Granules and Golgi Vesicles with Differential Reactivity to ACTH Antiserum in the Corticotroph of the Rat Anterior Pituitary*

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Abstract
Slices of unembedded rat anterior pituitaries, fixed with a periodate-lysine-paraformaldehyde (PLP) fixative, were incubated with guinea pig antiserum to ACTH and stained with a peroxidase-conjugated Ig[immunoglobulin]G fraction of anti-guinea pig .gamma.-globulin serum from rabbits. The fine structure of the stained cells was identical to that of the ACTH-secreting cell, as described by Siperstein and co-workers. Immunoreactive granules were mainly located at the periphery of the cell. Numerous granules of the inner cytoplasm and also the Golgi complex were nonreactive to the antiserum. The differential labeling of granules and Golgi apparatus appears to reflect stages in the maturation of the ACTH peptide.