Neurohypophyseal hormone receptors in the rat thymus, spleen, and lymphocytes

Receptor sites for the neurohypophyseal peptides arginine vasopressin (AVP) and oxytocin (OT) have been identified and characterized in some tissues involved in immune function in the rat. Novel radioiodinated ligands for the detection of neurohypophyseal hormone receptors, with a high specific radioactivity and affinity, enabled the selective detection of OT receptors in the thymus and vasopressin (VP) receptors in the spleen. OT receptors were detected in thymic membrane preparations and on thymocytes, which had a ligand selectivity similar to that of uterine OT receptors. AVP receptors of the V1 pressor type were present in a splenic membrane preparation. Specific AVP-binding sites, probably of the V1 type, were also present on splenic lymphocytes. Binding sites for AVP and OT could not be detected on mononuclear cells in peripheral blood of the rat. This study demonstrates that the use of the newly developed radioiodinated AVP and OT receptor ligands, with high specific radioactivity and affinity, enables the selective characterization of receptor sites for the neurohypophyseal hormones, even in the thymus, where previously no binding sites could be detected.