IMMUNOCYTOCHEMICAL LOCALIZATION OF CHROMOGRANIN-A AND SECRETOGRANIN-II IN FEMALE RAT GONADOTROPES

Ultrastructures of pituitary gonadotropes are known to show a prominen t sex-related difference: typical male rat gonadotropes contain both l arge- and small-sized granules, whereas typical female rat gonadotrope s appear to exhibit uniformly small-sized granules. Our preceding stud ies have demonstrated that two representative granins, chromogranin A (CgA) and secretogranin II (SgII), are separately localized to each ty pe of granule in male rat gonadotropes, To clarify whether or not ther e is a certain relationship between granin proteins and characteristic features of secretory granules in female rat gonadotropes, we examine d the expression levels and immunocytochemical localizations of CgA an d SgII in the cells. Northern blot and immunoblot analyses demonstrate d that both CgA and SgII were synthesized and stored in the female pit uitary, although the amount of CgA was much lower in the female than t hat in the male pituitary. Immunocytochemical observations clarified t hat gonadotropes in the female pituitary possessed intermediate secret ory granules containing both CgA and SgII, in addition to solely CgA-p ositive and SgII-positive ones. However, secretory granules containing CgA in the female gonadotropes were much smaller in size and appeared less frequently than those in the male cells, whereas no sexual diffe rence was discerned in SgII-positive granules. Moreover, the size and appearance of CgA-positive secretory granules varied depending on stag es of the estrous cycle. These findings suggest that the size and appe arance of secretory granules containing CgA are closely associated wit h the expression and storage levels of CgA in the pituitary.