Co-localization of neurophysin- and enkephalin-like immunoreactivity in cat pituitary.

Enkephalin and neurophysin immunoreactivity have been co-localized in terminals of frozen-dried cat posterior pituitary, using two methods of immunocytochemistry--the protein A-gold procedure and the PAP method. Absorption controls show reduced staining in all cases. Intermediate lobe cells are negative using the enkephalin and neurophysin antisera, but with alpha-MSH antiserum, posterior lobe terminals are negative and intermediate lobe cells are positive. The data are compatible with the hypothesis that inhibition of release of oxytocin and vasopressin by the pituitary opioid system is accomplished by an autoregulatory mechanism in which the release of enkephalin with oxytocin or vasopressin serves to inhibit release of the neurohormones.