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Receptors for Cor ticotropin-Releasing Hormone in Human Pituitary: Binding Characteristics and Autoradiographic Localization to Immunocytochemically Defined Proopiomelanocortin Cells

Department of Experimental Pathology, Vrije Universiteit Brussel Laarbeeklaan 103, 1090 Brussels, Belgium
Department of Radioisotopes, Vrije Universiteit Brussel Laarbeeklaan 103, 1090 Brussels, Belgium
Department of Protein Chemistry, Vrije Universiteit Brussel Laarbeeklaan 103, 1090 Brussels, Belgium
The Department of Zoology, Katholieke Universiteit Leuven Naamsestraat 59, 3000 Leuven, Belgium

Address all correspondence and requests for reprints to: G. Smets, Department of Experimental Pathology, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090 Brussels, Belgium.

Using autoradiography combined with iramunocytochemistry, we demonstrated that the target cells of CRH in the human pituitary were proopiomelanocortin cells. Scatchard analysis of [¹²⁵I]Tyr⁰-oCRH saturation binding revealed the presence of one class of saturable, high affinity sites on pituitary tissue homogenate. The equilibrium dissociation constant (K_d) for [¹²⁵I]Tyr⁰-oCRH ranged from 1.1–1.6 nM, and the receptor density was between 200–350 fmol/mg protein. Fixation of cryostat sections with 4% paraformaldehyde before tracer incubation improved both tissue preservation and localization of the CRH receptor at the cellular level. Additional postfixation with 1% glutaraldehyde inhibited tracer diffusion during subsequent immunocytochemistry and autoradiography. [¹²⁵I]Tyr⁰-oCRH was found in cytoplasmic inclusions or at the cell periphery of ACTH/β-endorphin cells in the anterior pituitary. Single cells of the posterior pituitary were also CRH receptor positive. Cells staining for PRL or GH were CRH receptor negative. We conclude that CRH binds only to high affinity receptors on ACTH/β-endorphin cells in the human pituitary.

Received October 22, 1990.