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

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 anti-vasopressin and anti-oxytocin preparations was found. Cross reaction of an anti-vasopressin plasma with oxytocin, at a dilution of less than 1:1600, 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 anti-plasma, or by its purification. Purification of the antibodies was performed by absorption to agarose beads coated with the cross reacting component. Upon incubation with anti-vasopressin (diluted unpurified 1:1600 or purified 1:80) and unpurified anti-oxytocin (1:400) 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 anti-vasopressin (1:1600) and anti-oxytocin (1:400) 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.