coated, Nissl-stained sections were preferentially located between cells, suggesting kappa receptor localization on nerve terminals and/or processes of pituicytes.