Abstract
We examined by immunocytochemistry the localization of cathepsins B and H in corticotrophs and melanotrophs in anterior and intermediate lobes of rat pituitary gland, using monospecific antibodies to cathepsins B and H. In serial semithin sections, immunodeposits for cathepsin H were detected throughout the cytoplasm of cells immunoreactive for ACTH and alpha-MSH in anterior and intermediate pituitary. Granular immunodeposits for cathepsin B were demonstrated in anterior and intermediate cells. Double immunostaining colocalized immunogold particles for cathepsin H and ACTH or alpha-MSH in secretory granules of corticotrophs or melanotrophs, whereas those for cathepsin B were detected only in their lysosomes. Enzyme assay demonstrated cathepsin B activity in both anterior and intermediate pituitary tissue, but did not detect cathepsin H activity in the intermediate pituitary. Western blotting, however, revealed the presence of cathepsin H and cystatin beta in intermediate pituitary. These results suggest that cathepsin B plays a role in protein degradation in lysosomes of corticotrophs and melanotrophs. Moreover, the presence of cathepsin H in secretory granules of the cells may indicate that the enzyme participates in the activation of secretory products.