Specific immunoelectronmicroscopic localization of vasopressin and oxytocin in the neurohypophysis of the rat

Summary An immunoelectronmicroscopic method for the specific localization of neurohypophyseal hormones was developed in neurohypophyses of Wistar and Brattleboro rats, the latter strain being homozygous for diabetes insipidus. If the proper precautions were omitted, a marked cross reactivity between antivasopressin and antioxytocin preparations was found. Cross reaction of an antivasopressin plasma with oxytocin, at a dilution of less than 11600, resulted in electron density of all granules within neurosecretory fibres of the Brattleboro and Wistar neurohypophyses. However, this cross reactivity could be eliminated either by sufficient dilution of the antiplasma, or by its purification. Purification of the antibodies was performed by absorption to agarose beads coated with the cross reacting component. Upon incubation with antivasopressin (diluted unpurified 11600 or purified 180) and unpurified antioxytocin (1400) plasma, sections of a Wistar neurohypophysis revealed two types of neurosecretory fibres, containing either electron dense or lucent granules. Oxytocin and vasopressin containing neurosecretory fibres were found as clusters in the neurohypophysis. The specificity of both unpurified antivasopressin (11600) and antioxytocin (1400) plasma was confirmed on serial sections of a Wistar neurohypophysis, alternately incubated with the solutions of the two antibodies.These data prove that the one-cell-one-hormone hypothesis holds true for the hypothalamic-neurohypophyseal system.The authors wish to thank Dr. L.A. Sternberger (Edgewood Arsenal, Md., U.S.A.) for the peroxidase-anti-peroxidase complex, Dr. J.G. Streefkerk (Free University, Amsterdam) and the members of our project group on neuroendocrinology for their suggestions and critical remarks, and Mrs. M. Mud, Mr. P. Wolters and Mrs. A. van der Velden for their skilful assistance