IMMUNOCYTOCHEMICAL LOCALIZATION OF LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE IN THE EQUINE PITUITARY

Gonadotropin-specific primary antisera and gold-conjugated secondary a ntibodies were used to immunocytochemically localize gonadotropins in the anterior pituitary of intact pony mares. Electron microscopy was t hen used to characterize the ultrastructure and immunoreactive stainin g characteristics of equine gonadotropes. Cells containing LH were mor phologically indistinguishable from those containing FSH. Gonadotropes were relatively large and commonly had eccentric nuclei. The rough en doplasmic reticulum was well developed and dilated. Secretory granules were present in two morphologically distinct forms. Large polymorphic granules were generally located in perinuclear cytoplasmic areas, whe reas small and uniformly shaped granules were in the peripheral cytopl asm, close to the cell membrane. Double-labeling revealed cells with g ranules that stained for both LH and FSH as well as cells that stained for either LH or FSH. Gonadotropes constituted 15 to 32% of all pitui tary cells in the anterior pituitaries from the three mares included i n this study. Cells that stained for only LH constituted 2 to 16% of a ll pituitary cells, cells that stained for only FSH ranged from 1 to 4 .5%, and cells staining for both hormones constituted 6.2 to 24% of th e pituitary cells. These results indicate that there are in fact three distinct subclasses of gonadotropes in the equine anterior pituitary based on immunocytochemical staining, which is similar to the situatio n described for several other mammalian species.