Leucine-enkephalin-like immunoreactivity in vasopressin terminals is enhanced by treatment with peptidases

When sections through rat neurohypophyses were treated with trypsin prior to incubation with enkephalin antibodies, vasopressin terminals invariably exhibited leucine-enkephalin-like immunoreactivity. Omitting tryptic cleavage the vasopressin terminals of some specimens only were immunostained. The enkephalin-like material was contained in the neurosecretory granules as shown by the protein A gold and the peroxidase anti-peroxidase method. We assume that the leucine-enkephalin sequence in vasopressin endings to some extent is present in a precursor form, possibly as dynorphin or alpha-neo-endorphin, from which the pentapeptide is liberated by enzymatic cleavage.