BINDING-SITES FOR VASOPRESSIN IN THE HUMAN PITUITARY ARE ASSOCIATED WITH CORTICOTROPHS AND MAY DIFFER FROM OTHER KNOWN VASOPRESSIN RECEPTORS

In view of the fact that vasopressin can induce pituitary adrenocorticotrophin release, we performed an autoradiographical study of [H-3]arginine vasopressin binding in human pituitary tissue obtained post-mortem from adults and foetuses. Sites of specific, high affinity binding (Ic50 3 to 5 nM) were detected as patches in the anterior lobe and at the junction between the anterior and neural lobes. The neural lobe was not labelled. Immunocytochemical studies performed on human pituitary tissue showed that [H-3]arginine vasopressin only marked zones which correspond to areas rich in cells immunoreactive to adrenocorticotrophin. We conclude that in the human pituitary, corticotrophs bear vasopressin binding sites. Since non-radioactive synthetic structural analogues of vasopressin acting as V1 and V2 agonists or antagonists failed to compete for binding of radioligand in the human pituitary, while a V1-type agonist displaced [H-3]arginine vasopressin binding in the rat pituitary, we postulate that binding sites in the human pituitary may differ from the previously known vasopressin receptors.